Abstract
Abstract We demonstrated a 202 W Tm:YLF slab laser using a reflecting volume Bragg grating (VBG) as an output coupler at room temperature. Two kinds of active heat dissipation methods were used for the VBG to suppress the shift of wavelength caused by its increasing temperature. The maximum continuous wave (CW) output power of 202 W using the microchannel cooling was obtained under the total incident pump power of 553 W, the corresponding slope efficiency and optical-to-optical conversion efficiency were 39.7% and 36.5%, respectively. The central wavelength was 1908.5 nm with the linewidth (full width at half maximum) of 0.57 nm. Meanwhile, with the laser output increasing from 30 to 202 W, the total shift was about 1.0 nm, and the wavelength was limited to two water absorption lines near 1908 nm. The beam quality factors M2 were measured to be 2.3 and 4.0 in x and y directions at 202 W.
Highlights
Lasers with 2 μm waveband have been widely used in various technical fields, including medical laser application[1], remote sensing[2,3], and 3–5 μm nonlinear frequency conversion as the pump source[4], owing to their excellent characteristics of being located in the atmospheric window, strong absorption band of water, and safety zone of human eyes[4,5,6]
As far as Tm:YLF material is concerned, it has a strong absorption near 791 nm[9], which is suitable for laser diode (LD) pumping
The wavelength was shifted 1.5 nm. This meant that if we continued to increase the output power of the laser, its wavelength was likely to drift to the water absorption line near 1908.97 nm as shown in Figure 2, which would cause damage to the laser
Summary
Lasers with 2 μm waveband have been widely used in various technical fields, including medical laser application[1], remote sensing[2,3], and 3–5 μm nonlinear frequency conversion as the pump source[4], owing to their excellent characteristics of being located in the atmospheric window, strong absorption band of water, and safety zone of human eyes[4,5,6]. A laser crystal doped with trivalent rare earth holmium (Ho) ions has a long upper-state lifetime and a large emission cross section, and is an efficient 2 μm solid laser material. As excellent pumping sources for Ho lasers, thulium-doped materials have several attractive properties of light generation, including a wide emission bandwidth, long lifetime upper laser level, and high quantum efficiency potential owing to the two-to-one cross-relaxation process[7,8]. As far as Tm:YLF material is concerned, it has a strong absorption near 791 nm[9], which is suitable for laser diode (LD) pumping. It is necessary to limit the output linewidth of Tm:YLF laser
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