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The properties of the designed anisotropic diffraction structures based on the spatially structured electrically-controlled liquid crystal elements have been studied. Such a di.raction structure represents interchanging layers of a nematic liquid crystal with planar and twist orientations of the director. It is formed when a photosensitive polymer is subjected to the e.ect of polarized ultraviolet radiation through a photolithographic mask. It is shown that increase in voltages leads to transformations of the liquid crystal structure. At minor voltages the diffraction structure may be considered as two amplitude gratings with orthogonal polarizations at the output. At the voltage associated with the broken Mauguin condition (optical threshold of the twist effect) the amplitude-to-phase transformation of the di.raction structure takes place and its diffraction e.ciency becomes higher. The proposed theoretical model enables one to explain the relationship between di.raction characteristics of a di.raction element and applied voltage or polarization of light. A good agreement of theoretical and experimental results is demonstrated.

The generation of spatial rogue waves, or “hot spots,” is demonstrated experimentally in the passively Q -switched Nd:YAG laser system operating in a low-power regime well below the self-focusing limit. Here, we report the dependence of rogue wave statistics on the number of transverse modes that interact in the laser cavity. Our observations show that spatial rogue waves are most likely to occur when the laser exhibits complex output beam configurations that are formed by a large number of interacting high-order transverse modes. These results confirm the hypothesis that one of the main factors affecting the emergence of spatial rogue waves in solid-state lasers is the number of laser transverse modes.

This paper presents the cavity dumping method by the second harmonic generation in a neodymium laser operating in the Q-switched mode. Theoretical modeling of the laser generation in dynamics is performed. The main characteristics of the output pulses and their dependence on the pump power and coefficient of losses are calculated. The proposed method can be implemented in the laser with a second harmonic crystal inside the cavity and an electro-optical crystal, which is operated by a step voltage pulse. The switching pulse length is defined by the time needed to achieve the maximum giant pulse intensity in the cavity, and is in the order of 0.1–1.0 ms depending on the pump power. Moreover, the voltage pulse jitter should not exceed several nanoseconds. In such case the second harmonic pulses with nanosecond duration and peak intensity of 10 –100 MW/cm2 are generated at the laser output. The output pulses duration is defined only by the cavity length under the conditions of a small response time of the electro-optical crystal compared to the cavity round-trip time. To achieve the maximal peak intensity, one should decrease the coefficient of inactive losses to the possible minimum and increase the pump power.

The influence of the corona discharge on the holographic recording and the subsequence chemical etching of the recording holographic gratings in the Cr/As40S60-xSex thin film structures was investigated. It was established that applied of the positive corona discharge leads to the increase of the holographic sensitivity during the recording in the As-S-Se films, as well as to the amplification of the diffraction efficiency of the recording gratings and of the relief-phase diffractive gratings obtaining in the result of the consecutive chemical etching. Among the investigated films of the As40S60-xSex system, the best results on the application of the Argon laser irradiation (488 nm) was obtaining for the composition As40S39Se21. Applied of the corona discharge bring to the increase of the holographic sensitivity more than up two order, and of the diffraction efficiency about three order in the respect of the of the ordinary recording. Reciprocally was reached a amplification of the diffraction efficiency of the relief diffraction gratings formed in the result of the sequent chemical etching up to 30%. Keywords: chalcogenide vitreous semiconductors, holographic diffractive grating, corona discharge, diffraction efficiency, selective etching.