Point spread function (PSF) of projector plays an important role in coaxial projection-imaging profilometry and binary defocusing fringe projection profilometry. In the proposed method, the SPI (Single Pixel Imaging)-based PSF measurement method has been used to obtain the PSF of the projector point by point. We use the camera to capture the SPI patterns projected by the projector on a white plane. By considering each pixel of the camera as a single-pixel detector, we can apply SPI technology to the camera pixels and acquire the light transport coefficients between the object points on the white plane and image points of projector, which is the spatially varying blur. Owing to the characteristic of SPI, the proposed method could obtain the spatially varying blur of every pixel directly. The experiment also verified that the proposed method could provide a more accurate blur kernel than the traditional Gaussian blur kernel to fit the blur model of the camera lens.
Diffractive optical elements (DOEs), with attractive features such as excellent performance and compact configuration, are now becoming increasingly important to a wide range of optical system applications. In this paper, we have used the patterned photoalignment method to produce switchable gratings. It is found that these gratings combine good optical quality with very fast dynamical response at very low driving voltage. A sub-millisecond steering with active FLC as a polarization selector and passive polarization grating (PG) as a diffractive element. A systematic analysis is conducted from the device fabrication to the element working mechanism with their potential problems and corresponding solutions included. The polymerizable liquid crystal PG shows compact size, light weight, robustness, and low cost. Switching time of 82μs is realized by binary switching between two circular polarizations before incident on PG utilizing FLC driven by two electrical polarities. Overall efficiency of 95.7% is achieved with steering angle of 17.66° by 1064nm laser.
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