Steve Li

Edge technique Doppler lidar wind measurements with high vertical resolution

We have developed a Doppler lidar system using the edge technique and have made atmospheric lidar wind measurements. Line-of-sight wind profiles with a vertical resolution of 22 m have a standard deviation of 0.40 m /s for a ten-shot average. Day and night lidar measurements of the vector wind have been made for altitudes from 200 to 2000 m. We validated the lidar measurements by comparing them with independent rawinsonde and pilot balloon measurements of wind speed and direction. Good agreement was obtained. The instrumental noise for these data is 0.11 m /s for a 500-shot average, which is in good agreement with the observed minimum value of the standard deviation for the atmospheric measurements. The average standard deviation over 30 mins varied from 1.16 to 0.25 m /s for day and night, respectively. High spatial and temporal resolution lidar profiles of line-of-sight winds clearly show wind shear and turbulent features at the 1 -2-m /s level with a high signal-to-noise ratio and demonstrate the potential of the edge-technique lidar for studying turbulent processes and atmospheric dynamics.

Low noise Planar External Cavity Laser for Interferometric Fiber Optic Sensors

A 1550 nm DWDM planar external cavity laser (ECL) is demonstrated to provide low phase/frequency noise, narrow linewidth, and low RIN. The cavity includes a semiconductor gain chip and a planar lightwave circuit waveguide with Bragg grating, packaged in a 14-pin butterfly package. This planar ECL laser is designed to operate under vibration and in harsh environmental conditions. The laser shows linewidth ≤ 2.6 kHz, phase/frequency noise comparable with that of long cavity fiber lasers, RIN ≤ -147dB/Hz at 1kHz, and power ≥ 10mW. Performance is suitable for various high performance fiber optic sensing systems, including interferometric sensing in Oil and Gas, military/security and other applications, currently served mostly by costly and less reliable laser sources.

A dual format communication modem development for the Laser Communications Relay Demonstration (LCRD) program

The LCRD will demonstrate optical communications relay services between a geosynchronous satellite and Earth over an extended period, and thereby gain the knowledge and experience base that will enable NASA to design, procure, and operate cost-effective future optical communications systems and relay networks. LCRD is the next step in NASA eventually providing an optical communications service on the Next Generation Tracking and Data Relay Satellites (TDRS). LCRD will demonstrate some optical communications technologies, concepts of operations, and advanced networking technologies applicable to Deep Space missions. In this paper we describe the integrated dual format (PPM/DPSK) modem testbed development and performance.

Development of optical parametric amplifier for lidar measurements of trace gases on Earth and Mars

Trace gases in planetary atmospheres offer important clues as to the origins of the planets hydrology, geology, atmosphere, and potential for biology. 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 light is single frequency with high spectral purity and is widely tunable both at 1600 nm and 3300 nm with an optical-optical conversion efficiency of ~40%. We demonstrated open-path atmospheric measurements of CH4 (3291 nm and 1651 nm), CO2 (1573 nm), H2O (1652 nm) with this laser source.

Overview of space qualified solid state lasers development at NASA Goddard Space Flight Center

NASA Goddard Space Flight Center (GSFC) has been engaging in Earth and planetary science instruments development for many years. With stunning topographic details of the Mars surface to Earths surface maps and ice sheets dynamics of recent years, NASA GSFC has provided vast amount of scientific data products that gave detailed insights into Earths and planetary sciences. In this paper we will review the past and present of space-qualified laser programs at GSFC and offer insights into future laser based science instrumentations.

Seeded nanosecond optical parametric generator for trace gas measurements

We report on the development effort of a nanosecond-pulsed seeded optical parametric generator (OPG) for remote trace gas measurements. The seeded OPG output light is single frequency with high spectral purity and is widely tunable both at 1600nm and 3300nm with an optical-optical conversion efficiency of ~40%. We demonstrated simultaneous tuning over the methane (CH4) absorption line at idler wavelength, 3270.4nm, and carbon dioxide (CO2) absorption line at signal wavelength, 1578.2nm. In this paper, we will also discuss open-path atmospheric measurements with this newly developed laser source.

Development and Vacuum Life Test of a Diode-Pumped Cr:Nd:YAG Laser (Heritage Laser) for Space Applications

The development and vacuum life-testing of a diode pumped Cr:Nd:YAG laser for space applications is presented. Furthermore results from long life-testing of 808-nm laser diode arrays in air and vacuum are discussed.

Design considerations of the LOLA laser transmitter

We present the design of the Lunar Orbiter Laser Altimeter laser transmitter which consists of two oscillators on a single bench, each capable of providing one billion shots.

LIDAR technology for measuring trace gases on Mars and Earth

Trace gases and their isotopic ratios in planetary atmospheres offer important but subtle clues as to the origins of a planets atmosphere, hydrology, geology, and potential for biology. An orbiting laser remote sensing instrument is capable of measuring trace gases on a global scale with unprecedented accuracy, and higher spatial resolution that can be obtained by passive instruments. For Earth we have developed laser technique for the remote measurement of the tropospheric CO2, O2, and CH4 concentrations from space. Our goal is to develop a space instrument and mission approach for active CO2 measurements. Our technique uses several on and off-line wavelengths tuned to the CO2 and O2 absorption lines. This exploits the atmospheric pressure broadening of the gas lines to weigh the measurement sensitivity to the atmospheric column below 5 km and maximizes sensitivity to CO2 changes in the boundary layer where variations caused by surface sources and sinks are largest. Simultaneous measurements of O2 column use a selected region in the Oxygen A-band. Laser altimetry and atmospheric backscatter can also be measured simultaneously, which permits determining the surface height and measurements made to thick cloud tops and through aerosol layers. We use the same technique but with a different transmitter at 1.65 um to measure methane concentrations. Methane is also a very important trace gas on earth, and a stronger greenhouse gas than CO2 on a per molecule basis. Accurate, global observations are needed in order to better understand climate change and reduce the uncertainty in the carbon budget. Although carbon dioxide is currently the primary greenhouse gas of interest, methane can have a much larger impact on climate change. Methane levels have remained relatively constant over the last decade but recent observations in the Arctic have indicated that levels may be on the rise due to permafrost thawing. NASA’s Decadal Survey underscored the importance of Methane as a greenhouse gas and called for a mission to measure CO2, CO and CH4. Methane has absorptions in the mid-infrared (3.3 um) and the near infrared (1.65 um). The 3.3 um spectral region is ideal for planetary (Mars) Methane monitoring, but unfortunately is not suitable for earth monitoring since the Methane absorption lines are severely interfered with by water. The near infra-red overtones of Methane at 1.65 um are relatively free of interference from other atmospheric species and are suitable for Earth observations. The methane instrument uses Optical Parametric Generation (OPG) along with sensitive detectors to achieve the necessary sensitivity. Our instrument generates and detects tunable laser signals in the 3.3 or 1.65 um spectral regions with different detectors in order to measure methane on Earth or Mars. For Mars, the main interest in methane is its importance as a biogenic marker.

Non- Topographic Space-Based Laser Remote Sensing

The advent of several key enabling electro-optics technologies afford advanced, non-topographic remote sensing instruments for space. We will present progress on several new, space-based laser instruments that are being developed at NASA GSFC. Long Abstract: In the past 20+ years, NASA Goddard Space Flight Center (GSFC) has successfully developed and flown lidars for mapping of Mars, the Earth, Mercury and the Moon. As laser and electro-optics technologies expand and mature, more sophisticated instruments that once were thought to be too complicated for space are being considered and developed. We will present progress on several new, space-based laser instruments that are being developed at GSFC. These include lidars for remote sensing of carbon dioxide and methane on Earth for carbon cycle and global climate change; sodium resonance fluorescence lidar to measure environmental parameters of the middle and upper atmosphere on Earth and Mars and a wind lidar for Mars orbit; in situ laser instruments include remote and in-situ measurements of the magnetic fields; and a time-of-flight mass spectrometer to study the diversity and structure of nonvolatile organics in solid samples on missions to outer planetary satellites and small bodies.