Non-linear optical properties of titanium nitride nanoparticles were examined using the modified z-scan technique with simultaneous acquisition of the Rayleigh scattering at the direct angle to the polarization plane of a probe laser beam. The real and imaginary parts of the effective dielectric function of nanoparticles, depending on the pump intensity, at the wavelength of 355 nm and the laser pulse energy of 5.8 mJ were reconstructed from the obtained experimental data and displayed using the Cole-Cole diagram technique.
The results on the low-frequency photo-conductivity of the thin randomly inhomogeneous WO3 layers are presented. The layers were formed using deposition of water-suspended WO3 micro-particles onto the glass substrates with flat interdigital electrode systems. The wavelength-dependent photo-conductivity was analyzed in the spectral interval covering the edge of the fundamental absorption band (from 440 nm to 520 nm). The estimated Urbach energy of the examined system occurred equal to ≈ 0.13 eV at 308 K.
We theoretically demonstrate a capability of injection-locked semiconductor laser to serve as a nonlinear device for suppression of the amplitude disturbances in a phase-modulated optical signal and significant BER improvement in DPSK optical communications.
Numerical model for calculations of spatio-temporal variations of amplitudes of counter-propagating pulses in a standing-wave laser cavity is proposed. Proposed model is based on the transport-type equations for the envelopes of oppositely running pulses, spatial discretization along the cavity axis, and calculation of temporal variations both electric field amplitude and active media polarization/inversion at these points.
The dynamics of radiation of a two-frequency laser with a vertical cavity is studied by numerical methods. The dependence of the amplitude of the electric field in the stationary regime of laser radiation on the gain is shown.
The numerical investigation of difference frequency generation in a system of two-wavelength semiconductor lasers with a vertical external resonator is presented. Maps of dynamic regimes on the plane of parameters “pump power - delay time in the external resonator" are constructed. The regions of continuous wave, periodic oscillations, as well as quasiperiodic and chaotic oscillations of the radiation intensity are distinguished. The existence of stable periodic motions of the system can be explained in terms of the concept of synchronizing the frequency of normal modes with the frequency of intermode beats.
The DC conductivity of thin random layers of anatase nanospheroids deposited onto the insulating substrates with interdigital electrode systems was experimentally studied using pulse-periodic laser irradiation near the edge of the fundamental absorption band of anatase. Evaluation of the conductivity slew rate at the beginning of laser irradiation depending on the laser wavelength was used for estimation of the Urbach energy of the examined system at various temperatures. Obtained results are compared with the previously reported data relating the Urbach energy of the densely packed ensembles of anatase nanotubes at room temperature.
We present a theoretical investigation of two longitudinal mode microelectromechanical system (MEMS)-tunable vertical-cavity surface-emitting laser (VCSEL). The spatio-temporal dynamics of semiconductor laser with particular focus on the parameters relevant for THz photomixing is studied. A four-level model which allows for the polarization of the laser field by including the spin sublevels of the conduction and valence bands of a semiconductor is introduced. The maximum obtained wavelength separation between modes is ~30 nm which corresponds to 3.77 THz in frequency range.
The transient power characteristics of a singly resonant optical parametric oscillator is theoretically described. When analyzing we apply the time delay mathematical model. It is shown that the system demonstrates a variety of regimes with the variation of control parameters.
We present a study of the features of generalized synchronization in laser models involving coupled class B lasers with delay, as well as the singularities of synchronization of large ensembles, arising from the antiphase synchronization of individual pairs of lasers.
We introduce a new type of microresonator for frequency selection in a terahertz (THz) generator. The THz source by itself is based on intracavity difference frequency generation in two-color fiber laser. We show that asymmetrical nanoscale deformation can fully localize whispering gallery modes and filter out two modes for difference frequency generation with high effectiveness. Our theory confirms localization of whispering gallery modes (WGMs) for typical longitudinal dimensions of the microresonator 10-100 μm. In this case the theory is in excellent agreement with the experimental results obtained previously. A simple condition for the stability of this geodesic corresponding to the appearance of a high Q-factor nanobump microresonator is found.
We investigate complex dynamics of two coupled nonidentical Land-Kobayashi oscillators. It is shown that at low values of feedback rate variation of delay only leads to alternation of periodic and stationary regimes. The analysis of characteristic regimes of the system in a wide range of parameters is provided. We demonstrate that the system under study is multistable. With the variation of control parameters sole fixed point repeatedly undergoes supercritical Andronov-Hopf bifurcations, which leads to an increase in the number of limit cycles co-existing in the phase space. It is shown that multistable states are formed by different combinations of the periodic, quasi-periodic and chaotic regimes.
We study the dynamics of a neodymium-doped fiber laser coupled to ytterbium-doped fiber laser via nonlinear crystal which is placed inside the resonator. The transient signals may present different profiles depending on several conditions (degree of coupling between both lasers, pump powers of each one, resonator length, etc.) In particular, an appropriate choice of working conditions makes possible to suppress relaxation oscillations and to shorten the time elapsed since the moment of pump switch-on till steady state.
Recently introduced Surface Nanoscale Axial Photonics (SNAP) is based on whispering gallery modes circulating around the optical fiber surface and undergoing slow axial propagation. In this paper we develop the theory of propagation of whispering gallery modes in a SNAP microresonator, which is formed by nanoscale asymmetric perturbation of the fiber translation symmetry and called here a nanobump microresonator. The considered modes are localized near a closed stable geodesic situated at the fiber surface. A simple condition for the stability of this geodesic corresponding to the appearance of a high Q-factor nanobump microresonator is found. The results obtained are important for engineering of SNAP devices and structures.
We propose a method of generation terahertz radiation based on difference frequency mixing of colliding femtosecond
pulses in the wavelength range 1550 nm. Obtaining a defined frequency difference is due to stimulated
Raman soliton generation via splitting of multisoliton replica pulses in a photonic-crystal fiber. Pulse train is
generated by a single laser. The results of numerical simulation of such process, based on the solution of the
modified nonlinear Schrödinger equation, which includes the impact of higher-order dispersion, the optical Kerr
effect and Raman amplification are presented. One of the easiest ways to generate pulses with a frequency
difference is to use the fibers with variable dispersion.
We present the numerical study of terahertz generation via different frequency mixing in two-wavelength vertical
external cavity surface emitting laser. Nonlinear crystal is placed inside the resonator to increase terahertz
radiation power. The dynamical model is based on modified Lang-Kobayashi equations. Numerical simulation
through varying round trip time in the external cavity and feedback rate is presented.
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