Light-induced states in the transient-absorption spectrum of a periodically pumped strong-field-excited system

TL;DR

This paper explores how periodic pump pulses induce light-induced states in the transient-absorption spectrum of a three-level quantum system, revealing detailed spectral features dependent on laser parameters.

Contribution

It demonstrates the emergence of light-induced states in the absorption spectrum under periodic excitation, even without assuming ultrashort probe pulses, and analyzes their dependence on laser control parameters.

Findings

Light-induced states appear in the absorption spectrum under periodic pumping.

Spectral features depend on the number, area, and phase shift of pump pulses.

Frequencies and time-delay features provide information on pulse action.

Abstract

The transient-absorption spectrum of a $V$-type three-level system is investigated, when this is periodically excited by a train of equally spaced, $\delta$-like pump pulses as, e.g., from an optical-frequency-comb laser. We show that, even though the probe pulse is not assumed to be much shorter than the pump pulses, light-induced states appear in the absorption spectrum. The frequency- and time-delay-dependent features of the absorption spectra are investigated as a function of several laser control parameters, such as the number of pump pulses used, their pulse area, and the pulse-to-pulse phase shift. We show that the frequencies of the light-induced states and the time-delay-dependent features of the spectra contain information on the action of the intense pulses exciting the system, which can thus complement the information on light-imposed amplitude and phase changes encoded in the absorption line shapes.