Standoff Raman measurement of nitrates in water

Sadate, Sandra; Kassu, Aschalew; Farley, Carlton; Sharma, Anup; Hardisty, J.; Lifson, Miles T. K.

doi:10.1117/12.893571

Cited by 6 publications

(4 citation statements)

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“…Standoff Raman detection offers a wide area of applications and recently, several research groups across the world have been actively developing standoff Raman systems. 1,–18 Because of the recent rise in worldwide terrorist activities, standoff detection of hazardous chemicals (such as those used in homemade explosives, flammable solids and liquids, and toxic chemicals) is of significant interest. Standoff Raman spectroscopy can detect several hazardous chemicals from a safe distance without need for making contact with the sample.…”

Section: Introductionmentioning

confidence: 99%

Single-Pulse Standoff Raman Detection of Chemicals from 120 m Distance during Daytime

et al. 2012

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The capability to analyze and detect the composition of distant samples (minerals, organics, and chemicals) in real time is of interest for various fields including detecting explosives, geological surveying, and pollution mapping. For the past 10 years, the University of Hawaii has been developing standoff Raman systems suitable for measuring Raman spectra of various chemicals in daytime or nighttime. In this article we present standoff Raman spectra of various minerals and chemicals obtained from a distance of 120 m using single laser pulse excitation during daytime. The standoff Raman system utilizes an 8-inch Meade telescope as collection optics and a frequency-doubled 532 nm Nd : YAG laser with pulse energy of 100 mJ/pulse and pulse width of 10 ns. A gated intensified charge-coupled device (ICCD) detector is used to measure time-resolved Raman spectra in daytime with detection time of 100 ns. A gate delay of 800 ns (equivalent to target placed at 120 m distance) was used to minimize interference from the atmospheric gases along the laser beam path and near-field scattering. Reproducible, good quality single-shot Raman spectra of various inorganic and organic chemicals and minerals such as ammonium nitrate, potassium perchlorate, sulfur, gypsum, calcite, benzene, nitrobenzene, etc., were obtained through sealed glass vials during daytime. The data indicate that various chemicals could easily be identified from their Raman fingerprint spectra from a far standoff distance in real time using single-shot laser excitation.

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Section: Introductionmentioning

confidence: 99%

Single-Pulse Standoff Raman Detection of Chemicals from 120 m Distance during Daytime

et al. 2012

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“…A good overview of this method and its applications can be found elsewhere [123,124]. For example, standoff Raman detection has been used to detect pollutants in air and water at great distances, as well planetary exploration for the detection of organics mixed in mineral matrices [125][126][127]. The reason why the TG principle plays an important role in this method stems from the need to reduce the disturbing amount of fluorescence and the background radiation of ambient light from the often unknown heterogeneous sample matrices under inspection.…”

Section: Tg Standoff Raman Detectionmentioning

confidence: 99%

Time-gated Raman spectroscopy – a review

Kögler

Heilala²

2020

Meas. Sci. Technol.

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Time-gated (TG) Raman spectroscopy (RS) has been shown to be an effective technical solution for the major problem whereby sample-induced fluorescence masks the Raman signal during spectral detection. Technical methods of fluorescence rejection have come a long way since the early implementations of large and expensive laboratory equipment, such as the optical Kerr gate. Today, more affordable small sized options are available. These improvements are largely due to advances in the production of spectroscopic and electronic components, leading to the reduction of device complexity and costs. An integral part of TG Raman spectroscopy is the temporally precise synchronization (picosecond range) between the pulsed laser excitation source and the sensitive and fast detector. The detector is able to collect the Raman signal during the short laser pulses, while fluorescence emission, which has a longer delay, is rejected during the detector dead-time. TG Raman is also resistant against ambient light as well as thermal emissions, due to its short measurement duty cycle.In recent years, the focus in the study of ultra-sensitive and fast detectors has been on gated and intensified charge coupled devices (ICCDs), or on CMOS single-photon avalanche diode (SPAD) arrays, which are also suitable for performing TG RS. SPAD arrays have the advantage of being even more sensitive, with better temporal resolution compared to gated CCDs, and without the requirement for excessive detector cooling. This review aims to provide an overview of TG Raman from early to recent developments, its applications and extensions.

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“…When using continuous wave (CW) lasers, stand-off Raman observations [13,14] have been demonstrated for measurement of nitrates and explosives from tens of metres up to 250 m using large 200-mm diameter telescopes. [15] Additionally, in this instance, the requirement for a low power density at the target poses significant challenges. Either the total laser power must be reduced or the spot at the target must be increased resulting in the target having a large etendue (see Section 2.4).…”

Section: The Raman Spectrometermentioning

confidence: 99%