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Description
This work investigates the power-scaling potential of a holmium-doped yttrium lithium fluoride (Ho:YLF) chirped pulse amplifier (CPA) for pumping a mid-infrared zinc germanium phosphide (ZGP) optical parametric chirped pulse amplifier (OPCPA). The demonstrated double-pass Ho:YLF CPA delivers 2.05 μm pulses with 6 mJ pulse energy, 8 ps duration, and 5 kHz repetition rate, enabling OPCPA outputs of 400 μJ at 2.5 – 5 μm and compressible to few-cycle pulse durations. This mid-infrared source has been successfully used to seed an Fe:ZnSe CPA and is being scaled toward few-millijoule pulse energies to support attosecond pulse generation via high harmonic generation (HHG).
Few-cycle, few-millijoule mid-infrared laser sources are critical for applications in attosecond science, spectroscopy, terahertz and frequency-comb generation, surgery, and remote chemical sensing. In particular, extending HHG into the soft X-ray and water-window spectral regions (280–530 eV) requires longer-wavelength driving lasers due to the quadratic scaling of the cutoff photon energy with wavelength. The ZGP OPCPA presented here generates an octave-spanning spectrum from 2.5 to 4.8 μm, offering a pathway toward keV-level HHG photon energies. ZGP is well suited for this application due to its large effective nonlinear coefficient (75 pm/V), broad transparency window (2–12 μm), and high conversion efficiency. Pumping ZGP above 2 μm minimizes absorption, making the 2.05 μm Ho:YLF CPA an optimal choice.
Compared to earlier Ti:sapphire-driven systems limited to 1 kHz operation, the present architecture employs a commercial Yb:KGW front-end and optimized Ho:YLF CPA cooling, enabling operation at 5 kHz with comparable pulse energies. In the Ho:YLF CPA, a conversion efficiency of 38% from absorbed pump power to output power was achieved at 31 W average power. Planned Ho:YLF booster stages are expected to scale the 2.05 μm pulse energy to 30 mJ, placing few-millijoule, CEP-stable mid-infrared pulses via OPCPA within reach. This work demonstrates a compact, high-repetition-rate, cryogen-free mid-infrared femtosecond source suitable for next-generation attosecond experiments.
| Keyword-1 | Attosecond |
|---|---|
| Keyword-2 | Mid-infrared |
| Keyword-3 | Femtosecond |