The Research On Weak Image Enhancement Based On Optical Parametric Amplification

Optical parametric image amplifier (OPIA) which is an important application of the optical parametric amplification, which is of great significance for biomedicine, chemical analysis and ultrahigh-speed imaging and other fields. In this thesis, an image enhancement method based on the OPIA has been investigated theoretically and experimentally. The phase matching conditions, walk-off effect, small signal gain, gain transfer function and the amplification process of the OPA are analyzed and numerically simulated by the three wave coupling equations. The optical image enhancement system is designed, and OPIA is studied experimentally. The innovations achieved in this thesis are summarized as follows:1.The OPA based weak optical imaging is explored. Using10Hz picosecond laser and BBO crystal, OPA weak image enhancement device is established. Using the355nm laser as the pump beam, the weak optical image of visible light532nm is enhanced directly; further using the signal-idler-conjugated generation property, the infrared signal is amplified and up-converted into the visible region simultaneously by parametric amplification and frequency up-conversion. We have demonstrated an optical image amplifier with60dB gain in the picosecond region, which is two orders of magnitude higher than the previous reports, and this work was published in Chin. Opt. Lett.11,(2013)111901.2.By combining the optical gate of picosecond pulse and high gain of OPA process, the millimeter longitudinal resolution was achieved, the images of various longitudinal positions of the target is extracted by the gated property of the OPA, and then a three-dimensional (3-D) surface topography of the target is reconstructed by a computer.3.In order to solve the problem that the largest nonlinear coefficient of the nonlinear crystal cannot be effectively utilized and the presence of beam walk-off effect, Quasi-Phase match optical parametric image enhancement device and method has been proposed for the first time, and applied for patent (application number:201310108408.6).4. In order to solve the problem that walk-off effect and image resolution limit the effective length of the crystal, nonlinear fiber optical parametric image enhancement device and method has been put forward, and applied for patent (application number:201310722753.9).