Dr. Alan Fried Profile

Dr. Alan Fried

Techn Development Facility Manager at National Ctr for Atmospheric Research

SPIE Involvement:

Author

Proceedings Article | 26 January 2009 Paper

Airborne atmospheric research using mid-infrared laser spectroscopy

Alan Fried, Petter Weibring, Dirk Richter, James Walega

Proceedings Volume 7222, 722202 (2009) https://doi.org/10.1117/12.803634

KEYWORDS: Spectroscopy, Sensors, Spectroscopic atmospheric monitoring techniques, Mid-IR, Absorption, Signal detection, Interference (communication), Fiber lasers, Laser spectroscopy, Beam splitters

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Proceedings Article | 13 February 2008 Paper

Mid-infrared QPM laser sources for high-precision atmospheric trace gas measurements

Dirk Richter, Petter Weibring, Alan Fried, James Walega, Osamu Tadanaga, Masaki Asobe, Hiroyuki Suzuki

Proceedings Volume 6875, 68750J (2008) https://doi.org/10.1117/12.762294

KEYWORDS: Absorption, Mid-IR, Laser crystals, Crystals, Laser sources, Waveguides, Spectrometers, Sensors, Atmospheric sensing, Fiber lasers

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Proceedings Article | 25 October 2006 Paper

Tunable diode laser and difference frequency generation absorption spectrometers for highly sensitive airborne measurements of trace atmospheric constituents

Alan Fried, Petter Weibring, Dirk Richter, James Walega, Chad Roller, Frank Tittel

Proceedings Volume 6378, 63780F (2006) https://doi.org/10.1117/12.691318

KEYWORDS: Sensors, Absorption, Signal detection, Spectrometers, Mirrors, Tunable diode lasers, Difference frequency generation, Atmospheric sensing, Calibration, Semiconductor lasers

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Proceedings Article | 23 September 2002 Paper

Optimization of cw-QC lasers for Doppler and sub-Doppler molecular spectroscopy

James Kelly, Robert Disselkamp, Robert Sams, Thomas Blake, Steven Sharpe, Dirk Richter, Alan Fried

Proceedings Volume 4817, (2002) https://doi.org/10.1117/12.452124

KEYWORDS: Modulation, Quantum cascade lasers, Frequency modulation, Doppler effect, Fermium, Absorption, Amplitude modulation, Sensors, Spectroscopy, Signal to noise ratio

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Inter-subband (Type I) quantum-cascade (QC) lasers have shown the potential to generate tunable mid-IR radiation with narrow intrinsic linewidths (< 160 KHz in 15 mSec sweeps) and excellent amplitude stability (< 3 ppm averaged over minutes). Our bench-scale efforts to develop the Type I distributed feedback (DFB)-QC lasers for fieldable atmospheric chemistry campaigns, where multipass (Herriot or White) cells are used to enhance path-length, have not yet realized performance to the low intrinsic noise levels seen in these devices. By comparison, many operational systems' levels of noise-equivalent-absorbance (NEA) using Pb-salt lasers can routinely achieve at least one-order of magnitude better cw-performance, and with much lower powers. We have found that instability effets from weak back-scattered laser light -primarily from the Herriot cell- results in feedback-implicated technical noise well above the thermal and shot-noise of standard IR detectors. Of more fundamental concern is the fact that planar-stripe DFB-QC lasers undergo beam steering and transverse spatial-mode competitions during current tuning. It is the development of fully automated sub-ppbV sensitive IR chem-sensors. It is possible to reach low-ppm levels of absorptance change-detection (ΔI/I₀) over small wavelength regions with careful alignment to 100 M Herriott cells, but extreme care in spatial filtering is critical. However in the case of optical configurations which preclude significant optical feedback and need for stringent mode coupling alignments, the cw-DFB-QC lasers show great promise to do high resolution sub-Doppler spectroscopy. By serendipitous events, a varient of 'mode- or level-crossing' spectroscopy was probably rediscovered, which may allow very high resolution, sub-Doppler features and/or hyperfine alignments to be probed with 'uni-directional' topologies. We will primarily discuss the basic features of the 'uni-directional' sub-Doppler spectroscopy concept in this report. It shows potential to be exploitable in multi-pass cells or ring configurations. The phenomena of satuation 'dips' in molecular transitions appear to be very accessible with sinusoidally current-modulated DFB-QC lasers. Observations of sub-Doppler structures, either induced by residual AM 'pulsation dips' and/or hyperfine level-crossing effects (due to weak Zeeman splittings by the earth's B-field) can be recovered with good contrast. If this phenomena is indeed implicated with long-lived coherent hyperfine alignments, due perhaps to coherent population trapping in 'dark-states,' then sub-Doppler signals from saturated 'level-crossings' can potentially be seen without recourse to expensive polarization optics, nor elaborate beam shaping and isolation techniques.

Proceedings Article | 23 September 2002 Paper

Airborne measurements of formaldehyde employing a high-performance tunable diode laser absorption system

Alan Fried, Bryan Wert, James Walega, Dirk Richter, William Potter

Proceedings Volume 4817, (2002) https://doi.org/10.1117/12.452084

KEYWORDS: Absorption, Tunable diode lasers, Temperature metrology, Calibration, Hydrogen, Off axis mirrors, Absorbance, Laser systems engineering, Atmospheric chemistry, Oxidation

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Proceedings Article | 23 September 2002 Paper

Tunable optical fiber pumped difference frequency laser sources: state of the art

Dirk Richter, Alan Fried, Frank Tittel

Proceedings Volume 4817, (2002) https://doi.org/10.1117/12.452082

KEYWORDS: Mid-IR, Spectroscopy, Laser sources, Semiconductor lasers, Absorption, Optical fibers, Fiber lasers, Calibration, Optical amplifiers, Carbon monoxide

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Proceedings Article | 25 October 1999 Paper

Enhancement of a tunable diode laser tropospheric trace gas measurement system

Bryan Wert, Alan Fried, Bruce Henry, James Drummond

Proceedings Volume 3758, (1999) https://doi.org/10.1117/12.366441

KEYWORDS: Tunable diode lasers, Hydrogen, Sensors, Gas lasers, Troposphere, Molecules, Thermography, Mirrors, Glasses, Absorption

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Proceedings Article | 25 October 1999 Paper

Airborne tunable diode laser measurements of formaldehyde during the 1997 North Atlantic Regional Experiment

Alan Fried, Bryan Wert, Bruce Henry, James Drummond, Gregory Frost, Yin-Nan Lee

Proceedings Volume 3758, (1999) https://doi.org/10.1117/12.366440

KEYWORDS: Tunable diode lasers, Spatial light modulators, Calibration, Atmospheric chemistry, Chemistry, Gases, Hydrogen, Troposphere, Atmospheric sciences, Oxidation

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Proceedings Article | 4 May 1998 Paper

Airborne tunable diode laser measurements of trace atmospheric gases

Alan Fried, Bryan Wert, Bruce Henry, James Drummond

Proceedings Volume 3285, (1998) https://doi.org/10.1117/12.307602

KEYWORDS: Gases, Carbon monoxide, Calibration, Tunable diode lasers, Atmospheric chemistry, Atmospheric sensing, Ozone, Data acquisition, Mirrors, Sensors

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Proceedings Article | 21 October 1996 Paper

Flash photolysis/tunable diode laser absorption spectroscopy studies of HCl as a product of the reactions: Cl + C2H6 and Cl + CH3CHO

Carla Kegley-Owen, Geoffrey Tyndall, John Orlando, Alan Fried

Proceedings Volume 2834, (1996) https://doi.org/10.1117/12.255316

KEYWORDS: Chlorine, Semiconductor lasers, Photolysis, Absorption, Excimer lasers, Absorption spectroscopy, Tunable diode lasers, Chemistry, Chemical reactions, Atmospheric chemistry

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Proceedings Article | 21 October 1996 Paper

Airborne measurements of tropospheric formaldehyde by tunable diode laser absorption spectroscopy

Bryan Wert, Alan Fried, Bruce Henry, James Drummond

Proceedings Volume 2834, (1996) https://doi.org/10.1117/12.255323

KEYWORDS: Contamination, Tunable diode lasers, Chemistry, Absorption spectroscopy, Ozone, Calibration, Atmospheric chemistry, Carbon monoxide, Absorption, Oxidation

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Proceedings Article | 21 October 1996 Paper

Ground-based tunable diode laser measurements of formaldehyde: improvements in system performance and recent field campaigns

Alan Fried, Scott Sewell, Bruce Henry, Bryan Wert, James Drummond

Proceedings Volume 2834, (1996) https://doi.org/10.1117/12.255322

KEYWORDS: Calibration, Tunable diode lasers, Absorption, Absorption spectroscopy, Spectroscopy, Photochemistry, Atmospheric chemistry, Laser spectroscopy, Optical filters, Semiconductor lasers

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Proceedings Article | 27 July 1994 Paper

Studies at the National Center for Atmospheric Research employing tunable diode laser absorption spectroscopy

Alan Fried, Bruce Henry, Scott Sewell, James Drummond

Proceedings Volume 2138, (1994) https://doi.org/10.1117/12.181351

KEYWORDS: Aerosols, Tunable diode lasers, Earth's atmosphere, Absorption spectroscopy, Spectroscopic atmospheric monitoring techniques, Stratosphere, Atmospheric particles, Atmospheric sensing, Troposphere, Atmospheric chemistry

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Proceedings Article | 3 June 1994 Paper

Field diode laser spectrometer employing an astigmatic Herriott cell

Scott Sewell, Alan Fried, Bruce Henry, James Drummond

Proceedings Volume 2112, (1994) https://doi.org/10.1117/12.177287

KEYWORDS: Mirrors, Semiconductor lasers, Calibration, Spectroscopy, Absorption, Laser spectroscopy, Laser systems engineering, Optical alignment, Absorbance, Data acquisition

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Proceedings Article | 26 January 1994 Paper

Laboratory and field tunable diode laser measurements of trace atmospheric species and processes of importance to the stratospheric aerosol sulfate layer

Alan Fried, Bruce Henry, Scott Sewell, Jack Calvert, James Drummond, Michael Mozurkewich

Proceedings Volume 2205, (1994) https://doi.org/10.1117/12.166201

KEYWORDS: Aerosols, Atmospheric particles, Tunable diode lasers, Climatology, Ozone, Earth's atmosphere, Spectroscopic atmospheric monitoring techniques, Absorption spectroscopy, Gases

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Proceedings Article | 1 May 1991 Paper

Tunable diode laser spectrometer for high-precision concentration and ratio measurements of long-lived atmospheric gases

Alan Fried, James Drummond, Bruce Henry, Jack Fox

Proceedings Volume 1433, (1991) https://doi.org/10.1117/12.46161

KEYWORDS: Data acquisition, Gases, Control systems, Modulation, Tunable diode lasers, Computing systems, Feature extraction, Sensors, Mirrors, Laser systems engineering

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