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 D2a line has been developed with a linewidth of 0.3 GHz, beam quality of M2=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 ±0.15 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 D2b re-pumping is accomplished by tuning the frequency of the electro-optic modulator with the right D2a-D2b offset. A bright sodium laser guide star with a photon return of 1820 photons/cm2/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.

Frequency-doubled Nd:YAG MOPA laser system with programmable rectangular pulses up to 200 microseconds

“…In combination with an acousto-optic modulator for pulse shaping of the cw master oscillator output, this enabled the generation of rectangular time-profile pulses with widths on the timescale of the fluorescence lifetime of the amplification medium. The single-frequency output with < 10 kHz linewidth, excellent beam quality in the second harmonic, and stable, high peak powers realized here using a compact 2-stage amplification setup compares favorably to other, previously demonstrated systems [7][8][9][10][11][12][13].…”

“…This may enable the amplification of low power tunable lasers in a gain medium like titanium:sapphire, or via optical parametric processes. Compared to existing systems, we combine pulse shaping capabilities [6,7] with pulse durations on the order of 100 microseconds [8][9][10][11][12][13], while avoiding spikes and ensuring a flat rectangular temporal profile. The spatial flat-top beam profile is maintained throughout the laser system using relay lenses (not shown) with the image planes indicated in green.…”

High-power, kHz-repetition-rate, long-pulse-duration, narrow-linewidth 1319 nm Nd:YAG solid-state laser for a guide star laser system

“…The physical mechanism of pulse package trains and spike suppression is described in detail in our previous work [30]. This results in high 589 nm sum-frequency efficiency when mixed with a smooth 1064 nm laser pulse [12].…”

“…High-power solid-state lasers operating at 1.3 μm have attracted considerable attention in recent years for their important requirements in optical communications, materials processing, laser medicine, and nonlinear frequency conversion [1][2][3][4][5][6]. Especially, high-power narrow linewidth pulsed 1319 nm laser is extremely important for 589 nm sodium laser using Sum-Frequency Generation (SFG) technique with 1064 nm laser [7][8][9][10][11][12] to efficiently generate sodium Laser Guide Star (LGS) for ground-based telescopes' Adaptive Optics (AO) system [13][14][15][16]. The pulsed output format of the laser is also an easier solution for solving LGS's Rayleigh back-scattering and fratricide problems [17][18][19].…”

“…Unfortunately, the low repetition rate is not fast enough to correct the atmosphere turbulence for LGS-AO system. More recently, using a double-stage double-pass Nd:YAG amplifier chain, we successfully achieved a 105 W QCW μs output power with beam quality of M 2 =1.85 for 1319 nm, and a 65 W SFG at 589 nm was realized at 500 Hz [12]. A prototype of the laser system had been installed on an astronomical telescope at Xinglong Observatory of China, and the highest return flux of Na LGS (1820 photonscm 2 s) was achieved for the field test.…”