A high resolution TDI-CCD system with measurement coding is proposed to acquiring high resolution image with the limitation that pixel size is not able to be smaller. The difficulty that enhancing the resolution alone the forward direction and its vertical direction at the same time without the changing of driving circuit and the con is solved by integrating several TDI-CCDs in a system, where each pixel of the TDI-CCD is coded by the measurement matrix. The high resolution image is reconstructed by the acquirement of each TDI-CCD and the measurement matrix in the end. The simulation shows the SSIM of the image acquired by proposed high resolution TDI-CCD system can reach beyond 0.95 in theory.
KEYWORDS: Upconversion, Cameras, Temperature metrology, Infrared imaging, Time metrology, Short wave infrared radiation, Nonlinear crystals, Image quality, Infrared radiation, Signal to noise ratio
In this paper, a low noise infrared imaging based on frequency upconversion is proposed. A function based on the quasi phase-match of two acquired images within 3dB width is formulated to evaluate the maximum step size of the nonlinear crystal temperature for each acquisition. The measurement time is reduced by acquiring images at these specific temperatures. The integration time of each frame is reassigned to improve the signal noise ratio of the acquired images. Comparing scanning the object, our method reduce the noise in background area to 17.14%.
The tight focused pump beam nonlinear frequency upconversion based on Hadamard coding is presented to acquire converted photon images. The pump beam is optimized by tight focusing to enhance its power
density in nonlinear crystal. In order to reduce the distortion caused by the point spread function effect, the object is encoded by measurement matrices and the converted photons corresponding to each pattern is measured. Thus the converted image with sharp edges can be reconstructed by the measurements and the measurement matrices. In the experiment, the image with 64 × 64 pixels is acquired and the peak of the dark noise is less than0.7photons/spatial/second element for 10 ms measurement time.
In this work, a field-of-view(FOV) expanded tight focusing up-conversion imaging system at 1550 nm is proposed. To satisfy the non-collinear phase-matching and increase the field-of-view, three groups 4f system are inserted. To enhance the intensity of converted images, the signal pulse at 1550 nm with the average power of 0.14mW is tight focused into a 1mm thick periodically poled lithium niobate (PPLN) bulk by a lens with 30mm focal length. Pumped by a continue-wave beam with the power of 1W, the 1550 nm pulse is converted to 863 nm and the pattern of target is captured by an industry camera. According to the experiment, the converted image with the pixel of 1000 × 1000 is reached and the diameter of FOV reaches 7.15 mm.
Due to advantages of room-temperature and low dark-noise, upconversion is an alternative to state-of-the-art mid-infrared (MIR) detecting technique. The upconversion technique has been applied in a diverse fields such as imaging, analsing spectroscopy and Lidar. A comprehensive theory for upconversion employing collinear quasi phase matching (QPM) is presented. In this work, we present a upconversion model with considering the collinear beams separately focused into periodically poled lithium niobate (PPLN) bulk. Based on the known comprehensive theory of QPM, we build the efficiency function about incident angle by investigating the minimum phase-mismatch of the signal in PPLN. Then we rewrite the upconversion efficiency function according to the pump light field distribution. Finally, by calculating the integral of the efficiency function over the incident angle, the upconversion theoretical model is developed for upconversion process with both beams focused. To check the upconversion theoretical model, we simulate the upconversion efficiency curve about temperature and measure the upconversion efficiency curve of our system with the same temperature range. In our system, the pulse signal at 1550 nm with the peak power 40mW is upconverted to 863 nm with the continuous wave pump laser at continuous-wave 1950 nm with 800mW in a 10 mm long and 1 mm thick PPLN bulk. The experimental results show that the upconversion modeling is agreement with experimental data and it can be used in upconversion imaging.
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