New Wavefront Measurement Method For High Power Laser Device

With the development of high-power laser devices, people have higher and higher requirements on the output capability and beam quality of the device, and also put forward new requirements for light field measurement. At present, the direct imaging method can only obtain the intensity distribution of the near and far fields of the beam on a limited fixed plane; the Hartman sensor can only measure low-frequency wavefront information, and precise mid-high frequency wavefront information cannot be obtained; and the laser pointer During the transmission process, the triple frequency damage and multi-wavelength effect also make traditional measurement methods stretched. Therefore, there has been no suitable technology to measure the intensity and phase of the high-power laser beam online with high enough accuracy online, and comprehensive online detection of the laser beam light field has not been achieved.

Based on years of technical accumulation, the High Power Laser Physics Joint Laboratory has proposed a new wavefront measurement method—coherent modulation imaging (CMI) method. In principle, it is different from the existing measurement technology. The coherent modulation imaging (CMI) method uses a phase plate with a known structure and a highly random distribution to perform phase modulation on the wavefront to be measured. A single diffraction spot is recorded by the CCD, and then iterates The algorithm reconstructs the amplitude and phase of the photometry simultaneously. The idea of ​​reconstruction is to transmit the guessed incident light field back and forth between the incident window surface and the CCD surface, and impose constraints on the amplitude on the two surfaces, so that the calculated light field gradually converges to the true value. How to ensure that the true complex amplitude is the result of convergence?

Strong Powerful Laser Pointer Blue Burning

From the perspective of space, the strong scattering effect of the random phase plate makes the points of the wavefront to be measured correlate with each other, so some differences in the wavefront to be tested will make a big difference in the diffraction spot collected by the CCD (as follows (Pictured). Therefore, due to the limitation of the diffraction spot intensity and the spatial domain of the incident window, the final calculated light field can only converge to the real light field.

Explained in the frequency domain, the frequency spectrum of the randomly distributed phase plate is wider, because it is a convolution process with the spectrum of the incident light. The wider the spectrum range of the phase plate, the more equations can be constructed. When the number of equations is greater than the unknown number (incident light spectrum), a unique solution can be obtained.

In short, the emphasis of the random phase plate strengthens the restrictions on the existing air and frequency domains, and enhances the ability to filter the wavefront, so that the true amplitude and phase can be obtained. After obtaining the true distribution of the wavefront to be measured, the required near-far field intensity distribution, beam pointing, energy concentration and other information can be further extracted to achieve a comprehensive diagnosis of the green laser pointer beam.

CMI wavefront measuring instrument has wide application prospects in national defense engineering and civil fields, and can break the technological monopoly of large-scale optical precision measuring instruments in developed countries. A few days ago, the project won the gold medal of the first “Chinese Civil and Civil Dual-use Technology Innovation and Application Competition” and was highly evaluated by the jury. The high-power laser physics unit is full of confidence in the future of CMI wavefront measuring instruments.