The Design And Research Of Full Aperture Backscattered System

Diagnosing parameters of full-aperture backscattering light is an important way to study laser plasma interaction in inertial confinement experiments. The coupling efficiency of the laser capsule, electron density and temperature in laser plasma’s interaction region are obtained by measuring energy and spectral of backscattering light which conclude stimulated Brillouin scattering light(SBS) and Raman scattering light(SRS). According to the requirements of measurement, a full aperture backscattering system(FABS) was designed and analyzed, which realizes the diagnosis of backscatter light around the target.Generation mechanism of SBS and SRS light are introduced in the first part of paper. According to domestic and international full aperture backscatter diagnostic system, the diagnostic process of backscattering light always contains four parts: collection of light, filtering, diagnostics and calibration. From the aspect of optical design, the full aperture backscatter diagnosis system is composed of three subsystems: collection of light system, filte r system and diagnostic system. In the design of the collection of light system, after investigating the characteristics of the current large diameter refraction and reflection lens, we proposes the off-axis parabola mirror which is combined with reflection lens, which realizes the purpose of collecting light and separates stray light from backscatter light; In the design of filter system, in view of the characteristic of stray light and the secondary stray light, the vacuum filter system with polishing inclined hole plate is researched, which eliminates stray light. In the diagnostic system, the long and short wave diagnostic systems are designed according to spectral separation characteristics of the dichroic splitter. In the measurement of time process and the time spectrum, the light speckle focused by coupling lens is smoothed by scatter plate. The spectral uniformity is less than 16%, which meets the requirements of measurement.In the second part of this paper, the calibration system and method are presented. In the design of calibration system, the choice of calibration laser, the design of analog lens and the principle of mechanical arm are analyzed. In the calibration method research, the principle of linearly polarized light calibration was analyzed on base of the energy transfer process of backscatter light. I n calibration, the emergent light energy of calibration laser and two orthogonal directions of full aperture can be measured by rotating same angle for vibration direction of polarized light. This method can calculate and fit the curve of vibration-transmittance.Finally, analysis of error and accuracy of the diagnostic system is given. The analysis of six light paths’ error verifies feasibility of the system and analyzes the precision of system. The total error of energy is 7.62%; the error of time process of long wave is 12.69% and 4.92% for short wave; the error of time spectrum is 0.134% for long wave and 0.105% for short wave. So the system can measure the back-scattering lights accurately.