Interferometry with computer-generated hologram (CGH) has been widely used in the field of precision optical testing and metrology. CGH can easily generate reference wavefronts of any desired shape by controlling the phase of the diffracted light. Traditional CGH is made by etching a specific pattern on a substrate, whose cost is extremely high and the phase of the diffraction wavefront is sensitive to the changes in etching depth. Based on photoalignment technology, liquid crystal (LC) can be fabricated into LC-CGH. The LC phase modulation elements made by this technology have the advantage of low cost and high accuracy. The existing phase modulation elements based on photoalignment technology are mostly qualitative phase controller, such as LC-grating and LC-wave plate. They are rarely used in high precision applications. In the field of optical testing, the high precision of diffractive wavefront of LC-CGH is critical. The wavefront changes due to phase retardation in adjacent areas of LC-CGH is affected by the flatness of the LC film. Therefore, it is essential to keep the surface of the LC-CGH flat. In this paper, we measure the surface flatness and the diffraction wavefront of the LC-CGH film to verify the feasibility of LC-CGH in optical testing. First, we introduce photoalignment technology and analyze the principle of LC-CGH. Second, we measure the surface flatness of LC-CGH. In the end, we evaluate the transmitted diffraction wavefront. The results can provide guidance for the LC-CGH process improvement.
Confocal Raman Microscopy (CRM) has matured to become one of the most powerful instruments in analytical science because of its molecular sensitivity and high spatial resolution. Compared with conventional Raman Microscopy, CRM can perform three dimensions mapping of tiny samples and has the advantage of high spatial resolution thanking to the unique pinhole. With the wide application of the instrument, there is a growing requirement for the evaluation of the imaging performance of the system. Point-spread function (PSF) is an important approach to the evaluation of imaging capability of an optical instrument. Among a variety of measurement methods of PSF, the point source method has been widely used because it is easy to operate and the measurement results are approximate to the true PSF. In the point source method, the point source size has a significant impact on the final measurement accuracy. In this paper, the influence of the point source sizes on the measurement accuracy of PSF is analyzed and verified experimentally. A theoretical model of the lateral PSF for CRM is established and the effect of point source size on full-width at half maximum of lateral PSF is simulated. For long-term preservation and measurement convenience, PSF measurement phantom using polydimethylsiloxane resin, doped with different sizes of polystyrene microspheres is designed. The PSF of CRM with different sizes of microspheres are measured and the results are compared with the simulation results. The results provide a guide for measuring the PSF of the CRM.