Multi-mJ, sub-200-fs, cw-pumped, cryogenically cooled, Yb,Na:CaF2 amplifier

A wide variety of high-field applications and the rapidly developing technology of chirped-pulse parametric amplification motivate the development of economic, directly diode-pumped, broadband, solid-state laser systems that are scalable in output energy and average power. Among broadband Yb³⁺-doped materials, CaF₂ is in the focus of attention for developing high-peak and average-power tunable femtosecond oscillators and chirped-pulse amplifiers (CPA). In this project we utilize the known advantages of low-temperature crystal cooling by applying it to a recently developed Na⁺-co-doped Yb³⁺-doped CaF₂ host and develop a CPA system capable of producing multi-mJ femtosecond pulses at kHz repetition rate.

Fig.1: Schematics of cryogenically cooledYb³⁺,Na⁺:CaF₂.

A front-end of the system is a chirped pulse cryogenically cooled regenerative amplifier (CRA) [1] based on a novel broadband Yb³⁺,Na⁺:CaF₂ active material [2]. The crystal is mounted inside a cryogenic chamber and cooled to a temperature of 110 K with a close-loop cryogenic refrigerator. The CRA is seeded with a stretched to 250 ps output of a femtosecond Yb fiber laser. A positive dispersion stretcher is based on a single transmission grating and a spherical mirror. The CRA generates 5.5-mJ pulses at a repletion rate of 1 kHz. The gain narrowing in the amplifier is compensated by shaping the spectrum of the seed pulses. The spectral shaping extends amplification bandwidth up to 15 nm FWHM supporting a 160 fs pulse duration, assuming ideal compression. Amplified pulses are recompressed from 250 ps to 173 fs with a 1700 lines/mm transmission grating compressor.

Fig.2: SHG FROG characterization of compressed pulses after the RA.

Further scaling of the energy to the level of tens of mJ at a kHz repetition rate can be achieved by designing a diode-laser-pumped, cryogenically cooled Yb3+,Na+:CaF2 multipass amplifier.

References

[1] A. Pugžlys, G. Andriukaitis, A. Baltuška, L. Su, J. Xu, H. Li, R. Li, W. J. Lai, P. B. Phua, A. Marcinkevičius, M. E. Fermann, L. Giniūnas, R. Danielius, S. Ališauskas, Multi-mJ, 200-fs, cw-pumped, cryogenically cooled, Yb,Na:CaF2 amplifier, Opt. Lett. 34 2075, (2009)

[2] A. Pugžlys, G. Andriukaitis, D. Sidorov, A. Irshad, A. Baltuška, W.J. Lai, P.B. Phua, L. Su, J. Xu, H. Li, R. Li, S. Ališauskas, A. Marcinkevičius, M.E. Fermann, L. Giniūnas, R. Danielius, Spectroscopy and lasing of cryogenically cooled Yb, Na:CaF2, Appl. Phys. B 97 339 (2009).