Erwan L. Normand

Fast, real-time spectrometer based on a pulsed quantum-cascade laser

We describe a mid-infrared spectrometer that is based on the combination of a multiple-pass absorption cell and a submicrosecond pulsed quantum-cascade laser. The spectrometer is capable of both making sensitive measurements and providing a real-time display of the spectral fingerprint of molecular vapors. For a cell with a path length of 9.6 m, dilution measurements made of the nu9 band transitions of 1,1-difluoroethylene indicate a sensitivity of 500 parts in 10(9), corresponding to a fractional absorbance of 4 x 10(-4).

Characterisation of the spectral behaviour of pulsed quantum cascade lasers using a high resolution Fourier transform infrared spectrometer

We present results that describe the evolution of the spectrum of a pulsed quantum cascade (QC) laser. By mapping the temporal characteristics of the light pulse into the wave number domain, we show how the spectral evolution depends on the duration and the quality of the current pulses used to excite the QC laser.

Quantum cascade laser (QCL) based sensor for the detection of explosive compounds

Following Cascade Technologies first success at using Quantum Cascade Lasers (QCL) for trace gas detection in the continuous emission monitoring market, the core technology platform is now being developed towards homeland security applications. This paper will highlight the potential of QCL based trace gas sensor for detecting vapours of explosives. Furthermore we will present results that let foresee the use of such technologies at addressing security gaps for protection against terrorism in infrastructures where high throughput screening of individuals or items is required. Preliminary measurements have shown that rapid identification, or fingerprinting, of explosive is achievable in 10ms at extrapolated sensitivities in the sub-part per billion range. The experiments were carried out with support form the Home Office Scientific Development Branch (HOSDB) in the UK and were focused at selecting a variety of explosive compounds and showing their detection using a novel sniffer platform system based on the use of quantum cascade lasers. Preliminary studies on the technology have indicated that direct fingerprinting (detection - identification) of explosive compounds such as NG and tagging agents such as EGDN by sniffing surrounding ambient air is achievable. Furthermore these studies have also indicated that detection of such compounds on packaging used to ship the sealed compounds is possible, making this platform a strong contender for detection through cross contamination on material that have been in contact with each other. Additionally, it was also possible to detect breakdown products associated with sample material NG providing a further capability that could be exploited to enhance the detection and identification of explosive compounds.

Highly Sensitive Detection of Trace Gases Using Pulsed Quantum Cascade Lasers

We show that by using a high resolution Fourier transform infrared spectrometer we can map the temporal characteristics of a pulsed quantum cascade laser into the wavenumber domain, and hence show that when a square current pulse is applied to a distributed feedback laser a linear sub-microsecond frequency chirp is developed. We describe a mid infrared spectrometer, that is based upon the use of this linear chirp, which can provide a real-time display of the spectral fingerprint of molecular gases. The sensitivity of the spectrometer is based upon the use of long pathlength White or Herriot cells, and the multiplex advantage associated with recording the entire spectral window during each electrical pulse. For a cell with a path length of 9.6 m, dilution measurements made on the ν9 band transistions of 1,1 difluoroethylene indicate a sensitivity of 30 parts per billion.

Bulk and trace detection of ammonia and hydrogen peroxide using quantum cascade laser technology - a tool for identifying improvised explosive devices

The type of explosive materials used in terrorist activities has seen a gradual shift from those that are commonly manufactured but difficult to obtain, such as trinitrotoluene (TNT) and nitroglycerine (NG), to improvised explosive devices (IEDs) made from substances that are more readily available. This shift has placed an emphasis on development of instruments capable of detecting IEDs and their precursors, which are often small, volatile molecules well suited to detection through mid-infrared absorption spectroscopy. Two such examples are ammonia, a breakdown product of ammonium nitrate and urea nitrate, and hydrogen peroxide, an efficient oxidiser used in the production of triacetone triperoxide (TATP) and hexamethyl triperoxide diamine (HMTD). At this meeting in 2007 we presented results of a hydrogen peroxide detection portal utilising quantum cascade laser (QCL) technology. This trace detection system has since undergone significant development to improve sensitivity and selectivity, and the results of this will be presented alongside those of a similar system configured for bulk detection of ammonia. Detection of ammonia produced from the breakdown of ammonium nitrate has been demonstrated, both on the optical bench and in a walkthrough portal. This research has been supported by the UK government.

Development of a QCL based IR polarimetric system for the stand-off detection and location of IEDs

Following the development of point sensing improvised explosive device (IED) technology[1] Cascade Technologies have initial work in the development of equivalent stand-off capability. Stand-off detection of IEDs is a very important technical requirement that would enable the safe identification and quantification of hazardous materials prior to a terrorist attack. This could provide advanced warning of potential danger allowing evacuation and mitigation measures to be implemented. With support from the UK government, Cascade Technologies is currently investigating technology developments aimed at addressing the above stand-off IED detection capability gap. To demonstrate and validate the concept, a novel stand-off platform will target the detection and identification of common high vapor pressure IED precursor compounds, such as hydrogen peroxide (H2O2), emanating from a point source. By actively probing a scene with polarized light, the novel platform will offer both enhanced selectivity and sensitivity as compared to traditional hyperspectral sensors, etc. The presentation will highlight the concept of this novel detection technique as well as illustrating preliminary results.

Quantum Cascade Laser based Screening Portal for the Detection of Explosive Precursors

In recent years, quantum cascade lasers (QCL) have been proven in robust, high-performance gas analyzers designed for continuous emission monitoring (CEM) in harsh environments. In 2006, Cascade Technologies reported progress towards adapting its patented technology for homeland security applications by publishing initial results on explosive compound detection. This paper presents the performance and results from a QCL-based people screening portal developed during the past year and aimed at the detection of precursors used in the make up of improvised explosive devices (IED). System tests have been carried out on a large number of potential interferents, together with target precursor materials, reinforcing original assumptions that compound fingerprinting can be effectively demonstrated using this technique. Results have shown that an extremely high degree of specificity can be achieved with a sub-second response time. Furthermore, it has been shown that unambiguous precursor signature recognition can be extended to compound mixtures associated with the intermediate stages in the make up of IEDs, whilst maintaining interferent immunity. The portal sensitivity was configured for parts per billion (ppb) detection level thresholds, but is currently being reconfigured for sub-ppb detection. In summary, the results obtained from the QCL based portal indicate that development of a low cost detection system, with enhanced features such as low false positive and high throughput screening of individuals or items, is possible. Development and testing was carried out with the support of the UK government.

The fusion of MIR absorbance and NIR Raman spectroscopic techniques for identification of improvised explosive materials in multiple scenarios

We demonstrate how molecular spectroscopy methods using NIR and MIR lasers can provide rapid detection and identification of many threat materials. It is increasingly recognised that one spectroscopic method will not be suited to every target in every scenario, both in terms of spectroscopic selectivity and the context e.g. vapour phase or within a sealed container. The orthogonal selection rules and capabilities of IR and Raman in combination allow the identification of a very broad range of targets, both in liquid and vapour phase. Therefore, we introduce the benefits of the combining infra-red absorbance based on Quantum Cascade lasers (QC-IR) and NIR Raman spectroscopy for nitrogenous and peroxide based materials. Rapid scan rates up to 10Hz for QC-IR and Raman and are demonstrated using current technology. However, understanding of the chemistry and spectroscopic signatures behind such materials is necessary for accurate fast fitting algorithms to benefit of the full advantage with advances in hardware. This is especially true as future users requirements move towards rapid multiplexed analysis and data fusion from a variety of sensors.

Exploiting high resolution Fourier transform spectroscopy to inform the development of a quantum cascade laser based explosives detection systems

Fourier Transform infrared spectroscopy (FTIR) is regularly used in forensic analysis, however the application of high resolution Fourier Transform infrared spectroscopy for the detection of explosive materials and explosive precursors has not been fully explored. This project aimed to develop systematically a protocol for the analysis of explosives and precursors using Fourier Transform infrared spectroscopy and basic data analysis to enable the further development of a quantum cascade laser (QCL) based airport detection system. This paper details the development of the protocol and results of the initial analysis of compounds of interest.