Dennis K. Killinger

Free Space Optics for Laser Communication Through the Air

Free space optics (FSO) communication involves the use of modulated optical or laser beams to send telecommunication information through the atmosphere. The concept of FSO light communication is not new: in his photophone patent of 1880, Alexander Graham Bell demonstrated use of an intensity-modulated optical beam (sunlight) to transmit telephone signals 200 m through the air to a distant receiver.

Optical and laser remote sensing

1 IR Differential-Absorption LIDAR (DIAL) Techniques.- 1.1 Airborne Remote Sensing Measurements With a Pulsed CO2 Dial System.- 1.2 Differential-Absorption Measurements With Fixed-Frequency IR and UV Lasers.- 1.3 Remote Sensing of Hydrazine Compounds Using a Dual Mini-TEA CO2 Laser DIAL System.- 1.4 The Hull Coherent DIAL Programme.- 1.5 Remote Measurement of Trace Gases With the JPL Laser Absorption Spectrometer.- 1.6 Laser Remote Sensing Measurements of Atmospheric Species and Natural Target Reflectivities.- 1.7 Airborne CO2 Laser Heterodyne Sensor for Monitoring Regional Ozone Distributions.- 2 Spectrometric Techniques.- 2.1 Tunable Laser Heterodyne Spectrometer Measurements of Atmospheric Species.- 2.2 Interferometric Measurements of Atmospheric Species.- 2.3 Remote Sensing by Infrared Heterodyne Spectroscopy.- 2.4 Detection of Trace Gases Using High-Resolution IR Spectroscopy.- 2.5 Gaseous Correlation Spectrometric Measurements.- 2.6 Measurements of Atmospheric Trace Gases by Long Path Differential UV/Visible Absorption Spectroscopy.- 2.7 Measurements of HONO, NO3, and NO2 by Long-Path Differential Optical Absorption Spectroscopy in the Los Angeles Basin.- 2.8 Remote Detection of Gases by Gas Correlation Spectroradiometry.- 3 UV-Visible DIAL Techniques.- 3.1 Atmospheric Pressure and Temperature Profiling Using Near IR Differential Absorption Lidar.- 3.2 Ground-Based Ultraviolet Differential Absorption Lidar (DIAL) System and Measurements.- 3.3 Remote Sensing of Tropospheric Gases and Aerosols With an Airborne DIAL System.- 3.4 Pollution Monitoring Using Nd:YAG Based Lidar Systems.- 4 Atmospheric Propagation and System Analysis.- 4.1 Effects of Atmospheric Obscurants on the Propagation of Optical/IR Radiation.- 4.2 The Effects of Target-Induced Speckle, Atmospheric Turbulence, and Beam Pointing Jitter on the Errors in Remote Sensing Measurements.- 4.3 Lidar System Analysis for Measurement of Atmospheric Species.- 4.4 CO2 DIAL Sensitivity Studies for Measurements of Atmospheric Trace Gases.- 4.5 Signal Averaging Limitations in Heterodyne- and Direct-Detection Laser Remote Sensing Measurements.- 5 UV-Fluorescence Remote Sensing.- 5.1 Rayleigh and Resonance Sounding of the Stratosphere and Mesosphere.- 5.2 High-Resolution Lidar System for Measuring the Spatial and Temporal Structure of the Mesospheric Sodium Layer.- 5.3 Remote Sensing of OH in the Atmosphere Using the Technique of Laser-Induced Fluorescence.- 5.4 Use of the Fraunhofer Line Discriminator (FLD) for Remote Sensing of Materials Stimulated to Luminesce by the Sun.- 5.5 Ozone and Water Vapor Monitoring Using a Ground-Based Lidar System.- 5.6 The NASA/Goddard Balloon Borne Lidar System.- 6 Laser Sources and Detectors.- 6.1 Development of Compact Excimer Lasers for Remote Sensing.- 6.2 Solid-State Laser Sources for Remote Sensing.- 6.3 Progress in Laser Sources for Remote Sensing.- 6.4 Review of NDRE Remote Sensing Program and Development of High Pressure RF Excited CO2 Waveguide Lasers.- 6.5 Progress in Dye and Excimer Laser Sources for Remote Sensing.- 6.6 IR Detectors: Heterodyne and Direct.- 7 Advanced Optical Techniques.- 7.1 Optical Remote Sensing of Environmental Pollution and Danger by Molecular Species Using Low-Loss Optical Fiber Network System.- 7.2 In situ Ultratrace Gas Detection by Photothermal Spectroscopy: An Overview.- 7.3 Laser-Induced Breakdown Spectroscopy (LIBS): A New Spectrochemical Technique.- 7.4 The High Spectral Resolution Lidar.- 8 Lidar Technology.- 8.1 Lidar Measurements of Clouds.- 8.2 Coherent IR Radar Technology.- 8.3 Tactical and Atmospheric Coherent Laser Radar Technology.- 8.4 Atmospheric Remote Sensing Using the NOAA Coherent Lidar System.- 8.5 Coherent CO2 Lidar Systems for Remote Atmospheric Measurements.- 8.6 Wide-Area Air Pollution Measurement by the NIES Large Lidar.- 8.7 ALPHA-1/Alarm Airborne Lidar Systems and Measurements.- Index of Contributors.

Development of a tunable, narrow-linewidth, cw 2.066-μm Ho:YLF laser for remote sensing of atmospheric CO 2 and H 2 O

A smoothly tunable, narrow-linewidth, cw, 32-mW, 2.066-mum Ho:YLF laser was constructed and used for the first time in preliminary spectroscopic measurements of atmospheric CO(2) and H(2)O. The laser was constructed with a 4.5-mm-long, TE-cooled, codoped 5% Tm and 0.5% Ho yttrium lithium fluoride crystal (cut at Brewsters angle) pumped by an Ar(+)-pumped 500-mW Ti:sapphire laser operating at 792 nm. Intracavity etalons were used to reduce the laser linewidth to approximately 0.025 cm(-1) (0.75 GHz), and the laser wavelength was continuously and smoothly tunable over approximately 6 cm(-1) (180 GHz). The Ho:YLF laser was used to perform spectroscopic measurements on molecular CO(2) in a laboratory absorption cell and to measure the concentration of CO(2) and water vapor in the atmosphere with an initial accuracy of approximately 5-10%. The measurement uncertainty was found to be due to several noise sources, including the effect of asymmetric intensity of the laser modes within the laser linewidth, fluctuations caused by atmospheric turbulence and laser beam/target movement, and background spectral shifts.

Remote probing of the atmosphere using a CO 2 DIAL system

An overview of our laser remote sensing effort is presented. Using both fundamental and frequency-doubled CO 2 laser radiation in a differential absorption LIDAR (DIAL) system, background concentrations of CO, NO, and C 2 H 4 in the atmosphere as well as increases due to localized emission sources have been measured. These species have been detected using the backscattered laser radiation from topographic targets at ranges to 2.7 km with a sensitivity of ± 10 ppb. In addition, using a dual-laser DIAL system, the effect of induced correlation of the LIDAR returns due to atmospheric turbulence has been investigated. These results have been used to help quantify the accuracy of the DIAL measurements and are shown to be consistent with theory.

Enhancement of Nd:YAG LIBS emission of a remote target using a simultaneous CO(2) laser pulse.

For the first time to the best of our knowledge, a simultaneous 10.6 mum CO(2) laser pulse has been used to enhance the Laser Induced Breakdown Spectroscopy (LIBS) emission from a 1.064 mum Nd:YAG laser induced plasma on a hard target. The enhancement factor was on the order of 25 to 300 times, depending upon the emission lines observed. For an alumina ceramic substrate the Al emission lines at 308 nm and Fe impurity line at 278 nm showed an increase of 60x and 119x, respectively. The output energy of the Nd:YAG laser was 50 mJ/pulse focused to a 1 mm diameter spot to produce breakdown. The CO(2) laser pulse had a similar energy density of 40 mJ/mm(2). Timing overlap of the two laser pulses within 1 microsecond was important for enhancement to be observed. An observed feature was the differential enhancement between different elemental species and also between different ionization states, which may be helpful in the application of LIBS for multi-element analysis.

Laser Remote Sensing of the Atmosphere

Laser beams can be used as long-range spectroscopic probes of the chemical composition and physical state of the atmosphere. The spectroscopic, optical, and laser requirements for atmospheric laser remote sensing are reviewed, and the sensitivity and limitations of the technique are described. A sampling of recent measurements includes the detection of urban air pollution and toxic chemicals in the atmosphere, the measurement of global circulation of volcanic ash in the upper atmosphere, and the observation of wind shear near airports.

Temporal correlation measurements of pulsed dual CO 2 lidar returns

The temporal correlation and statistical properties of backscattered returns from specular and diffuse topographic targets have been measured by using a pulsed dual-laser direct-detection lidar system operating near 10.6 microm. Our results show that atmospheric-turbulence fluctuations can effectively be frozen for pulse separation times of the order of 1-3 msec or less. However, only incomplete correlation was achieved; the diffuse target returns yielded much lower correlation than that obtained with the specular targets. This is shown to be due to uncorrelated system noise effects and different statistics for the two types of target returns.

Limitations of signal averaging due to temporal correlation in laser remote-sensing measurements.

Laser remote sensing involves the measurement of laser-beam transmission through the atmosphere and is subject to uncertainties caused by strong fluctuations due primarily to speckle, glint, and atmospheric-turbulence effects. These uncertainties are generally reduced by taking average values of increasing numbers of measurements. An experiment was carried out to directly measure the effect of signal averaging on back-scattered laser return signals from a diffusely reflecting target using a direct-detection differential-absorption lidar (DIAL) system. The improvement in accuracy obtained by averaging over increasing numbers of data points was found to be smaller than that predicted for independent measurements. The experimental results are shown to be in excellent agreement with a theoretical analysis which considers the effect of temporal correlation. The analysis indicates that small but long-term temporal correlation severely limits the improvement available through signal averaging.

Laser remote sensing of hydrazine, MMH, and UDMH using a differential-absorption CO 2 lidar

A dual mini-TEA CO(2) laser differential-absorption lidar system has been used to test the remote sensing of hydrazine, unsymmetrical dimethylhydrazine (UDMH), and monomethylhydrazine (MMH) in atmospheric conditions. Average concentrations of these compounds were measured using backscattered laser radiation from a target located at a range of 2.7 km. The experimental results indicate that average atmospheric concentration levels of the hydrazine compounds of the order of 40-100 ppb can be detected over ranges between 0.5 and 5 km. The level of concentration sensitivity over this interval was found to be limited primarily by atmospheric fluctuations. An investigation of the effect of these fluctuations on measurement uncertainties indicated that the fluctuations reduce the benefits of signal averaging over N pulses significantly below the expected square root of N improvement. It is also shown that uncertainties due to long-term atmospheric drifts can be effectively reduced through use of dual-laser lidar return ratios.

Remote sensing of NO using a differential absorption lidar

Single-ended remote sensing measurements of atmospheric NO have been made using differential absorption of frequency-doubled pulsed CO(2) laser radiation backscattered from topographic targets. Returns were obtained from targets at ranges out to 1.4 km, and significant NO concentrations above ambient were observed over a path which crossed a traffic roadway at a range of 0.5 km. In view of the severe atmospheric water vapor absorption in the spectral region containing the NO absorption band, the range dependence of the lidar returns was also measured in order to determine the differential absorption of the ambient atmosphere.The results differed significantly from those computed from atmospheric transmission data tapes.