29 July 2003 Portable multichannel multiwavelength near-infrared diffusive light imager
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We have developed a near infrared optical tomography system features fast optical switching, three-wavelength excitations, and avalanche photodiode (APD) detectors with a high dynamic range. Pigtailed laser diodes at 660, 780, and 830 nm are used as light sources and their outputs are distributed sequentially to one of nine source fibers. The crosstalk between source channels is around 65 dB, equivalent to 130 dB in opto-electrical signals. 10 Silicon APD’s detect diffusive photon density waves simultaneously. The dynamic range of an APD is several orders higher than that of a photomultiplier tube (PMT), which eliminates the need of multi-step system gain control. However, the internal gain of the APD we are using is about 3 orders lower than an ordinary PMT. Efforts have been made to suppress the feed through interferences from the transmission part to the reception part so as to reduce the errors in amplitude and phase measurements.
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Nan Guang Chen, Nan Guang Chen, Hongjun Xia, Hongjun Xia, Daqing Piao, Daqing Piao, Quing Zhu, Quing Zhu, } "Portable multichannel multiwavelength near-infrared diffusive light imager", Proc. SPIE 4955, Optical Tomography and Spectroscopy of Tissue V, (29 July 2003); doi: 10.1117/12.478165; https://doi.org/10.1117/12.478165

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