High Quality-Factor Kerr-Lens Mode-Locked Tm:Sc2O3 Laser Beyond the Gain Bandwidth Limitation

Tm doped materials are very attractive for highly efficient short pulse lasers in the wavelength range of 2 μm due to their broad gain bandwidth and the two-for-one pumping process with 800 nm laser diodes (LD). Among them, Tm doped sesquioxides (Tm:Re<inf>2</inf>O<inf>3</inf>, Re=Sc, Lu or Y) are the most promising gain materials as they possess excellent thermal and mechanical properties and a broad gain bandwidth above 1980 nm where less H<inf>2</inf>O absorption and Tm reabsorption exist [1]. Pulses as short as 63 fs, were obtained previously by a Ti³⁺:Al<inf>2</inf>O<inf>3</inf> laser pumped saturable absorber mode-locked Tm³⁺:LuScO<inf>3</inf> mixed ceramic laser [2]. We have also reported on an 1611 nm in-band pumped Kerr-lens mode-locked (KLM) Tm³⁺:Sc<inf>2</inf>O<inf>3</inf> laser generating pulses as short as 115 fs pulses with a spectral bandwidth of 42.6 nm [3]. Here we report on our recent efforts towards further shortening of the pulse duration by a high quality-factor cavity consist with dispersion compensation mirror. Spectral bandwidth above 70 nm (supporting sub-70-fs pulse durations) at 35 mW average power were obtained. In addition, the spectrum contains unusual component around 2200nm∼2350nm where outside the gain band of Tm³⁺:Sc<inf>2</inf>O<inf>3</inf>.