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Tunable Laser Spectrometers
Above: A low-power dissipation interband cascade (IC) laser fabricated at MDL inside a package designed specially for TLS. This device emits at 3.27 µm and was designed specifically to target absorption lines of methane.

Tunable Laser Spectrometers

Since the 1980s JPL has pioneered the development and deployment of Tunable Laser Spectrometers for NASA for in situ atmospheric and planetary applications.

The vast majority of gaseous chemical substances exhibit fundamental vibrational absorption bands in the mid-infrared spectral region (≈ 2–10 µm), and the absorption of light by these fundamental bands provides a nearly universal means for their detection. A main feature of optical techniques is the non-intrusive in situ detection capability for trace gases.

Tunable laser spectrometers offer a wide diversity of capability for highly sensitive measurement of atmospheric gases or those evolved (pyrolysis heating, laser ablation, etc.) from solid samples. Because it is based on IR laser absorption of individual rotational lines within a vibrational band, the method is very sensitive (parts-per-billion to parts-per-trillion), direct, non-invasive, easy to calibrate and unambiguous in its species identification and isotope ratio determinations without interference.

Although mass spectrometers have strength in wide survey capability and uniqueness in noble gas detection and noble gas isotope ratios, small planetary instruments are not well suited to low abundance H2O and confuse H2O, NH3, and CH4 isotopic species that overlap in mass number, especially when present in similar abundances. TLS is the preferred detection method for a variety of gases including H2O, CH4, N2O, CO, CO2, NO, NO2, HNO3, O2, O3, HCl, HF, and for stable isotopes in C, H, and O.

Laser sources are now available at room temperature with several to tens of milliwatts continuous-wave (CW) output power spanning a wide wavelength range. Detectors are single-element, and miniature all-solid-state spectrometers are already being developed. Three detection methods (direct absorption, second-harmonic, and cavity ring-down) will be employed as appropriate.

Tunable laser spectroscopy can be applied in a variety of simple configurations: closed mutipass cell (Herriott cell or cavity ringdown cell), open cradle cell, or direct to target ranging using topographically-scattered and return laser light. Hand-held portable systems are also feasible for many specific applications. Using tunable laser spectrometers, trace molecules in the Earth’s atmosphere or the atmosphere surrounding another planet may be precisely identified and studied by measuring their infrared absorption spectrum. Such measurements can reveal a wealth of information about the atmosphere, its composition, chemistry, evolution, and winds. Furthermore, as demonstrated by TLS, part of the Sample Analysis at Mars (SAM) instrument suite on the Mars Curiosity rover, isotope ratios of gases released from heating rocks can reveal details about the planet’s evolution and volatile history. NASA is developing ideas to conduct ice-core sampling at the Martian poles to measure water isotopes using a TLS instrument to reveal the climate record over millions of years past- just as is done on Earth.

Tunable Laser Spectrometers

Products & Processes

Image from MDL Core Competency Project: TLS Mars

TLS Mars

The tunable laser spectrometer (TLS) aboard the Mars Science Laboratory Curiosity rover—using lasers developed and space-qualified at MDL— has paved the way for semiconductor lasers to play an important role in future...

Image from MDL Core Competency Project: Harvard Collaboration

Harvard Collaboration

Harvard and JPL have been collaboratively pursuing the development of high power pulsed and CW laser systems for demanding spectroscopic applications since 2010. This partnership has resulted in two recent...

Image from MDL Core Competency Project: Spacecraft Fire

Spacecraft Fire

Fires can happen anywhere—even in space. So, for the astronauts who live and work there, it is critical to understand how fire spreads in a microgravity environment and how to manage it safely...

Image from MDL Core Competency Project: TLS Development

TLS Development

Amazing discoveries have come from the tunable laser spectrometer (TLS) aboard the Curiosity Mars rover, which is part of NASA's Mars Science Laboratory mission (MSL) since it landed in August 2012...

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