Yb:CALGO thin-disk femtosecond oscillator

Summary form only given. Thin-disk laser (TDL) technology has a crucial interest for high-power ultrafast laser oscillators. The thermal control of the gain medium allows the generation of high average power and high energy fs pulses directly out of an oscillator. From the past few years, some research efforts have focused on reducing the pulse duration using this technology [1]. In this point of view, we are presenting here the first femtosecond thin-disk oscillator using a very promising crystal, Yb:CALGO. This material combines atypical advantageous spectroscopic and thermal properties for an Yb-doped one. Moreover it has already demonstrated interesting results in bulk configuration with sub-50-fs pulses at low power and sub-100 fs with 12 W. These results motivated its use in the TDL configuration and the demonstration of high-power fs TDL using Yb:CALGO is shown with the production 28 W, 1.3 μJ, 300 fs pulses and 20 W, 0.9 μJ, 197 fs pulses.The femtosecond experiment was performed with a 2%-doped, 350-μm-thick, Yb:CALGO crystal. The setup is presented in fig. 1. The crystal diameter is 6 mm, and it is cut for the laser beam to propagate along the σ-axis, with access to both σ- and π-polarization. The pump diode delivers up to 230 W. The pump spot diameter on the disk is 2.9 mm and the laser beam waist diameter is 2.1mm. When the crystal is glued on a copper heat sink, one can observe a deleterious thermal astigmatism occurring for pump power around 130 W. In order to overcome this problem the crystal was glued on a diamond mount (fig. 1). In this case, in a multimode configuration we obtained up to 86 W in cw regime, corresponding to an optical-to-optical efficiency of 37.5 %. The cavity is optimized to operate in spatially single mode operation (fig. 1), with M2