Mark A. Stephen

Kilowatt-level stimulated-Brillouin-scattering-threshold monolithic transform-limited 100 ns pulsed fiber laser at 1530 nm

We demonstrate a high-stimulated-Brillouin-scattering-threshold monolithic pulsed fiber laser in a master oscillator power amplifier configuration that can operate over the C band. In the power amplifier stage, we used a newly developed single-mode, polarization maintaining, and highly Er/Yb codoped phosphate fiber with a core diameter of 25 microm. A single-frequency actively Q-switched fiber laser was used to generate pulses in the hundreds of nanoseconds at 1530 nm. We have achieved peak power of 1.2 kW for 105 ns pulses at a repetition rate of 8 kHz, corresponding to a pulse energy of 0.126 mJ, with transform-limited linewidth and diffraction-limited beam quality.

High SBS-threshold, narrowband, erbium codoped with ytterbium fiber amplifier pulses frequency-doubled to 770 nm.

We present results of pulsed, narrowband amplification at 1540.6nm using a polarization maintaining, large mode area gain fiber codoped with erbium and ytterbium. At a repetition rate of 55 kHz, 2.9 W of average 1540.6nm power were generated with a pulse duration of 136 ns, corresponding to an SBS free peak power of 360 W. The amplified signal was frequency doubled in peridically poled potassium titanyl phosphate and conversion efficiencies of up to 56% were generated. When varying the repetition rate between 55-150 kHz the conversion efficiency changed from 56% to 35% due to the limited pump power.

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.

A laser sounder for measuring atmospheric trace gases from space

Mounting concern regarding global warming and the increasing carbon dioxide (CO2) concentration has stimulated interest in the feasibility of measuring CO2 mixing ratios from space. Precise satellite observations with adequate spatial and temporal resolution would substantially increase our knowledge of the atmospheric CO2distribution and allow improved modeling of the CO2 cycle. Current estimates indicate that a measurement precision of better than 1 part per million (1 ppm) will be needed in order to improve estimates of carbon uptake by land and ocean reservoirs. A 1-ppm CO2 measurement corresponds to approximately 1 in 380 or 0.26% long-term measurement precision. This requirement imposes stringent long-term precision (stability) requirements on the instrument In this paper we discuss methods and techniques to achieve the 1-ppm precision for a space-borne lidar.

Narrowband, tunable, frequency-doubled, erbium-doped fiber-amplifed transmitter

We report on the development of a fiber-based laser transmitter designed for active remote sensing spectroscopy. The transmitter uses a master oscillator power amplifier (MOPA) configuration with a distributed feedback diode-laser master oscillator and an erbium-doped fiber amplifier. The output from the MOPA is frequency-doubled with a periodically poled potassium titanium oxide phosphate crystal. With 35 W of single-frequency peak optical pump power, 8 W of frequency-doubled peak power was achieved. The utility of this single-frequency, wavelength tunable, power scalable laser was then demonstrated in a spectroscopic measurement of diatomic oxygen A band.

Pulsed airborne lidar measurements of atmospheric optical depth using the Oxygen A-band at 765 nm

We report on an airborne demonstration of atmospheric oxygen optical depth measurements with an IPDA lidar using a fiber-based laser system and a photon counting detector. Accurate knowledge of atmospheric temperature and pressure is required for NASAs Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) space mission, and climate modeling studies. The lidar uses a doubled erbium-doped fiber amplifier and single photon-counting detector to measure oxygen absorption at 765 nm. Our results show good agreement between the experimentally derived differential optical depth measurements with the theoretical predictions for aircraft altitudes from 3 to 13 km.

Laser Sounder for Global Measurement of CO2 Concentrations in the Troposphere from Space

We report progress in assessing the feasibility of a new satellite-based laser-sounding instrument to measure CO2 concentrations in the lower troposphere from space.

Space qualification and environmental testing of quasicontinuous wave laser diode arrays

NASA’s mission requirements for spaceborne laser diode arrays lead to a set of tests peculiar to space flight. The goal of these tests is to determine if vibration, radiation, or vacuum will impair the operation or lifetime of nominally 100W quasicontinuous wave 808nm laser diode arrays. To simulate the stresses expected during a mission, terrestrial tests involve mechanical vibration, simulating the acceleration of launch, exposure to the equivalent doses of ionizing radiation, and operation in a vacuum. Three sets of devices were tested: one set with random vibration up to 20 g root-mean-square (grms) applied along three axes, a second set of devices was irradiated with γ radiation (1.17 and 1.33MeV) at 744rad(Si)∕min up to 200krad(Si), and the third set was exposed to a flux of 5×1011 or 1012p∕cm2 of 200MeV protons up to 60krad total dose. Only the proton irradiated devices showed any effect attributable to the test: a slight rise in lasing threshold, which recovered over time with self-annealing. A se...

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.

Oxygen Spectroscopy Laser Sounding Instrument for Remote Sensing of Atmospheric Pressure

We report on the progress of an oxygen spectroscopy laser sounding instrument designed as a calibration channel for a carbon dioxide (CO2) laser sounding instrument. We have developed a pulsed, frequency-doubled, fiber laser transmitter for use in an oxygen instrument. The instrument concept uses the pressure broadening of spectroscopic lines of the diatomic oxygen A-band to deduce atmospheric pressure. There are many uses for this measurement but we are developing it primarily to make a measurement of the dry mixing ratio of CO2. The CO2 measurement can be affected by changes in atmospheric properties such as humidity, temperature and pressure. To remove these variances requires measuring a stable, well-mixed gas like oxygen. We will report on the basic theory behind the instrument, measurements made at a test site at Goddard, review the current state of the instrument technologies and the necessary steps to bring them to space readiness, and review the current state of the instrument development.