Short-wavelength cutoff of the light bullet spectrum in calcium fluoride

摘要

For the first time, we studied the change in a short-wavelength cutoff of a mid-IR pulse spectrum with an increase in a nonlinear optical interaction length in calcium fluoride. We investigate a transformation of an anti-Stokes wing in a pulse spectrum during light bullet formation under anomalous group velocity dispersion. An experimental scheme allowing a variation of a pulse propagation length in dielectric sample was employed. We compare results of numerical simulations provided by both, slowly-evolving-wave approximation method and unidirectional pulse propagating equation, under experimental conditions. It was found that a short-wavelength cutoff of an isolated anti-Stokes wing in light bullet's spectrum shifts towards short-wave region by several hundred nanometers during light bullet formation. Moreover, the shift of a short-wavelength cutoff is 100 nm per 100 mu m of a pulse propagation length in a sample at the initial stage of light bullet appearance. The short-wavelength cutoff of already formed propagating light bullet changes slightly. With an increase in pulse energy, the short-wavelength cutoff decreases. The observed shift of the cutoff wavelength during the light bullet formation exhibits a general behaviour for all considered pulse energies.