Modulation Improves Terahertz Spectroscopy

Time-domain terahertz spectroscopy shows promise for applications in many disciplines, but the resolution threshold of the technique has been unsuitable for the analysis of thin films. Now a team at RWTH Aachen in Germany has incorporated modulation into a terahertz setup to obtain measurements from 1.2-µm-thick polymer and 100-nm-thick SiO₂ films.

In the experiment, which the researchers describe in the Sept. 2 issue of Applied Physics Letters, a shaker operating at 10 to 200 Hz moves the sample and reference out of the focus of the terahertz signal, and a chopper modulates the beam itself. The modified technique may have application in identifying doping variances as low as 4 x 10¹³/cm³ and in marker-free gene analysis.