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

Abstract

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.

Review of explosive detection methodologies and the emergence of standoff deep UV resonance Raman

“…Misra et al demonstrated that visible Raman spectra can be measured from greater than 100 m standoff distances . Single 100 mJ pulses of 532 nm light‐excited NB, potassium perchlorate, and NH 4 NO 3 samples inside sealed glass vials 120 m away (Fig.…”

Advances in explosives analysis—part II: photon and neutron methods

“…These are essentially the same instrumental requirements as those of LIBS, and both are often used together [118][119][120][121]. Very good signal-to-noise has been obtained for bulk explosive materials (tens of gram quantities) in single-shot [122] and multiple-pulse [123] spectra measured beyond 100 m in daylight conditions, and at 470 m for multiple-pulse measurement (1-10 s) during heavy rainfall [124,125].…”

Applying stand-off LIBS to paleoclimatic research: A case study on geochemical content of carbonate rocks

“…Because all elements emit light of characteristic frequencies when excited to sufficiently high temperatures, LIBS can (in principle) detect all elements, limited only by the power of the laser as well as the sensitivity and wavelength range of the spectrograph & detector (Pasquini et al, 2007). Stand-off or remote LIBS is able to excite plasma and retrieve information from plasma at long distance from the samples (Misra et al, 2012;Zachhuber et al, 2011). The apparatus coupled with appropriate excitation laser source and telescope system has been reported to detect samples more than 50 m away.…”