Multicolor and supercontinuum radiation generation in terahertz and mid-infrared ranges due to the gas ionization by two-color chirped laser pulses

A method for generating multicolor phase-stable pulses tunable in a wide range from terahertz (THz) to mid-infrared (mid-IR) is proposed. It is based on gas ionization by a laser pulse containing a linearly chirped fundamental field and several double-frequency components with different time delays. Our closed-form analytical formulas and numerical calculations show that the generated current density contains unchirped components at several detuning frequencies determined by the difference between the instantaneous frequencies of the additional laser components and twice the instantaneous frequency of the fundamental field, as well as at all triple combination detuning frequencies. The generated frequencies can be changed by varying the time delay or the chirp value. The generated pulse durations are determined by the gas ionization duration, which is much shorter than the laser pulse duration and can be varied in a wide range by changing the laser pulse duration or intensity. Under a sufficiently short ionization duration, the peak widths at the generated frequencies increase greatly, forming a supercontinuum extending from THz to the mid-IR range.