Abstract
A novel compact dual-crystal optical parametric amplification (DOPA) scheme, collinearly pumped by a Ti:sapphire laser (0.8 μm), is theoretically investigated for efficiently generating broadband IR pulses at non-degenerate wavelengths (1.2 μm~1.4 μm and 1.8 μm~2.1 μm). By inserting a pair of barium fluoride (BaF(2)) wedges between two thin β-barium borate (BBO) crystals, the group velocity mismatch (GVM) between the three interacting pulses can be compensated simultaneously. In this case, the obtained signal spectrum centered at 1.3 μm is nearly 20% broader and the conversion efficiency is increased, but also the pulse contrast and beam quality are improved due to the better temporal overlap. Furthermore, sub-two-cycle idler pulses with carrier-envelope phase (CEP) fluctuation of sub-100-mrad root mean square (RMS) can be generated. Because a tunable few-cycle IR pulse with millijoule energy is attainable in this scheme, it will contribute to ultrafast community and be particularly useful as a driving or controlling field for the generation of ultrafast coherent x-ray supercontinuum.
Highlights
High-order harmonic generation (HHG) driving by femtosecond laser pulses has attracted a lot of attention for producing fully coherent radiation in the extreme ultraviolet (XUV) region, which may serve as a table-top alternative to the x-ray lasers [1]
In single-crystal OPA (SOPA) scheme, the large temporal walk-off leads to rapid saturation of the amplified pulses, while in dual-crystal optical parametric amplification (DOPA), the compensation of GVMps and GVMpi improves three-pulse overlap, the signal and idler pulses can stay under the central part of the pump and get continuously amplified instead of reaching saturation
The signal energy evolution for pump-delayed SOPA is calculated, even though the signal gain efficiency is improved in SOPA, the signal-to-noise ratio (SNR) in DOPA is still one order of magnitude higher because thinner barium borate (BBO) crystals are employed
Summary
High-order harmonic generation (HHG) driving by femtosecond laser pulses has attracted a lot of attention for producing fully coherent radiation in the extreme ultraviolet (XUV) region, which may serve as a table-top alternative to the x-ray lasers [1]. In order to generate sub-100-as IAPs in soft-x-ray region, a two-color synthesis, combing a 12.5-fs/2.0-μm driving pulse and a weaker 0.8-μm controlling field, was recently proposed by Hong et al [15]. These pioneering experimental results and theoretical predictions depict a bright prospect for soft-x-ray IAPs, and simulate the quest for sub-15-fs intense laser sources with central wavelengths around, for example, 2.0 μm and so on. Apart from the compensation of GVMsi for a broader gain bandwidth, it is of importance to compensate the GVM between the pump and signal/idler (GVMps and GVMpi) to increase the conversion efficiency in OPA, for ultrashort interacting pulses.
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