Ultra-sensitive Infrared Image Based On Optical Parametric Process

Nonlinear optics as an emerging discipline develop srapidly with the progress of laser technology, Optical parametric amplification, as one of the important contents of nonlinear optics, becomes a hotspot in the research. The basic principle of optical parametric process is to take advantage of nonlinear optical crystal laser frequency conversion, and to strengthen a weak signal light. This paper deeply discusses about the propagation law and the basic equations of light waves in nonlinear crystal, nonlinear optical phase matching technology and its weak image enhancement system design. Meanwhile, Optical parametric frequency up-conversion and amplification, which is aimed to ultra-weak infrared image detection, is investigated both numerically and experimentally. As follows:Firstly, the optical imaging system of telecentric optical path and the large field of view optical path is designed by ZEMAX, the system aberrations and MFT curves are discussed, and the image of the identification plate in the front surface of the nonlinear crystal BBO is simulated using the image simulation function in ZEMAX.Secondly, the optical parametric frequency conversion and enhancement technologies are investigated theoretically and experimentally, which can be used for the ultra-weak infrared image detection. A circum-circle model of spatial filtering is proposed to suppress the parametric fluorescence background noise. Combined with the spatial filter, image relay module and band-pass filter, the fluorescence noise suppression ratio was improved greatly. Accordingly, the image quality is significantly improved and the peak signal to noise ratio is increased by 22%. Based on the 10 Hz, m J-level, 355 nm picosecond pump laser, the weak infrared image is amplified and up-converted into the visible region, and over 1.3×108(82 d B) optical gain is obtained at the same time. Our experiment demonstrates that the detection sensitivity of the conventional uncooled CCD can be as high as 7.4 photons per pixel when the high gain OPA is used as the image preamplifier.Finally, this paper deeply studied the depolarization characteristics on the surface of the object, and has obtained certain achievements: the depolarization serious object, by changing the polarization direction of the detecting light to try to change the image quality. The experimental results show that the depolarization of smaller objects, using P polarization detecting light can get higher gain and better image; For serious depolarization object, use the S polarization detecting light, can effectively improve the image quality.