Tunable near- to mid-infrared pump terahertz probe spectroscopy in reflection geometry

TL;DR

This paper presents a tunable ultrafast broadband infrared pump--THz probe system in reflection geometry, capable of studying transient photoinduced changes in strongly correlated materials across a wide wavelength range.

Contribution

The authors developed a novel reflection geometry pump--THz probe setup with broad tunability from 1.2 to 15 micrometers, enabling advanced studies of strongly correlated materials.

Findings

Demonstrated 15 μm pump--THz probe measurements on EuSbTe₃

Resolved a 0.5% transient change in reflected THz electric field

System allows mode-selective excitation in strongly correlated systems

Abstract

Strong-field mid-infrared pump--terahertz (THz) probe spectroscopy has been proven as a powerful tool for light control of different orders in strongly correlated materials. We report the construction of an ultrafast broadband infrared pump--THz probe system in reflection geometry. A two-output optical parametric amplifier is used for generating mid-infrared pulses with GaSe as the nonlinear crystal. The setup is capable of pumping bulk materials at wavelengths ranging from 1.2 $\mu$m to 15 $\mu$m and beyond, and detecting the subtle, transient photoinduced changes in the reflected electric field of the THz probe at different temperatures. As a demonstration, we present 15 $\mu$m pump--THz probe measurements of a bulk EuSbTe$_{3}$ single crystal. A $0.5\%$ transient change in the reflected THz electric field can be clearly resolved. The widely tuned pumping energy could be used in mode-selective excitation experiments and applied to many strongly correlated electron systems.