James L. Lambert

Planetary Geochemical Investigations Using Raman and Laser-Induced Breakdown Spectroscopy

An integrated Raman spectroscopy and laser-induced breakdown spectroscopy (LIBS) instrument is a valuable geoanalytical tool for future planetary missions to Mars, Venus, and elsewhere. The ChemCam instrument operating on the Mars Curiosity rover includes a remote LIBS instrument. An integrated Raman-LIBS spectrometer (RLS) based on the ChemCam architecture could be used as a reconnaissance tool for other contact instruments as well as a primary science instrument capable of quantitative mineralogical and geochemical analyses. Replacing one of the ChemCam spectrometers with a miniature transmission spectrometer enables a Raman spectroscopy mineralogical analysis to be performed, complementing the LIBS chemical analysis while retaining an overall architecture resembling ChemCam. A prototype transmission spectrometer was used to record Raman spectra under both Martian and Venus conditions. Two different high-pressure and high-temperature cells were used to collect the Raman and LIBS spectra to simulate surface conditions on Venus. The resulting LIBS spectra were used to generate a limited partial least squares Venus calibration model for the major elements. These experiments demonstrate the utility and feasibility of a combined RLS instrument.

Acousto-optic tunable filter imaging spectrometer for NASA applications: breadboard demonstration

An acousto-optic tunable filter imaging spectrometer is introduced. The design criterion meeting system issues such as image quality, spectral response, field of view (FOV), programmability, and system compactness are discussed. Experimental demonstration obtained from using a 1/2 x 1/2 x 2 AOTF imaging spectrometer breadboard is presented. Identification of Nd+3 containei in a Bastnasite rock using the spectrogram recorded by this imaging spectrometer is also provided.

Strontium iodide gamma ray spectrometers for planetary science(Conference Presentation)

Gamma rays produced passively by cosmic ray interactions and by the decay of radioelements convey information about the elemental makeup of planetary surfaces and atmospheres. Orbital missions mapped the composition of the Moon, Mars, Mercury, Vesta, and now Ceres. Active neutron interrogation will enable and/or enhance in situ measurements (rovers, landers, and sondes). Elemental measurements support planetary science objectives as well as resource utilization and planetary defense initiatives. Strontium iodide, an ultra-bright scintillator with low nonproportionality, offers significantly better energy resolution than most previously flown scintillators, enabling improved accuracy for identification and quantification of key elements. Lanthanum bromide achieves similar resolution; however, radiolanthanum emissions obscure planetary gamma rays from radioelements K, Th, and U. The response of silicon-based optical sensors optimally overlaps the emission spectrum of strontium iodide, enabling the development of compact, low-power sensors required for space applications, including burgeoning microsatellite programs. While crystals of the size needed for planetary measurements (>100 cm3) are on the way, pulse-shape corrections to account for variations in absorption/re-emission of light are needed to achieve maximum resolution. Additional challenges for implementation of large-volume detectors include optimization of light collection using silicon-based sensors and assessment of radiation damage effects and energetic-particle induced backgrounds. Using laboratory experiments, archived planetary data, and modeling, we evaluate the performance of strontium iodide for future missions to small bodies (asteroids and comets) and surfaces of the Moon and Venus. We report progress on instrument design and preliminary assessment of radiation damage effects in comparison to technology with flight heritage.

In situ gas sensing instrument for planetary science

James L. Lambert, Michael Bender, Forian V. Englich, Anita Fisher, Richard Quinn, Tullis C Onstott and Aaron P Zent

Applications of optical code division multiple access (CDMA) to wireless communication

The theoretical foundations for code division multiple access (CDMA) are similar for microwave and optical implementations, and the advantages of this form of multiple access communications are similar, also. The advantages include the ability to support bursty, asynchronous, concurrent communications and to tolerate multipath interference. Optical implementations of CDMA are different in that they tend to require guided lightwaves (e.g., fiber cable), the coding is imposed on the intensity rather that on the amplitude of the lightwave, the various codes are not strictly orthogonal, and the receiver uses direct detection. This gives rise to the term optical CDMA. These pseudo- orthogonal CDMA codes usually require wide bandwidths to represent the encoded data, so that optical CDMA is sometimes considered bandwidth inefficient. Two classes of optical CDMA codes which ar sufficiently bandwidth efficient for wireless communications applications are (1) incoherent spectral CDMA and (2) optical matrix CDMA. In addition, the wireless communications applications may need to support various data rates (for the various services), and these two classes of optical CDMA are both very tolerant of data rate variations. An appropriate topology for applications such as a local area network (LAN) is a star and, for multimedia data distribution, a tree.

System to measure fixation shifts with a scanning laser ophthalmoscope

A scanning laser ophthalmoscope (SLO) uses a novel principal to view the retina while simultaneously projecting high resolution targets onto the retina. Consequently, the SLO is potentially an excellent instrument to measure fixation stability in humans. We used a commercially available Rodenstock SLO to project a small cross onto the retina of normal subjects with the HeNe laser and simultaneously view their retinal vasculature with the SLOs infrared diode laser. The video images from the SLO were continuously recorded (at 30 frames per second) with a video-cassette recorder. The video was digitized in 16 consecutive frame increments with a 4 Mbyte frame grabber in a microcomputer. By marking the audio track of the video tape and measuring from the audio mark before digitizing, long segments (1,000s of consecutive frames) can be digitized. We developed software to automatically map the locations of venous crossings at multiple retinal locations. In early work with the system, we verified that the digitization process worked correctly by time-stamping the video and confirming that all video frames were captured without duplication or drop out. We measured the location of 2 retinal points in 1024 consecutive frames of 4 normal subjects and showed that these points could be accurately followed with the automatic system.

Investigation of optic nerve development using neuronal tracing dyes

Numerical techniques are described which allow quantitative interpretation of 2D and 3D histological imagery obtained from tissue samples which are stained with the neuronal tracer Fast Blue. The methods illustrated in this investigation are readily extensible to many different types of micro neuro-anatomy, and are particularly well suited for investigating pharmacological or environmental perturbations on neuron development. These techniques were used to quantitatively describe neurological development of the optic nerve in the pigmented rat. This analysis was used to show that most of the significant refinement in the retinotectal map occurs during the second to fourth week of life and with coincident with eye opening.

High-performance FDDI NIU for streaming voice, video, and data

A 100-Mbit/s FDDI network interface unit (NIU) is described that supports real-time data, voice and video. Its high-speed interrupt-driven hardware architecture efficiently manages stream and packet data transfers to the FDDI network. Other enhancements include modular single-mode laser-dioce fiber optic links to maximize node spacing, optic bypass switches for increased fault tolerance, and a hardware performance monitor to gather real-time network diagnostics.