High-peak power diode-pumped Yb:CaF2 laser

With the advent of efficient semiconductor high-power lasers, compact diode-pumped solid-state laser systems are becoming an attractive approach for the generation of high-peak intensities. Due to their low quantum defect and a long fluorescence lifetime, ytterbium-doped gain media are preferably used in diode-pumped laser amplifiers with high- average power and high-pulse energy. Furthermore, owing to their broad gain spectrum Ytterbium-doped alkaline-earth fluorides (Yb:CaF₂, Yb:SrF₂, Yb:BaF₂) are promising gain media for diode-pumped, femtosecond lasers and amplifiers. This paper reports on a diode-pumped chirped-pulse amplifier employing Yb:CaF₂ to amplify femtosecond laser pulses to the terawatt level. Cylindrical Yb:CaF₂ crystals with a diameter of 28 mm and a length of 20 mm are used. A multi-pass Yb:CaF2 amplifier is built which is being pumped by two stacks of 25 fast-axis collimated diode-laser bars at a total peak output power of 7.4 kW. A maximum pump energy of 29.6 J is obtained at a pump duration of 4 ms. The seed pulses with a duration of 85 fs (FWHM) are generated in a commercial Ti:sapphire oscillator and then pre- amplified from 1.3 nJ to 20 muJ at a repetition rate of 1 Hz in a regenerative Yb:glass amplifier.