Nonlinear Optical Method of Determination the Chirp of Broadband Femtosecond Laser Pulse in IR-Range

Abstract

A new method for determining the chirp of a femtosecond broadband IR laser pulse at a central wavelength of 2.5 μm, based on the generation of a spectral supercontinuum in the field of a spectrally limited femtosecond laser pulse, propagating in a single mode fiber based on chalcogenide glass, and subsequent noncollinear generation of radiation at summary frequency by spectrally limited and spectral broadened supercontinuum femtosecond pulses is proposed. The time dependences of the instantaneous frequency of a femtosecond broadband pulse, obtained both from the results of numerical integrations of the equation describing the process of spectral supercontinuum generation and from the results of two-dimensional distributions of dynamic spectrograms are presented. It is shown that the proposed method allows one to determine the chirp of a broadband femtosecond IR laser pulse, formed during the soliton propagation mode in a fiber, with a relative error of no more than 5%, but the chirp of a broadband femtosecond IR laser pulse, formed in the process of non-soliton propagation in a fiber, with a relative error of no more than 10%.The presented results can be used in the development of a nonlinear optical phase correlator for determination the phase and time profile of a femtosecond laser pulse in the mid-IR range.