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
CaCO<sub>3</sub>. Analysis of the results reveals the short (~10<sup>-13</sup> 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 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.
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.
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.
An Indium Gallium Arsenide linear photodiode array in the 1.1-2.5 μm spectral range was characterized. The array has 1024X1 pixels with a 25 μm pitch and was manufactured by Sensors Unlimited, Inc. Characterization and analysis of the electrical and optical properties of a camera system were carried out at room temperature to obtain detector performance parameters. The signal and noise were measured while the array was uniformly illuminated at varying exposure levels. A photon transfer curve was generated by plotting noise as a function of average signal to obtain the camera gain constant. The spectral responsivity was also measured, and the quantum efficiency, read noise and full-well capacity were determined. This paper describes the characterization procedure, analyzes the experimental results, and discusses the applications of the InGaAs linear array to future earth and planetary remote sensing mission.
Custom-designed charge-coupled devices (CCD) for Gas and Aerosols Monitoring Sensorcraft instrument were developed. These custom-designed CCD devices are linear arrays with pixel format of 512x1 elements and pixel size of 10x200 μm<sup>2</sup>. These devices were characterized at NASA Langley Research Center to achieve a full well capacity as high as 6,000,000 e<sup>-</sup>. This met the aircraft flight mission requirements in terms of signal-to-noise performance and maximum dynamic range. Characterization and analysis of the electrical and optical properties of the CCDs were carried out at
room temperature. This includes measurements of photon transfer curves, gain coefficient histograms, read noise, and spectral response. Test results obtained on these devices successfully demonstrated the objectives of the aircraft flight mission. In this paper, we describe the characterization results and also discuss their applications to future mission.