Systems and methods for high-contrast, near-real-time acquisition of terahertz images

摘要

A cw terahertz image beam is upconverted by a nonlinear optical process (e.g., sum- or difference-frequency generation with a near IR cw upconverting beam). The upconverted image is acquired by a near IR image detector. The bandwidths and center wavelengths of the terahertz image beam and the upconverting beam are such that wavelength filtering can be employed to permit an upconverted image beam to reach the detector while blocking or substantially attenuating the upconverting beam.

主权项

1. A method for acquiring an upconverted terahertz image of an object, the method comprising:
(a) illuminating the object with a continuous-wave terahertz imaging beam characterized by a terahertz frequency between about 0.05 THz and about 10 THz, a terahertz bandwidth, and a terahertz average power; (b) collecting at least a portion of the terahertz imaging beam, transmitted by or around the object or reflected or scattered from the object, and directing that portion to propagate as a terahertz image beam through a nonlinear optical medium, wherein the terahertz image beam is characterized by a terahertz image beam size at the nonlinear optical medium; (c) directing a continuous-wave upconverting beam to propagate through the nonlinear optical medium, wherein the upconverting beam at least partly spatially overlaps the terahertz image beam in the nonlinear optical medium and is characterized by an upconverting wavelength, an upconverting bandwidth, an upconverting average power, and an upconverting beam size at the nonlinear optical medium; (d) upconverting, by nonlinear optical interaction of the terahertz image beam and the upconverting beam in the nonlinear optical medium, at least a portion of the terahertz image beam to form an upconverted image beam characterized by one or both wavelengths produced by sum- or difference-frequency generation between the terahertz image beam and the upconverting beam; (e) receiving at least a portion of the upconverted image beam using an image detector and detecting with the image detector an upconverted image formed at the image detector by the upconverted image beam; and (f) allowing less than about 1 part in 106 of the upconverting beam to reach the image detector using an image filtering element, (g) wherein the terahertz average power is greater than about 0.1 W, the upconverting wavelength is between about 400 nm and about 3500 nm, the upconverting bandwidth is less than about 0.1 nm, and the upconverting average power is greater than about 1 W.