We present a new type of handheld laser-induced breakdown spectroscopy (LIBS) spectrometer for developing mobile atomic spectroscopy solutions for real world applications. A micro diode-pumped passive Q-switched solid-state laser with high repetition rate of well above 1 kHz in comparison to 1-10 Hz as used in a traditional LIBS instrument is employed to produce a train of laser pulses. The laser beam is further fast scanned over a pre-defined area, hence generating several hundreds of micro-plasmas per second at different locations. Synchronized miniature CCD array spectrometer modules collect the LIBS signal and generate LIBS spectra. By adjusting the integration time of the spectrometer to cover a plurality of periods of the laser pulse train, the spectrometer integrates the LIBS signal produced by this plurality of laser pulses. Hence the intensity of the obtained LIBS spectrum can be greatly improved to increase the signal-to-noise ratio (SNR). This unique feature of the high repetition rate laser based LIBS system allows it to measure elements at trace levels, hence reducing the limit of detection (LOD). The increased signal intensity also lessens the sensitivity requirement for the optical spectrometer. In addition, the energy of the individual laser pulse can be reduced in comparison to traditional LIBS system to obtain the same signal level, making the laser pulse less invasive to the sample. The typical measurement time is within 1 second. Several examples of real world applications will be presented.
Miniaturized field-deployable spectrometers used for the rapid analysis of chemical and
biological substances require high-sensitivity photo detectors. For example, in a Raman
spectroscopy system, the receiver must be capable of high-gain, low-noise detection performance
due to the intrinsically weak signals produced by the Raman effects of most substances. We are
developing a novel, high-gain hetero-junction phototransistor (HPT) detector which employs two
nano-structures simultaneously to achieve 100 times higher sensitivity than InGaAs avalanche
photodiodes, the most sensitive commercially available photo-detector in the near infrared (NIR)
wavelength range, under their normal operation conditions. Integrated into a detector array, this
technology has application for Laser-Induced Breakdown Spectroscopy (LIBS), pollution
monitoring, pharmaceutical manufacturing by reaction monitoring, chemical & biological
transportation safety, and bio-chemical analysis in planetary exploration.
Patrick Gardner, Jie Yao, Sean Wang, Jack Zhou, Ken Li, Irina Mokina, Michael Lange, Weiguo Yang, Leora Peltz, Robert Frampton, Jeffrey Hunt, Jill Becker
KEYWORDS: Laser induced breakdown spectroscopy, Raman spectroscopy, Chemical analysis, Sensors, Avalanche photodiodes, Near infrared, Signal to noise ratio, Phototransistors, Receivers, Signal detection
Miniaturized field-deployable spectrometers used for the rapid analysis of chemical and biological substances
require high-sensitivity photo detectors. For example, in a Raman spectroscopy system, the receiver must be
capable of high-gain, low-noise detection performance due to the intrinsically weak signals produced by the Raman
effects of most substances. We are developing a novel, high-gain hetero-junction phototransistor (HPT) detector
which employs two nano-structures simultaneously to achieve 100 times higher sensitivity than InGaAs avalanche
photodiodes, the most sensitive commercially available photo-detector in the near infrared (NIR) wavelength range,
under their normal operation conditions. Integrated into a detector array, this technology has application for Laser-
Induced Breakdown Spectroscopy (LIBS), pollution monitoring, pharmaceutical manufacturing by reaction
monitoring, chemical & biological transportation safety, and bio-chemical analysis in planetary exploration.
Miniaturized field-deployable spectrometers used for rapid analysis of chemical and biological substances require high-sensitivity photo detectors. For example, in a Raman spectroscopy system, the receiver must be capable of high-gain, low-noise detection performance due to the intrinsically weak signals produced by the Raman effects of most substances. We are developing a novel, high-gain hetero-junction phototransistor (HPT) detector which employs two nano-structures simultaneously: a 3-30 nm passivation layer that enables micron-sized devices, large-scale integration and low-cost products; and a 50-65 nm amplification layer that offers high sensitivity with 1,000x amplification and zero avalanche access noise. We report preliminary tests on single pixels, validating the design target of >1,000 Ampere/Watt responsivity at the near infrared wavelength of 1550nm, which is 100 times more sensitive than InGaAs avalanche photodiodes, the most sensitive commercially available photo-detector in this wavelength range, under their normal operation conditions. Integrated into a detector array, this technology has application for Laser-Induced Breakdown Spectroscopy (LIBS), pollution monitoring, pharmaceutical manufacturing by reaction monitoring, chemical & biological transportation safety, and bio-chemical analysis in planetary exploration.
It is demonstrated that the inherent fluorescence of a dental composite resin can be utilized to monitor the
curing status, i.e. degree of conversion of the resin. The method does not require any sample preparation and is
potentially very fast for real time cure monitoring. The method is verified by Raman spectroscopy analysis.
A fiber acousto-optic tunable filter (FAOTF) is developed for near infrared (NIR) spectroscopy applications. The FAOTF
is built on a 7-cm long cladding etched high numerical aperture (NA) single mode fiber. By tailoring the dispersion of
the fiber, the core mode to higher order cladding mode coupling of the FAOTF is completely suppressed, leaving only
LP01 mode (the core mode) to LP11 mode (the first order cladding mode) coupling enabled. This technique enables the
FAOTF to operate with a record large free spectral range (FSR) of >700nm, which is required by NIR spectroscopy
applications. Other features of the fiber AOTF include a large wavelength tuning range of >500nm (from 1700nm to
2200nm), a narrow bandwidth of <5.5nm, a low insertion loss of <0.2dB, and a small electrical power consumption of
<100mW. For test purposes, the fiber AOTF spectrometer is utilized to measure the output spectrum of a
super-luminescence diode (SLD) light source emitting at around 2100nm. In comparison with the same spectrum
measured with a PbS array spectrometer, the spectrum acquired with the AOTF spectrometer shows much better
resolution and reveals fine spectral features of the SLD light source.
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