109 W Yb:YAl3(B03)4 thin-disk oscillator

In this contribution, what is believed to be the first demonstration of an Yb:YAl₃(BO₃)₄ (Yb:YAB) thin-disk laser is reported. Due to its broad gain bandwidth of >40 nm (σ- polarization), Yb:YAB offers the potential for generating ultrafast laser pulses with sub-100-fs durations; the thin-disk geometry should allow to scale the average power of such pulses beyond the 100 W range. For these experiments, Yb:YAB boule material with a doping concentration of 12 % was polished to a disk with a diameter of 6.3 mm and a thickness of 250 μm. The thin-disk crystal was glued with its HR coated backside on a copper heat sink. Although the Yb YAB crystal was damaged during the mounting process, an usable optical aperture of the disk of up to 3 mm remained. For this reason pump spot diameters of 2.3 and 2.6 mm were selected for the high power laser experiments. A fiber-coupled laser diode high-power laser operation at a central wavelength of 976 nm emitting up to 1 kW of power was utilized as the pump source. In order to guarantee sufficient pump light absorption, a pump module allowing 24 passes of the pump radiation through the thin-disk was chosen. During laser operation the thin-disk crystal was efficiently cooled by an impingement cooling operated at a water temperature of 15 °C. Prior to the high power experiments a thermal characterization of this thin-disk crystal with a thermal-imaging camera was performed. The temperature of the front side of the crystal was measured both during fluorescence and laser operation. For a pump power density of 2.7 kW/cm² the maximum surface temperatures was determined to be 71 °C in fluorescence and 56 °C in laser operation. These values confirmed the good suitability of Yb YAB for high-power laser operation in thin-disk configuration.