Compact High-Power Widely Tunable Mid-IR Light Source for Planetary Exploration

Los Gatos Research, Inc. (LGR) and Professor Martin Fejer and his group at Stanford University propose to develop and demonstrate a compact, monolithic, efficient, high-power, narrow-linewidth tunable laser source operating in the 3.2-3.4 um wavelength region. LGR's mid-infrared (mid-IR) light source, based on a fiber-laser pumped monolithic optical parametric oscillator (OPO) developed at Stanford, will assist NASA in completing its trace-gas-detection objectives by supplying NASA with a critical, difficult-to-obtain laser source suitable for continuous-wave (cw) spectroscopy. During Phase I, LGR and Stanford will manufacture a monolithic OPO crystal, using techniques established by Stanford, generating between 1-2 W of single-frequency radiation between 3.2-3.4 um. At the end of Phase I, the OPO system will be used to measure transmission through a 50-cm-long methane cell (manufactured by LGR) at wavelengths corresponding to the C-H stretch vibrational resonance, 3.3 um. Technology readiness level (TRL) 4 will be reached at the completion of Phase I. During Phase II, remote detection of methane will be performed using a methane cell and measuring the backscattered light from the cell as the OPO mid-IR frequency is scanned ~5 GHz. The size of the housing for the monolithic OPO will be designed to reduce the overall size and weight of the mid-IR-laser head. Fiber-coupling for the incoming pump and the outgoing mid-IR radiation will be added to the OPO housing enabling simple fiber delivery. Modeling of the system sensitivity in ppm of methane will be performed for the final remote sensing system for ground-, air-, and space-based operation.

The portability and robustness of LGR's high-power (>1 W) monolithic mid-IR light source makes it suitable for many non-NASA commercial applications. It is suitable for sensitive detection of methane and ethane for oil and natural gas exploration missions both in ground- and air-based missions. The eye-safe radiation could be used for detection of gases in exhaled human breath providing advanced detection for certain diseases such as diabetes (acetone), oxidative stress and post-operative organ rejection (ethane), and suspected cancer biomarkers (ethane, formaldehyde, and acetaldehyde). There have been several advances in the field of medical imaging using optical coherence tomography (OCT) as well as photoacoustic imaging using near-IR radiation. LGR's monolithic OPOs are well suited for biomedical imaging due to the tunability and spectral purity. The application of LGR's eye-safe, fiber-coupled mid-IR light source would be suitable for photoacoustic detection of gases as well as biomedical imaging, photoacoustic ultrasound. The tunability of the monolithic OPOs allows for operation in the well-known water-transparency window between 3-4 um. LGR's monolithic OPOs could be used for laser-based data transmission for air- and space-based applications. The monolithic OPO would be used as the transmitter and receiver unit. Access to additional frequency bands allows for larger transfer rates of information in parallel with current space-based laser communication systems.

Absorption spectroscopy using a tunable OPO is a simple measurement technique known for its high sensitivity (parts per billion) and potentially superior size, weight, and power consumption (SWAP) compared to competing technologies. Also important are sources for remote measurements of carbon-based trace gases (CH4, CO2, and CO) for total column measurements from aircraft and spacecraft, as well as for profiling measurements from the ground using atmospheric backscatter. These systems need tunable, narrow-linewidth lasers that operate in the 3-4 um wavelength band. LGR's monolithic OPOs can also be used for ground-based applications such as detection of gases emitted from combustion processes including jet engines and chemical-rocket exhaust. A high-power laser system in the 3-4 um wavelength region would complement NASA's robust 1- and 2-um systems developed under the Laser Risk Reduction Program. NASA requires LIDAR instruments for accurate measurements of atmospheric parameters with high spatial resolution from ground, airborne, and space-based platforms with an emphasis placed on compactness, efficiency, reliability, and lifetime. NASA needs advanced components for direct-detection LIDAR instruments on new UAV platforms, ground-based test beds, and eventually in space. For gas measurements using tunable laser spectrometers, available platforms such as aircraft, balloons, surface and entry probes and landed rovers impose severe limitations on instrument SWAP.

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