MEMS deformable mirrors (DM) have many merits of low drive voltage, high response speed, small power consumption, low cost and small size. Its surface shape and displacement versus applied voltage are significant factors of MEMS DM. Phase-shifting interferometer (PSI) has many advantages such as non-contact, quickness and high precision. A phase-only liquid crystal spatial light modulator (LC-SLM), as a linear phase-shifter in PSI, is linear calibrated for its phase-shift characteristics. The PSI is set up to measure the static characteristic of MEMS DM. Five-step phase-shifting method is used to calculate the phase distribution from interference fringes, and Global phase unwrapping algorithm to solve the holes, noise and breakpoint of interfere images. Compared to the measurement results using Zygo instrument, these two experimental results are very close. The experiment results show, this measuring system is very reliable, convenient and cheap. Moreover, this test system need not stitch some fringe images to get the whole surface shape of the mirror like the Zygo instrument.
The generation of a variable diameter annular flat-top laser beam in the far field based on an adaptive weight FFT-based iterative algorithm (AWFFT-IA) and a phase only liquid crystal spatial light modulators (poLCSLM) is demonstrated. The iterative algorithm is used to design the needed phase distribution written on the poLCSLM for the target diameter annular flat-top laser beam shaping. The experimental results show that the method proposed can concentrates about 71% of the incident laser energy into the desired region and the root mean square error (RMSE) of the tailored flat-top intensity profile is more or less 12%.
An adaptive-weight fast-Fourier-transform-based iterative algorithm is proposed for far-field flat-top beam shaping. This algorithm inherits the projection optimization idea from the Gerchberg-Saxton algorithm, but the far-field amplitude for inverse fast Fourier transform is adaptively modified by using a novel optimized adaptive-weight strategy. First, the application of this method to square flat-top intensity-profile beam shaping is discussed as an example. The pure-phase distribution simulated by 100 iterations of this method concentrates 93.89% of the incident laser energy into the desired region and the root mean square error (RMSE) of the tailored flat-top intensity profile is 0.0094. Less than 20 iterations of this method concentrate more than 90% of the incident laser energy into the desired region and the RMSE of the tailored flat-top intensity profile is under 0.05. Then, the applicability of the method to designing the phase distributions for variable-shape or variable-diameter flat-top beam shaping is demonstrated.
Multi-beam technology is one of the key technologies in optical phased array systems for multi-object treatment and
multi-task operation. A multi-beam forming and steering method was proposed. This method uses isosceles triangle
multilevel phase grating (ITMPG) to form multiple beams simultaneously. Phase profile of the grating is a quantized
isosceles triangle with stairs. By changing the phase difference corresponding to the triangle height, multiple beams can
be steered symmetrically. It took 34 ms to calculate a set of parameters for one ITMPG, namely one steering. A liquid
crystal spatial light modulator was used for the experiment, which formed 6 gratings. The distortion of which had been
compensated with the accuracy of 0.0408 λ. Each grating included 16 phase elements with the same period. Steering
angle corresponded to the triangle height, which is the phase difference. Relative diffraction efficiency for multiple
beams was greater than 81%, intensity nonuniformity was less than 0.134, and the deflection resolution was 2.263 mrad.
Experimental results demonstrate that the proposed method can be used to form and steer symmetrical multiple beams
simultaneously with the same intensity and high diffraction efficiency in the far field, the deflection resolution is related
to the reciprocal of grating period.
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