It is an important part to measure the distortion and divergence of laser pulse wavefront in ICF (Inertial Confinement Fusion). The paper described a radial shearing interference system with spatial phase modulation. It can be used for testing the wavefront distortion and control the beam quality. Because it is a cyclical common path interference system and no any reference surface, both radial sheared wavefront are formed by a Galilean optical system. A 512x512 pixels CCD camera recorded interference pattern. The wavefront reconstructed is finished by means of optical information processing method and software. The software procedure consists of the Fourier transform, shifting frequency, inverse Fourier transform, unwrapping 2π and wave iterations reconstructed. The interferometer has been used for testing a wavefront distortion of laser pulse with 1064nm near-infrared wavelength and 10 ns pulse time width. Results of the pulse wavefront quality and distribution of energy can be displayed by a perfect software procedure. Diameter of beam be measured is up to 150 mm. The testing precision of RMS(root-mean-square) is better than 1/15 wavelength.
The approximate Strehl Ratio expressions that need only the wave phase distribution is not appropriate in the laser fusion system when the phase has great aberration. The accurate Strehl Ratio value need both the phase and the amplitude distribution information. The paper provide a method of reconstructing wave phase and amplitude
distribution by a single radial shearing interferogram. The radial shearing interferometer based on spatial phase modulation is simple and stable, needs only one interferogram. The principle and structure of cyclic radial shearing interferometer are briefly discussed and the process of spatial phase modulation, Fourier transform method and wavefront reconstruction are analyzed. It also illluminates the physical meaning and establish the mathematical model. The process of getting SR value is simulated by computer. The simulation result indicates that the RMS error of the reconstructing wavefront can achieve λ/100.
The interferometer can measures accurately a static or dynamic wavefront . It can be done using a system of circular radial shearing interference with spatial phase modulated. Because the method only needs one frame interferogram so that can rejected the effect of vibrations and noises. The wavefront errors measured make adaptive optic system (AOS) that contain a deformable mirror correct the wavefront aberrations again. This paper described a system of radial shearing interference with spatial phase modulation. It is based on the Fourier transform method that the analysis and data processing of the interference fringe pattern with suitable linear carrier. An algorithm of shearing wavefront reconstructed can obtain the original wavefront. The system of diagnostics can check the operation of the AOS and quantify laser beam quality. Finally, the interference experiment and data processing results have been given in this paper.