Train of high-power femtosecond pulses: Probe wave in a gas of prepared atoms

TL;DR

This paper introduces a novel method to generate high-power femtosecond pulse trains using a prepared atomic medium, with pulse characteristics tunable by atomic density and interaction parameters, potentially reaching THz repetition rates.

Contribution

The study presents a new approach for producing ultrashort pulse trains in a two-level atomic medium, incorporating non-saturating refractive index effects beyond the dipole approximation.

Findings

Pulse energy exponentially increases with atom density.

Repetition rate can reach around 1 THz or higher.

Non-saturating terms affect refractive index dependence.

Abstract

We present a new method for generating a regular train of ultrashort optical pulses in a prepared two-level medium. The train develops from incident monochromatic probe radiation travelling in a medium of atoms, which are in a quantum mechanical superposition of dressed internal states. In the frame of used linear theory for the probe radiation, the energy of individual pulses is an exponentially growing function of atom density and of interaction cross section. Pulse repetition rate is determined by the generalized Rabi frequency and can be around 1 THz and greater. We also show that the terms, extra to the dipole approximation, endow the gas by a new property: non-saturating dependence of refractive index on the dressing monochromatic field intensity. Contribution of these nonsaturating terms can be compatible with the main dipole approximation in the wavelength region of about ten micrometers (the range of CO_2 laser) or larger.