Phase anisotropy in laser resonant cavity will bring about an influence on laser frequency and polarization, such as laser frequency splitting, of which the frequency difference is determined by their introduced phase retardation. For a helium-neon laser with a small phase retardation in the cavity, the two split modes are very close to each other whose burned holes are overlapped. Then only one mode oscillates while the other is always in lock-in state due to strong mode competition, which forms hidden frequency split. Meanwhile the spacing between adjacent longitudinal modes deviates from original value and produces a certain variation equal to twice the hidden splitting frequency difference. As a result the longitudinal modes spacing variation is dominated by the phase retardation. On the other hand, by applying transverse magnetic field to a laser tube along the polarization direction, the neon atoms will undergo transverse Zeeman effect and be divided into two groups to provide the gain for polarized light beams parallel to the magnetic field and perpendicular to the magnetic field respectively. Then the laser mode competition is greatly weakened so that the two split modes can oscillate simultaneously to obtain the frequency difference. In order to make profound study of the consistency between longitudinal mode spacing variation and splitting mode frequency difference in the presence of transverse magnetic field, the samples of tilted quartz plate or half wave plate is placed into laser cavity to produce phase retardation. By the two mentioned methods, the splitting frequency difference varying with phase retardation of samples is deduced to make a comparison. Two measurements show that the average relative deviation is less than 1%, while the experimental results accord with theoretical analyses quite well. In this way splitting frequency difference of Zeeman dual-frequency laser can be determined accurately, and a new method to measure the phase retardation of half wave plate is provided.
The fishnet metastructure has plane, near-optical lossless characteristic, and can excite surface plasmons in a specific light field. It has great potential in enhancing the response efficiency of photonic devices. Based on the finite difference time domain method and rigorous coupled wave analysis, in this paper, we systematically study the plasmon resonance mode of the fishnet metastructure and its light wave regulation performance on the crystalline silicon thin film solar cells. The research results show that the characteristics of absorption, scattering and extinction for the fishnet structure strongly depend on the thickness, line width, period and other characteristic parameters of the metal layer. Through optimizing the design, the resonant peak is red-shifted to 770 nm, and the relative extinction cross-section reaches 1.69, and the scattered light occupies a dominant position in the extinction spectrum. The crystalline silicon thin film solar cell with a response layer thickness of 2 μm constructed in this way has a significantly enhanced absorption efficiency in the wavelength band greater than 800 nm, and the final energy conversion efficiency of the device increases from 6.67% to 8.25%. The light intensity distribution shows that the enhanced backscattering caused by resonance and the large-angle deflection of the photon propagation direction are important reasons for the response gain of the solar cell.
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