Abstract
We report on a kHz, mJ-level, carrier-envelope phase (CEP)-stable ultrabroadband optical parametric chirped-pulse amplifier (OPCPA) at 2.1-μm wavelength, pumped by a high-energy, 14 ps, cryogenic Yb:YAG pump laser, and its application to high-order harmonic generation (HHG) with Xe. The pre-amplifier chain is pumped by a 12-ps Nd:YLF pump laser and both pump lasers are optically synchronized to the signal pulse of the OPCPA. An amplified pulse energy of 0.85 mJ was obtained at the final OPCPA stage with good beam profile. The pulse is compressed to 4.5 optical cycles (<32 fs) with a spectral bandwidth of 474 nm supporting 3.5 optical cycles. The CEP stability was measured to be 194 mrad and the super-fluorescence noise is estimated to be ~9%. First HHG results are demonstrated with Xe showing significant cutoff extension to >85 eV with an efficiency of ~10-10 per harmonic, limited by the maximum gas pressure and flow into the chamber. This demonstrates the potential of this 2.1-μm source for scaling of photon energy and flux in the water-window range when applied to Ne and He at kHz repetition rate.
Highlights
High-order harmonic generation (HHG) with long-wavelength driver pulses [1,2,3,4,5,6,7,8,9] has been regarded as a promising source of high-flux coherent extreme ultraviolet/soft X-ray (XUV) radiation with photon energies approaching the keV regime via cutoff extension
The ultrabroadband 2.1-μm optical parametric chirped-pulse amplifier (OPCPA) system operating at 1 kHz repetition rate consists of a master oscillator with a difference-frequency generation (DFG) stage, a Nd:YLF pump laser, a cryogenic Yb:YAG pump laser, and three OPCPA stages followed by a compressor
We demonstrated a mJ-level ultrabroadband 2.1-μm OPCPA operating at 1 kHz repetition rate, pumped by a novel high-energy cryogenic Yb:YAG chirped-pulse amplification (CPA) chain and a Nd:YLF CPAchain
Summary
High-order harmonic generation (HHG) with long-wavelength driver pulses [1,2,3,4,5,6,7,8,9] has been regarded as a promising source of high-flux coherent extreme ultraviolet/soft X-ray (XUV) radiation with photon energies approaching the keV regime via cutoff extension. Phase-matched HHG with covering the water window range was experimentally demonstrated [8] using a 10-Hz, 2.4-mJ, 2-μm optical parametric amplifier (OPA) pumped by a Ti:sapphire chirped-pulse amplification (CPA) laser. Fuji et al [13] pioneered a kHz, few-cycle OPCPA system at 2.1-μm wavelength using an intra-pulse difference-frequency generation (DFG) seed and a ~50-ps Nd:YLF pump laser. They obtained output energies of up to 80 μJ, which was limited by excessive super-fluorescence (SF). The system delivers 1 mJ-level kHz-repetition-rate pulse trains for experimental demonstration of high-flux long-wavelength HHG, geared towards keV photon energy.
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