As one of the important performance evaluation indexes of lasers, beam quality has always been a research hotspot in the field of laser optics. As we all know, the “National Ignition Device” (NIF) of the Lawrence Livermore Laboratory in the United States is currently the largest optical engineering project. As early as the 1970s, the Lawrence Livermore laboratory established Argus, Shiva and other devices. These inertial confinement fusion laser pointer drive devices are laser devices that carry out image transmission through a spatial filter and finally focus and target.
Laser beam quality detection parameters: near field, far field and wave surface. The spatial filter is a low-pass filtered 4f system. Its image transmission is to avoid the introduction of a Fresnel diffraction ring with an excessively large modulation amplitude through the transmission of the light beam, which causes self-focus damage in the subsequent amplification medium and other optical elements.
The function of the spatial filter is to improve the quality of the laser beam. Strictly speaking, each image transfer node needs to monitor the near field (beam intensity distribution near the image transfer surface) and the far field (beam transfer of the image transfer surface beam to infinity) Strong distribution). In addition, the input and output wavefront of the spatial filter is an important parameter to ensure its basic performance. The aperture of the optical components of the previous laser device is relatively small, and the wavefront is mainly affected by the collimation of the optical path.
As the aperture of the optical element increases, wavefront errors such as aberrations and intermediate frequency ripples introduced by manufacturing equipment will affect the near-field and far-field distributions. Therefore, monitoring the beam quality requires complete consideration of near-field, far-field, and wavefront parameters. The three parameters of the same position at the same time are the most ideal. The laser beam passes through each optical element with the transmission direction, and the wave surface also changes with the wave element error and diffraction effect of the optical element. The near field and the far field are affected by the wave surface distortion at the same position, and only the “eyes” can recognize its “real body”. .
Detection of space parameter of green laser pointer beam of Shenguang device. With the development of the Shenguang series of devices, laser parameter detection has been carried out from the Shenguang I device to complete laser parameter measurement, which includes laser beam spatial parameter detection-near field, far field and wave surface. Twenty years ago, during the development of Shenguang II, further optimized near-field and far-field instruments played an important role in rational optical path arrangement and beam quality monitoring and control.