Tuneable, hybrid Ho:YAG laser

Abstract

The efficient, high energy Ho:YAG lasers can be resonantly pumped by Tm:crystalline lasers (see e.g. [1]) or applying hybrid concept with Tm:fiber lasers [2,3]. The aim of this work was to examine feasibility of tuneable work of compact hybrid laser based on Ho:YAG crystal pumped by Tm:fiber laser. The simple linear cavity with gain medium and dispersive element inside was set up. The 1% Ho:YAG rod of 4-mm diameter and 20-mm length with AR broadband coating was mounted inside water cooled copper heatsink. The pumping was realized by the Tm:fiber laser emitting up to 20 W at 1920-nm wavelength. After relay optical system the pump beam was focused to 0.33-mm diameter spot in the waist. The Ho:YAG crystal was placed in the vicinity of flat dichroic mirror (HR@2000–2200 nm, HT@1900 nm) inside a near semi-concentric cavity. The cavity length was set to obtain the best mode matching between pump and laser mode in gain medium. The output coupler was curved mirror (r=−150 mm) with 95% reflectance in 2000–;2150 nm range. In non-lasing condition the absorption efficiency of 20-mm long Ho:YAG rod has changed with pump power (50% for 4-W pump power up to 76% for 1-W pump corresponding to threshold). For laser tuning a Lyot filter consisted of Brewster angle tilted one quartz plate with 2.1-mm thickness was applied.