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R. Barry Johnson, D.Sc.

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R. Barry Johnson, D.Sc. Research Professor Physics Department (A-145) Alabama A&M University P.O. Box 1268 Normal, Alabama 35762 256.372.8148 ralph.johnson_at_aamu.edu – PowerPoint PPT presentation

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Title: R. Barry Johnson, D.Sc.


1
Terahertz Sensors and Applications
  • R. Barry Johnson, D.Sc.
  • Research Professor Physics Department
    (A-145) Alabama AM University
  • P.O. Box 1268
  • Normal, Alabama 35762
  • 256.372.8148 ralph.johnson_at_aamu.edu

18 July 2008
2
Terahertz Detectors
  • Bolometers
  • Conventional
  • Electrostatic
  • Golay
  • Pyroelectric
  • Diodes

3
Terahertz Spectral Region 0.06 10 THz 2
300 cm-1 5000-30 µm
Typical Range 300 GHz - 3 THz 1000-100 µm
X-rays
Radio wave
UV
microwaves
Infrared
NIR
visible
Molecular rotations (gas)
Low frequency bond vibrations
Crystalline phonon Vibrations (solid)
Hydrogen-bonding stretches and torsions (liquids)
4
Bolometer
  • Samuel Langley invented the bolometer in 1878.
  • Any radiation absorbed by the bolometer raises
    its temperature above that of its heat sink.
    Temperature change causes a change in some
    parameter, such as device resistance, that can be
    measured directly or indirectly.
  • Often used in a Wheatstone configuration with a
    hot and a cold detector.
  • Can be made very sensitive, but have low
    frequency response.
  • Used from mm-wave to beyond visible light.

5
Principle of Bolometer
6
Electrostatic Bolometer
  • Broad spectral coverage.
  • MEMS structure, which allows arrays to be easy
    fabricated.
  • Cantilevered configuration electrostatically
    charged.
  • Incident flux converted to heat which then
    discharges the electrostatic charge on the
    device.
  • Good sensitivity and modest speed possible.

7
Cryogenically Cooled Bolometer
  • The cryogenically cooled silicon bolometers offer
    excellent signal to noise ratio and nearly flat
    response for THz wavelengths from 15 µm to 2 mm.

RadiaBeam Technologies BLIS-03-BLM
8
Silicon Bolometer
9
Golay Cell Detector
  • A Golay Cell is a room temperature bolometer,
    which is a convenient choice for the moderate to
    high intensity THz signal measurements.
  • Cell is a metal cylinder having a blackened metal
    plate at one end and a flexible metalized
    diaphragm at the other. It is filled with an
    inert gas and then sealed. Radiation incident
    upon the blackened metal plate is absorbed and
    heats the gas which increases the pressure
    thereby deforming the deforms the diaphragm.
  • Light is reflected by the diaphragm motion onto a
    detector to measure the incident flux.
  • Wide spectral range of 0.02-20 THz

RadiaBeam Technologies BLIS-03-GYC and Microtech
Instruments, Inc.
10
Pyroelectric Detector
  • Convert the changes in incoming flux to electric
    signals.
  • Pyroelectric materials are characterized by
    having spontaneous electric polarization, which
    is altered by temporal temperature changes (
    ) when irradiated by flux.
  • High sensitivity,
  • Room temperature operation
  • Low cost
  • Robust under severe environmental conditions
  • Suffers from microphonics (minimal for SBN)

11
LiTaO3 Pyroelectric Detector
  • Large area to 9 mm diameter
  • Broad spectral response 0.1 to 1000 µm
  • Current and Voltage hybrid circuits
  • NEP 3x10-10 W/(Hz)1/2
  • High bandwidth to 20 MHz
  • High voltage output, 50KV/W

Spectrum Detector Inc.
12
Superconducting Hot Electron Bolometer
  • Operates at superconducting transition region.
  • Small temperature change yields large change in
    device resistance.

13
B-field Tuned InSb Detectors
  • Magnetic Resonance Enhanced Indium Antimonide
    (InSb) Hot Electron Bolometer Type QFI/XB
  • Fast and sensitive detection from below 100 GHz
    to 3 THz
  • In the type QFI/XB device, the detector is
    mounted within a quasi-uniform magnetic field
    geometry so that magnetic resonance effects can
    be used to enhance free carrier absorptivity at
    much higher frequencies.
  • Speed Approx. 1MHz (-3dB) at 4.2K.
  • Detector Optical N.E.P is below 1 x 10-12 W
    Hz-1/2

QMC Instruments Ltd
14
Zero-Bias GaAs Schottky Diode Detectors
Responsivity and Noise Measurements of Zero-Bias
Schottky Diode Detectors http//www.virginiadiod
es.com/VDI/pdf/VDI20Detector20Char20ISSTT2007.p
df
15
THz Source
J. Hesler, D. Porterfield, W. Bishop, T. Crowe,
A. Baryshev, R. Hesper and J. Baselmans,
"Development and Characterization of an
Easy-to-Use THz Source", Proc. 16th Intl.
Symposium on Space Terahertz Technology, May,
2005, Goteborg, Sweden. http//www.virginiadiodes.
com/VDI/pdf/Hesler20200520stt20thz20source20a
nd20measurements.pdf
16
Applications of THz Sensors
  • Pharmaceutical
  • Medical
  • Industrial
  • Security

17
Terahertz Spectral Region Molecular Vibrations
  • Terahertz Spectral Region
  • Intermolecular bond vibrations
  • Directly affected by crystal changes
  • Infrared Spectral Region
  • Intramolecular bond vibrations
  • Indirectly affected by crystal changes

18
THz Pulsed Imaging Basics
  • THz Pulsed Imaging
  • Time-of-flight analysis
  • Production of spectral information
  • Refractive index discontinuities reflect back a
    part of the incident pulse
  • Imaging
  • Depth profiling using multiple detected pulses
  • 3D image created by raster scanning

19
TeraView Ltd. Terahertz Pulsed Imaging and
Spectroscopy
20
Photoconductive THz Generator
Zhang, J. Hong, Y. Braunstein, S.L. Shore,
K.A., Terahertz pulse generation and detection
with LT-GaAs photoconductive antenna,
Optoelectronics, IEE Proceedings, Vol. 151, Issue
2, 26 April 2004 (98 101). The characteristics
of optically induced teraherz (THz) radiation
from a biased low-temperature-grown GaAs
(LT-GaAs) photoconductive antenna were
investigated using a femtosecond Tisapphire
laser.
21
Photoconductive THz Detection
J. Zhang et al., Terahertz pulse generation and
detection with LT-GaAs photoconductive antenna,
IEE Proceedings Optoelectronics, April 2004,
Vol.151, Issue 2, (98-101 ).
22
Applications of Terahertz Sensors to
Pharmaceutical Analysis
With Courtesy of Dr. Philip F Taday TeraView
Limited Cambridge, UK
23
Pharmaceuticals
  • Applications
  • Process improvement
  • Polymorph screening
  • Tablet Inspection
  • Early stage of application
  • Commercial instrumentation available

24
Consequences of Bad Coating Quality
  • Unpredictable dosing rate
  • Dose dumping life threatening
  • Legal and commercial implications

25
Coating Integrity Investigation using Terahertz
Pulsed Imaging
Reflected Thz pulses probe coating structures.
26
Non-Destructive Mapping of Coating Thickness in
Tablets
  • Terahertz pulses reflect from each coating layer.
  • Mapping of coating layers accomplished by time of
    flight and x-y scanning.

27
TPI - Coating Layer Thickness
28
Enteric Coated Tablets
15 solids level
16 w.g. enteric coating
10 w.g. enteric coating
29
Terahertz Pulsed Imaging Penetration through most
pharmaceutical excipients. Non-destructive
coating analysis. Fully automated process.
30
Initial Setup for Measuring Water Ingress
10 ml water
HPMC tablet
900 microns
31
K4M Change In Terahertz Image with Time After
the Addition of Water
30 minutes
30 minutes
40 minutes
50 minutes
60 minutes
32
TPI Tablet Evaluation
Tablet Coating Structure
Comparison of X-ray CT TPI
Good vs. Poor Tablet Coatings
33
THz Medical Imaging
  • Applications
  • Skin cancer basal cell carcinoma
  • Aid for surgeon in tissue typing
  • Endoscopy prostrate other cancers
  • In use for clinical trials

34
Non-Destructive Testing 3D THz Imaging of IC
Package
35
Security Applications
  • Checkpoint screening of people to locate hidden
    weapons and explosives.
  • Stand-off detection of explosives.
  • Baggage screening for explosives.
  • Screening for biological and chemical agents.
  • Drug detection.

36
Issues Regarding Terahertz Technology for
Security
  • Signatures
  • Do threat materials have characteristic
    signatures?
  • Are they distinct from non-threat materials?
  • Shielding/Barriers
  • Can terahertz flux penetrate clothing and other
    barriers?
  • Mode
  • Can signature be detected in reflection?
  • Performance
  • Can systems be used at distance up to 10 m?
  • Source power and detector sensitivity
  • Atmospheric absorption
  • Practical Systems Achievable?

37
Terahertz Spectra of Explosives
  • Energetic compounds and explosives
  • Most features above 500 GHz.
  • Barrier material absorption limits upper
    frequency to lt 3 THz.

Kemp et al., Proc. SPIE 5070, 44 (2003)
38
Water Windows Correspond to Spectral Features of
Explosives
39
Possible Confusion Materials
  • Large data base of materials has been collected.
  • No significant confusion found between explosives
    and harmless materials.

Tribe et al., Proc SPIE 5354, 168 (2004)
40
Clothing and Barrier Materials
  • Clothing materials are partially transparent.
  • Absorption increases with frequency.
  • Useful frequency range limited to lt 2-3 THz.

Tribe et al., Proc SPIE 5354, 168 (2004)
41
Detecting Materials Hidden Under Clothing
42
Terahertz Image of Shoe with Hidden Ceramic Knife
Plastic Explosive
43
Conclusions
  • Terahertz technology has made significant
    progress in recent years and is being exploited
    for a variety of applications.
  • Instrumentation is becoming available
    commercially.
  • Components are available for various vendors.
  • Research continues to improve performance and
    lower cost of terahertz components and systems.
  • Terahertz pulsed imaging and spectroscopy has
    been shown to be of use in a number of key areas.
  • Understanding of the thermodynamics of
    polymorphic systems
  • Process understanding of complex coating
    structures
  • Techniques are fast enough to be used in
    environments where tablets have fast random
    motions
  • Advances in medical applications have been
    demonstrated and expected to be further
    exploited.
  • Industrial applications for examining a variety
    of products is expanding.
  • Terahertz systems have demonstrated definitive
    capability is addressing important security
    applications. Initial deployment of screening
    systems in airports around the world.
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