To improve the laser beam quality affected by atmospheric turbulence, adaptive optics (AO) is needed. Nowadays, using simple AO systems to achieve low-latency and accurate beam purification is a hot spot in the direction of AO technology. The traditional AO system is greatly simplified by wavefront sensor-less (WFS-less) AO. However, the current WFS-less methods generally have a serious problem that search algorithms is used, which means a lot of iterative calculations and measurements are needed, and they can result in high latency. In order to solve this problem, this article proposes a novel compensation technique based on deep learning and eigenmodes of deformable mirrors (DM), which can obtain the compensation voltages directly from single frame of far-field intensity images. Compared with the existing WFS-less methods, it does not require any iterative operations and has good real-time performance. A convolutional neural network (CNN) model is built in this article, which takes 224*224 far-field intensity images as input and 67-dimensional eigenmode coefficients of DM as output. We completed the closed-loop experiment based on this method, and almost achieved the same result as the closed-loop correction based on the Shack-Hartmann Wavefront Sensor (HSWS).
Due to the thermal effects, the airflow disturbance and the platform vibration, the random jitters of laser axis are caused, which have a serious impact on the laser coherent combining. If the conventional PID controller is used to reject the disturbance, the control bandwidth will be lager, but the high frequency noise of the system will be significantly amplified, so that the control error increases. The open-loop disturbance data spectrum is analyzed to add a lag compensator. The results show that the system has a good effect on rejecting the jitters of the middle-and-low frequency optical axis, while the high frequency noise has on amplification effect, which decreases the control error of the system.
We developed a tunable-line-width 101 W average-power all-solid-state 589nm double spectral line sodium beacon laser. The laser was based on the technical route of 1064nm and 1319nm Nd:YAG laser extra cavity sum frequency generation. The laser contained two spectral lines: 589.1591 nm and 589.1571 nm. The former line was matched to the sodium D2a absorption line with the average power of 81W, while the other line was matched to the sodium D2b absorption line with the average power of 20W. The beam quality of the two spectral line lasers was both less than 1.3. The two lasers were polarized-combined to transmit coaxially. The initial line width of the laser was about 0.3GHz, which was in the comb-like discrete structure of about three longitudinal modes. We used a white noise generator to modulate the 1064nm single frequency seed laser in frequency domain. The line width’s tunability was accomplished by tuning the driving power of the white noise generator. The final line width tuning range of the 589nm laser was ~0.3GHz to ~1.1GHz.
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