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A wide variety of detection methods are involved in explosive detection including X-rays, infrared, THz, microwave, gamma-rays, etc. The field of terahertz THz spectroscopy has been investigated many times over previous years as a technique for the detection of explosive vapour signatures. THz waves can penetrate through many dielectric materials, such as clothing, pa- per, plastics, leather, wood and ceramics. In addition, THz radiation has low photon energies and will not cause harmful photoionization in biological tissues. Owing to these advantages, THz technology is a competitive method for inspecting explosives carried by a person or concealed in packages.

The time-constant averaging of the lock-in amplifier was set to 1 second. The distance between the THz emitter and the detector array was 80 cm. If 64 detectors were used rather than a single detector, the THz image could be acquired in less than 1 second with the present electronic phase modulation method. The system according to FIG. The output of each laser was evenly split using the first pair of beam splitters 8.

A single THz detector 22 was used. The detector 22 was mounted on an X-Y computer controlled stage 32 Newport ESP and scanning of stage 32 allowed the placement of the THz detector 22 at each point along a spiral path to simulate the performance of a detector array by movement of a single THz detector The spiral geometry 35 of the detector array is also presented in FIG.


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With the detector array of 32 positions and a time constant of 5 s, it took about 3 min. No image correction algorithms were applied. Therefore, some artifacts of Fourier inversion sidelobs can be observed in these images. Therefore, the higher the THz frequency, the better the image resolution. This dependence can be seen in FIGS. As a practical example of this method, spectral interferometric images of a point THz source transmitting through a C-4 sample 40 were obtained using the system of FIG.

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The sample 40 was inserted between the THz emitter 20 and detector 22 , and images at several frequencies were obtained. The experiment was performed in open air. The THz frequencies for imaging were selected to be away from water absorption lines. See, Martin van Exter et al. In order to take into account the strong frequency dependent response of the CW THz system, the image without the sample reference image together with the image when the sample was inserted signal image were acquired at every frequency.

The absorption peak of RDX at 0. Express 14, This result is in a good agreement with spectral data obtained with a pulsed T-ray system for the same sample The maximum possible phase modulation frequency is limited mostly by the response of the photoconductive antenna THz modules. Also, performance of interferometric imaging system 10 can be improved significantly with a higher optical power: the time constant can be reduced and the image can be produced in less than 1 second.

It will be understood that in a full interferometer system, multiple detectors will be used simultaneously; therefore, the imaging time can be reduced further compared to a single detector that is translated to multiple positions. In accordance with this embodiment a scanning mirror 38 is employed in place of a phase modulator. In current state of the art apparatus that employ a scanning mirror, the mirror needs to move distances of about 1 cm.

Since this distance is much smaller than the 1 cm required for in the current state of the art practice, a much faster scanning mirror can be employed. In accordance with one embodiment a PZT stack is used to oscillate the mirror at tens of kilohertz frequencies. The present inventions can be applied in any environment where rapid scanning of samples is necessary or desirable, including but not limited to airports, arenas, schools, office buildings, government buildings, military installations, mobile military units, vehicles and the like.

Applicants have attempted to disclose all embodiments and applications of the described subject matter that could be reasonably foreseen.

Terahertz imaging

However, there may be unforeseeable, insubstantial modifications that remain as equivalents. While the present invention has been described in conjunction with specific, exemplary embodiments thereof, it is evident that many alterations, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description without departing from the spirit or scope of the present disclosure. Accordingly, the present disclosure is intended to embrace all such alterations, modifications, and variations of the above detailed description.

Year of fee payment : 4. Methods and apparatus are provided employing rapid scanning continuous wave terahertz spectroscopy and imaging for the non-destructive evaluation of materials such as animal hides and natural cork, and explosive detection, concealed weapon detection, and drug detection. A system employing an aperiodic detector array and implementing phase modulation at kHz significantly reduces the imaging time and enables interferometric images of a THz point source to be obtained at several frequencies between 0. All references cited herein are incorporated fully by reference.

A method of analyzing a sample employing rapid scanning continuous wave terahertz spectroscopy comprising: providing at least two individual laser beams containing THz radiation, splitting each of the individual laser beams, mixing the split laser beams, recombining the laser beams and coupling the laser beams into fibers,. The method of claim 1 wherein the PDA is a low-temperature-grown GaAs bowtie-type photo-conductive dipole antennae.

The method of claim 1 further comprising applying a bias of between 0. The method of claim 1 wherein the THz radiation in the at least two individual laser beams is in the range of 0. The method of claim 1 comprising applying an AC voltage to the phase modulator. The method of claim 1 further comprising obtaining images at more than one THz frequency.

The method of claim 1 further comprising the step of comparing spectral information obtained to known data. The method of claim 1 wherein the sample optionally includes an explosive material. The method of claim 1 wherein the sample is a container. The method of claim 1 wherein the sample is luggage. A rapid scanning continuous wave terahertz spectroscopy apparatus comprising at least one THz generator, at least one THz transmitter configured to introduce a THz signal to a sample, a receiver configured to receive THz radiation transmitted through the sample; at least one beam splitter, and at least one electronic phase modulator operable to modulate the phase of THz radiation to be introduced to a sample.

The apparatus of claim 11 further comprising a device adapted to collect spectral data from the received THz radiation. The apparatus of claim 11 comprising a device adapted to compare an absorption value of the received THz radiation to a known absorption value. The apparatus of claim 11 further comprising a lock-in amplifier operable to obtain at least one of THz amplitude and phase.

The apparatus of claim 11 further comprising a movable stage to which the THz receiver is operably connected.

PhD student in terahertz spectroscopy and imaging of key properties of wood

The apparatus of claim 11 comprising a plurality of THz transmitter and receiver pairs. A system employing the apparatus of claim 11 adapted to operate at a single THz frequency within a band of 0. USP true Methods and apparatus for rapid scanning continuous wave terahertz spectroscopy and imaging. USB2 en. Wojdyla et G.

Real-time broadband terahertz spectroscopic imaging by using a high-sensitivity terahertz camera

Gallot Opt. Masson et G.

Publication details

Gallot J. A 29, Hache et G. B 29, Lundh, J. Lim, C. Rechatin, L. Ammoura, A. Davoine, G.

Introduction

Gallot, J. Goddet, E. Lefebvre, V.

Malka et J. Faure Nature Physics 7,