37-channel modal liquid crystal wavefront correctors with a 30 and 80 mm diameter aperture are developed. Optical response, voltage-phase and dynamic properties of the devices have been studied. The possibility of synthesis of low order aberrations was experimentally demonstrated.
For the first time, experimental samples of adaptive liquid-crystal lenses that require no additional lighting for wave front shaping by the wave's intensity variation are presented. Both spherical and cylindrical lenses are fabricated and investigated.
Spherical and cylindrical lenses with intensity dependent focal length are investigated experimentally. The lenses were photosensitive enough for incident laser power about 0.5 mW/cm2. Two adaptive systems are implemented to demonstrate
feasibility of a) power-in-diaphragm stabilization and b) auto-correction of defocus, in all-optical setups. With very little efforts on optimization, the first system reduced intensity variation of 150% down to less than 5%, and the second one practically removed the optical power variation in the output beam when of the input beam optical power increased up to 0.46 dptr.
A novel design for optically addressed modal liquid-crystal adaptive lens is presented. Described is the implementation of the 2-layer lens, a simplified model explaining its performance, and first experimental results on wave front shaping and focusing by the optically addressed lens.
Static and dynamic numerical models of electro-optical characteristics of nematics are presented. A numerical model is used for the optimization of phase delay distribution in modal LC lenses. The dynamic control mode for modal LC lenses is simulated. The results are in a good agreement with experiment.
We suggest a new way to compensate for the thermal lensing effect in the mid-power solid-state lasers. This can be done by the use of a liquid-crystal adaptive lens with optically controlled focal length (optically addressed lens -- OAL) which is a modification of the modal liquid crystal lens (MLCL) which has recently been suggested and successfully implemented. The phase shift introduced by OAL into the transmitted light wave is theoretically shown to correspond to a converging lens whose focal length depends on the light intensity distribution across the aperture. OAL implements an intra-cavity optical feedback, which can effectively compensate for the laser beam defocus resulted from the emerging thermal lensing. For various types of resonators the beam stability is improved by the use of OAL. Correction becomes more effective if the OAL is positioned close to the laser rod.
A novel method to control LC phase modulators is presented. Various modifications of modal LC correctors are described in detail, including adaptive spherical and cylindrical lenses and a 37-element wavefront corrector. Physical mechanisms are explained with the emphasis on their practical implications.
Detailed analysis of electric voltage distribution and electric currents in adaptive liquid crystal (LC) based lenses is presented. Approximation of constant LC layer impedance is shown to be useful for physical insight. More generally, a computer simulation is developed, taking into account the voltage dependencies of the LC capacitance and conductance. Computer simulated phase shift distributions are in good agreement with experimental profiles produced via Zigo interferometer measurements. Also addressed is the influence of the lens's electrical parameters on its dynamics.
Model adaptive liquid crystal lenses are described with the emphasis on their performance. Process of the lens calibration is described and numerical and experimental calibrations are carried out. Imaging by the modal adaptive lens is implemented, as well as the focusing in the feedback system based on the adaptive LC lens.
A new type of phase liquid crystal modulators with distributed electrical parameters is proposed. These modulators make it feasible to use minimal number of electrodes to from a desirable phase shape. We devised methods of control and investigated the modal liquid crystal cylindrical and spherical lenses, and the multi-element wavefront corrector with controlled influence as well. The focusing by means of the adaptive lenses is presented. We demonstrate two approaches in optimal control. The first consists in computing the optimal control voltage through liquid crystal and lens parameters. The second consists in feedback use.
A novel approach to the liquid crystal modulators design is suggested under which the liquid crystal is treated as a distribution capacitor. To control the capacitor, we introduced a distribution high resistance control electrode. We devised methods of control and investigated modal liquid crystal modulators that can be used as adaptive cylindrical and spherical lenses. Analytical derivations, computer and experimental results are presented and discussed.
We used a combined approach, investigating capacitance, resistance, and electrooptic reply of nematic liquid crystals within the same experimental framework, which enabled us to plot the phase delay as a function of electric parameters. Phase delay vs. capacitance curves are almost linear, but the slope is frequency dependent for the liquid crystal with the low-frequency dispersion of the dielectric anisotropy. To interpret the results, equivalent electric parameters definition, consistent with the AC current measurement techniques, is presented and phenomenological theory of the RC-parameters is developed. When completed by the Ericksen-Leslie equation for the liquid crystal molecules realignment in the external electric field, the theory is in good agreement with the experiment.
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