New Type Online Measuring Instrument of Laser Beam Light Field

At present, the direct measurement far field method reported by each device adopts the “main lobe” and “side lobe” separate measurement methods to solve the first problem. But there is no optimal solution to the second problem. In fact, the best way to solve the second difficulty in far-field measurement is to obtain a high-resolution wavefront distribution, and calculate the best far-field position based on the relationship between the far-field, near-field, and phase.

The measurement of the wave surface is undoubtedly more difficult than the measurement of the near and far fields. The commonly used measurement method of the Hartmann diaphragm sensor can only respond to the low frequency wave surface, and the mid and high frequency components of the wave surface cannot be measured. Although the shear interference method has been used since the Shenguang I device, it is also widely used at home and abroad to measure the laser pointer wavefront, but it is difficult to adjust to the applicable range, it is not easy to resolve a single interferogram, and the measurement resolution and accuracy are not ideal.

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The large-diameter laser beam wavefront online precision measurement is a photo of the system being used for actual measurement. The main part only includes a random phase plate and a CCD, and the structure is very compact. When a USAF 1951 resolution plate is placed on the rear surface of the beam converging lens, the measured near-field beam intensity image shows that the resolution is about 1.5 mm, which is much higher than the resolution of the Hartmann sensor.

Using the interferometer and the measuring equipment developed to measure the transmission function of the same optical plate, the comparison shows that the two are in good agreement. The measurement accuracy of the developed measuring equipment is currently about one tenth of the wavelength, which is ideal for online wavefront detection of laser drivers.

The “new laser beam light field on-line measuring instrument” developed by the team of Liu Cheng and Zhu Jianqiang of the high-power green laser pointer physics joint laboratory that won the gold medal in the first Chinese military-civilian technology innovation application competition is based on wavefront beam-splitting coded imaging. The technology realizes the direct measurement of the complex amplitude of the beam, and can simultaneously obtain the light field distribution and wave surface at the same position of the beam, providing a new method for the beam quality detection of the high-power laser device.