Long-wave infrared multi-wavelength optical source for standoff detection of chemical warfare agents

Abstract

We have designed and built a wavelength-tunable optical source for standoff detection of gaseous chemicals by differential absorption spectrometry in the long-wave infrared. It is based on a nanosecond 2 µm single-frequency optical parametric oscillator, whose idler wave is amplified in large aperture Rb:PPKTP crystals. The signal and idler waves are mixed in Z n G e P 2 crystals to produce single-frequency tunable radiation in the 7.5–10.5 µm range. The source was integrated into a direct detection lidar to measure sarin and sulfur mustard inside a closed chamber, in an integrated path configuration with a noncooperative target.

Optical parametric sources from the SWIR to the LWIR for standoff gas sensing

“…The rest of the laser energy is used to pump several crystals (usually PPKTP), separated by a signal/idler dichroic mirror to mitigate backconversion effects occurring when the three waves are not in phase at the input of a crystal, or when the pump becomes depleted near the center of the beam. After that, LWIR radiation can be generated by difference frequency in a crystal such as ZnGeP 2 , as we have shown previously and will not be detailed here [11]. The MOPA concept can be transposed further into the infrared by choosing adequate optics and crystals (Figure 5b).…”

“…The emitter architecture is of the "2 µm MOPA" type described in Figure 5a. It is an improved, more ruggedized, version of our previous MOPA setups [11,14,15]. A picture of the setup is shown in Figure 6.…”

High Energy Parametric Laser Source and Frequency-Comb-Based Wavelength Reference for CO2 and Water Vapor DIAL in the 2 µm Region: Design and Pre-Development Experimentations

“…However, angle tuning is necessary for such configuration to target different gas species, which is not robust for an integrated instrument. Since PPKTP enables us to reach the highest nonlinear coefficient of KTP, without walk-off, it makes it an excellent candidate for high-efficiency, high-energy amplification with good beam quality [43][44][45]. In addition, gamma radiation testing showed a high tolerance of these crystals to the space environment, especially for infrared wavelengths [46].…”

“…Importantly, the technology allowing high-fidelity and large aperture structuring has been developed for PPKTP [43]. Large optical aperture crystals have been implemented in high-energy OPA and OPO settings before, although in different spectral ranges [43][44][45]. For the current project, a quasi-phase-matching period of 38.75 µm has been chosen for the PPKTP crystals.…”

Detection of gaseous nerve agent simulants with broadband photoacoustic spectroscopy

“…The simplest detectors such as electrochemical (Liu and Lin, 2005), colorimetric (Davidson et al, 2020) and fluorimetric sensors (Khan et al, 2018;Meng et al, 2021), surface acoustic wave detectors (Kim et al, 2020) and ion-mobility spectrometers (Puton and Namieśnik, 2016) provide a low-cost option for screening, but they suffer from poor sensitivity, insufficient selectivity and/or susceptibility to changes in temperature and humidity. Technologies with improved performance include gas chromatography mass spectrometry (Smith et al, 2004), Raman spectroscopy (Lafuente et al, 2020) and infrared absorption spectroscopy (Pushkarsky et al, 2006;Mukherjee et al, 2008;Gurton et al, 2012;Levy, 2009;Sharpe et al, 2003;Ruiz-Pesante et al, 2007;Ohrui et al, 2020;Melkonian et al, 2020), which are preferred in different scenarios due to their specific characteristics. Infrared absorption spectroscopy is typically well suited for rapid identification of volatile NAs in ambient air, techniques ranging from extremely sensitive photoacoustic spectroscopy (PAS) (Pushkarsky et al, 2006;Mukherjee et al, 2008;Gurton et al, 2012) to Fourier transform infrared spectroscopy (FTIR) (Sharpe et al, 2003;Ruiz-Pesante et al, 2007;Ohrui et al, 2020) capable of selective multi-species detection.…”