Volume Bragg gratings (VBGs) with programmable angular selectivity from 0.1mrad to 10mrad and high efficiency of 99 % is an effective filtering element to clean up the spatial modulations in laser beams. The FM-to-AM conversion is studied with a sinusoidal phase modulation laser pulse with the bandwidth of 0.30nm and 0.15nm, and is demonstrated with an YLF laser with the wavelength of 1053 nm and pulse width of 3ns. The experimental results show that FM to AM conversion level is increasing with the decrease of the spectrum selectivity bandwidth of the VBGs. At the VBG spectrum selectivity bandwidth of 7.9 nm, the FM to AM conversion level is reduced to about 6% for 0.3 nm and 3.5% for 0.15nm, which can be used in high power laser for controlling the beam spot on the target.
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Fiber Bragg gratings
High power lasers
Pulsed laser operation
Xiao Yuan, Xiang Zhang, Fan Gao, Xiaojie Sun, "Frequency-to-amplitude modulation in angular filtering based on volume Bragg gratings (Conference Presentation)," Proc. SPIE 10085, Components and Packaging for Laser Systems III, 100850O (21 April 2017);