Ultraviolet Stand-off Raman Measurements Using a Gated Spatial Heterodyne Raman Spectrometer.

A spatial heterodyne Raman spectrometer (SHRS) is evaluated for stand-off Raman measurements in ambient light conditions using both ultraviolet (UV) and visible pulsed lasers with a gated ICCD detector. The wide acceptance angle of the SHRS simplifies optical coupling of the spectrometer to the telescope and does not require precise laser focusing or positioning of the laser on the sample. If the laser beam wanders or loses focus on the sample, as long as it is in the field of view of the SHRS, the Raman signal will still be collected. The SHRS is not overly susceptible to vibrations, and a vibration isolated optical table was not necessary for these measurements. The system performance was assessed by measuring stand-off UV and visible Raman spectra of a wide variety of materials at distances up to 18 m, using 266 nm and 532 nm pulsed lasers, with 12.4 in. and 3.8 in. aperture telescopes, respectively.

Single-pulse standoff Raman detection of chemicals from 120 m distance during daytime.

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.

Remote-Raman spectroscopic study of minerals under supercritical CO2 relevant to Venus exploration.

The authors have utilized a recently developed compact Raman spectrometer equipped with an 85 mm focal length (f/1.8) Nikon camera lens and a custom mini-ICCD detector at the University of Hawaii for measuring remote Raman spectra of minerals under supercritical CO(2) (Venus chamber, ∼102 atm pressure and 423 K) excited with a pulsed 532 nm laser beam of 6 mJ/pulse and 10 Hz. These experiments demonstrate that by focusing a frequency-doubled 532 nm Nd:YAG pulsed laser beam with a 10× beam expander to a 1mm spot on minerals located at 2m inside a Venus chamber, it is possible to measure the remote Raman spectra of anhydrous sulfates, carbonates, and silicate minerals relevant to Venus exploration during daytime or nighttime with 10s integration time. The remote Raman spectra of gypsum, anhydrite, barite, dolomite and siderite contain fingerprint Raman lines along with the Fermi resonance doublet of CO(2). Raman spectra of gypsum revealed dehydration of the mineral with time under supercritical CO(2) at 423 K. Fingerprint Raman lines of olivine, diopside, wollastonite and α-quartz can easily be identified in the spectra of these respective minerals under supercritical CO(2). The results of the present study show that time-resolved remote Raman spectroscopy with a compact Raman spectrometer of moderate resolution equipped with a gated intensified CCD detector and low power laser source could be a potential tool for exploring Venus surface mineralogy both during daytime and nighttime from a lander.

Time-resolved remote Raman study of minerals under supercritical CO2 and high temperatures relevant to Venus exploration.

We report time-resolved (TR) remote Raman spectra of minerals under supercritical CO(2) (approx. 95 atm pressure and 423 K) and under atmospheric pressure and high temperature up to 1003 K at distances of 1.5 and 9 m, respectively. The TR Raman spectra of hydrous and anhydrous sulphates, carbonate and silicate minerals (e.g. talc, olivine, pyroxenes and feldspars) under supercritical CO(2) (approx. 95 atm pressure and 423 K) clearly show the well-defined Raman fingerprints of each mineral along with the Fermi resonance doublet of CO(2). Besides the CO(2) doublet and the effect of the viewing window, the main differences in the Raman spectra under Venus conditions are the phase transitions, the dehydration and decarbonation of various minerals, along with a slight shift in the peak positions and an increase in line-widths. The dehydration of melanterite (FeSO(4).7H(2)O) at 423 K under approximately 95 atm CO(2) is detected by the presence of the Raman fingerprints of rozenite (FeSO(4).4H(2)O) in the spectrum. Similarly, the high-temperature Raman spectra under ambient pressure of gypsum (CaSO(4).2H(2)O) and talc (Mg(3)Si(4)O(10)(OH)(2)) indicate that gypsum dehydrates at 518 K, but talc remains stable up to 1003 K. Partial dissociation of dolomite (CaMg(CO(3))(2)) is observed at 973 K. The TR remote Raman spectra of olivine, alpha-spodumene (LiAlSi(2)O(6)) and clino-enstatite (MgSiO(3)) pyroxenes and of albite (NaAlSi(3)O(8)) and microcline (KAlSi(3)O(8)) feldspars at high temperatures also show that the Raman lines remain sharp and well defined in the high-temperature spectra. The results of this study show that TR remote Raman spectroscopy could be a potential tool for exploring the surface mineralogy of Venus during both daytime and nighttime at short and long distances.

Near-infrared micro-Raman spectroscopy for in vitro detection of cervical cancer.

Near-infrared Raman spectroscopy is a powerful analytical tool for detecting critical differences in biological samples with minimum interference in the Raman spectra from the native fluorescence of the samples. The technique is often suggested as a potential screening tool for cancer. In this article we report in vitro Raman spectra of squamous cells in normal and cancerous cervical human tissue from seven patients, which have good signal-to-noise ratio and which were found to be reproducible. These preliminary results show that several Raman features in these spectra could be used to distinguish cancerous cervical squamous cells from normal cervical squamous cells. In general, the Raman spectra of cervical cancer cells show intensity differences compared to those of normal squamous cell spectra. For example, several well-defined Raman peaks of collagen in the 775 to 975 cm(-1) region are observed in the case of normal squamous cells, but these are below the detection limit of normal Raman spectroscopy in the spectra of invasive cervical cancer cells. In the high frequency 2800 to 3100 cm(-1) region, it is found that the peak area under the CH stretching band is lower by a factor of approximately six in the spectra of cervical cancer cells as compared with that of the normal cells. The Raman chemical maps of regions of cancer and normal cells in the cervical epithelium made from the spectral features in the 775 to 975 cm(-1) and 2800 to 3100 cm(-1) regions are also found to show good correlation with each other.

A Raman spectral study of stream waters and efflorescent salts in Rio Tinto, Spain.

Acidic waters and sulfate-rich precipitates are found in mine tailings such as Rio Tinto (Huelva, SW, Spain). In this work we have characterized the chemical constituents of stream water and have identified some efflorescent salts and precipitates by means of Raman spectroscopy. Variable amounts of sulfate and bisulfate are found in the aqueous samples, suggesting changes in the acidity of the solutions. An estimation of the sulfate/water relative abundance is also given. Solid samples are readily identified as gypsum and as mixtures of hydrated hydroxysulfates belonging to the copiapite group. These results are consistent with previous works reporting the mineralogy and water composition of acid mine drainage-related sites, and proves the importance of Raman spectroscopy as a tool for accurate and noninvasive analyses of acid waters and associated geochemistry.