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Journal of the Optical Society of America B

Journal of the Optical Society of America B


  • Vol. 17, Iss. 3 — Mar. 1, 2000
  • pp: 452–461

Influence of noise on the characterization of materials by terahertz time-domain spectroscopy

Lionel Duvillaret, Frédéric Garet, and Jean-Louis Coutaz  »View Author Affiliations

JOSA B, Vol. 17, Issue 3, pp. 452-461 (2000)

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We analyze the contributions of various error sources to uncertainty in the far-infrared optical constants (refractive index and absorption coefficient) measured by terahertz (THz) time-domain spectroscopy. We focus our study on the influence of noise. This noise study is made with a thick slab of transparent material for which the THz transmitted signal exhibits temporal echoes owing to reflections in the sample. Extracting data from each of these time-windowed echoes allows us to characterize the noise sources. In THz time-domain spectroscopy experiments in which photoswitches are used as antennae, the transmitting antenna constitutes the principal noise source. The uncertainty in the far-infrared optical constants can be strongly reduced when the extraction is performed with THz echoes that have encountered many reflections in the sample.

© 2000 Optical Society of America

OCIS Codes
(120.4530) Instrumentation, measurement, and metrology : Optical constants
(300.6240) Spectroscopy : Spectroscopy, coherent transient

Lionel Duvillaret, Frédéric Garet, and Jean-Louis Coutaz, "Influence of noise on the characterization of materials by terahertz time-domain spectroscopy," J. Opt. Soc. Am. B 17, 452-461 (2000)

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  23. See, for example, E. D. Palik, ed., Handbook of Optical Constants of Solids (Academic, Orlando, Fla., 1985). Nevertheless, this is not the case for highly absorbing materials, such as superconducting thin films, for which another simplification holds.8 The general case does not lead to analytical expressions but can be numerically treated by a reliable and fast method.22
  24. Indeed, the Johnson noise is linked to the photoswitch resistance, which varies under laser illumination. Nevertheless, because of the slight decrease of the mean photoswitch resistance induced by the laser illumination, the Johnson noise is rather independent of the signal. Moreover, the shot noise is proportional to the square root of the signal amplitude and not to its amplitude.
  25. Both noise analysis and uncertainty reduction procedures have been applied with time-domain reflectometry equipment in our laboratory for the characterization of guided structures in the microwave domain. First results confirm the possibility of extending these two methods to another area of time-domain characterization.
  26. M. L. Boas, Mathematical Methods in the Physical Sciences (Wiley, New York, 1983).

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