We report mid-infrared (MIR) nonlinear absorption in As2S3 glasses which results from two-photon excitation of valence electron to the Urbach extension followed by strong linear absorption of excited states. The measured MIR nonlinear absorption can be 3 to 4 orders of magnitude stronger than the two-photon absorption in the near-infrared for similar laser intensities and does not result from contaminants, but it is intrinsic to As2S3 glasses. As2S3 fibers are widely used to generate supercontinuum by pumping them with high peak power laser pulses. For a 100 kilowatt peak power MIR soliton propagating in single mode As2S3 fiber, the nonlinear absorption can be of similar magnitude than the fiber background loss. Finally, for laser peak power around 1 MW, the MIR nonlinear absorption can be ~2 orders of magnitude larger than the fiber background loss in single mode As2S3 fiber.

We report on infrared supercontinuum (SC) generation through laser filamentation and subsequent nonlinear propagation in a step-index As2S3 fiber. The 100 μm core and high-purity As2S3 fiber used exhibit zero-dispersion wavelength around 4.5 μm, a mid-infrared background loss of 0.2  dB/m, and a maximum loss of only 0.55  dB/m at the S-H absorption peak around 4.05 μm. When pumping with ultrashort laser pulses slightly above the S-H absorption band, broadband infrared supercontinua were generated with a 20 dB spectral flatness spanning from 1.5 up to 7 μm. The efficiency and spectral shape of the SC produced by ultrashort pulses in large-core As2S3 fiber are mainly determined by its dispersion, the S-H contaminant absorption, and the mid-infrared nonlinear absorption.

A standoff sensor called BioSense was developed to demonstrate the capacity to map, track and classify bioaerosol clouds from a distant range and over wide area. The concept of the system is based on a two steps dynamic surveillance: 1) cloud detection using an infrared (IR) scanning cloud mapper and 2) cloud classification based on a staring ultraviolet (UV) Laser Induced Fluorescence (LIF) interrogation. The system can be operated either in an automatic surveillance mode or using manual intervention. The automatic surveillance operation includes several steps: mission planning, sensor deployment, background monitoring, surveillance, cloud detection, classification and finally alarm generation based on the classification result. One of the main challenges is the classification step which relies on a spectrally resolved UV LIF signature library. The construction of this library relies currently on in-chamber releases of various materials that are simultaneously characterized with the standoff sensor and referenced with point sensors such as Aerodynamic Particle Sizer® (APS). The system was tested at three different locations in order to evaluate its capacity to operate in diverse types of surroundings and various environmental conditions. The system showed generally good performances even though the troubleshooting of the system was not completed before initiating the Test and Evaluation (T&E) process. The standoff system performances appeared to be highly dependent on the type of challenges, on the climatic conditions and on the period of day. The real-time results combined with the experience acquired during the 2012 T & E allowed to identify future ameliorations and investigation avenues.

We report the generation of mid-infrared supercontinua in a step-index fluoroindate-based fiber. The large core of the fluoroindate fiber allows the guiding of multiwatt laser power over a broad spectral range. These fibers exhibit zero dispersion at 1.83 μm, minimal loss of 0.1 dB/m at 3.2 μm up to only 0.8 dB/m at 5 μm. These specifications enable mid-infrared supercontinuum generation and propagation with low loss. By using mid-infrared ultrashort laser pulses from an optical parametric amplifier, we demonstrate generation of a 20 dB spectral flatness supercontinua from 2.7 to 4.7 μm in the fluoroindate fiber, which is twice the spectral broadening compared to a ZBLAN fiber under similar conditions.

We have evaluated the influence of growth media and washing on the laser-induced fluorescence spectra of bacteria. Three different bacterial simulants were cultured in three types of growth media. Three kinds of samples were generated from each culture: the culture itself, the growth medium alone, and a triple-washed sample. The materials were injected as aerosols in a lab-sized lidar aerosol chamber to obtain their spectra. Using two different analysis approaches, signature variations were observed between the three kinds of samples for most combinations of growth media/bacteria. This study concludes that the culture media used influences the spectral signatures.

Standoff detection of explosives residues on surfaces at few meters was made using optical technologies based on Raman scattering, Laser-Induced Breakdown Spectroscopy (LIBS) and passive standoff FTIR radiometry. By comparison, detection and analysis of nanogram samples of different explosives was made with a microscope system where Raman scattering from a micron-size single point illuminated crystal of explosive was observed. Results from standoff detection experiments using a telescope were compared to experiments using a microscope to find out important parameters leading to the detection. While detection and spectral identification of the micron-size explosive particles was possible with a microscope, standoff detection of these particles was very challenging due to undesired light reflected and produced by the background surface or light coming from other contaminants. Results illustrated the challenging approach of detecting at a standoff distance the presence of low amount of micron or sub-micron explosive particles.

Tunable far-infrared laser pulses were generated efficiently during two-color filamentation in air. Understanding the creation of few-cycle far-infrared laser pulses is important since it is at the frontier between two possible generation mechanisms. The first one is the four-wave mixing generation, associated to the generation of wavelengths from ultraviolet up to mid-infrared laser pulses. The second process is the formation of transient photocurrent, which was recently used to describe the generation of submillimetric (terahertz) waves. Comparison between experiments and simulations revealed that the four-wave mixing mechanism is dominant for the far-infrared generation during two-color filamentation.

All matters in the path of filaments induced by an intense femtosecond laser pulse propagating in air could be fragmented and result in the emission of characteristic fluorescence spectra from the excited fragments. The fluorescence spectra exhibit specific signatures (fingerprints) that can be used for the identification of various substances including chemical and biological species. In this paper, we present an overview of the recent progress in our laboratory concerning the "remote" sensing of chemical and biological agents/pollutants in air using filamentation-induced nonlinear fluorescence techniques.

Ultraviolet and infrared conical emissions were observed during the filamentation in air of powerful femtosecond laser pulses produced by a portable terawatt laser system. The broadband spectrum was measured from 200 nm up to 14 microm and covered the complete optical transmission window of the atmosphere. The angularly resolved spectrum showed some X-wave structure across the frequency range analyzed. However, we demonstrated that the strong conical emission observed in the mid- and far-infrared is mainly owing to the four-wave mixing between the pump pulse and its blueshifted conical emission.

Threats associated with bioaerosol weapons have been around for several decades. However, with the recent political developments that changed the image and dynamics of the international order and security, the visibility and importance of these bioaerosol threats have considerably increased. Over the last few years, Defence Research and Development Canada has investigated the spectrometric LIDAR-based standoff bioaerosol detection technique to address this menace. This technique has the advantages of rapidly monitoring the atmosphere over wide areas without physical intrusions and reporting an approaching threat before it reaches sensitive sites. However, it has the disadvantages of providing a quality of information that degrades as a function of range and bioaerosol concentration. In order to determine the importance of these disadvantages, Canada initiated in 1999 the SINBAHD (Standoff Integrated Bioaerosol Active Hyperspectral Detection) project investigating the standoff detection and characterization of threatening biological clouds by Laser-Induced Fluorescence (LIF) and intensified range-gated spectrometric detection techniques. This article reports an overview of the different lessons learned with this program. Finally, the BioSense project, a Technology Demonstration Program aiming at the next generation of wide area standoff bioaerosol sensing, mapping, tracking and classifying systems, is introduced.

Remote-filament-induced breakdown spectroscopy (R-FIBS) was used for probing a cloud of aqueous aerosols containing a mixture of PbCl2, CuCl2, FeCl2 and NaCl. We demonstrated experimentally that it can be used as a sensitive sensing technique to remotely retrieve the composition of microdroplets in clouds located at a distance. In fact, fluorescence from all the metallic ions dissolved was observed. Moreover, these spectrally narrow atomic transitions excited by the low-density plasma did not show any signal overlap. These characteristic spectra demonstrate that R-FIBS can be used to simultaneously recognize and distinguish every single metallic constituent dissolved inside such a cloud.

Remote filament-induced breakdown spectroscopy (R-FIBS) is a novel technique that could be applied at long distance up to a few kilometers. Our work demonstrates that by creating short and strong filaments in the atmosphere with a telescopic beam delivering system, continuum background in R-FIBS spectrum will be significantly reduced. This allows for a non-gated R-FIBS configuration for identifying solid targets. As an example, we used an aluminum plate located 50 in away from our detection system. The obtained fingerprint spectrum is so strong that the detection limit could reach 1.9 kin in distance and ppm level in terms of minor element concentration. (c) 2007 Elsevier B.V. All rights reserved.

R-FIBS is used for probing salt water aerosol. We demonstrate experimentally that it can be used to sense ppm level concentrations up to 70 m away and shows potential for kilometer range applications.

The authors report on an approach for simultaneous monitoring of multigas pollutants based on fluorescence emission of trace gases, induced by the filamentation of intense femtosecond laser pulses in air. The high intensity inside a filament can dissociate the gas molecules into small fragments which emit characteristic fluorescence. This method is illustrated for simultaneously sensing atmospheric trace gases, methane and acetylene. The spectra of an “unknown” mixture were analyzed by using a genetic algorithm, showing good concentration agreement with the experimental results within an error of 25%.

We analyze the advantages of remotely sensing metallic targets using femtosecond laser-induced breakdown spectroscopy by studying the temperature and electron density of the plasma ejected from a lead target produced by femtosecond laser pulse filamentation in ambient air. The electron density of 8×1017cm−3 and the plasma temperature of 6794K were obtained for a 20ns time delay with respect to the laser pulse arriving on the target. With these values the signal is high, while the continuum blackbody radiation is low. The continuum emission in the fluorescence spectra is mainly associated with the supercontinuum of the distorted pulse during filamentation (white light laser) in air and this can be controlled. Extrapolation of the single-shot detection limit shows that this technique of filament-induced breakdown spectroscopy could be extended up to the kilometer range, opening up potential applications in metallurgic industry for remote material analysis and process controls.

One of today's primary security challenges is the emerging biological threat due to the increased accessibility to biological warfare technology and the limited efficiency of detection against such menace. At the end of the 90s, Defence R&D Canada developed a standoff bioaerosol sensor, SINBAHD, based on intensified range-gated spectrometric detection of Laser Induced Fluorescence (LIF) with an excitation at 351 run. This LIDAR system generates specific spectrally wide fluorescence signals originating from inelastic interactions with complex molecules forming the building blocks of most bioaerosols. This LIF signal is spectrally collected by a combination of a dispersive element and a range-gated ICCD that limits the spectral information within a selected atmospheric cell. The system can detect and classify bioaerosols in real-time, with the help of a data exploitation process based on a least-square fit of the acquired fluorescence signal by a linear combination of normalized spectral signatures. The detection and classification processes are hence directly dependant on the accuracy of these signatures to represent the intrinsic fluorescence of bioaerosols and their discrepancy. Comparisons of spectral signatures acquired at Suffield in 2001 and at Dugway in 2005 of bioaerosol simulants, Bacillius subtilis var globiggi (BG) and Erwinia herbicola (EH), having different origin, preparation protocol and/or dissemination modes, has been made and demonstrates the robustness of the obtained spectral signatures in these particular cases. Specific spectral signatures and their minimum detectable concentrations for different simulants/interferents obtained at the Joint Biological Standoff Detection System (JBSDS) increment II field demonstration trial, Dugway Proving Ground (DPG) in June 2005, are also presented.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text S. L. Chin, F. Thebergel, H. Xu, Q. Luo, W. Liu, S. A. Hosseini, M. Sharifi, J. Daigle, N. Akozbek, A. Becker, G. Roy, and P. Mathieu, "New Applications of Intense Femtosecond Laser Filamentation: Efficient Generation of Tunable Few-Cycle Pulses and Remote Sensing of Chem-Bio Agents*," in Frontiers in Optics, OSA Technical Digest (CD) (Optica Publishing Group, 2006), paper JTuC2. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article