Analysis and optimization of radial smoothing based on optical Kerr effect for irradiation improvement. (November 2016)

• Record Type: Journal Article
• Authors: Hou, Pengcheng; Zhong, Zheqiang; Zhang, Bin
• Is Part Of: Optics & laser technology. Volume 85(2016)
• Page Start: 48
• Page End: 54
• Publication Date: 2016-11
• Subjects: Irradiance uniformity -- Radial smoothing -- Optical kerr effect; Optics -- Periodicals; Lasers -- Periodicals; Electronic journals; 621.366
• DOI: 10.1016/j.optlastec.2016.06.005
• Languages: English
• ISSNs: 0030-3992

Abstract

Abstract: In radial smoothing scheme, taking a super-Gaussian pulse train obtained by the pulse stacking scheme based on fibers and spatial shaping technology based on serrated-aperture apodizers as the pump laser, due to the hemispherical shape of the optical Kerr medium, the induced refraction index by the interaction of the optical Kerr medium and the pump laser is spherically distributed with periodical variation. Consequently, the transmission wavefront of the laser quads in the beamline is periodically modulated, resulting in the rapidly and periodic focal zooming in far field. This focal zooming smoothes the speckles on target plane in the radial direction in the sense of averaged over a finite time interval. The performance of the pump laser and the optical Kerr medium strongly affect the radial smoothing effect. In order to obtain better smoothing effect as that of smoothing by spectral dispersion, the propagation model of laser quads in the beamline with the radial smoothing scheme has been built up and further used to optimize the parameters of the pump laser and the optical Kerr medium. The beam smoothing effects of the joint use of continuous phase plate and polarization control plate with smoothing by spectral dispersion, as well as radial smoothing have been analyzed and compared in detail. Results indicate that, the delay time between each super-Gaussian pulse in the pump laser should be matched with the pulse width of each super-Gaussian pulse to achieve the best and stable radial smoothing effect, while the fluctuation of the peak intensity of each super-Gaussian pulse in the pump laser would degrade the radial smoothing effect. The selection of the optical Kerr medium directly determines its thickness and peak intensity of the pump laser to obtain the required wavefront modulation, which affects the feasibility of the radial smoothing scheme. Highlights: A novel beam smoothing technology called "Radial Smoothing (RS)" is proposed. The propagation model of laser quads based on the RS scheme has been built up. The pump laser and the optical Kerr medium have been discussed and optimized. The same smoothing effect as smoothing by spectral dispersion has been achieved.