Phase diverse speckle (PDS) is a novel imaging technique, can be used to overcome image degradation arising from
unknown phase aberrations, such as atmospheric turbulence. The wave-front phase expanded on the Zernike polynomials
is estimated from a pair of images (in focus and out of focus). This paper analyses the principle of PDS, uses genetic
algorithm as the iterative algorithm, verifies its validation with numerical and experimental data, and studies some
characteristics in simulation, such as the influence of Zernike polynomials' mode, defocusing amount and amplitude of
turbulence on the phase estimation.
Study on the combination of different optimal algorithms to improve the performance of the algorithm is crucial to design optical multiplayer. A method based on GA (Genetic Algorithm) and NLSM (nonlinear least square method) is presented in this paper. GA is used to optimize the refractive index of the optical multilayer to get the original structure parameters. Then the NLSM is used to optimize the thickness of the optical multilayer based on the previous result. The algorithm model is explained in detail and the optimization design examples prove that the result is better. The results also indicate that the method is simple, effective and general for the optical multilayer design.
The radial sheering interference technique is used to measure the laser wave-front. In the system, the near field and far field wave-front of the laser beam of large caliber are measured respectively. Many evaluation parameters of the laser wave-front can be obtained, such as scattering angle, M2 of the laser beam, peak-to-peak-value (PPV), strehl value et. al. The interferogram is acquired by CCD camera, pretreated by high-capability computer and then used to reconstruct the wave surface. Mathematical principle to reconstruct the wave-front is expatiated in the paper. The interference system can be adjusted easily and operate real-time during the experiment.
Stimulated Brillouin Scattering (SBS) is an important means to achieve optical phase conjugation beam, which has the characteristics of self-pumping, producing phase conjugation wave and compensating wave-front aberration. Using SBS in glass fibers as phase conjugator, the field of application of SBS phase conjugation can be expanded, for fibers can offer low power threshold and stable behavior even at high peak and average input power. In this article, phase conjugation based on SBS in undoped multimode quartz fibers was observed. With the 13-15ns pump beam at 1.06 µ m wavelength from a Q-switched Nd:YAG laser, the reflectivity of SBS for the fibers with core diameter of 100 µ m and 62.5 µ m and different length was characterized at different input energy and lens focal length, considering of the reflection loss at the fiber surface. The reflectivity during the SBS process, affected greatly by system parameters, was measured no more than 70% due to saturation. The waveform of SBS was recorded and investigated. With the change of the waveform at the fiber length changing from 1.6m to 0.6m, the pulse duration of SBS decreased from 5ns to 2ns. The multi-peak modulation did not occur, which indicated that SBS had taken place in stable condition. Based on these experiments, some references to control SBS waveform were put forward.