Abstract

The Yb-based chirped pulse amplification laser systems have been established as a viable technology for generating femtosecond ultrashort pulses of high multi-mJ energy at multi-kHz repletion rates for numerous applications. The laser transitions between ²F_5/2 – ²F_7/2 manifold energy levels determine the unique properties of the Yb-doped crystalline materials of relatively broad, overlapping absorption and luminescence bands that can be pumped by widespread InGaAs laser diodes. However, one of the remaining challenges in the development of femtosecond Yb-based lasers is achieving high pulse energy of multi mJ-levels and high average power, combined with short pulse durations of sub-100 fs. Although there are Yb-crystals with broad bandwidth of emission such as Yb:KGW, disordered Yb:CaGdAlO₄ (Yb:CALGO), and Yb:CaF₂, obtaining high energy amplified pulses of more than 1 mJ with pulse duration down to 100 fs is still a technological quest. While Yb:CALGO is relatively well explored for generation of shorter femtosecond pulses, the state-of-the-art systems have either low energy of sub-60 μJ and short pulse duration of ~220 fs, or pulse energy at the mJ-level but with longer pulses, with most systems being limited to dual-crystal amplifying architectures [1]. On the other hand, Yb:CaYAlO₄ (Yb:CALYO) is not well investigated, and the most advanced amplifiers developed to date have sub-100 μJ energies, at high repetition rates, with long pulse durations of 190 - 215 fs [2].

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