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The characteristics of a small, lightweight portable lidar system for measuring aerosol (Mie) scatter at wavelengths of 1064 and 532 nm are described. It uses a 20-Hz Nd:YAG pulsed laser as a source and a 12.7-cm-diameter telescope as a receiver. By using a minimal number of commercially available components, the cost of construction has been reduced. The lidar has a useable range of 60–3000 m for clean marine conditions. Its performance has been demonstrated using measurements of tropospheric aerosols on the island of Hawaii.

There is a need for an instrument that can be used for remote in situ identification of biogenic and a-biogenic minerals, various types of ices, and organic and inorganic materials on planetary surfaces. In this paper, we explore the use of remote pulsed laser Raman spectroscopy for mineral analysis at distances from 10 to 66 m on planetary surfaces. We have constructed a remote Raman system utilizing a small pulsed Nd:YAG laser and a 5-in. telescope coupled to a spectrograph with an optical fiber. The performance of our system is demonstrated by presenting spectra of benzene and marble (calcium carbonate) while varying the integration time (i.e., number of laser shots), as well as single laser shot spectra of marble while decreasing laser power. Finally, Raman spectra of representatives of several different mineral groups are presented, including hydrated substances, carbonates, silicates (e.g., olivine, pyroxene, feldspars, etc.), water, and ice.

Total dephasing decay profiles of the ν12 (1002 cm−1) ring-stretching mode of toluene have been measured in the time domain in a range extending from the low viscosity, normal liquid (380 K, 0.26 cP) to the high viscosity, supercooled liquid (140 K, 4600 cP). In the region from 1 to 5 cP (250 to 200 K), the profile makes a transition from exponential to partially Gaussian, consistent with a loss of motional narrowing. In contrast to many interpretations of dephasing in terms of collisional dynamics, these data clearly indicate an important role for diffusive dynamics in vibrational dephasing. Above 10 cP, oscillations appear, and their period decreases with increasing viscosity. An analysis of the low to moderate viscosity region with a Kubo model shows that the frequency modulation time is dependent on the viscosity. The dephasing decay profiles are used to test a recent viscoelastic theory of dephasing [Chem. Phys. 233, 257 (1998)], which attributes the perturbation of the vibrational frequency to shear...

A recent continuum model of non-polar electronic solvation [M. Berg, J. Phys. Chem., A 102 (1998) 17] is extended to treat vibrational dephasing at moderate to high viscosities. Standard theories of vibrational dephasing in low-viscosity liquids predict an unphysical divergence of the linewidth at high viscosity. The current theory corrects this problem by explicitly accounting for the existence of both inertial and diffusive components in the liquid dynamics. At high viscosity or in a glass, the Raman line is predicted to be inhomogeneous and to have a finite width. In contrast to existing theories, this theory predicts that structural dynamics dominate the Raman linewidth. Collision-like processes only contribute weak, broad wings to the line. This theory also predicts quantitative connections between vibrational dephasing and electronic-state solvation.

Raman spectroscopy is a powerful technique for materials analysis, and we are developing and analyzing a remote Raman system for use on a planetary lander or rover. We have acquired data at a distance of 10 m from a variety of geologic materials using different instrument designs. We have employed a pulsed laser with both an ungated detector and a gated detector. A gated detector can reduce long-lived fluorescence while still collecting all Raman signal. In order to design a flight instrument, we need to quantify how natural surfaces will respond to laser stimulus. We define remote Raman efficiency of natural surfaces 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, the projected solid angle, and the full-width-half-maximum of the Raman signal. We have determined the remote Raman efficiency for a variety of rocks and minerals. The best efficiencies are achieved for large, clear, single crystals that produce the most radiant exitance, while darker fine-grained mineral mixtures produce lower efficiencies. By implementing a pulsed laser, gated detector system we have improved the signal detection and have generally decreased the integration time necessary to detect Raman signal from natural surfaces.

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.

We have designed and developed two breadboard versions of stand-off Raman spectroscopic systems for landers based on a 5-in. Maksutov-Cassegrain telescope and a small (4-in. diameter) Newtonian telescope receiver. These systems are capable of measuring the Raman spectra of minerals located at a distance of 4.5-66 m from the telescope. Both continuous wave (CW) Ar-ion and frequency doubled Nd:YAG (532 nm) pulsed (20 Hz) lasers are used as excitation sources for measuring remote Raman spectra of rocks and minerals. We have also made complementary measurements on the same rock samples with a micro-Raman system in 180 and 135 degrees geometry for evaluating the system performance and for estimating effect of grain size and laser-induced heating on the spectra of minerals using alpha-quartz as a model mineral. A field portable remote pulsed Raman spectroscopic system based on the 5-in. telescope and an f/2.2 spectrograph has been developed and tested. We have also demonstrated a prototype of a combined Raman and laser-induced breakdown spectroscopy (LIBS) system, capable of providing major element composition and mineralogical information on both biogenic and inorganic minerals at a distance of 10 m from the receiver.