Russell J. De Young

Profiling atmospheric water vapor using a fiber laser lidar system

A compact, lightweight, and efficient fiber laser lidar system has been developed to measure water vapor profiles in the lower atmosphere of Earth or Mars. The line narrowed laser consist of a Tm:germanate fiber pumped by two 792 nm diode arrays. The fiber laser transmits approximately 0.5 mJ Q- switched pulses at 5 Hz and can be tuned to water vapor lines near 1.94 microm with linewidth of approximately 20 pm. A lightweight lidar receiver telescope was constructed of carbon epoxy fiber with a 30 cm Fresnel lens and an advanced HgCdTe APD detector. This system has made preliminary atmospheric measurements.

Method for the reduction of signal-induced noise in photomultiplier tubes

A new method to reduce photomultiplier tube detector signal-induced noise (SIN) in a lidar system is successfully demonstrated. A metal ring electrode placed external to the photomultiplier tube photocathode is pulsed during the intense near-field lidar return with a potential between 15 and 500 V, resulting in a significant reduction in SIN. The effect of the metal ring voltage on the decay time constant and the magnitude of a simulated lidar signal is presented. Optimal experimental conditions for the use of this device in lidar receivers, such that the lidar decay time constant is not affected, are determined. Mechanisms for this SIN suppression system are discussed in detail, and data were recorded to show that the voltage on the metal ring functions by altering the photomultiplier electron optics.

A lunar rover powered by an orbiting laser diode array

A conceptual design of a high‐power, long‐duration lunar rover powered by a laser beam is presented. The laser transmitter in lunar orbit consists of an SP‐100 reactor prime power source providing 100 kW of electricity to a laser diode array that emits 50 kW of laser radiation. The laser radiation is beamed to the lunar surface where it is received by a GaAlAs solid‐state, laser‐to‐electric converter. This converter provides 22.5 kW of electrical power to the rover vehicle for science, locomotion, and crew needs. The mass of one laser transmitter is approximately 5000 kg, whereas the mass of the rover power system is 520 kg. The rover power system is significantly less massive (23 kg/kW) than alternative rover power units.

Laser elemental mass analysis at large distances

A Nd:YAG laser is used to produce a plasma on targets of Al, Cu, Ge, Ag, and a lunar simulant. Ion energies for 1×109 W/cm2 were found to be between 550 and 900 eV. Some of these ions travel down a 11.1‐m evacuated tube to an ion trap 1‐m time‐of‐flight spectrometer producing a mass spectrum of a lunar simulant, demonstrating the ability to analyze targets at significant remote distances.

Advanced detectors, optics, and waveform digitizers for aircraft DIAL water vapor measurements

NASA Langley has an active water vapor differential absorption lidar program taking measurements from both C-130 and ER-2 aircraft. A research effort has started to increase the signal-to-noise ratio in the DIAL receiver by 1) evaluating new very low noise avalanche photo didoes (APD), 2) designing an optics system that will focus the return light signal to the APD efficiently and 3) constructing a 10-MHz waveform digitizer board that will be small enough to be placed at the APD and telescope. With these advances we anticipate improving the signal-to-noise ratio by a factor of ten over the current receiver system.

Visible spectrum optical absorption in Te2 vapor

The absorption spectrum of Te2 vapor has been measured throughout the visible spectrum. The absorption cross section (A state) was determined to be 2.18×10−18 cm2. At wavelengths above 500 nm, absorption takes place from vibrational levels above the ground level, allowing more efficient absorption of visible (solar) spectrum light. From an absorption point of view, Te2 appears to be a good candidate for a direct solar‐pumped laser.

A Study of Air Quality in the Southeastern Hampton–Norfolk–Virginia Beach Region with Airborne Lidar Measurements and MODIS Aerosol Optical Depth Retrievals

Abstract A study of air quality was performed using a compact, aircraft aerosol lidar designed in the Science Directorate at NASA Langley Research Center and Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth (AOD) retrievals. Five flights of lidar measurements conducted in the Hampton–Norfolk–Virginia Beach, Virginia, region showed complex regional aerosol distributions. Comparisons with MODIS AOD at 10 km × 10 km and 5 km × 5 km resolutions show good agreement, with correlation R2 values of 0.82 and 0.88, respectively. Linear regressions of particulate matter with a diameter of less than 2.5 μm (PM2.5) and AOD within the ranges of 5–40 μg m−3 and 0.05–0.7, respectively, result in R2 values of ∼0.64 and ∼0.82 for MODIS and the Compact Aerosol Lidar, respectively. The linear regressions reflect approximately 51 μg m−3 to 1 AOD. These relationships are in agreement with previous findings for air pollution aerosols in the eastern United States and in northern Italy. However, large v...

Advanced water-vapor lidar detection system for aircraft and space deployment

An advanced compact differential absorption lidar detection system for atmospheric water vapor measurement is reported. This system interfaces the lidar receiver telescope to a personal computer and contains an advanced avalanche photodiode detector, signal conditioning circuit, 14-bit, 10 MHz digitizer and a microcontroller. The whole system was realized on one electronic card. Characterization results indicate low noise with reduced size, reduced mass and an extended measurement range over current lidar detection systems. The new system can be incorporated in spacecraft lidar systems. Simulated lidar return measurements were performed with the new system in order to obtain its minimum detectable signal limits.

A compact mobile ozone lidar for atmospheric ozone and aerosol profiling

A compact mobile differential absorption lidar (DIAL) system has been developed at NASA Langley Research Center to provide ozone, aerosol and cloud atmospheric measurements in a mobile trailer for ground-based atmospheric ozone air quality campaigns. This lidar is integrated into the Tropospheric Ozone Lidar Network (TOLNet) currently made up of four other ozone lidars across the country. The lidar system consists of a UV and green laser transmitter, a telescope and an optical signal receiver with associated Licel photon counting and analog channels. The laser transmitter consists of a Q-switched Nd:YLF inter-cavity doubled laser pumping a Ce:LiCAF tunable UV laser with all the associated power and lidar control support units on a single system rack. The system has been configured to enable mobile operation from a trailer and was deployed to Denver, CO July 15-August 15, 2014 supporting the DISCOVER-AQ campaign. Ozone curtain plots and the resulting science are presented.

Tm:germanate fiber laser for planetary water vapor atmospheric profiling

The atmospheric profiling of water vapor is necessary for finding life on Mars and weather on Earth. The design and performance of a water vapor lidar based on a Tm:germanate fiber laser is presented.