Investigation of red-shift of an Er:Yb:Kigre phosphate glass microchip laser at 1535nm due to pump thermal loading

Abstract

Er:Yb doped phosphate glass microlasers have received attractive interests, and significant progress has been achieved in the past decade, as described in a recent review. Although a lot of papers have been published on such type lasers, most of them concern merely on the laser performance such as threshold, slope efficiency as well as cavity designs. In this paper, emission cross section spectrum of the transition from ⁴I_13/2 to ⁴I_15/2 was experimentally measured in an Er:Yb codoped Kigre phosphate glass microchip, and the absorption cross section spectrum was derived using the McCumber theory. Based on these absolute cross section spectra, the gain spectrum was calculated in terms of different pumping ratios, which allows to determine the maximum lasing wavelength around 1535 nm and the total cavity loss being equal to 0.151 cm^-1. Both values are in good agreement with direct measurements. Under pumping with a Ti:sapphire laser at 975 nm, a high performance microchip laser at 1535 nm was realized with a low threshold of 5 mW and a high slope efficiency of 22% as well as a maximum output power of 22 mW operating in single frequency at 130 mW incident pump power. Red-shift effect of the 1535 nm microchip laser was also experimentally observed as the pump power was increased, as shown in Fig.1, and this is believed to originate from a compromise between the thermally induced expansion of the cavity and the change of refractive index due to temperature variation.

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