Terahertz imaging has been shown to be a powerful tool for analyzing a variety of materials. From the amount of water in a leaf over time to looking at the spectroscopic species in a flame, this technique shows great potential for commercial applications. However, in order to work in a commercial environment, the present free-space optical systems must be abandoned in favor of fiber-optic delivery. To this end, we have developed a compact, fiber-pigtailed terahertz imaging system that utilizes a hermetically sealed, photoconductive, transmitter and receiver. The receiver uses an integrated amplifier to obtain a 1000:1 S/N with only 1 mW of power on both the transmitter and receiver and with a one second integration time. This system has usable energy extending from 0.04 to 2 THz and has both a rapid (20 Hz) scanner for short, 40-ps, scans as well as a long rail for scans up to 1 ns. The system hardware is contained in a 1.5 cu. ft. box with fibers feeding both the transceiver units. These units can be configured into either a transmission or reflection mode depending on the user's application. An advanced software system controls the hardware, collects the data, and does image processing.
Electronic holography and speckle interferometry are combined with femtosecond gating techniques to form images of absorbing structures embedded in organic tissue. The method takes advantage of the inherent instability of living tissue.
A holographic technique ('light-in-flight' (LIF) holography) is described, which combines classic off-axis holography with the latest ultrashort-pulse laser technology to produce three-dimensional images with femtosecond temporal resolution. The LIF holography can be used to study the distortions of pulses moving through optical fibers (Abramson, 1987), visualize relativistic effects (Abramson, 1985), measure the shape and deformation of fast moving objects, and make observations through nonrigid scattering media (Spears et al., 1989). The technique can also be applied in ultrafast optical science, metrology, and medical imaging.
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