Control of spectral shift, broadening, and pulse compression during mid-IR self-guiding in high-pressure gases and their mixtures.

Precise control of the nonlinear optical phenomena is the limiting factor for the spectral broadening and pulse compression techniques for high-power laser systems. Here we demonstrate that generation of the blue and red components under filamentation of 4.55-µm mid-IR pulses can be easily adjusted independently through the use of inert and molecular gases, while uniform broadening up to 1-µm bandwidth at the 1/e2 level relies on the proper choice of gas mixture and its compounds partial pressure. Such synthesized media provide a feasible route for the free of damage control of pulse spectral broadening and compression for gigawatt peak power laser systems operating in the mid-IR. Additional management of a generated spectrum can be realized through the adjustment of focusing conditions. The resulted pulse is compressed by a factor of 2.6 down to 62 fs pulse duration (4.1 optical cycles) with additional dispersion compensation. Controllable nonlinear compression down to four optical cycles keeping the millijoule energy level of a mid-IR laser pulse provides direct access to extreme nonlinear optics.

3.5-mJ 150-fs Fe:ZnSe hybrid mid-IR femtosecond laser at 4.4 µm for driving extreme nonlinear optics.

We report on entering a new era of mid-IR femtosecond lasers based on amplification in a relatively new gain chalcogenide medium, Fe:ZnSe. Our hybrid all-solid-state laser system is based on direct pulse amplification of femtosecond seed from three-stage AGS-based-optical parametric amplification (OPA) in a Fe:ZnSe laser crystal optically pumped by a Cr:Yb:Ho:YSGG Q-switched nanosecond laser. The development of the pump source with output energy up to 90 mJ operating at a 10 Hz repetition rate regime and highly efficient grating compressor (80%) provides 3.5-mJ 150-fs femtosecond pulses centered at 4.4 µm. Diode-pumped Er:YAG/Er:YLF lasers make it possible to increase the beam quality and repetition rate of the proposed laser system up to 100 Hz. Focusing such a laser radiation into the ∼3λ beam diameter allows us to reach a focus laser intensity up to 1016 W/cm2 which is only an order of magnitude lower than a relativistic intensity of 1017 W/cm2 and enough to drive strong nonlinear optics in mid-IR. We show as a proof-of-principle experiment the generation of four-octave spanning (from 350 nm up to 5.5 µm) supercontinuum in xenon.