Patent ID: 8314391

Claim:
A terahertz scanning sensor system for making temporal delay measurements of THz pulses that are caused upon interaction of such pulses with a moving sheet from which measurements material properties of the moving sheet can be detected, the system comprising: a mobile carriage reciprocally movable in a direction transverse to a direction of movement of the moving sheet; a THz transmitter and a THz detector each of which is carried by the mobile carriage and arranged such that THz radiation when emitted by the transmitter will interact with the sheet prior to such radiation being received at the detector; a laser source, an optical delay device and a beam splitter each of which is stationary with respect to the carriage, the laser source being operative to develop a laser pulse for application to the beam splitter, the beam splitter being operative to develop a first pulse and a second pulse in response to the laser pulse being applied thereto; a first optic fiber and a second optic fiber, each of the first optic fiber and the second optic fiber respectively having a first end and a second end, the first pulse being received at the first end of the first optic fiber for transmission along a first optical path to the second end thereof for illumination by the first pulse of the THz transmitter which in response thereto is operative to emit THz radiation, the second pulse being received at the first end of the second optic fiber for transmission along a second optical path to the second end thereof for illumination by the second pulse of the THz detector which in response thereto is operative to receive THz radiation, the first optic fiber and the second optic fiber being coextensively disposed so that the first optic fiber and the second optic fiber substantially maintain identical temperature gradients respectively along the first optical path and the second optical path; and a take-up mechanism in which a constant bend length and radius on each of the first optic fiber and the second optic fiber is maintained and further in which substantially the same tension on each of the first optic fiber and the second optic fiber is maintained as the mobile carriage is moved such that an optical path difference between the first optical path and the second optical path remains substantially constant whereby the first pulse and the second pulse transmitted respectively through the first optic fiber and the second optic fiber exhibit consistent (i) time of arrival, (ii) phase duration and (iii) polarization state and energy.