Novel Terahertz Sensing System

Technology #14073

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FIG. 1 is a block diagram of a terahertz sensing system according to an embodiment of the present invention.FIG. 2 is a block diagram of a terahertz upconversion receiver that upconverts a measurement signal from terahertz frequencies to optical frequencies by mixing the measurement signal with an optical pump beam in a nonlinear crystal.  FIG. 3 is a block diagram of a terahertz upconversion spectrometer according to an embodiment of the present invention. FIG. 4 illustrates the diffusion bonding process used to create quasi-phase matched (QPM) GaAs crystals suitable for use in terahertz upconversion receivers. Bulk crystals and other forms of phase-matched materials may also be employed.  FIG. 5 is a plot of optical idler power versus crystal length for a theoretical bulk GaAs crystal (dashed line), an actual GaAs bulk crystal (diamonds), and an actual two-layer QPM GaAs crystal (triangle).FIG. 6 is a block diagram of a laboratory implementation of a terahertz sensing system according to an embodiment of the present invention.FIG. 7 is a plot of terahertz transmit and receive spectra measured with the system shown in FIG. 6. In this measurement, the unconverted signal was directly connected to and measured with a commercial optical spectrum analyzer (OSA).FIG. 8 is a plot of sensor dynamic range versus frequency measured using the Geiger-mode APD detector; the dynamic range exceeds state-of-art by at least 30 dB showing capability of system. FIG 10A illustrate standoff spectroscopy at 5-m on dilute RDX pellets placed in front of a retro-reflector.FIGS. 9A and 9B illustrate standoff imaging (5-m) of a pirate mask obscured from view by recycling bin. Change detection enables identification of C4 explosive on the ear of the pirate mask.
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Inventors
Mohammad Jalal Khan
Lincoln Laboratory, MIT
Jerry Chen
Lincoln Laboratory, MIT
Sumanth Kaushik
Lincoln Laboratory, MIT
Managed By
Dave Sossen
MIT Technology Licensing Officer
Patent Protection

Terahertz sensing system and method

US Patent 8,514,393

Terahertz sensing system and method

US Patent 9,200,959

Applications

This invention is a terahertz sensing system and its remote sensing applications, including explosive detection, vibrometry, concealed weapons detection, hyper-spectral imaging, and medical imaging. The sample’s composition can be acquired by analyzing the reflection, scattering, and absorption spectra in the terahertz region.

Problem Addressed

Detecting terahertz radiation is extremely slow and difficult process, which is why a need exists for improved systems for and methods of sensing terahertz radiation. Also prior systems with serial architectures are limited to detecting stationary objects.

Technology

The invented system collects terahertz radiation scattered from a target and upconverts the collected radiation to optical frequencies. A frequency-domain spectrometer senses spectral components of the upconverted signal in parallel to produce a spectroscopic measurement of the entire band of interest in a single shot. The detected spectrum can then be used to derive information about spectroscopic characteristics of the sample. Because the spectrometer detects different spectral components of the measurement signal in a parallel manner, the system can measure moving samples and fast events.

Advantages


  • Can measure a complete spectrum once per pulse, resulting in much higher scan speeds (e.g., thirty times higher if the system measures thirty frequency components in parallel) due to its parallel architectures
  • Can detect moving object due to the ability to measure a spectrum on a “single shot” basis  
  • Can measure terahertz spectra at standoff, making them better suited to concealed weapons detection and other imaging applications