Abstract
Abstract We present a 2 μm Tm:YAG disk laser multi-pass pumped by a 1 μm laser. The transitions in competition of up conversion (UC) and excited state absorption (ESA) are analyzed in detail based on a numerical model that considers stimulated emission, fluorescence, non-radiative decay, UC, andESA, showing good agreement with experiments. The proportions and fractional thermal loads of all transitions are derived quantitatively. The results show that UC and ESA are critical in Tm:YAG disk lasers, resulting in a decrease in the absorbed pump power and temperature after lasing for two different disk thicknesses. In addition, although the absorbed pump power of the 0.5 mm disk is lower than in the 1 mm case, its relatively weak UC and ESA and low total fractional thermal load can improve laser performance. A 0.5 mm Tm:YAG disk laser thus delivered the maximum output power of1.05 W with beam quality of Mx2 = 2.02 and My2 = 2.03.
Highlights
Tm:YAG lasers operating at 2 μm wavelengths have attracted a lot of attention owing to their strong absorption in water, as well as the eye-safe wavelength bands, which have been utilized extensively in soft-material processing, medical diagnostics, direct optical communications, and so on[1,2,3]
Experimental and theoretical results show that the up conversion (UC), excited state absorption (ESA), and stimulated emission (SE) compete with each other to consume the 1 μm pump photons, and the proportions of UC and ESA are more dominant than that of SE in a 1 μm pumped Tm:YAG disk laser, leading the absorbed pump power to decrease abnormally after lasing
Serious red and blue light was observed in experiments, indicating that the UC and ESA were more dominant than the SE in a Tm:YAG disk laser when pumped by a 1 μm laser
Summary
Tm:YAG lasers operating at 2 μm wavelengths have attracted a lot of attention owing to their strong absorption in water, as well as the eye-safe wavelength bands, which have been utilized extensively in soft-material processing, medical diagnostics, direct optical communications, and so on[1,2,3]. Efficient heat removal is realized by increasing the surfaceto-volume ratio of the gain medium, as in fiber, slab, and disk lasers[4,5,6,7]. Because a high population inversion is necessary to compensate for the limitation of the disk’s thickness, the intensities of transitions in competition, up conversion (UC) and excited state absorption (ESA), cannot be ignored, as is done in rod and fiber-shaped lasers[4]. The enhancement of output power is limited and more heat is generated in Tm:YAG disk lasers. Verifying the proportions of all transitions and evaluating their effects on operation characteristics and heat generation are extremely important for Tm:YAG disk lasers
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