This PDF file contains the front matter associated with SPIE Proceedings Volume10549, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

The effects of the electromagnetic field on material systems are governed by joint light-matter conservation laws. An increasing number of these balance equations are currently being considered both theoretically and with an eye to their practical applicability. I will present a unified theory to treat conservation laws in light-matter interactions. It can be used to describe and engineer the transfer of any measurable property from the electromagnetic field to any object. The theory allows to explicitly characterize and separately compute the transfer due to asymmetry of the object and the transfer due to field absorption by the object. It also allows to compute the upper bound of the transfer rate of any given property to any given object, together with the corresponding most efficient illumination which achieves the bound. Due to its algebraic nature, the approach is inherently suited for computer implementation.

Beams with structured phase and beams with partial spatial coherence have both been considered for a variety of applications for many years, and it would seem natural to combine their advantageous properties. However, there is a conceptual difficulty in doing so because partially coherent beams lack a definite phase, which would seem to rule out a direct synthesis. Nevertheless, research over the past decade has clarified the relationship between phase singularities of coherent fields and correlation singularities of two-point correlation functions, showing that coherent vortices survive the disruption of spatial coherence. In this presentation we discuss a number of theoretical models of what we refer to as “partially coherent vortex beams,” considering their relative merits.

In recent years, there has been a dramatic progress in the photonics field of disordered media, ranging from applications in solar collectors, photocatalyzers, random lasing, and other novel photonic devices, to investigations into fundamental topics, such as localization of light and other phenomena involving photon interactions. Anderson localization of light is an open researcher frontier, which has greatly attracted the attention of researchers in the past few decades. In this work, we study the transport of light in a strongly disordered optical medium composed by core-shell nanoparticles (TiO₂@Silica) suspended in ethanol solution. We demonstrate the crossover from a diffusive transport to a localization transition regime as TiO₂@Silica nanoparticle concentration is increased. A striking phenomenon of enhanced absorption, mainly near the input border, arises at the localization transition, from which an increase of refractive index was inferred. An increase of the density of localized states and absorption near the input border is reported when the incidence angle is increased. The specular reflection, measured for the photons that enter the sample, is considerably lower than the effective internal reflection undergone by the coherently backscattered photons in the exact opposite direction, indicating a nonreciprocal propagation of light (parity-symmetry breaking). A theoretical simulation, performed through random-matrix theory, agrees satisfactorily with the experimental results, showing the generality of this approach to address transport phenomena.

In this paper we analyze the novel quantum properties of atomic photo-excitations generated by Orbital Angular Momentum (OAM) photons. It was previously predicted for Bessel beams (BB), that transitionsin atomic systems driven by twisted laser beams obey a modified set of position-dependent angular-momentum selection rules. It was also shown, that in the case of perfect alignment of the atom on the beam axis, total angular momentum of the photon must be fully transferred to the internal degrees of freedom of the target, which causes dramatic enhancement of higher-multipole processes. As a result, weak atomic transitions, which are hardly observable in interactions with simple states of light, become accessible with OAM photons. In the current paper, we extend the earlier developed theory to describe atomic photoexcitations by Bessel-Gauss (BG) and Laguerre-Gauss (LG) modes. It allowed us to infer the information about the phase structure of the beam, such as mode content and topological charge. The formalism exhibits a high level of sensitivity to the polarization content of the laser beam, which is on the order of 0.005% of the polarization admixture. The theoretical predictions are confirmed experimentally for photo-excitation of Ca40+ ions, trapped in a micro-structured, segmented Paul trap. The full set of quadrupole transitions from the S-state were generated by 729nm OAM laser beam shaped with a holographic phase-plate with a fork-dislocation. The experiment was conducted by Ferdinand Schmidt-Kaler's group at the University of Mainz.

We analyze the novel features of high-multipole excitation of quantum systems with twisted light, i.e, by the photons that carry extra orbital angular momentum (OAM) along the propagation direction. It was previously demonstrated experimentally [1] that OAM of the twisted light is passed to the internal degrees of freedom of an atom for electric quadrupole transitions. We extended these results to the analysis of individual S->D transition amplitudes by measuring Rabi frequencies for Ca40+ ions placed in a Paul trap. It is shown that relative strengths transitions into different Zeeman-split levels - most of them forbidden for plane-wave photons - depends on the target atom’s position with respect to the optical vortex center. The data compare favorably with the theoretical predictions. The selection rules also point to circular dichroism and birefringence of the twisted light interacting with non-chiral atomic matter. Collaboration with Carl E. Carlson, Christian T. Schmiegelow, Ferdinand Schmidt-Kaler, and Maria Solyanik is gratefully acknowledged. [1] C. T. Schmiegelow, J. Schulz, H. Kaufmann, T. Ruster, U. G. Poschinger, and F. Schmidt-Kaler, Nature communications, 7 (October 2016), DOI: 10.1038/ncomms12998.

The fundamental notion of fixed order between two events is challenged by formulations of quantum mechanics that makes no reference to a global time. The indefinite causal order arising from these formalisms can be realised using the quantum switch, a device where two operations can act in two different orders simultaneously. Similar to entanglement verification which employ entanglement witness, we verify indefinite causal order using a causal witness. In our experiment, we use polarisation as a control for the order of the operations that act on the spatial mode of a photon. We measure a causal witness value of -0.16±0.013, below the threshold of zero, thus demonstrating indefinite causal order in the quantum switch.

On 23rd of January 2017 the first Bose-Einstein Condensate (BEC) in Space was created on-board the sounding rocket mission MAIUS-1. The successful launch marks a major advancement in the effort of performing matter wave interferometry with BECs on space vehicles. Its high BEC-flux enables more than 100 experiments during flight, characterizing the creation of BECs in space, their free evolution, state preparation, and the creation of cold atoms in highly dynamic environments. MAIUS-1 opens a new path towards space borne inertial sensing employing interferometers with high accuracy and sensitivity. Two follow-up missions will investigate dual-species interferometry. Recently several missions were proposed ranging from tests of the universality of free fall to gravimetry. Due to their small initial size and low expansion rates BECs are the ideal source for such an interferometric measurement. The findings of the mission will contribute to the NASA CAL project and BECCAL (NASA and DLR). This research is funded by DLR under grant 50WP1435.

Fractals are mathematical series that exhibit replicating patterns at every scale. If the repeated patterns are identical at every scale, the fractal is termed self-similar. Fractals have found their way into applications such as communication and cosmology. Theoretical simulations showed that the eigenmodes of unstable laser resonators possess a fractal character, in contrast with the well-known stable-cavity eigenmodes. Unstable laser resonators have a special plane, called self-conjugate, in which the eigenmodes not only have the same pattern, but are also magnified copies of themselves. Here, we show a novel optical resonator that is capable of generating eigenmodes with self-similar fractal features. Our novel resonator is considered as an analogue to both the monitor-insidemonitor effect and monitor-outside-monitor effects. The fractal feature is proved by finding a typical image of the eigenstate at different scales. More quantitatively, we measured the pattern dimension which had a non-integer value, as is characteristic of self-similar fractals.

There is interest in using spatial modes of light to increase the data speed of free-space optical communication where, each spatial mode can be used as a state or channel with which to encode or carry data, respectively. Here, the use of Hermite-Gaussian modes for free-space optical communication is investigated. It is shown that due their symmetry with respect to lateral displacement, as compared to other spatial modes, such as, orbital angular momentum modes, a subset of Hermite-Gaussian modes can experience less mode-crosstalk and -dependent loss when laterally displaced at the data receiver.

Scattering media are of great current interest, due to their potential applications in photovoltaic cells, efficient photocatalyzers, random lasers and novel optical functional devices. Here, we have introduced a core–shell scattering medium for random lasing composed by core-shell nanoparticles (TiO₂@Silica) suspended in an ethanol solution of Rhodamine 6G. Higher efficiency, lower laser threshold and long photobleaching lifetime were demonstrated in random laser. A promising method called fraction of absorbed pumping (FAP) has been introduced, which opens a new avenue to characterize and study scattering media. In this article, we also investigate the random laser action at the critical regime of localization by increasing considerably the concentration of TiO₂@Silica nanoparticles. Narrow peaks arising in the random laser emission spectrum are observed. The classical superfluorescence band of the random laser was measured separately by collecting the emission at the back of the samples, showing a linear dependence with pumping fluence without gain depletion. However, frontal collection showed the saturation of emission and absorption. The emission spectrum of the peak mode (localized modes) shows approximately equal intensity, indicating suppression of the interaction between the peaks modes. The linewidth of these peaks is lower than that of the passive modes of the scattering medium, which was attributed to an anomalous nonlinear increase of the refractive index by localization.

The on-demand tailoring of the properties of light, such as phase, polarization or spatial shape, has completely changed the landscape of photonic-based applications. In this way, complex light fields have become an ubiquitous tool in areas of research such as classical and quantum communications, optical tweezers and super-resolution microscopy, among many others. Here we will present some novel applications to optical metrology. First we will show how appropriate tailoring of the properties of light interacting with chiral molecules can enhance their chiral response by two orders of magnitude compared to circularly polarized light. As a second application, we will present a highly sensitive digital technique capable to measure layer thickness in the nanometer regime. This technique is interferometric in nature and contrary to others based on the same principle does not require the highly engineered construction of holders. Finally, we will describe a novel laser remote sensing technique that enables the direct measurement of the transverse component of velocity, a measure that up to now has relied in complicated techniques based on measurements of the longitudinal component of the velocity. This technique offers the possibility to also measure in a direct way the vorticity in fluids, a measure that is commonly measured through the curl of the fluid velocity.

Spatially resolved spectroscopy of vortex beams is able to test the state of optical systems, to decode specific information or to sensitively indicate light-matter interactions. Spectral maps of ultrashort vortex pulses generated by hybrid diffractive-reflective spiral phase plates were studied experimentally and theoretically. Local spectral maps were detected by high-resolution scanning with a fiber-coupled spectrometer. Distributions of spectral centers of gravity and second moments were analyzed for femtosecond pulses. Gouy rotation of characteristic spectral features in the proximity of a phase singularity as a function of propagation distance was indicated in the spectral domain. Angular rotation was found to be modulated by weak oscillations. Analysis of spectral meta-moments indicates a fast switching and twisting behavior of spatial chirp.

Light carries both spin and orbital angular momentum and the superpositions of these two dynamical properties have found many applications. Many techniques exist to create such light sources but none allow their creation at the femtosecond laser. Here we report on a novel mode-locked ytterbium-doped fiber laser that generates femtosecond pulses with higher-order Poincaré sphere beams. The controlled generation of such pulses such as azimuthally and radially polarized light with definite orbital angular momentum modes are demonstrated. A unidirectional ring cavity constructed with the Yb-doped fiber placed at the end of the fiber section to reduces unnecessary nonlinear effects is employed for self-starting operation. Two pairs of diffraction gratings are used for compensating the normal group velocity dispersion of the fiber and other elements. Mode-locked operation is achieved based on nonlinear polarization evolution, which is mainly implemented with the single mode fiber, the bulk wave plates and the variable spiral plates (q-plate with topological charge q=0.5). The conversion from spin angular momentum to the OAM and reverse inside the laser cavity are realized by means of a quarter-wave plate and a q-plate so that the polarization control was mapped to OAM mode control. To demonstrate the total spatiotemporal and vectoral characterization of the new type femtosecond laser beams, here, a polarization-sensitive Mach–Zehnder interferometer temporal scan technique was used, at the first time, to capture the complete information of the pulse. The corresponding measurement device, placed on the collimated and attenuated beam at the laser output and simply consists of a special Mach–Zehnder interferometer, a polarizing beam-splitter and two charge-coupled device (CCD) cameras. The reference beam with vertical polarization is exported from the cavity and attenuated to a suitable intensity by using a neutral-density filter. After Fourier filtering, removal of the reference curvature, correction of achromatic wave-front distortions, spectral phase and amplitude reconstructions, as well as the measurement for the intrinsic phase of the reference pulse, the complete information of the pulse will be obtained. This new measurement capability opens the way to in-depth characterization and optimization of the vector vortex femtosecond laser pulse and ultimately to the detection of new phenomena of the interactions between materials and structured femtosecond laser beams in space–time and polarization.

Circularly polarized optical vortices are known to possess spin and angular momenta dependent on the degree of circular polarization and topological charge. And it is expected to rotate when circularly polarized optical vortices are irradiated on nanoscale materials possessing electric susceptibility. This phenomenon can be understood from the time average of optical Lorentz force and when applying the electromagnetic field of arbitrary optical vortex, the direction of rotational force is not dependent on the frequency of incident light that has been confirmed by previous studies. Therefore, the rotational force can be induced by white light with common rotation axis. And it means that can convert sunlight into circularly polarized optical vortices, which has the merit of being an increase in light intensity and renewable energy. In addition, if it is possible to exert rotational motion on the object only by light irradiation, it is possible to rotate a nanoscale gear without requiring an electric circuit. In this study, in order to generate a white light optical vortex with circular polarization, a computer generated hologram (CGH) with structural birefringence was fabricated by electron beam lithography. The CGH exhibits a beam splitting property, in which arbitrary polarized light is split to a transparent light and two diffracted beams with mutually opposite handedness. By extracting a diffracted beam, a circularly polarized white light optical vortex beam was obtained. And the interaction between the generated optical vortex and a matter is investigated.

Optical vortex (OV) beams have received considerable interest in the recent years. For miscellaneous OV-based applications, one important issue is the generation of OV beams. A lot of approaches including both external and intra-cavity methods have been demonstrated. Meanwhile, using fibers for generating OV beams has also attracted more and more attention because of the inherent advantages of fibers, such as compactness, low cost, remote delivery and flexibility. Although, successful generation of OV beams with optical fibers has been demonstrated, one may also see several challenges, like narrow bandwidth, complex structures, and high insertion loss. In this paper, we propose and experimentally demonstrate a simple approach to realize controllable broadband OV generator using optical fibers. The generator consists of a single-mode fiber (SMF) of which the output end is spliced to a two-mode fiber (TMF) with a defined offset, two polarization controllers (PCs) applied on the SMF and TMF, and one polarizer. The polarizer located behind the output end of the TMF is used to filter the non-OV beams. By adjusting the two PCs, one can selectively convert an input fundamental mode to high-purity OV modes within a wide bandwidth (1480 nm ∼1640 nm). The measured extinction ratio of generated OV modes is larger than 20 dB. The proposed simple low-cost broadband fiber-based OV generator may have wide applications in the area such as fiber communications, sensing and imaging.

Here, we review our recent works about the realization of the spin-dependent manipulation of structured light by tailoring the polarization. We develop a theory for spin-dependent manipulation based on the polarization design. As the exemplary demonstration, our experimental results show that such a theory can attain the spin-dependent splitting, and spindependent diffraction. Furthermore, we demonstrate this theory can be also applied to the spindependent focusing. The scheme provides a possible route for the manipulation of spin states of photons, and enables spin-photonics applications.

Vector beams where the polarization state is spatially dependent are being examined as new optical communication channels. We demonstrate a vector beam spectrum analyzer capable of simultaneously determining the topological charge and the state of polarization of an input vector beam. We encode a two-dimensional polarization diffraction grating that generates six different q-plate channels from -3 to +3 in the horizontal direction, and each is split in the vertical direction into the six polarization channels at the cardinal points of the corresponding higher-order Poincaré sphere. The horizontal q-plate grating is a optimized phase-only grating that produces harmonics of a given input q-plate having a charge of +1 all of which have equal strengths. The vertical polarization grating is specially designed to produce 6 orders where the amplitude and phase of each order can be independently controlled. Different gratings are required for the horizontal and vertical polarizations to create the desired polarization states in each diffracted order. Consequently, we generate 36 different channels in parallel. We demonstrate this polarization diffraction element using a single phase-only liquid-crystal spatial light modulator in a reflective optical architecture. Details are given regarding experimental details on this process. Finally, we demonstrate that this system can act as a vector beam polarization state spectrum analyzer allowing both the topological charge and the polarization state of the input vector beam to be simultaneously determined in a single experiment.

The topological charge (l) is the parameter that defines the amount of orbital angular momentum (OAM) of beams carrying optical vortices. In this article we expand on a robust experimental method to determine the topological charge that we previously developed [B. Khajavi & E. J .Galvez, Opt. Lett. 42, 1516-1519 (2017)]. This method consist of using a pair of confocal lenses and a wedged optical flat as a shearing interferometer. The interference pattern produced by a pure OAM mode directly reveals the magnitude and sign of the topological charge: two conjoined forks with |l| + 1 number of tines pointing away from (towards) one another for l > 0 (l < 0). Superpositions of two modes with the same value of |l| but with the opposite sign produce shearing interference patterns that can be used the infer the value of l and the relative weight of the component modes.

The speckle pattern produced when a laser illuminates a random medium can, with appropriate analysis, be used to uniquely identify the wavelength of the illuminating source. We have demonstrated that principal component analysis can be used as a very sensitive probe of the speckle pattern produced by random prisms [1] and integrating spheres [2]. However, to date, the state-of-the-art realisations of speckle spectrometers have been based on the use of multi-mode fibres as the scattering medium [3] and on transmission matrix analysis approaches, achieving a compact and stable device with picometre resolution. Here, we show that the speckle pattern produced by propagation through a metre-long step-index multi-mode optical fibre can be analysed with principal component analysis to achieve a femtometre-precision wavemeter, and present progress in the measurement of complete spectra, which demonstrates the applicability of our approach to many existing experiments. Moreover, we demonstrate that the speckle wavemeter can be used as part of a feedback loop to stabilise lasers to a fractional stability of 10-9. With the freedom to lock the laser at any user-desired frequency and a robust, compact setup, the method holds promise for the new generation of portable cold atom experiments currently being developed for quantum technology applications. [1] M Mazilu, et al. Opt Lett 39, 96 (2014) [2] N K Metzger, et al. Nat. Commun. 8, 15610 (2017) [3] H Cao, J. Opt. 19, 060402 (2017)

Simultaneous spatio-temporal focusing describes the technique of spectrally dispersing an ultrashort pulse to increase it’s duration, before recombining all the spectral components to reform the short pulse at the focus of a lens. This has several advantages for optical applications using ultrashort pulses, enabling a focus with large lateral extent but displaying much greater axial confinement than with conventional focussing. Meanwhile non-linear propagation inside samples is also minimised. We extend the technique to generate multiple SSTF focal spots via holography. In contrast to previous implementations, a phase hologram is placed in the ultrafast beam while it is spatially chirped. Thus, we show that it is possible to create multiple focal spots formed by SSTF arranged in three dimensions. Demonstrations are given for ultrashort pulse laser machining on the surface and inside glass. Furthermore, due to the strong pulse front tilt exhibited by an SSTF spot, we show how multiple spots can be stitched together in space and time to generate extended intensity distributions. Spatially overlapped regions can be overlapped in time using the property of pulse front tilt such that holographic arrays of SSTF spots can be created with apparently no spatial separation.

Subsequently to the previous generation of ultrashort and ultra-broadband optical-vortex (OV) pulses (pulse energy: several tens of μJ) in few-cycle regime, we performed the generation of axisymmetrically polarized pulses with spatial complex amplitude modulation, which is suitable for a broadband spectrum. The generation system employs the combination of spatial light modulators in the 4-f configuration and a space variant wave plate as a common path interferometer. The spatial light modulators in the 4-f configuration offer the spatial dispersion compensation with respect to wavelength; in addition, the common path interferometer provides the stability to perturbation. We experimentally demonstrated the generation of various axisymmetrically polarized pulses by applying modulations of fundamental and higher-order Laguerre-Gauss modes with high purity. The experimental results show that we are able to generate arbitral axisymmetrically polarized pulses with spatial complex amplitude modulation.

A beam of light may exhibit a spatially varying polarization distribution. Furthermore, the polarization can also be locally singular or undefined, similar to the case of phase singularities found in scalar fields. In this context, Nye introduced a classification of such polarization singularities, which provides a very useful language for the study of polarized fields. If electromagnetic fields get spatially confined, exotic polarization phenomena and topologies can be observed. For instance, Freund proposed the appearance of so-called optical polarization Möbius strips in tailored three-dimensional electromagnetic field distributions created by intersecting two differently shaped and polarized light beams. The existence of such exotic structures was recently also proven experimentally for tightly focused polarization tailored light beams. In this presentation, we will briefly introduce our experimental scheme for measuring the electromagnetic field distribution of light at the nanoscale. Furthermore, we will review our recent and ongoing work on three-dimensional polarization topologies created by tight focusing of tailored or conventionally polarized light beams. We will also elaborate on the connection between points of transverse angular momentum and the existence of (Möbius-like) polarization structures in the propagation plane.

We study the pattern of polarization that results in the crossing of two complex light beams with orthogonal circular polarizations. We recently showed experimentally that crossed beams in opposite circular polarization produce a twisting of the polarization in 3-dimensions. We did this with one beam in a mode bearing an optical vortex and the other in a Gaussian mode. In this work we extend to both beams bearing optical vortices. We find that Mobius strips appear when the difference in topological charge is odd, and twisted ribbons appear when the difference is even.

Light structured in phase and polarization has proven extraordinary benefit for optical tweezing. However, the customization of focal, non-paraxial light landscapes still poses a challenge. We tailor novel focal landscapes including its intensity as well as three-dimensional polarization structure by complex vector beams, even combined with phase vortices. By focusing vector fields, whose polarization is oriented in flower- or web-shape, we fabricate intensity structures resembling bright flowers or dark stars. These structures are formed by transverse E_x,y as well as longitudinal E_z electric field components. We tune the z-polarization components as well as threedimensional focal volume E (x, y, z) = [E_x, E_y, E_z]^T on demand, optimizing its structure for optical trapping applications. Beyond, we prove their benefit for advanced optical trapping schemes by tweezing and orienting zeolite-L nano-containers.

Orbital angular momentum (OAM) beams, have attracted great attention in recent years. An OAM beam with a phase singularity is characterized by a helical phase front which provides an additional degree of freedom for wide amount of classical and quantum optical applications. However, despite many attempts to generate and manipulate OAM beams, a robust, reliable and scalable technique to directly address generation, multiplexing and low-loss transmission of the distinct OAM beams is still in great demand. Here, we review the development of all-fiber, ring core photonics lantern mode multiplexer to generate high quality OAM beams up to the second order within a broad spectral range of >550 nm. Our device is a 5-mode mode selective photonic lantern (MSPL) with an annular refractive index profile which is fully compatible with well-established ring core and vortex transmission fibers. Through the excitation of pairs of degenerate linearly polarized (LP) modes of the MSPL, we demonstrate the generation of high quality OAM beams up to the second order. In addition, we demonstrate multiplexing of two OAM modes (OAM+1+ OAM-2) to verify complex beam pattern generation of our all fiber devices. Furthermore, by splicing the end-facet of the photonic lantern to a ring core fiber, we achieve low-loss coupling of OAM modes while maintaining high contrast spiral phase patterns. These results demonstrate the potential of photonic lanterns for generating complex optical beams.

We experimentally demonstrate a robust Si-photonic waveguide architecture that realizes dynamically encircling an exceptional point (EP) in the optical domain and broadband asymmetric modal transmission as an essential consequence. The structure consists of a pair of coupled channel waveguides and an adjacent slab-waveguide patch that enable precise lithographic controls on the phase velocities and radiation rates of the guided photonic modes. Complex modal index and inter-mode coupling constant profiles required for the encircling-an-EP parametric control are precisely coded in the geometry of those elements. The device created on this basis induces the symmetry-exchanging adiabatic state flip for one transmission direction and symmetry-preserving anti-adiabatic state-jump for the transmission in the opposite direction. In fabrication, we use a state-of-the-art electron-beam lithography for creating mm-long devices with nm-scale transversal precision. A comprehensive spectral measurement for the intensity and phase distributions of the transmitted optical states is obtained with a specially designed phase-sensitive infrared microscopy integrated with a tunable diode-laser system and spectrum analyzer. On this basis, we confirm in the experiment the highly asymmetric modal transmission persisting over a broad spectral band exceeding 100 nm in the telecommunications window around 1,550 nm. Hence, we establish a substantive experimental step toward broadband non-reciprocal photonic devices based on the unique non-Hermitian dynamics.

We derive some of the properties of blackbody radiation using thermodynamic identities. A few of the results reported earlier (in Part 1 of the present paper) will be re-derived here from a different perspective. We show that the fluctuations of thermal radiation can be expressed as the sum of two contributions: one resulting from classical considerations in the limit when Planck’s constant ℏ goes to zero, and a second one that is rooted in the discrete nature of electromagnetic particles (photons). Johnson noise and the Nyquist theorem will be another topic of discussion, where the role played by blackbody radiation in generating noise within an electronic circuit will be emphasized. In the context of thermal fluctuations, we also analyze the various sources of noise in photodetection, relating the statistics of photocounts to energy-density fluctuations associated with blackbody radiation. The remaining sections of the paper are devoted to an analysis of the thermodynamic properties of a mono-atomic gas under conditions of thermal equilibrium. This latter part of the paper aims to provide a basis for comparisons between a photon gas and a rarefied gas of rigid identical particles of matter.

Optical trapping has proved to be a valuable research tool in a wide range of fields including physics, chemistry and material science. The ability to place and manipulate individual colloidal particles in a precise three-dimensional location has been highly useful for the understanding of soft matter phenomena and inter-particle interactions. It also holds great promise for nanoscale fabrication and ultra-sensitive medium sensing by enabling precise positioning of specific material building blocks. An interesting consequence of optical trapping is seen when a large number of particles are trapped in a single holographic trap that is significantly larger than the particle diameter. Due to the interference effects between the incident light and scattered light, the particles become strongly bound to one another. This can lead to the creation of large, highly ordered structures of colloidal particles, termed optical matter. The geometry of the structure is dependent on the phase and polarization profile of the incident optical beam. In this talk we discuss our research on the structural and dynamical effects on optical matter composed of plasmonic nanoparticles. We describe how the structures are formed from one particle up, and how their dynamics and structure are shaped by the size, phase profile, and polarization of the incident optical beam. Specifically we discuss how circular polarization can create an isotropic optical binding potential and induce rotation in the system, and how the rotation depends on the particle and beam characteristics.

When the light is illuminated to the tip-sample geometry, the thermal and the dipole responses are simultaneously created. Each of the response shows exactly different spectral behavior. The thermal response shows non-dispersive spectrum because of its absorptivity but the dipole response shows dispersive spectra because it is based on the refractive index. There is an interesting debating in this field by developing the photo-induced force microscopy (PiFM). The PiFM measures the force interaction between the sharp metal tip and the sample under a light illumination condition. Because both of the thermal and the dipole interaction may be contributed to the system, the origin of the chemical selectivity of the PiFM is not clear. Here, we address that the origin of PiFM is contributed by both of the thermal and the dipole response but they can be distinguished with respect to their experimental conditions: pulse width, sample size and tip size. We provide the rigorous theoretical modeling and experimental demonstration. Our understanding can be extend to the recent advances of the opto-mechanical nanoscopy and spectroscopy such as Photo-induced force microscopy, Photothermal infrared microscope (PTIR) and the Peak force infrared microscope (PFIR). We suggest the general theory to understand these opto-mechanical microscopy by using simple effective stiffness concept. Finally we provide the experimental demonstration for the each of the chemical imaging mode.

We report the observation of the optomechanical strain applied to thermal and to quantum degenerate $^{87}Rb$ atomic clouds when illuminated by an intense, far detuned homogeneous laser beam. In this regime the atomic cloud acts as a lens which focuses the laser beam. As a back action, the atoms experience a force opposite to the beam deflection, which depends on the atomic cloud density profile. We experimentally demonstrate the basic features of this force, distinguishing it from the well-established scattering and dipole forces. The observed strain saturates, ultimately limiting the momentum impulse that can be transferred to the atoms. This optomechanical force may effectively induce inter-particle interactions, which can be optically tuned.

Light can exert differential forces on left- and right-handed enantiomers, promising an all-optical route towards chiral resolution and controlled assembly of chiral nanostructures. However, enantioselective optical forces on nano-specimens are challenging to both control and quantify, since their magnitudes are predicted to be sub-piconewton-scale with nanometer-scale spatial variation. Here we demonstrate new methods to both strengthen and visualize these forces using achiral nanostructures. First, we show how plasmonic optical tweezers can enable selective optical trapping of enantiomers. Our technique combines plasmonic optical tweezers with a chiral atomic force microscope (AFM) probe. Illumination of the plasmonic tweezers with left- and right- circularly polarized light (CPL) results in distinct forces on the chiral AFM tip: the total optical forces exerted on a left-handed chiral tip are 10 pN stronger when illuminated with left-CPL than with right-CPL. Additionally, the transverse optical forces on this chiral tip are attractive with left-CPL, but repulsive with right-CPL. We use the AFM tip to map such chiral optical forces over the plasmonic tweezers with 2 nm lateral spatial resolution, showing distinct force distributions in all three dimensions for each handedness. Then, we show how high-index dielectric nanostructures and metasurfaces can increase enantiomer separation yields more than 50 times beyond CPL in free space. Mie theory and a local optimization algorithm indicate that magnetic multipolar Mie resonances supported by sub-micron silicon spheres increase both the circular dichroism signal and Kuhn's dissymmetry factor compared to CPL in free space. Importantly, these enhancements maintain the total molecular absorption rate, enabling efficient selective photoexcitation. Combined, our results suggest that achiral photonic nanostructures can significantly enhance chiral light-matter interactions, potentially enabling controlled enantiopure chemical syntheses, single molecule chiral spectroscopy, and dynamic monitoring of structural changes of chiral molecules with sub-nanometer resolution.

Laser materials processing has been widely investigated as a promising technology to develop and fabricate advanced structured materials on a nano or micro scale. Optical vortex, i.e. helical light, carries an annular intensity profile and orbital angular momentum arising from its helical wavefront, and it induces the wavefront-sensitive mass transport (so-called optical angular momentum transfer effects) with the help of the spin angular momentum associated with the circular polarization. Recently, we and our coworkers discovered that laser materials processing based on optical vortex illumination enables us to establish chiral structures in various materials, such as a metal, a silicon and an azo-polymer owing to the wavefront-sensitive mass transport effects. Such chiral structures will pave a pathway towards new optical devices, including chiral plasmonic metasurfaces for screening, collecting and identifying the chiral chemical composites at high accuracy and high sensitivity. They might also act as advanced functional materials such as water repellent finished surfaces as well as perfect absorbers. In this presentation, we review state-of-the-art chiral structures formed by optical vortex illumination, and we also detail the direct observation of the chiral structures formation by utilizing an ultrahigh speed camera. Further, we address a theoretical analysis of the optical radiation force induced by optical vortex illumination.

The extent to which structured light might conceivably resolve the handedness of chiral matter is a topic of resurgent interest, and it is one that has been a challenge since the earliest days of optical vortex studies. It has not even been certain whether or not the orbital angular momentum of light could interact in such a way – though it has been established that electric quadrupole interactions enable twisted light to engage with local electronic transitions. Crucially, certain recent experiments have provided tantalizing evidence to support the existence of a chiral effect that is sensitive to handedness, against initial expectations. By detailed electrodynamic calculation, a new study has now fully identified the mechanism, and also provided an in-depth analysis of the role of electric quadrupole transition moments as they engage with the phase gradient of beams with a twisted wavefront. Focusing on single photon absorption, it emerges that the orbital angular momentum associated with the vorticity of a structured beam can indeed be exhibited in chiral effects, provided the material itself is not only chiral, but also has some structural order – which essentially limits the effect to chiral solids, poled liquid crystals, and oriented arrays of chiral nanoparticles. Circular polarization is still required, and the extent of circular dichroism proves to vary around the beam, being locally determined by the absorber orientation with reference to the beam axis. In agreement with earlier studies, and consistent with symmetry principles, the new analysis verifies that any dependence on wavefront vorticity vanishes in a freely mobile fluid. The reformulation of theory now paves the way for an extension to other kinds of chiroptical phenomena in orientationally ordered systems.

We propose a novel high resolution microscopy technique for enantio-specific detection of chiral samples based on force measurement down to sub-100 nm where spectroscopic techniques for chirality detection encounter major challenges due to the very weak interaction of light with chiral nanoparticles. Specifically, we delve into the differential photo-induced optical force exerted on an achiral plasmonic probe in the vicinity of a chiral sample, when left and right circularly polarized beams separately excite the sample-probe interactive system. We analytically prove that the differential force is entangled with the enantiomer type of the sample enabling enantio-specific detection of chiral inclusions. Moreover, we demonstrate that the aforementioned differential force is linearly dependent on both the chiral response of the sample and the electric response of the tip and is inversely related to the quartic power of probe-sample distance. We support our theoretical achievements by several numerical examples, highlighting the potential application of the derived analytic properties. Lastly, we demonstrate the sensitivity of our method to enantio-specify nanoscale chiral samples. By establishing this high resolution measurement technique for biomedical applications, we essentially advance the characterization of chiral samples for controlling constructive reaction between drugs and receptors.

Photopolymerization, the process of using ultraviolet light to activate polymerization within resins, is a powerful approach to create arbitrary, transparent micro-objects with a resolution below the diffraction limit. We investigate photopolymerization of ultraviolet curing resins with a light field possessing orbital angular momentum (OAM). Due to total internal reflection of the beam within the cured polymer, the material acts as a waveguide, which develops into an optical fibre as long as submillimeters. Importantly, the cured polymer mirrors the energy flow and helical nature of the incident OAM field, resulting in an equivalent spiralling of the cured polymer waveguide itself. Moreover, the chirality of the helix, which is the direction of the spiral, can be controlled by inverting the handedness (reversing the sign of the azimuthal index or topological charge) of the incident field. As the fibre diameter becomes narrower due to self-focusing effects, incident light with higher topological charge cannot be maintained within the single-mode structure of the fibre. We show that the fibre repeatedly branches into a bundle of intertwined fibre guides, each of which carries a fundamental mode of the OAM. Such fibre structures represent a novel form of photonic lanterns. This research opens up a range of new vistas and has broad consequences for the fields of structured light, new approaches to writing novel mesoscopic structures and applications such as in detecting or sorting the OAM mode in areas including optical communications and manipulation.

Fully-structured light, light with non-uniform intensity, phase and polarization, lies at the heart of an extremely promising field of research, with applications in high-resolution imaging and optical trapping and manipulation of nanoparticles. Such fields are readily constructed from superpositions of two orthogonally polarized Laguerre-Gaussian modes carrying different orbital angular momentum (OAM). This opens new possibilities in engineering complex light distributions for specific applications. We simulate the propagation of fully-structured light in a self-focusing nonlinear medium using a coupled two-dimensional nonlinear Schrödinger equation with saturable self-focusing nonlinearity and show that the spatial structure of the polarization can be used to control both the collapse dynamics of the beams [1] and the amount of polarisation rotation. These findings provide a novel approach to transport high-power light beams in nonlinear media with controllable distortions to their spatial structure and polarization properties. Complex light can also have non-uniform helicity density and the resultant gradients in helicity density will generate a force that will interact differently with opposite enantiomers of chiral molecules [2]. Here we demonstrate how the energy and helicity gradients in the fields, and the corresponding dipole and chiral forces, can be engineered for specific applications. We also investigate the use of nonlinearity to control and manipulate the spatially-varying chiral force. [1] F. Bouchard et al., Phys. Rev. Lett 117, 233903 (2016) [2] R. Cameron et al., New J. Phys. 16, 013020 (2014)

Optical magnetism has long been the elusive, missing component in light-matter interaction. Interesting applications may emerge if optical magnetism is effectively harnessed and exploited. Of particular interest is the possible manipulation of the optical magnetic force, in the form of photo-induced magnetic force microscopy. We propose an optical system for inducing magnetic forces in an axis-aligned Si disk under azimuthally polarized beam illumination. The designed Si disk can support a magnetic resonance in the visible range under azimuthal polarization by interacting with the longitudinal magnetic field at the overlapping axis. Such structure can serve as the unique magnetic probe to “feel” the magnetic force of light. In our current step, we use photo-induced force microscopy to characterize the near-field electric field distribution of this system. Measurements show a stronger electric field enhancement near the edge of the Si disk which indicates a longitudinal magnetic field enhancement at the overlapping axis. This measurement is in accordance with theoretical modeling, confirming the observed magnetic enhancement. This indirect measurement on the magnetic response of the Si disk defines an important step towards our final goal of achieving direct mapping of the local magnetic field with photo-induced magnetic force microscopy. Also, our methodology can be extended to the characterization of arbitrary nanostructures, including metamaterials and metasurfaces, under structured light illumination.

Pancharatnam-Berry (PB) phase is known as the geometric phase associated with the polarization transformation of light. In this work, we reveal the PB phase of light generated during the transformation from a single polarization to a spacevariant one. To realize the space-variant polarization transformation, we utilized our early developed approach based on a Sagnac interferometer. The two spin states of the output field contain different PB phases. By tailoring the PB phase, we demonstrate the spin-dependent propagations of light beams. Besides, the PB phase can also be used for measuring the polarization distribution of vector beams.

We demonstrate the transfer of orbital angular momentum (OAM) to optically levitated microparticles in vacuum. We create two-dimensional (2D) and three-dimensional (3D) optical potentials possessing OAM. In the former case the microparticle is placed within a Laguerre-Gaussian (LG) beam and orbits the annular beam profile with increasing angular velocity as the air drag coefficient is reduced. Our results reveal that there is a fundamental limit to the OAM that may be transferred to a trapped particle, dependent upon the beam parameters and inertial forces present. Whilst a LG beam scales in size with azimuthal index, recently we have created a “perfect vortex” beam whose radial intensity profile and radius are both independent of topological charge. As the Fourier transform of a “perfect vortex” yields a Bessel beam, imaging a “perfect vortex”, with its subsequent propagation thus realises a complex three-dimensional optical field. In this scenario we load individual silica microparticles into this field where the optical gradient and scattering forces interplay with the inertial and gravitational forces acting on the trapped particle. As a result the trapped microparticle exhibits a complex three-dimensional motion that includes a periodic orbital motion between the Bessel and the “perfect vortex” beam. We are able to determine the three dimensional optical potential in situ by tracking the particle. This first demonstration of trapping microparticles within a complex 3D optical potential in vacuum opens up new possibilities for fundamental studies of many-body dynamics, mesoscopic entanglement, and optical binding.

Structured light is readily used to control and investigate microsystems. Dynamic manipulation of microscopic particles of matter has enabled non-contact investigations of a large number of complex physical, biological and chemical systems. In recent years, ever more sophisticated techniques to control microsystems have been developed, shadowing rapid advances in computer technology. This work utilises computational and other signal processing techniques to dynamically control input light fields and modulate the scattered output light fields to improve the specificity of measurements using either optical switching or beam shaping. The aggregate properties of structured light such as linear and angular momentum are changed when scattered from a particle. We present improvements to measurement of signals otherwise hidden in noise or other larger signals by selectively filtering considering the amplitude, phase or wave function symmetry. Measurements are demonstrated using both liquid crystal spatial light modulators and digital micromirror devices. Further challenges that occur in development of these techniques will be discussed as well as their use when applied to specific experiments. We will give an overview of both past successes in measurement of position, force and angular momentum transfer and other current research developments.

After years of working on light-driven trapping and manipulation, we can see that a confluence of developments is now ripe for the emergence of a new area that can contribute to nanobiophotonics - Light Robotics - which combines advances in microfabrication and optical micromanipulation together with intelligent control ideas from robotics, wavefront engineering and information optics. In the Summer 2017 we are publishing a 482 pages edited Elsevier book volume covering the fundamental aspects needed for Light Robotics including optical trapping systems, microfabrication and microassembly as well as underlying theoretical principles and experimental illustrations for optimizing optical forces and torques for Light Robotics.

In contrast to many micromanipulation and microassembly techniques, optical tweezers (OT) are non-contact and are fully capable of 3D positioning. While OT have been used extensively for the ultra-precise measurement of small biomechanical forces and displacements, more recently, OT have been proposed for applications such as cell sorting, tissue engineering, and micro/nano fabrication, which all require larger translation distances and stronger forces. In these applications, manipulation speed is a key specification, but the majority of OT systems do not have the ability to reach the high velocities necessary to compete with other micromanipulation techniques in terms of throughput. In order to create faster OT systems, it is essential to understand the factors that limit the maximum manipulation speeds for different objects. Here, we present our measurements of the maximum lateral transport speeds of polystyrene, gold, and silver spheres ranging from 100 nm to 5 µm in diameter as a function of trapping beam power over a long translation distance of >0.5 mm. In particular, we investigate the behavior at high laser powers, beyond the traditional linear relationship between laser power and maximum manipulation velocity that is predicted by the balance of Stokes’ drag and optical gradient forces. We find that the nonlinear relationship between laser power and maximum velocity depends on the particle size and material, and may be caused by different factors, such as mechanical vibrations or thermal effects. Furthermore, to our knowledge, we demonstrate the fastest recorded object manipulation speed achieved using optical tweezers of 0.22 mm·s-1.

In this contribution, the efficient trapping of low refractive index nanoparticles, with radii down to 50 nm, is numerically demonstrated in gold dimers coupled with SOI waveguides. This coupled scheme provides a strong excitation of the plasmonic resonators [1] that, in combination with the field enhancement occurring in dimers, leads to an ultra-efficient trapping. Without any needs of cumbersome optical elements, this excitation scheme does not affect the overall portability of the system and stands out as a perfect candidate for integration inside microfluidic systems [2], for nanoparticle immobilisation and analysis. The possibility to trap smaller nanoparticle, with radii down to 5 nm, having higher refractive index will be discussed. The impact of the geometrical parameters of the dimer on the optomechanical well stiffness and depth, the optimisation strategies, the simple fabrication approach and the ongoing experimental demonstration will be as well detailed.

[1] M. Fevrier, P. Gogol, A. Aassime, R. Megy, C. Delacour, A. Chelnokov, A. Apuzzo, S. Blaize, J.-M. Lourtioz et B. Dagens, ≪Giant Coupling Effect between Metal Nanoparticle Chain and Optical Waveguide,≫ Nano Letters, pp. 1032-1037, 2012.

[2] G. Magno, A. Ecarnot, C. Pin, V. Yam, P. Gogol, R. Megy, B. Cluzel et B. Dagens, ≪Integrated plasmonic nanotweezers for nanoparticle manipulation,≫ Optics Letters, vol. 41, n° 16, 2016.

Optical manipulation of gold nanoparticles has facilitated a wide range of innovative science and applications such as nanothermometry, cell poration, optical binding and optomechanics, with many exploiting the surface plasmon resonance. However, conventional gold nanoparticles usually depart from spherical shape and typically exhibit icosahedron, decahedron, triangular or hexagonal prism, thus making such studies less controlled and leading to potential artefacts in trapping behaviour. We successfully synthesise ultrasmooth gold nanoparticles of 50nm and 100nm in diameter with an improved monodispersity both in shape and size compared to conventional gold nanoparticles. We demonstrate the first optical manipulation of such ultrasmooth gold nanoparticles in a near infrared optical trap, and show trap stiffness with up to a three-fold reduction in standard deviation both in liquid and air, compared to conventional gold nanoparticles. Our trapping study highlights the exceptional sensitivity of the trapping parameters of gold nanoparticles on their morphology. Furthermore, we for the first time quantify the particle temperature of airborne gold nanoparticles for a range of optical powers based on the trap stiffness measurements and reveal the effects of particle morphology. We show our ultrasmooth gold nanoparticles exhibit lower temperature than the conventional counterparts due to the lack of additional morphological features that induce plasmonic heating. The use of ultrasmooth gold nanoparticles can pave the way for more controlled studies of optical binding and plasmon mediated light-matter interactions and novel applications in optomechanics such as optically controllable nanoprobes of weak forces and torques.

Optical trapping using focused laser beams has been proven extremely useful for contact-less manipulation of a variety of small objects, including colloidal plasmonic nanoparticles [1]. We found that single-crystal gold nanorods with side-lengths of the order 160 nm could be easily trapped and manipulated in 2D by laser tweezers inside thin liquid cells compatible with standard optical microscopy [2]. The nanorods could be driven to rotate at frequencies above 40 kHz (2.5x106 r.p.m.) by applying circularly polarized laser light with power as low as a few mW. The driving torque, caused by transfer of photon angular momentum (spin), is dominated by plasmonic resonant scattering rather than absorption, which drastically reduces laser-heating effects and allows for sensitive control of the optomechanical properties through the particles nanoscale morphology. Single nanorods could be operated as rotational nanomotors and kept spinning for hours. By varying the applied laser power, the surface temperature of the rotating nanorods could be varied from close to room temperature to well above the boiling point of water. This provides a simple means of thermal control over chemical or conformational reactions of adsorbed molecules on the particles, which can be read out via either changes in the rotation frequency or rotational Brownian fluctuations [3]. References [1] A. Lehmuskero, P. Johansson, H. Rubinsztein-Dunlop, L. Tong, M. Käll, Laser trapping of colloidal metal nanoparticles, ACS Nano 9, 3453-3469 (2015) [2] L. Shao, Y. Zhong-Jian, D. Andrén, P. Johansson, M. Käll, Gold nanorod rotary motors driven by resonant light scattering, ACS Nano 9, 12542-12451 (2015). [3] F. Hajizadeh, L. Shao, D. Andrén, P. Johansson, H. Rubinsztein-Dunlop, M. Käll, Brownian fluctuations of an optically rotated nanorod, Optica 4, 746-751 (2017).

We design and implement a software for use in real-time light shaping and biophotonics applications. Design considerations are addressed as well as options to mitigate common performance issues that arise in actual use. Testing was done on actual spatial light modulator hardware at 800x600 and 2048x2048 resolutions. Software performance is measured and analyzed.

The past several years have seen an accelerated development of technologies and methods that enable the non-invasive analysis of single cells. These are vital as single cell studies provide important evidence and deepen our understanding of how networks of cells work and evolve. Exploring the full potential of our dynamic user-interactive optical trapping system (Biophotonics Workstation), we can surround various types of cells with other cells or other microscopic objects, thus studying the relation between confinement and cell growth.

Scattering scanning near field optical microscopy (s-SNOM) is a useful tool for providing optical resolution well below the diffraction limit with chemical selectivity. s-SNOM relies on recording the scattering light of a scanning probe tip, coupling the near-field interaction to a far field photo-detector. Photo-induced force microscopy (PiFM) is a much newer technique that also provides chemical resolution well below the diffraction limit. In PiFM, the signal arises from measuring the light induced force on a scanning probe tip of a sample interacting with laser light. It measures and records all information in the near field, with no need for a photo-detector. In this presentation, we describe results comparing and contrasting s-SNOM and PiFM displaying the strengths and weaknesses of both methods.