Steven X. Li

Wind measurements with 355-nm molecular Doppler lidar

A Doppler lidar system based on the molecular double-edge technique is described. The system is mounted in a modified van to permit deployment in field operations. The lidar operates with a tripled Nd:YAG laser at 355 nm, a 45-cm-aperture telescope, and a matching azimuth-over-elevation scanner to permit full sky access. Validated atmospheric wind profiles were measured from 1.8 to 35 km with a 178-m vertical resolution. The range-dependent rms deviation of the horizontal wind speed is 0.4-6 m/s. The measured wind speed and direction are in good agreement with the rawinsonde wind measurements made simultaneously from the same location.

Compact, passively Q-switched Nd:YAG laser for the MESSENGER mission to Mercury

A compact, passively Q-switched Nd:YAG laser has been developed for the Mercury Laser Altimeter, an instrument on the Mercury Surface, Space Environment, Geochemistry, and Ranging mission to the planet Mercury. The laser achieves 5.4% efficiency with a near-diffraction-limited beam. It passed all space-flight environmental tests at subsystem, instrument, and satellite integration testing and successfully completes a postlaunch aliveness check en route to Mercury. The laser design draws on a heritage of previous laser altimetry missions, specifically the Ice Cloud and Elevation Satellite and the Mars Global Surveyor, but incorporates thermal management features unique to the requirements of an orbit of the planet Mercury.

Space laser transmitter development for ICESat-2 mission

The first NASA Ice, Cloud and land Elevation Satellite (ICESat) was launched in January 2003 and placed into a nearpolar orbit whose primary mission was the global monitoring of the Earths ice sheet mass balance. ICESat has accumulated over 1.8 B shots in space and provided a valuable dataset in the study of ice sheet dynamics over the past few years. NASA is planning a follow-on mission ICESat-2 to be launched tentatively in 2015. In this paper we will discuss the development effort of the laser transmitters for the ICESat-2 mission.

Ground demonstration of trace gas lidar based on optical parametric amplifier

Abstract. We report on the development effort of a nanosecond-pulsed optical parametric amplifier (OPA) for remote trace gas measurements for Mars and Earth. The OPA output has ∼ 500     MHz linewidth and is widely tunable at both near-infrared and mid-infrared wavelengths, with an optical—optical conversion efficiency of up to ∼ 39 % . Using this laser source, we demonstrated open-path measurements of CH 4 (3291 and 1652 nm), CO 2 (1573 nm), H 2 O (1652 nm), and CO (4764 nm) on the ground. The simplicity, tunability, and power scalability of the OPA make it a strong candidate for general planetary lidar instruments, which will offer important information on the origins of the planet’s geology, atmosphere, and potential for biology.

Laser transmitter for the Lunar Orbit Laser Altimeter (LOLA) instrument

We present the final configuration of the space flight laser transmitter as delivered to the LOLA instrument. The laser consists of two oscillators on a single bench, each capable of providing one billion plus shots.

Laser transceivers for future NASA missions

NASA is currently developing several Earth science laser missions that were recommended by the US National Research Council (NRC) Earth Science Decadal Report. The Ice Cloud and Land Elevation Satellite-2 (ICESat-2) will carry the Advanced Topographic Laser Altimeter System (ATLAS) is scheduled for launch in 2016. The Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) mission and will measure column atmospheric CO2 concentrations from space globally. The Gravity Recovery And Climate Experiment (GRACE) Follow-On (GRACEFO) and GRACE-2 missions measure the spatially resolved seasonal variability in the Earths gravitational field. The objective of the Lidar Surface Topography (LIST) mission is to globally map the topography of the Earths solid surface with 5 m spatial resolution and 10 cm vertical precision, as well as the height of overlying covers of vegetation, water, snow, and ice. This paper gives an overview of the laser transmitter and receiver approaches and technologies for several future missions that are being investigated by the NASA Goddard Space Flight Center.

Single-frequency lasers for remote sensing

We have designed and built two versions of a space-qualifiable, single-frequency Nd:YAG laser. Our approach to frequency stabilization of the seeded oscillator is a variation of the “ramp and fire” technique. In this design, the length of the pulsed laser cavity is periodically varied until a resonance with the seed laser is optically detected. At that point the pulsed laser is fired, ensuring that it is in resonance with the seed laser. For one of the lasers the resulting single frequency pulses are amplified and frequency tripled. This system operates at 50 Hz and provides over 50 mJ/pulse of single-frequency 355 nm output. It has been integrated into the GLOW (Goddard Lidar Observatory for Winds) mobile Doppler lidar system for field testing. The second laser is a 20o Hz oscillator only system that is frequency doubled for use in the High Spectral Resolution Lidar (HSRL) system being built at NASA Langley Research Center. It provides 4 mJ of single-frequency 532 nm output that has a spectral purity of >10,000. In this paper we describe the design details, environmental testing, and integration of these lasers into their respective lidar systems.

Spaceborne laser transmitters for remote sensing applications

NASA Goddard Space Flight Center (GSFC) has been engaging in Earth and planetary science remote sensing instruments development for many years. The latest instrument was launched in 2008 to the moon providing the most detailed topographic map of the lunar surface to-date. NASA GSFC is preparing for several future missions, which for the first time will perform active spectroscopic measurements from space. In this paper we will review the past, present and future of space-qualified lasers for remote sensing applications at GSFC.

The Lunar Orbiter Laser Altimeter (LOLA) laser transmitter

We present the final configuration of the space flight laser transmitter as delivered to the Lunar Orbiter Laser Altimeter (LOLA) instrument. The instrument was launched in 2009 and has been in operation for close to two years and accumulated over 1.3 billion laser shots in space.

Spaceborne laser development for future remote sensing applications

At NASAs Goddard Space Flight Center, we are developing the next generation laser transmitters for future remote sensing applications including a micropulse altimeter for ice-sheet monitoring, laser spectroscopic measurements and high resolution mapping of the Earths surface as well as potential missions to other planets for trace gas measurement and mapping. In this paper we will present an overview of the spaceborne laser programs and offer insights into future spaceborne lasers for remote sensing applications.