We developed a liquid-crystal spatial light modulator having a 30 mm active area and a multilayered dielectric mirror for industrial infrared lasers to establish an innovative manufacturing and fabrication technique in the smart-manufacturing post-pandemic era. The reconstruction of computer-generated holograms was achieved to demonstrate the concept of this device in the IR region. The incident phase performance characteristics of this device under high-power laser irradiation were obtained using a 1030 nm ultrashort pulse laser. The work presented here will accelerate the use of liquid-crystal SLMs in high-precision laser processing of the process-resistant materials and high-throughput processing for additive manufacturing.
In this study, we developed a liquid-crystal spatial light modulator with high laser power capacity for industrial ultrafast pulse lasers to demonstrate innovative manufacturing and fabrication techniques using a cyber-physical system. The incident phase performance characteristic of this device was obtained with a 60 W, 1035 nm ultrafast laser. This research work will help to accelerate the use of liquid crystal spatial light modulators for high-precision laser processing of resistant materials and high-throughput for additive manufacturing.
Beam shaping techniques with diffractive optical elements have garnered considerable attention for laser material processing and microscopy because of their high efficiency of light utilization. Particularly, the design of top-hat beams with several shapes including circular and rectangular is required to facilitate a high-throughput system for line scanning and surface peeling applications. In this study, we propose a diffractive beam shaping method for the generation of a tophat beam with arbitrary shapes under tight focusing conditions. We implemented the iterative Fourier-transform algorithm (IFTA) with an error function in the form of a Gaussian distribution in the input laser beam to calculate an optimized phase distribution for generating a top-hat beam with arbitrary shape. This phase distribution was generated with a phase-only spatial light modulator and relayed with an optical system to the pupil of an objective lens with a numerical aperture of 0.75. The point spread function under the focal spot was observed with a microscopic imaging system placed opposite to the beam focusing optics. We experimentally demonstrate that the size of the focused top-hat beam is twice the size of the airy disk under tight focusing conditions. Further, we measure the profile of the generated beams. The proposed method with a spatial light modulator offers an adaptive control on the uniformity of the generated distribution, which fluctuates according to the effect of slightly different laser conditions on the diameter and profile of the input beam.
Dynamics of micrometer-sized dielectric objects can be controlled by optical tweezers with scanning light, however, the trapped objects fail to track the scan when drag exceeds the trapping by too quick movement. On the other hand, optical vortices (OVs), which have a property of carrying angular momenta, can directly control torque on objects rather than their position. Laguerre-Gaussian (LG) beams are the most familiar examples of OV and have been studied extensively so far. Revolution of the objects trapped by the LG beams provides typical models of nonequilibrium statistical system, but stable mid-water trapping by the LG beams becomes essential to evaluate physical properties of the system without extrinsic hydrodynamic effects,. Nevertheless, off-axis revolutions of small objects trapped in mid-water by the LG beams have not yet been established with secure evidences. Here we report stable off-axis trapping of dielectric spheres in mid-water using high-quality LG beams generated by a holographic complex-amplitude modulation method. Direct evidence of the three-dimensional off-axis LG trapping was established via estimating the trapping position by measuring the change of revolution radii upon pressing the spheres onto glass walls. Resultantly, the axial trapping position was determined as about half the wavelength behind the beam waist position. This result provides a direct scientific evidence for possibility of off-axis three-dimensional trapping with a single LG beam, moreover, suggests applications as powerful tools for studying energy-conversion mechanisms and nonequilibrium nature in biological molecules under torque.
We report holographic generation of higher-order Laguerre-Gaussian (LG) beams using a liquid crystal on silicon
spatial light modulator (LCOS-SLM) device. In our experimental set-up, a flat-top light beam was projected
on the LCOS-SLM to generate LG beams of various mode indices without changes of the optical system. Additionally,
the size of the holographic phase pattern was optimized for each beam to maximize the mode purity
of the obtained beam. Holographic generation of LG beams is easily influenced by a distortion of the optical
system and deviation of the phase setting from an ideal one. Nevertheless, we obtained high-quality LG beams
with an additional phase pattern on the LCOS-SLM for canceling the distortion of the optical system and with
calibration of the phase control voltage for precise expression of the phase patterns. Numerical analyses are
also performed for two-dimensional beam profiles to verify the quality of the obtained beams. Through fitting
the obtained profiles to theoretical ones, we calculate the correlation coefficients R between the observed and
fitted profiles to find that R > 0.95 for all beams and that the correlation coefficients behave similarly to the
theoretically estimated mode purities, facts indicating that the quality of the obtained LG beams is close to the
theoretical limit in our experiments.
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