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Terahertz heterodyne imager for biomedical applications

Siegel, Peter H. and Dengler, Robert J. (2004) Terahertz heterodyne imager for biomedical applications. In: Terahertz and Gigahertz Electronics and Photonics III. Proceedings of SPIE. No.5354. Society of Photo-Optical Instrumentation Engineers , Bellingham, WA, pp. 1-9. ISBN 9780819452627.

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Terahertz heterodyne imaging is an established technique that offers the potential for extremely large dynamic range and high signal-to-noise ratio while maintaining fast data acquisition, stable magnitude and phase measurements, reasonable frequency flexibility and mm level penetration in tissue and other materials. The authors have set up an imaging system based around a custom fabricated 2.5 THz planar Schottky diode mixer pair and two optically pumped far IR lasers. One laser is used for the signal beam and supplies as much as 70mW at 2.5 THz. The other laser acts as a local oscillator (LO) source for the two mixers. Line pairs very close to each other (CH3OH and CH2F2) are chosen to provide a workable intermediate frequency output (IF=24 GHz). Broader RF bandwidth is possible with tunable signal sources and wider IF band amplifiers. A novel frequency stabilization scheme has been implemented to track and calibrate the laser power (magnitude and phase) over a sample run. The system uses the second THz mixer, a low frequency (GHz) reference oscillator and a lock-in amplifier to monitor and normalize the two lasers (LO and Signal). Stability of ~0.1 dB and <5 degrees have been achieved with a dynamic range of more than 90dB. The present system scans the sample through the focused beam and measures transmission or reflection at a fixed RF frequency. Applications to date include establishing contrast mechanisms in a range of test and biological materials. The measurement system is described and the merits and demerits discussed. Early results on a variety of samples are presented as well as plans to enhance the performance in the near future.

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Siegel, Peter H.0000-0002-2539-4646
Additional Information:© 2004 Society of Photo-Optical Instrumentation Engineers. The authors gratefully acknowledge the support of Dr. Warren S. Grundfest (UCLA) and Prof. Scott E. Fraser (Caltech Biological Imaging Center). They would also like to acknowledge the continued interest and frequent help of Dr. Eric Mueller at Coherent DEOS, who first suggested the amplitude tracking laser scheme. Dr. Carol Readhead and Mr. Tim Hiltner, both at Caltech, have been a huge help in providing the mouse samples and training for the biological prep work. Members of the Submillimeter Wave Advanced Technology (SWAT) team at JPL also deserve mention for continuing program and project support. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration and at the California Institute of Technology, Beckman Institute, Division of Biology. Funding was supplied jointly by NASA Code R and NIH through grant K25 EB00109-02.
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Caltech Beckman InstituteUNSPECIFIED
NIHK25 EB00109-02
Series Name:Proceedings of SPIE
Issue or Number:5354
Record Number:CaltechAUTHORS:20180925-133800329
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Official Citation:Peter H. Siegel, Peter H. Siegel, Robert J. Dengler, Robert J. Dengler, } "Terahertz heterodyne imager for biomedical applications", Proc. SPIE 5354, Terahertz and Gigahertz Electronics and Photonics III, (8 April 2004); doi: 10.1117/12.540027;
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:89923
Deposited By: Tony Diaz
Deposited On:25 Sep 2018 21:50
Last Modified:09 Mar 2020 13:19

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