B Integral

Abstract: A theory is developed for predicting a second-order hot-image formation in high-power laser systems. Light diffracted from a small optical scatterer interferes with an intense original wave in the nonlinear medium to produce a hologram like a Fresnel-zone plate. The theoretical model shows that the hologram produces a negative first-order diffractive wave focused to the traditional hot image and negative second-order diffraction that causes another intense image, namely, a second-order hot image. It is found by analysis that the location of the second-order hot image arises in a downstream plane with a half-distance from the medium to the scatterer. Results of the numerical calculations show that the peak intensity of the nonlinear image may reach a level high enough to damage optical components with the increase of the breakup integral (B integral), indicating that the image may also potentially damage expensive optical components in high-power laser systems.

Abstract: In high power laser facility for inertial confinement fusion research, final optics assembly (FOA) plays a critical role in the frequency conversion, beam focusing, color separation, beam sampling and debris shielding. The design and performance of FOA in SG-II Upgrade laser facility are mainly introduced here. Due to the limited space and short focal length, a coaxial aspheric wedged focus lens is designed and applied in the FOA configuration. Then the ghost image analysis, the focus characteristic analysis, the B integral control design and the optomechanical design are carried out in the FOA design phase. In order to ensure the FOA performance, two key technologies are developed including measurement and adjustment technique of the wedged focus lens and the stray light management technique based on ground glass. Experimental results show that the design specifications including laser fluence, frequency conversion efficiency and perforation efficiency of the focus spot have been achieved, which meet the requirements of physical experiments well.

Abstract: Small-scale self-focusing is the main cause of power limitation in nanosecond Nd:glass lasers We report pioneer observation in experiment of laser beam noise amplification for B -integral (nonlinear phase) order of unity, ie, without destruction of nonlinear medium Analytical dependences of noise amplification coefficient on the B-integral have been obtained for one nonlinear medium as well as for two nonlinear media separated by an air gap with image relay A simple analytical dependence has been found for an optimal distance between two nonlinear media for which the maximum allowable value of B -integral increases from 27 to 43 The maximum attainable energy in neodymium-phosphate glass lasers with rod amplifiers 10 cm in diameter is 400 J with a pulse duration of 1 ns

Abstract: The B-integral accumulated in a chirped-pulse-amplification (CPA) laser can be canceled using a semiconductor with a negative nonlinear index of refraction. We demonstrate this experimentally using GaAs at 1.053 /spl mu/m. The compressed-pulse duration was broadened due to self-phase modulation (SPM) of the chirped pulse. It was reduced to its unmodulated value with substantial wing reduction after passing through a semiconductor wafer before compression. Optimum semiconductor sample parameters for minimizing the B-integral such as gap energy, nonlinear and linear absorption, nonlinear refraction, and thickness for different pulse durations and intensities are discussed.