One of the main challenges in remote Fourier transform infrared (FT-IR) spectroscopy is the collection of a
reliable background spectrum. Although suggested as a method to address the problem in prior literature,
super clip apodization (SCA) has had little reported success for wide spectral features. SCA is a technique that
involves the manipulation of different parts of the interferogram to calculate an absorbance spectrum from a
single interferogram. A new method called complementary super clip apodization (CSCA) is developed here and
is successfully used in conjunction with SCA in an iterative optimization algorithm. The umbrella term of super
clip mathematics is also defined to encompass spectral calculation using SCA, CSCA or both in combination.
The validity of super clip mathematics is demonstrated in an experimental study of gas-phase nitromethane. In
an effort to mimic errors present in standoff detection, uniformly distributed noise and/or wavenumber shifting
is added to the interferometric sample data to test the robustness of the algorithm. It will be shown that the
implementation of SCA and CSCA in combination is more successful for concentration assessment than using
SCA or CSCA alone.
Peter Kuffner, Kathryn Conroy, Toby Boyson, Greg Milford, Mohamed Mabrok, Abhijit Kallapur, Ian Petersen, Maria Calzada, Thomas Spence, Kennith Kirkbride, Charles Harb
A consortium of researchers at University of New South Wales (UNSW@ADFA), and Loyola University New
Orleans (LU NO), together with Australian government security agencies (e.g., Australian Federal Police), are
working to develop highly sensitive laser-based forensic sensing strategies applicable to characteristic substances
that pose chemical, biological and explosives (CBE) threats. We aim to optimise the potential of these strategies
as high-throughput screening tools to detect prohibited and potentially hazardous substances such as those
associated with explosives, narcotics and bio-agents.
We demonstrate a novel intensity noise suppression configuration which combines laser injection locking and electronic feedback. We use two feedback loops which together suppress the intensity noise of the injection locked laser to 4 dB above the quantum noise limit.
Solid state laser sources, such as diode-laser pumped Nd:YAG lasers, have given us a cw laser light of high power with unprecedented stability and low noise performance. In these lasers most of the technical sources of noise can be eliminated and thereby allow operation close to the theoretical limit set by the quantum properties of the light. We present progress in the experimental realization of such lasers. These investigations include the control of noise by electronic feedback, passive external cavities; and the reliable generation of amplitude squeezed light through second harmonic generation. At the same time we have developed theoretical models describing the quantum noise properties of coupled systems of lasers and cavities. The agreement between our experimental results with noise spectra calculated with our realistic theoretical models demonstrates the ability to predict the performance of various laser systems.
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