Abstract

Radio-Frequency (RF) modulated pulsed lasers are demanded in increasing number applications of high resolution detection in turbid media [1, 2], especially for the coherent dual-frequency underwater detection [3]. The coherent dual-frequency lidar employing RF modulated pulsed laser can overcome the limitation of spectral resolution and accuracy of the speed measurement in coherent single-optical-frequency lidar [4], and benefit from the pulse-to-pulse coherence [5]. Furthermore, the modulation frequencies >100MHz are decorrelated in backscattered light for the underwater scenario, especially frequencies approaching 1 GHz are beneficial for discriminating against forward-scattered light [6]. Up to now, coherent dual-frequency lidars are demonstrated starting from an injection-locked laser [7], or by external modulation of a laser [8], or mode-locked lasers for pulsed operation in order to obtain a higher observable range [4, 9]. However, for the reasons of modulation depth, pulse energy and compact package, the trick question of the up-GHz modulated coherent laser pulse in gain- or Q-switched lasers remains to be solved. We propose, for the first time, to investigate a coherent RF-comb-modulated passively Q-switched laser based on a multipass shifting external cavity. And the RF modulation frequency of pulsed laser is up to GHz through the use of an acousto-optic (AO) frequency shifter which is driven only 85 MHz.

© 2016 Optical Society of America