High-power QCW microsecond-pulse solid-state sodium beacon laser with spiking suppression and D_2b re-pumping

Abstract

A 65 W quasi-continuous-wave microsecond-pulse solid-state sodium beacon laser tuned to the sodium ${\mathrm{D}}_{\mathrm{2a}}$ line has been developed with a linewidth of 0.3 GHz, beam quality of $M^2=1.38$, and pulse width of 120 μs at a repetition rate of 500 Hz by sum-frequency mixing 1319 and 1064 nm diode-pumped Nd:YAG master-oscillator power-amplifier systems. The laser wavelength stability is less than $\pm 0.15\mathrm{GHz}$ through feedback controlling. The laser spiking due to relaxation oscillations is suppressed by inserting frequency doublers in both 1319 and 1064 nm oscillators. Sodium ${\mathrm{D}}_{2b}$ re-pumping is accomplished by tuning the frequency of the electro-optic modulator with the right ${\mathrm{D}}_{2a}-{\mathrm{D}}_{2b}$ offset. A bright sodium laser guide star with a photon return of $1820\mathrm{photons}/{\mathrm{cm}}^2/\mathrm{s}$ was achieved with the laser system when a 32 W circular polarized beam was projected to the sky during our field test at the Xinglong Observatory.