Passively Q switched dual channel Tm:YLF laser by intracavity spectral beam combination with volume Bragg gratings

Abstract

A novel dual channel Tm:YLF laser system was developed where two degenerate laser cavities were coupled by spectrally beam combining their emission and by implementing a common output coupler. Under continuous wave running conditions, each channel's slope efficiency was greater than 45% and the maximum combined output power was 11 W. Passive Q-switching was achieved using an 80%, Cr:ZnSe saturable absorber. The output pulses had a maximum energy of 5.8 mJ and duration of 90 ns (~65 kW of peak power) at 5.7 W of absorbed pump power. Each channel showed less than 1 nm of spectral width with central wavelengths around 1880 nm and 1908 nm correspondingly. The system had adjustable spectral difference between the channels ranging from 5 to 20 nm which corresponds to 0.4 - 1.7 THz if the system is used for nonlinear difference frequency generation.

Experimental and Modeled Output Characteristics of a Compact, Passively Q-Switched Tm:YLF Laser

“…For LRF and LIDAR, a larger pulse energy increases the maximum operating range, and a shorter pulse duration improves the range resolution. Due to the efficiency advantage offered by the cross relaxation process which yields two excited-state ions for each pump photon [4], Tm-doped crystal hosts [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] are the favored solid-state laser gain materials for generation of emission near 2 µm. Compared to other Tm-doped crystals, Tm:YLF offers the significant advantage of a very low thermo-optic coefficient, reducing the effect of thermal lensing that can cause significant changes in the laser output characteristics with pump power.…”

“…Both active and passive Q-switching (PQS) Tm:YLF and Tm:YAP lasers have been explored [8][9][10][11][12][13][14][15][16]. A maximum pulse energy of 10.5 mJ, with 22 ns pulse duration, was generated using an acousto-optic-modulator (AOM) Q-switched Tm:YLF laser operating at a pulse repetition frequency (PRF) of 10 Hz [8].…”

“…In addition, since no radio frequency (RF) driver is needed, PQS lasers can achieve higher overall laser electrical efficiency than AOM Q-switched versions. Recently, Tm:YLF and Tm:YAP PQS lasers using Cr 2+ :ZnS and Cr 2+ :ZnSe saturable absorbers have been reported [10][11][12][13][14][15][16]. A passively-Q-switched laser (PQSL) with Tm:YLF and a Cr 2+ :ZnSe saturable absorber generated 4.2 mJ, 26 ns-long pulses, corresponding to a peak power of 162 kW peak power [14].…”

“…A passively-Q-switched laser (PQSL) with Tm:YLF and a Cr 2+ :ZnSe saturable absorber generated 4.2 mJ, 26 ns-long pulses, corresponding to a peak power of 162 kW peak power [14]. A two-channel spectrally combined Tm:YLF laser with Bragg gratings (VBGs) and a Cr 2+ :ZnS saturable absorber, generated 5.8 mJ, 90 ns pulses [15]. A 230 mm-long Tm:YLF PQSL utilizing a Cr 2+ :ZnS with an unsaturated PQS transmission (T Q ) of 89% generated 10 mJ, 29 ns-long pulses at 1886 nm, corresponding to a peak power of 350 kW [2].…”

The single‐wavelength 561 nm laser based on reflective volume Bragg grating

“…By adjusting the angle of the VBG, the output power of 11 W was obtained. 28 In 2020, Q. Berthome et al reported a wavelength-tunable narrowlinewidth Tm:YAP laser, using a laterally chirped VBG as the output coupling mirror and acousto-optic modulator to achieve a wavelength tuning of 1940-1960 nm. 29 To summarize, VBG is currently used as an output coupling mirror to achieve design requirements such as compressed linewidth and wavelength selection in many frequency bands.…”