Abstract

Despite the considerable recent interest in tera-hertz time-domain spectroscopy (THz-TDS), there are several aspects of these optical systems for which no careful optimization has been performed. One important example is the design of the substrate lens. Grischkowsky and co-workers first described the use of a substrate lens to improve the performance of THz-TDS systems,¹ and these advantages have been discussed by a number of authors.²-⁴ Most researchers have used one of two distinct lens design, both borrowed from earlier microwave and millimeter-wave techniques. In one, the collimating lens, the emitter is located at the focus of the substrate lens. In the other, the aplanatic hyperhemisphere, the emiller is located so that a minimum of the emitted rays are lost to internal reflection inside the lens. Although a number of researchers have discussed the relative merits of these two designs in lower frequency, narrow-band radiation systems,5 there has been no discussion of the case of broadband emission. As a result, the dramatic influence of the substrate lens design on the achievable bandwidth in THz-TDS system has not been generally appreciated.

© 2002 Optical Society of America