Amino acids and nucleobases are of particular interest to NASA’s science goal of “Search for life” because they are essential for life as the basic constituents of proteins and deoxyribonucleic acids (DNA). Their detection would point to possible biosignatures and potential life bearing processes and thus there is a need for technologies capable of identifying them. Raman spectroscopy provides univocal and accurate chemical characterization of organic and inorganic compounds and can be used to detect biological materials and biomarkers in the context of planetary exploration. While micro-Raman systems are useful, a remote Raman instrument can increase the analysis area around a rover or lander. At the University of Hawai‘i we developed a portable, compact time-resolved remote-Raman instrument using a small 3” diameter mirror lens telescope, and used it to demonstrate daytime detection of amino acids and nucleobases from a distance of 8 m. The measured spectra allowed us to univocally identify 20 proteinogenic amino acids, four nucleobases, and some non-proteinogenic amino acids, despite the presence of native fluorescence, especially in aromatic compounds. We were also able to distinguish between α and β amino acids, as well as between different polymorphs. We found the remote Raman system is well suited for planetary exploration applications, with no requirement for sample preparation or collection, and rapid measurement times.
We have developed a multiwavelength Scanning Standoff Time-Resolved Raman spectroscopy (S2TR2S)
system to detect minerals and chemicals from a long distance (10-100 m) over a large area. The
multiwavelength SSTRRS system uses 532 and 785 nm pulsed lasers and two separate 5x beam expanders to
excite spontaneous Raman spectra of the chemicals with 10 mm diameter laser beams. The VIS-NIR system
employs a common Meade telescope (F/10, aperture 20.3 cm). In order to improve detection efficiency, the
light collected by the telescope is directly coupled into two f/1.8 transmission spectrograph covering the VIS
and NIR spectral regions by changing the volume Holographic Raman gratings for 532 and 785 nm laser lines,
respectively. The spectrograph is equipped with a gated intensified CCD camera and edge filters are used to
reject the reflected and Rayleigh scattered laser light. The S2TR2S system is operated using pan-tilt pointing
capability for precise measurements of selected distant points (under computer control). By making standoff
Raman measurements over a predefined grid array, a large area can be sampled and Raman composition maps
are constructed off the distant target area. This mapping capability of the instruments has been used to identify a
wide variety of minerals and hazardous chemicals from their Raman fingerprints and Raman images. The use of
pulsed laser and gated detection allow the measurement of the Raman spectra of minerals with minimum
interference from photoluminescence from transition metal ions and rare-earths ions, and ambient light.
The “Standoff Biofinder” is a powerful “search for life” instrument that is able to detect biomolecules from a collection of rocks and minerals in a large area with detection time less than a second using a non-contact, non-destructive approach. Biological materials show strong, short-lived fluorescence signals when excited with ultraviolet-visible (UVVis) wavelengths. The Standoff Biofinder takes advantage of the short lifetimes of bio-fluorescent materials to obtain real-time images showing the locations of biological materials among luminescent minerals in a geological context. The Standoff Biofinder uses an expanded and diffused nanosecond pulsed laser to illuminate a large geological region and a gated detector to record time-resolved fluorescence images. The instrument works in daylight as well as nighttime conditions and bio-detection capability is not affected by the background light. The instrument is able to detect both live and dead biological materials, and is a useful tool for detecting the presence of both extant and extinct life on a planetary surface. The Standoff Biofinder instrument will be suitable for locating fluorescent polyaromatic hydrocarbons, amino acids, proteins, bacteria, biominerals, photosynthetic pigments, and diagenetic products of microbial life on dry landscapes and Ocean Worlds of the outer Solar System (e.g., Enceladus, Europa, and Titan). An important feature of the Standoff Biofinder instrument is its capability to detect biomolecules which are inside ice, without sample collection.
At the University of Hawaii, we have developed compact time-resolved (TR) Raman, and fluorescence spectrometers
suitable for planetary exploration under NASA's Mars Instrument Development Program. The compact Raman and
fluorescence spectrometers consist of custom miniature spectrographs based on volume holographic gratings, and
custom miniature intensified CCD cameras. These spectrographs have been interfaced with a regular 50 mm camera
lens as well as with a three and a half inch diameter telescope for remotely interrogating minerals, water, water-ice and
dry ice. Using a small frequency-doubled Nd:YAG pulsed laser (35 mJ/pulse, 20 Hz) and 50 mm camera lens, TRRaman
and LINF spectra of minerals, and bio-minerals can be measured within 30 s under super-critical CO2, and with
3.5-inch telescope these samples can be interrogated to 50 m radial distance during day time and nighttime. The
fluorescence spectrograph is capable of measuring TR- laser-induced fluorescence excited with 355 nm laser in the
spectral range 400-800 nm spectral range. The TR-fluorescence spectra allow measurement of LINF from rare-earths
and transition-metal ions in time domain, and also assist in differentiating between abiogenic minerals from organic and
biogenic materials based on the fluorescence lifetime. Biological materials are also identified from their characteristic
short-lived (<10 ns) laser-induced fluorescence lifetime. These instruments will play important role in planetary
exploration especially in NASA's future Mars Sample Return Mission, and lander and rover missions.
We used micro- and resonance Raman spectroscopy with 785 nm and 514.5 nm laser excitation, respectively, to
characterize a plant pathogenic bacteria, Xanthomonas axonopodis pv. dieffenbachiae D150. The bacterial genus
Xathomonas is closely related to bacterial genus Stenotrophomonas that causes an infection in humans. This study has
identified for the first time the unique Raman spectra of the carotenoid-like pigment xanthomonadin of the
Xanthomonas strain. Xanthomonadin is a brominated aryl-polyene pigment molecule similar to carotenoids. Further
studies were conducted using resonance Raman spectroscopy with 514.5 nm laser excitation on several strains of the
bacterial genus Xanthomonas isolated from numerous plants from various geographical locations. The current study
revealed that the Raman bands representing the vibrations (v1, v2, v3) of the polyene chain of xanthomonadin are 1003-1005 (v3), 1135-1138 (v2), and 1530 (v1). Overtone bands representing xanthomonadin were identified as 2264-2275
(2v2), and combinational bands at 2653-2662 (v1+ v2). The findings from this study validate our previous finding that
the Raman fingerprints of xanthomonadin are unique for the genus Xanthomonas. This facilitates rapid identification
(~5 minutes) of Xanthomonas spp. from bacterial culture plates. The xanthomonadin marker is different from Raman
markers of many other bacterial genus including Agrobacterium, Bacillus, Clavibacter, Enterobacter, Erwinia,
Microbacterium, Paenibacillus, and Ralstonia. This study also identified Xanthomonas spp. from bacterial strains
isolated from a diseased wheat sample on a culture plate.
The University of Hawaii has been developing portable remote Raman systems capable of detecting chemicals in
daylight from a safe standoff distance. We present data on standoff detection of chemicals used in the synthesis of
homemade explosives (HME) using a portable standoff Raman system utilizing an 8-inch telescope. Data show that
good-quality Raman spectra of various hazardous chemicals such as ammonium nitrate, potassium nitrate, potassium
perchlorate, sulfur, nitrobenzene, benzene, acetone, various organic and inorganic chemicals etc. could be easily obtained
from remote distances, tested up to 120 meters, with a single-pulse laser excitation and with detection time less than
1 μs. The system uses a frequency-doubled Nd:YAG pulsed laser source (532 nm, 100 mJ/pulse, 15 Hz, pulse width
10 ns) capable of firing a single or double pulse. The double-pulse configuration also allows the system to perform
standoff LIBS (Laser-Induced Breakdown Spectroscopy) at 50 m range. In the standoff Raman detection, the doublepulse
sequence simply doubles the signal to noise ratio. Significant improvement in the quality of Raman spectra is
observed when the standoff detection is made with 1s integration time. The system uses a 50-micron slit and has spectral
resolution of 8 cm-1. The HME chemicals could be easily detected through clear and brown glass bottles, PP and HDPE
plastic bottles, and also through fluorescent plastic water bottles. Standoff Raman detection of HME chemical from a 10
m distance through non-visible concealed bottles in plastic bubble wrap packaging is demonstrated with 1 s integration
time. Possible applications of the standoff Raman system for homeland security and environmental monitoring are
discussed.
We have developed a simple and potentially a low-cost method for the sensitive detection of target proteins via surface-enhanced
Raman scattering (SERS). The immunosensor constructed by the conjugation of monoclonal antibodies to
20 nm diameter gold nanoparticles via the bifunctional Raman reporter molecule, 5, 5'dithiobis (succinimidyl-2-nitrobenzoate) (DSNB) is the basis of a membrane-bound detection system. Traditionally, a common laboratory
technique called a dot blot, which is a colorimetric method where detection of proteins is accomplished through the
application of assorted dyes followed by their measurement via a densitometer. Dot blotting is a convenient and time
saving method that involves the spotting of a protein onto an immobilizing matrix, such as nitrocellulose (NC) or
polyvinylidene fluoride (PVDF) membrane. We found that for detection via SERS spectroscopy NC is the matrix of
choice because it offers low background, minimal preparation prior to protein application, and optimal position of
Raman bands. Furthermore, SERS detection of protein on NC requires only minimal sample preparation and
demonstrates increased sensitivity when compared to other dot blot detection methods. Depending on the dye used for
visualization, dot blots analyzed by commonly used optical methods have limits of detection in the nanogram range,
some as low as 20 pg/ml. Here we demonstrate the use of the dot blot method for detecting target proteins (e.g., protein
A and prostate specific protein (PSA)) by SERS spectroscopy down to a concentration of 100 fg/ml.
Surface-enhanced Raman scattering (SERS) utilizing colloidal silver and gold has been demonstrated to provide a rapid
means of measuring the Raman spectra of microorganisms in the fingerprint region. In this study, we have introduced
microcavity substrates coated with alternating layers of silver and gold thin films for measuring the Raman spectra of
four strains of E. coli. These microcavitiy substrates have been prepared by placing glass microspheres between two
polished aluminum substrates and pressing them together using a standard lab press. After removing the glass
microspheres from the substrates, the substrates have been coated with 15 to 70 nm thick films of chromium, silver and
gold in a precise order. The cavities were evaluated for SERS enhancement by measuring Raman spectra of dilute
rhodamine 6G (R6G) down to 10-8 M. With these microcavities, we have investigated the SERS spectra of four
chemically competent strains of E. coli (One Shot OmniMAX 2-T1, Mach1-T1, Stbl3, and TOP10). Replicate SERS
spectra of all the four e-coli strains show excellent reproducibility. Visual examination of the spectra, however, reveals
differences in the spectra of these strains. To confirm this observation, we have used multivariate analysis for positive
identification and discrimination between the strains.
Raman spectra of anti-HIV-1 antibody, HIV-1 antigen (p24), and HIV-1 antibody-antigen complex have been measured
in near-infrared and UV regions: 785 nm; 830 nm; and 244 nm laser excitations. The spectrum of the HIV-1 antigen was
excited with an infrared laser and contains numerous Raman peaks. The most prominent peaks are broad bands at 1343,
1449, 1609 and 1655 cm-1, which are characteristic of the Raman spectra of biological cells. The UV Raman spectrum of
the HIV-1 antigen has a completely different structure. It has two strong peaks at 1613 cm-1 and 1173 cm-1. The peak at
1613 cm-1 is associated with vibrations of the aromatic amino acids tyrosine (Tyr) and tryptophan (Try). The second
strongest peak at 1173 cm-1 is associated with the vibration of Tyr. The Raman peak pattern of the HIV-1 antigen-antibody
complex is very similar to that of the HIV-1 antigen. The only difference is that the peak at 1007 cm-1 of the
Raman spectrum of the HIV-1 antigen-antibody complex is slightly enhanced compared to that of the HIV-1 antigen.
This indicates that the peaks of the HIV-1 antigen dominate the Raman spectrum of the HIV-1 antigen-antibody
complex.
Micro- Raman spectroscopic investigation of ALVAC virus and of normal chicken embryo fibroblast cells and the cells
infected with ALVAC virus labeled with green fluorescence protein (GFP) were performed with a 785 nm laser. Good
quality Micro-Raman spectra of the Alvac II virus were obtained. These spectra show that the ALVAC II virus contains
buried tyrosine residues and the coat protein of the virus has α-helical structure. A comparison of Raman spectra of
normal and virus infected chicken embryo fibroblast cells revealed that the virus infected cells show additional bands at
535, 928, and 1091 cm-1, respectively, corresponding to δ(C-O-C) glycosidic ring, protein α-helix, and DNA (O-P-O)
modes. In addition, the tyrosine resonance double (833 and 855 cm-1) shows reversal in the intensity of the higher-frequency
band as compared to the normal cells that can be used to identify the infected cells. In the C-H stretching
region, the infected cells show bands with higher intensity as compared to that of the corresponding bands in the normal
cells. We also found that the presence of GFP does not affect the Raman spectra of samples when using a 785 nm micro-Raman system because the green fluorescence wavelength of GFP is well below the Stokes-Raman shifted spectral
region.
At the University of Hawaii, we have developed a compact, portable remote Raman and Laser-Induced Breakdown
Spectroscopy (LIBS) system with a 532 nm pulsed laser for planetary exploration under the Mars Instrument
Development Program. The compact time-resolved remote Raman and LIBS system consists of (i) a regular 85 mm
Nikon (F/1.8) camera lens with clear aperture of 50 mm as collection optics, (ii) a miniature spectrograph that occupies
1/14th the volume of a comparable commercial spectrograph from Kaiser Optical Systems Inc., (iii) a custom mini-ICCD
detector, and (iv) a small frequency-doubled 532 nm Nd:YAG pulsed laser (30 mJ/pulse, 20 Hz) with a 10x beam
expander. In the standoff Raman mode the system is capable of measuring various minerals, water, ices, and
atmospheric gases from a 50 meter range with a 10 s integration time. At shorter distances of 10 m or less, good quality
Raman spectra can be obtained within 1 s. The time-gated system is capable of detecting both the target mineral as well
as the atmospheric gases before the target using their Raman fingerprints. Various materials can easily be identified
through glass, plastic, and water media. The time-gating capability makes the system insensitive to window material,
which is highly desirable for future missions to Venus where instruments are expected to be within the lander. The
standoff LIBS range is 10 m and LIBS spectra of various minerals can be obtained with single laser pulse excitation. The
standoff LIBS capability provides additional elemental verification of the targeted material.
The University of Hawaii and NASA Langley Research Center are developing small, compact, and portable remote
Raman systems with pulsed lasers for planetary exploration under the Mars Instrument Development Program. The
remote Raman instruments developed previously utilized small telescopes with clear apertures of 125 mm and 100
mm diameters and were able to detect water, ice, water bearing minerals, carbon in carbonate form in calcite,
magnesite, dolomite, and siderite from a distance of 10 to 50 m under daytime and nighttime conditions. Recently,
we significantly reduced the size of our time-resolved (TR) remote Raman system in order to build a compact
system suitable for future space missions. This compact time-resolved Raman system was developed by utilizing (i)
a regular 85 mm Nikon (F/1.8) lens with a clear aperture of 50 mm as a collection optic, and (ii) a miniature Raman
spectrograph that is 1/14th in volume in comparison to the commercial spectrograph used in our previous work. In
this paper, we present the TR remote Raman spectra obtained during daytime from various hydrous and anhydrous
minerals, water, water-ice, and CO2-ice using this new compact remote Raman system to 50 m radial distance.
We present data on standoff detection of chemicals used in synthesis of homemade explosives (HME) using a compact
portable standoff Raman system developed at the University of Hawaii. Data presented in this article show that good
quality Raman spectra of various organic and inorganic chemicals, including hazardous chemicals such as ammonium
nitrate, potassium nitrate, potassium perchlorate, sulfur, nitrobenzene, benzene, acetone, and gasoline, can be easily
obtained from remote distances with a compact standoff Raman system utilizing only a regular 85 mm Nikon camera
lens as collection optics. Raman spectra of various chemicals showing clear Raman fingerprints obtained from targets
placed at 50 m distance in daylight with 1 to 10 second of integration time are presented in this article. A frequency-doubled
mini Nd:YAG pulsed laser source (532 nm, 30 mJ/pulse, 20 Hz, pulse width 8 ns) is used in an oblique
geometry to excite the target located at 50 m distance. The standoff Raman system uses a compact spectrograph of size
10 cm (length) × 8.2 cm (width) × 5.2 cm (height) with spectral coverage from 100 to 4500 cm-1 Stokes-Raman shifted
from 532 nm laser excitation and is equipped with a gated thermo-electrically cooled ICCD detector. The system is
capable of detecting both the target as well as the atmospheric gases before the target. Various chemicals could be easily
identified through glass, plastic, and water media. Possible applications of the standoff Raman system for homeland
security and environmental monitoring are discussed.
We present results of in vitro micro-Raman spectroscopy of normal and cancerous cervical and ovarian tissues excited
with 785 nm near-infrared (NIR) laser. Micro- Raman spectra of squamous cervical cells of both cervix and ovarian
tissues show significant differences in the spectra of normal and cancerous cells. In particular, several well-defined
Raman peaks in the 775-975 cm-1 region are observed in the spectra of normal cervix squamous cells but are completely
missing in the spectra of invasive cervical cancer cells. In the high-frequency 2800-3100 cm-1 region it is shown that the
peak area under CH stretching band is much lower than the corresponding area in the spectra of normal cells. In the case
of ovarian tissues, the micro-Raman spectra show noticeable spectral differences between normal cells and ovarian
serous cancer cells. In particular, we observed the accumulation of β-carotene in ovarian serous cancer cells compared
to normal ovarian cells from women with no ovarian cancer. The NIR micro-Raman spectroscopy offers a potential
molecular technique for detecting cervical and ovarian cancer from the respective tissues.
A compact remote Raman spectroscopy system was developed at NASA Langley Research center and was
previously demonstrated for its ability to identify chemical composition of various rocks and minerals. In
this study, the Raman sensor was utilized to perform time-resolved Raman studies of various samples such
as minerals and rocks, Azalea leaves, and a few fossil samples. The Raman sensor utilizes a pulsed 532 nm
Nd:YAG laser as excitation source, a 4-inch telescope to collect the Raman-scattered signal from a sample
several meters away, a spectrograph equipped with a holographic grating, and a gated intensified CCD
(ICCD) camera system. Time resolved Raman measurements were carried out by varying the gate delay
with fixed short gate width of the ICCD camera, allowing measurement of both Raman signals and
fluorescence signals. Rocks and mineral samples were characterized, including marble, which contains
CaCO3. Analysis of the results reveals the short (~10-13 s) lifetime of the Raman process and shows that the
Raman spectra of some mineral samples contain fluorescence emission due to organic impurities. Also
analyzed were a green (pristine) and a yellow (decayed) sample of Gardenia leaves. It was observed that
the fluorescence signals from the green and yellow leaf samples showed stronger signals compared to the
Raman lines. It was also observed that the fluorescence of the green leaf was more intense and had a
shorter lifetime than that of the yellow leaf. For the fossil samples, Raman shifted lines could not be
observed due to the presence of very strong short-lived fluorescence.
A novel method for improving the detection limit of normal Raman spectra of chemicals using a micro-Raman system
and pico-liters volume is presented. A micro-cavity substrate uses various mechanisms that collectively improve the
normal Raman signal from the sample without surface-enhanced Raman scattering (SERS) enhancement. The microcavity
substrate enhances the entire Raman spectra of the molecules under investigation and maintains the relative
intensity ratios of the various Raman bands. This feature of maintaining the overall integrity of the Raman features
during signal enhancement makes the micro-cavity substrate ideal for forensic science applications requiring chemical
detection of residual traces and other applications requiring low sample volumes and concentrations. It will be further
shown that micro-cavities coated with nano films of gold and silver takes advantage of both SERS and micro-cavity
method and significantly improve the detection limits of samples.
We have used a remote time-resolved telescopic Raman system equipped with 532 nm pulsed laser excitation and a
gated intensified CCD (ICCD) detector for measuring Raman spectra of a number of minerals at high temperature to 970
K. Remote Raman measurements were made with samples at 9-meter in side a high-temperature furnace by gating the
ICCD detector with 2 micro-sec gate to minimize interference from blackbody emission from mineral surfaces at high
temperature as well as interference from ambient light. A comparison of Raman spectra of gypsum (CaSO4.2H2O),
dolomite (CaMg(CO3)2), and olivine (Mg2Fe2-xSiO4), as a function of temperature shows that the Raman lines remains
sharp and well defined even in the high-temperature spectra. In the case of gypsum, Raman spectral fingerprints of
CaSO4.H2O at 518 K were observed due to dehydration of gypsum. In the case of dolomite, partial mineral dissociation
was observed at 973 K at ambient pressure indicating that some of the dolomite might survive on Venus surface that is at
~750 K and 92 atmospheric pressure. Time-resolved Raman spectra of low clino-enstatite (MgSiO3) measured at 75 mm
from the sample in side the high-temperature furnace also show that the Raman lines remains sharp and well defined in
the high temperature spectra. These high-temperature remote Raman spectra of minerals show that time-resolved
Raman spectroscopy can be used as a potential tool for exploring Venus surface mineralogy at shorter (75 mm) and long
(9 m) distances from the samples both during daytime and nighttime. The remote Raman system could also be used for
measuring profiles of molecular species in the dense Venus atmosphere during descent as well as on the surface.
A compact remote Raman sensor system was developed at NASA Langley Research Center. This sensor is an
improvement over the previously reported system, which consisted of a 532 nm pulsed laser, a 4-inch telescope, a
spectrograph, and an intensified CCD camera. One of the attractive features of the previous system was its portability,
thereby making it suitable for applications such as planetary surface explorations, homeland security and defense
applications where a compact portable instrument is important. The new system was made more compact by replacing
bulky components with smaller and lighter components. The new compact system uses a smaller spectrograph
measuring 9 x 4 x 4 in. and a smaller intensified CCD camera measuring 5 in. long and 2 in. in diameter. The previous
system was used to obtain the Raman spectra of several materials that are important to defense and security applications.
Furthermore, the new compact Raman sensor system is used to obtain the Raman spectra of a diverse set of materials to
demonstrate the sensor system's potential use in the identification of unknown materials.
We have developed a remote Raman system, using an 8-in telescope and a 532-nm pulse laser (20 Hz and 20 mJ/pulse),
which is capable of operating in daylight. From distances of 50 and 100 m and with an integration time of just 1 second
(equivalent to 20 laser pulses at 20 Hz), good quality Raman spectra with high signal-to-noise ratios were readily
obtained. The Raman system was also tested using only single-laser-pulse excitation (8 ns pulse width) with an
integration time of 2 μs. The spectra obtained from single-laser-pulse excitation also show clear Raman features and can
be used for rapid, unambiguous identification of various chemical substances. We successfully identified a number of
substances, including organic chemicals (acetone, naphthalene, nitro-methane, nitro-benzene and cyclohexane);
inorganic chemicals and minerals (nitric acids, sulfuric acid, potassium perchlorate, gypsum, ammonium nitrate,
epsomite, melanterite, calcite and sulfur); and amino acids. The remote Raman system has a range of applications, such
as environmental monitoring (e.g., detection of hazardous chemicals and chemical spills from a safe distance in real
time) or homeland security (e.g., rapid identification of chemicals on a conveyor belt or from a fast-moving object).
Recent and future explorations of Mars and lunar surfaces through rovers and landers have spawned great interest in
developing an instrument that can perform in-situ analysis of minerals on planetary surfaces. Several research groups
have anticipated that for such analysis, Raman spectroscopy is the best suited technique because it can unambiguously
provide the composition and structure of a material. A remote pulsed Raman spectroscopy system for analyzing
minerals was demonstrated at NASA Langley Research Center in collaboration with the University of Hawaii. This
system utilizes a 532 nm pulsed laser as an excitation wavelength, and a telescope with a 4-inch aperture for collecting
backscattered radiation. A spectrograph equipped with a super notch filter for attenuating Rayleigh scattering is used to
analyze the scattered signal. To form the Raman spectrum, the spectrograph utilizes a holographic transmission grating
that simultaneously disperses two spectral tracks on the detector for increased spectral range. The spectrum is recorded
on an intensified charge-coupled device (ICCD) camera system, which provides high gain to allow detection of
inherently weak Stokes lines. To evaluate the performance of the system, Raman standards such as calcite and
naphthalene are analyzed. Several sets of rock and mineral samples obtained from Ward's Natural Science are tested
using the Raman spectroscopy system. In addition, Raman spectra of combustible substances such acetone and isopropanol are also obtained.
We have designed and tested a portable stand-off gated-Raman system that is capable of detecting organic and inorganic
bulk chemicals at stand-off distances to 100 m during day and night time. Utilizing a single 532 nm laser pulse (~25
mJ/pulse), Raman spectra of several organic and inorganic compounds have been measured with the portable Raman
instrument at a distance of 10 m in a well-illuminated laboratory. Raman spectra, obtained during a very short period of
time (2 micro second), from organic compounds such as acetone, benzene, cyclohexane, 2-propanol, naphthalene, and
inorganic nitrates, showed all major bands required for unambiguous chemical identification. We have also measured
the Raman spectra of acetone, sulfuric acid, hydrogen peroxide (50%) aqueous solution, nitro-methane containing fuel,
and nitrobenzene in glass containers with a 532 nm, 20 Hz pulsed laser excitation and accumulated the spectra with 200
to 600 laser shots (10 to 30 sec integration time) at 100 m with good signal-to-background ratio. The results of these
investigations show that the stand-off Raman spectra to 100 m distance can be used to identify Raman fingerprints of
both inorganic and organic compounds and could be useful for Homeland security and environmental monitoring.
We have developed a combined remote telescopic Raman and laser-induced native fluorescence (LINF) spectrograph
with 532 nm pulsed laser excitation and a gated CCD detector. With this system, we have measured time-resolved
Raman and LINF spectral measurements at 9 m with 10-ns time resolution. A comparison of Raman spectra of calcite
crystal and that of chicken eggshell show that the CaCO3 in the chicken eggshell is arranged in a calcite structure. The
strong LINF band in the spectrum of the calcite crystal has lifetime longer than 1 μs, whereas the lifetime of LINF bands
of the eggshell are in 10's of nano-sec (ns). The time-resolved Raman spectra of tomato and poinsettia (Euphorbiapulcherrimum) green leaves show resonance Raman features of carotenes. The time-resolved remote LINF spectrum of
ruby crystals, and LINF spectra of tomato and poinsettia green leaves yield information that the LINF lifetime of ruby
lines is much longer (in milliseconds (ms)) as compared with the fluorescence lifetime of the tomato and the poinsettia
leaves (in 10s of ns). These results show that it will be possible to discriminate between inorganic and biogenic materials
on the basis of LINF lifetimes even with 8 nano-sec laser pulses and gated detection.
For exploration of planetary surfaces, detection of water and ice is of great interest in supporting existence of life on other planets. Therefore, a remote Raman spectroscopy system was demonstrated at NASA Langley Research Center in collaboration with the University of Hawaii for detecting ice-water and hydrous minerals on planetary surfaces. In this study, a 532 nm pulsed laser is utilized as an excitation source to allow detection in high background radiation conditions. The Raman scattered signal is collected by a 4-inch telescope positioned in front of a spectrograph. The Raman spectrum is analyzed using a spectrograph equipped with a holographic super notch filter to eliminate Rayleigh scattering, and a holographic transmission grating that simultaneously disperses two spectral tracks onto the detector for higher spectral range. To view the spectrum, the spectrograph is coupled to an intensified charge-coupled device (ICCD), which allows detection of very weak Stokes line. The ICCD is operated in gated mode to further suppress effects from background radiation and long-lived fluorescence. The sample is placed at 5.6 m from the telescope, and the laser is mounted on the telescope in a coaxial geometry to achieve maximum performance. The system was calibrated using the spectral lines of a Neon lamp source. To evaluate the system, Raman standard samples such as calcite, naphthalene, acetone, and isopropyl alcohol were analyzed. The Raman evaluation technique was used to analyze water, ice and other hydrous minerals and results from these species are presented.
A combined inelastic (Raman) and elastic (Mie-Rayleigh) scattering and Laser-Induced Fluorescence (LIF) active remote sensing (RLIF) system is proposed as a mast-mounted instrument for the Mars Science Laboratory (MSL). This remote RLIF system will be capable of reconnaissance and identification of mineral, organic, and biogenic materials as well as conducting atmospheric studies of Mars. This system is based on the prototypes developed with partial support from NASA at the University of Hawaii. The proposed RLIF system will perform active optical imaging and spectroscopy out to 100 m on the surface features. In the elastic backscattering mode, the range of RLIF can be extended to >5-km because the cross section of Mie-Rayleigh scattering is several orders of magnitude higher than that of Raman cross-sections of molecular species. Results obtained with the University of Hawaii’s portable remote Raman and LIF system and the portable Mie-Rayleigh prototype lidar are presented. With the remote Raman system, measurements of mineral calcite (CaCO3), liquid hydrocarbons and solid naphthalene polycrystals have been verified to 100 m range. The LIF sensor will provide near real time in situ remote data that will complement analytical laboratory and contact suite instrumentation on the Mars rover.
Landers and rovers are important to solar system exploration, and we are designing and analyzing a remote Raman system for a planetary mission. Raman spectroscopy is a common and powerful technique for materials analysis. We have developed a system that enables Raman spectroscopic measurements at distances of more than 50 meters. In order to design a flight instrument, we need to quantitatively understand the Raman efficiency of natural surfaces. We define remote Raman efficiency as the ratio of radiant exitance leaving a natural surface to the irradiance of the incident laser. The radiant exitance of a natural surface is the product of the sample radiance (minus background), the projected solid angle in steradians, and the spectral bandwidth of the spectrometer. The laser irradiance is the product of the energy of the laser (mJ/pulse) and the pulse rate (Hz), divided by the area of the laser spot. We have determined the remote Raman efficiency for several minerals and rocks: dolomite marble, dacite, milky quartz, anorthosite, calcite, biotite granite, magnesite, chert, gypsum (selenite), fibrous gypsum, and sandstone. By quantifying the remote Raman efficiency, we will be able to determine the number and quality of spectra that a remote Raman system can acquire on a planetary surface where available power is limited. Studies on hematite indicate that Raman shift (and thus remote Raman efficiency) depends on laser wavelength.
There is a need for portable, low-cost lidar systems that can be used for cloud, aerosols and chemical monitoring from a stand-off distance. At the University of Hawaii we have developed lidar systems based on a 12.7-cm diameter telescope and a 20 Hz frequency-doubled Nd:YAG laser source. For stand off Raman detection of organic liquid and vapors, and plastic explosives, we are using a 0.25-m HoloSpec f/2.2 spectrometer equipped with a gated intensified detector (PI Model I-MAX-1024-E). The samples of interest are excited with 532-nm laser light (35 mJ/pulse). The operational range of the Raman system is in 10's of meters and has been tested at distance of 66 m. This system can also be operated as a Raman lidar by using appropriate filters for atmospheric nitrogen, oxygen and other gaseous species of interest. The Mie-Rayleigh lidar system uses the same telescope and laser, but we have three (1064, 532 and 355-nm) wavelengths available for monitoring clouds and aerosols. A small Hamamatsu H6779 photomultiplier tube (PMT) located near the focal point of telescope detects 532-nm backscatter signal. An avalanche photodiode (APD, EG & G C3095) detector equipped with a 2.5-cm diameter aspheric lens is used for detecting 1064-nm backscatter. The Mie-Rayleigh lidar has usable range of 60 - 4000 m. Results obtained with this system for marine aerosols and clouds are discussed.
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