In this paper, a high slope efficiency, low threshold, Single-Longitudinal Mode (SLM) Q-switched Nd:YVO4 laser emitting at 1064 nm was demonstrated. Using a Reflecting Bragg Grating (RBG) as the output coupler for mode selection, stable SLM operation with maximum output power of 1.01 W at 1 kHz repetition rate was achieved. The linewidth was less than 4 pm, and the pulse duration was around 3.2 ns. The optical-to-optical conversion efficiency was 17.1% and slope efficiency was up to 24.4%, and the laser beam quality factors M2 were 1.21 and 1.13 for horizontal and vertical directions, respectively.
The efficiency of optical pumping that enhances the brightness of sodium laser guide star with circularly polarized light is reduced substantially due to the precession of sodium atoms in geomagnetic field. Switching the laser between left and right circular polarization at the Larmor frequency is proposed to improve the photon return. With ESO's cw laser guide star system at Paranal as example, numerical simulation for both square-wave and sine-wave polarization modulation is conducted. For the square-wave switching case, the return flux is increased when the angle between geomagnetic field and laser beam is larger than 60°, as much as 40% at 90°. The method can also be applied for remote measurement of magnetic field with available cw guide star laser.
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