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The interaction matrix significantly affects the correction accuracy of wavefront correctors. For diffractive liquid crystal wavefront correctors (LCWFCs), the diffraction wavefront error must be taken into account to improve the accuracy of the interaction matrix. In this paper, a tunable Zernike polynomial coefficient method is demonstrated that decreases the effect of the diffraction wavefront error on the interaction matrix. Moreover, to eliminate the effect of the random error, a least squares method is combined with the tunable coefficient method. Experimental results show that, with the combined method, the error of the interaction matrix is decreased by a factor of 2.5 compared to that when the least squares method is used alone. Furthermore, an open loop adaptive correction experiment was performed and a considerable improvement of the image resolution was obtained by the novel method. Therefore, this method is very useful for liquid crystal adaptive optics systems to acquire the high correction accuracy. [ABSTRACT FROM AUTHOR]

• The performance degradation and compensation method of the beam-steering device based on liquid crystal polarization grating (LCPG) and liquid crystal adjustable half-wave plate (LCAHWP) is studied. • This beam-steering device can still work at a laser power density of 16 W/cm2 irradiation. • The laser tolerance of the device is higher than that of liquid crystal optical phased array (LCOPA) and liquid crystal micro-lens array (LCMLA). The effects of laser irradiation thermal deposition on the performance degradation of liquid crystal (LC) devices in high-power laser systems are extremely vital. In this study, the first-order beam-steering system (FBS) was developed using a passive liquid crystal polarization grating (LCPG) and liquid crystal adjustable wave-plate (LCAW). The LCPG was prepared by holographic exposure technology, and the LCAW was prepared using the standard LC cell preparation process. We investigated the influences of diffraction efficiency of FBS under a 1070-nm continuous-wave (CW) laser irradiation. The energy is concentrated in the −1st order at first. When the half-wave retardation was reached, all the energy is concentrated in the +1st order (∼97 %), and the beam is deflected. Once the phase retardation decreases below the half-wave retardation, the energy gradually reconcentrates in the −1st order. When the LCAW fails, the diffraction the energy is refocused to the −1st order by the LCPG. The results indicated that both thermal deposition and driving voltage reduce the phase retardation of the LCAW, generating a variation of energy between in ± 1 st orders. By reducing the driving voltage, this half-wave retardation can be recovered under a certain half-wave voltage and laser power density, and the diffraction efficiency of the +1st order can be compensated to ∼97 %. If the reduced phase retardation is not less than half-wave, the FBS can still be modulated in high-power continuous lasers. Our research provides a reference for the development of beam-steering technology based on LC materials in high-power laser systems. [ABSTRACT FROM AUTHOR]

The laser performance of liquid-crystal devices (LCDs) must be considered because of their applications in laser systems. The phase modulation variation mechanisms, as well as the key absorption factor under continuous-wave (CW) laser loading, remain unclear. In this study, the influence of indium tin oxide (ITO) layers on the laser tolerance of LCDs under CW laser loading was investigated. Comparing the phase modulation variations and thermal effects of passive and active LCDs, the influence of the ITO absorbing layer and the decisive role of temperature on the laser tolerance of the LCDs were confirmed. The results showed that the laser tolerance of the LCD with ITO layers was approximately one-seventh of that of the LCD without ITO layers. ITO layers have proven to be the main absorption factor for active LCDs. However, the variations in phase modulation and morphology under CW laser loading were similar for LCDs with or without ITO layers. The phase modulation variations of the LCDs increased with increasing temperature in the irradiated area. For LCDs with or without ITO, once the CW laser loading induced a similar temperature increase, their phase modulation variations were almost the same. The temperature rise of LCDs is confirmed to be an effective parameter for evaluating the phase modulation degradation of LCDs in high-power CW laser applications. The coincidence between the theoretical and experimental phase modulation variations for LCDs with or without ITO indicates that the temperature-induced refractive index change was the main reason for the LCD phase modulation variation under CW laser loading. These results clarify the basic mechanisms of the phase modulation variation of LCDs under CW laser loading and provide guidance for process optimization and application of LCDs in high-power laser systems. [ABSTRACT FROM AUTHOR]

Liquid crystal devices (LCDs) are widely used in several applications involving high-power lasers, such as laser processing, laser shaping, laser communication, laser radar and so on. Investigation on the performance of the LCDs working in high-power laser has always been of concern. In this study, a modified nearly common-path interferometry technique is proposed to investigate the phase modulation characteristics of the LCD irradiated by 1064 nm continuous-wave (CW) laser with Gaussian beam profile and an effective area of 0.1 cm2. In addition, the temperature rise of the LCD induced by laser irradiation was synchronously measured with an infrared thermal imager. A quantitative and dynamic investigation of the relation between the thermal effect caused by the laser and the phase-modulation variation is reported. Experimental results showed that the trend of temperature increase of the LCD was similar to that of phase shift variation. The theoretical phase shift calculated using the temperature-dependent LC refractive index coincided with the experimental results. This indicated that the refractive index change induced by temperature was the main reason for the phase-modulation variation of the LCD under laser irradiation. When the laser power was further increased, interference fringe distortion appeared, and morphological changes in the LC were observed. This implied that the laser-induced temperature rise had reached the clearing point of the LC and that the LCD was inactive. The temperature simulation along the laser incidence direction implied that, under the irradiation CW laser, indium tin oxide (ITO) layer absorbs laser energy, resulting in a temperature rise and a small temperature gradient between the ITO, polyimide (PI) and LC layers. The rising temperature is too low to induced damage of ITO layer and PI layer, but influences the refractive index of the LC. Compared with other layers of the LCD, the LC material will fail first when the irradiated laser power is further risen. The transmission variation of an LCD induced by laser irradiation was found. Possibly owing to the refractive index change of the LC as well as the multilayer film structure of the LCD, there seemed to be a cyclical transmission variation. • In our study, a modified nearly common-path interferometry technique was proposed to investigate the phase modulation characteristics of the LCD under continuous-wave (CW) laser irradiation. • A quantitative and dynamic investigation of the relation between the thermal effect caused by the laser and the phase-modulation change was reported. • This indicated that the refractive index change induced by temperature was the main reason for the phase-modulation variation of the LCD under laser irradiation. • The temperature simulation along the laser incidence direction implied that, under the irradiation CW laser, ITO layer absorbed laser energy, resulting in a temperature rise and a small temperature gradient between the ITO, PI and LC layers. • Besides, the transmission variation of the LCD without polarizer induced by laser irradiation was first reported. [ABSTRACT FROM AUTHOR]