Abstract
Over the last decade, the development of ultrafast laser pulses in the mid-infrared (MIR) region has led to important breakthroughs in attosecond science and strong-field physics. However, as most such broadband MIR laser sources are near-IR pumped, the generation of high-intensity, long-wavelength MIR pulses is still a challenge, especially starting from picosecond pulses. Here we report, both experimentally and numerically, nonlinear pulse compression of sub-millijoule picosecond pulses down to sub-300 fs at 2050 nm wavelength in gas-filled Kagome-type hollow-core photonic crystal fibers for driving MIR optical parametric amplifiers. The pump laser is comprised of a compact fiber laser-seeded 2 μm chirped pulse amplification system based on a Ho:YLF crystal at 1 kHz repetition rate. Spectral broadening is studied for different experimental conditions with variations of gas pressure and incident pulse energies. The spectrally broadened 1.8 ps pulses with a Fourier-limited duration of 250 fs are compressed using an external prism-based compressor down to 285 fs and output energy of 125 μJ.
Highlights
In recent years, high-energy, ultrashort mid-infrared (MIR) laser sources have experienced rapid technological advancements due to their wide range of application
As the input pulse duration is in the ps range, the output spectrum does not support very short pulse duration; GVD from the window is of very little significance and can be neglected
To explore the effect of fiber core diameter on the nonlinear spectral broadening in these fibers, the previous experiments are repeated with 7-cell fiber (MFD 44 μm) of length 3 m with slightly smaller core diameter and similar experimental conditions as those for the 19-cell fiber in the presence of air and Ar pressures of 3 and 5 bar
Summary
High-energy, ultrashort mid-infrared (MIR) laser sources have experienced rapid technological advancements due to their wide range of application. Nonlinear pulse compression in a waveguide is the most common approach for generation of femtosecond pulse durations and can be implemented in various ways—for instance, spectral broadening in noble gas-filled large-core hollow capillaries where the noble gas acts as a nonlinear medium. IC-based HC-PCFs are of advantage over both hollow capillaries and PBG-based fibers, guiding light over a large bandwidth and overcoming the damage threshold of solid-core fibers These fibers have allowed for a dramatic reduction in transmission loss and have broken records in pulse-energy handling and compression [29,30], leading to the demonstration of 1 mJ 600 fs Yb laser beam handling [30]. We further study numerically the propagation of ps pulses in these fibers and the model matches the experimental behavior of spectral evolution for different input conditions
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