مجال
التميز
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تميز دراسي وبحثي
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البحوث المنشورة
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البحث (1):
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عنوان البحث:
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Self-Mixing Interferometry With Terahertz Quantum
Cascade Lasers
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رابط إلى البحث:
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Click
here
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تاريخ النشر:
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12
Sep 2012
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موجز عن البحث:
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Terahertz frequency quantum cascade lasers
(THz QCLs) are compact sources of coherent THz radiation with potential
applications that include astronomy, trace-gas sensing, and security imaging.
However, the reliance on slow and incoherent thermal detectors has limited
their practical use in THz systems. We demonstrate THz sensing using
self-mixing (SM) interferometry, in which radiation is reflected from an
object back into the QCL cavity, causing changes in the laser properties; the
THz QCL thus acts simultaneously as both a source and detector.
Well-established SM theory predicts a much weaker coupling in THz QCLs than
in diode lasers, yielding a near-linear relationship between the phase of SM
signals and the external cavity length. We demonstrate velocimetry of an
oscillating reflector by monitoring SM-induced changes in the QCL drive
voltage. We show that this yields data equivalent to that obtained by sensing
the emitted THz power, thus allowing phase-sensitive THz-SM sensing without
any external detector. We also demonstrate high-resolution SM-imaging at a
round-trip distance of 21 m in air-the longest-range interferometric sensing with
a THz QCL to date.
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البحث (2):
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عنوان البحث:
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Coherent three-dimensional terahertz imaging through
self-mixing in a quantum cascade laser
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رابط إلى البحث:
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Click
here
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تاريخ النشر:
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30
Oct 2013
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موجز عن البحث:
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We demonstrate coherent terahertz (THz) frequency
imaging using the self-mixing effect in a quantum cascade laser (QCL).
Self-mixing voltage waveforms are acquired at each pixel of a two-dimensional
image of etched GaAs structures and fitted to a three-mirror laser model,
enabling extraction of the amplitude and phase parameters of the reflected
field. From the phase, we reconstruct the depth of the sample surface, and we
show that the amplitude can be related to the sample reflectance. Our
approach is experimentally simple and compact, and does not require frequency
stabilization of the THz QCL.
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البحث (3):
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عنوان البحث:
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Detection of terahertz frequency radiation via the
photothermoelastic response of zincblende crystals
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رابط إلى البحث:
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Click
here
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تاريخ النشر:
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07
Nov 2013
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موجز عن البحث:
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We present experimental evidence for a
photothermoelastic response in zincblende crystalsilluminated by quantum
cascade laser sources in the frequency range 2.2−2.9 THz. Results
obtainedusing an optically-balanced sampling arrangement indicate a mechanism
whereby the stressdistribution established through localised heating of the
crystal induces a change in opticalbirefringence via the photoelastic
response of the crystal. A full mathematic model of this photothermoelastic
mechanism in (110)-orientated crystals is presented, and shown to agree well
withexperimental measurements of the magnitude, and the orientational and
spatial dependencies of thesampled signal in ZnTe and GaP crystals.
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المؤتمرات العلمية:
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المؤتمر (1):
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عنوان المؤتمر:
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UK Semiconductors 2012
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تاريخ الإنعقاد:
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04
Jul 2012
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بلد
ومكان الإنعقاد:
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University of Sheffield, Sheffield, UK
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طبيعة المشاركة:
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Invited Talk
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عنوان المشاركة:
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Terahertz sensing and imaging through
self-mixing in a quantum cascade laser
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ملخص المشاركة:
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Quantum cascade lasers (QCLs) are
compact, semiconductor sources of narrowband terahertz (THz) frequency
radiation. Owing to their coherence and high power, they are potentially
well-suited for use in a broad range of application areas, including chemical
sensing and biomedical imaging. However, their implementation in such
applications requires a compact and sensitive detection system. We address
this by using the THz QCL not only as the source but also as an
interferometric (self-mixing (SM)) detector. SM occurs when radiation from a
laser is partially reflected from an external object and injected back into
the laser cavity. The reflected radiation interferes (‘mixes’) with radiation
in the laser cavity, producing variations in the threshold gain, emitted
power, lasing spectrum and terminal voltage. This technique thus allows
simple, self-aligned and robust system to be constructed for measuring
displacement and reflectivity.
We investigate the use of SM sensing
with a THz QCL for three-dimensional imaging and surface profiling. Whilst
the laser SM signals were obtained by monitoring the voltage variations
across the laser terminals, we have also demonstrated that SM signals can
also be obtained by monitoring the perturbations in power collected from the
back facet of the laser.
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المؤتمر (2):
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عنوان المؤتمر:
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International Quantum Cascade Lasers
School & Workshop 2012
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تاريخ الإنعقاد:
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02
Sep 2012
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بلد
ومكان الإنعقاد:
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Baden near Vienna, Austria
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طبيعة المشاركة:
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Poster presentation
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عنوان المشاركة:
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Surface-profiling through self-mixing
in a THz quantum cascade laser
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ملخص المشاركة:
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Terahertz frequency quantum cascade lasers (THz
QCLs) are semiconductor sources of coherent THz radiation, and have numerous
potential applications in chemical sensing and industrial inspection, as well
as security and biomedical imaging. However, these applications require a compact
and sensitive detection system. We address this by using a THz QCL as both
the radiation source and as an interferometric detector.
Self-mixing (SM) occurs when radiation
is reflected from an external object back into the QCL cavity. The resulting
interference modulates the emitted power and QCL voltage, depending on the
amplitude and phase of the reflection. This allows simple, ‘detector-free’,
sensing of displacement and reflectivity, with high-sensitivity owing to its
coherent nature. We demonstrate 3D imaging using SM in a THz QCL. Although
the SM signals were obtained from changes to the laser voltage, we show that
SM signals can also be obtained from the THz emission from the back
laser-facet. Owing to the high SM sensitivity, we have been able to demonstrate
stand-off imaging at round-trip distances of up to 20 m through air.
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