Generation of mid-IR and visible radiation from four-wave amplification of ultrashort laser pulses in transparent dielectrics

Abstract

We analyze and simulate the generation of mid-IR radiation from the propagation of bichromatic laser pulses in transparent, centrosymmetric dielectrics. The process relies on using the beatwave associated with the bichromatic pulse to seed four-wave parametric amplification in the mid-IR. We derive propagation equations describing the evolution of the pump waves and scattered waves including the effects of third-order nonlinearity, dispersion, and finite laser spot size. An expression for the growth rate of the scattered waves due to four-wave mixing is derived in the limit of negligible pump depletion and is characterized for various transparent dielectric materials. For fused silica, it is found that a bichromatic pump with wavelengths near 1 μm can generate forward-directed radiation near 3 μm. Fully explicit particle-in-cell modeling shows exponential growth and high conversion efficiency to mid-IR and visible radiation when the beat-wave-generated frequency comb is tuned to overlap the gain band of the four-wave amplification process.