THz Overview

Terahertz spectroscopy emerged in the early 1990s as a powerful new way to perform spectroscopic studies in the far-infrared region of the spectrum.  While some people refer to any electromagnetic radiation in the far-IR region as “THz”, the Schmuttenmaer group reserves this designation for sub-picosecond pulsed far-IR radiation that is typically generated by ultrafast laser systems.  This is a much brighter photon source than arc lamps or globars.  In addition, THz spectroscopy allows for synchronous coherent detection of the electromagnetic field (rather than its intensity) and for pump/probe studies to be carried out in the far-IR.

A little over half the work being done in the Schmuttenmaer group is explicitly time-resolved and is often referred to as time-resolved THz spectroscopy, or TRTS.  With this method, an optical pulse photoexcites a sample, and a THz pulse probes changes in its far-IR optical properties at varying times after photoexcitation.  We can investigate changes on time scales ranging from 100 femtoseconds to nearly 1 nanosecond.  We also perform time-resolved THz emission experiments wherein the sample itself generates a THz pulse upon photoexcitation.  The shape of the emitted pulse provides information on the timescale and dynamics of the change in electric or magnetic polarization of the sample. 

The remainder of our effort involves non-time-resolved work using a technique known as THz time-domain spectroscopy, or THz-TDS.  This method allows us to make measurements in a traditionally underrepresented region of the electromagnetic spectrum from about 5 to 120 wavenumbers.  Since the advent of THz spectroscopy roughly 20 years ago, there has been a general renaissance in far-IR spectroscopy due to new measurements facilitated by the technique.

Terahertz spectroscopy is quite versatile.