This overview covers progress in the following areas in which Pacific Northwest Laboratory contributes to the CALIOPE Program: (1) Fabrication of electro-optic modulators to generate FM-coding on IR lasers in the 8-12 and 3-5 {mu}m regions. (2) IR spectroscopy of signature species, abnormal isotopic distributions, hydrolysis and kinetics of effluents interacting with the atmosphere, and reflectance measurements of natural surfaces. (3) Systems analysis of FM-DIAL concepts, including lateral phase coherence and MTF measurements, and laboratory tests of detector technology and demodulation methods. (4) Field tests of FM-DIAL, covering field validation of portable diode laser concepts, FM-CO{sub 2} interrogation of Hanford sites, and signal returns from natural specular surfaces. (5) Ancillary matters: ground-truthing at Hanford (and RSTR?), countermeasures, and new laser design concepts

Kelly, J.F.

McDowell, R.S.

Sharpe, S.W.

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c.!Cw&-q 50 3 I 'c 3 - -6 PNL-S A-2 62 5 4 PACIFIC NORTHWEST LABORATORY CALIOPE OVERVIEW R. S. McDowell J. F. Kelly S. W. Sharpe March 1995 Presented at the CALIOPE Interim Technical Review Conference March 27-3 1, 1995 . Albuquerque, New Mexico Prepared for the U.S. Department of Energy under Contract DE-AC06-76RLO 1830 Pacific Northwest Laboratory Richland, Washington 99352 ST I DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. PACIFIC NORTHWEST LABORATORY CALIOPE OVERVIEW Robin S. McDowell,? James F. Kelly,$ and Steven W. Sharpet ?Environmental Molecular Sciences Laboratory and 5 Materials and Chemical Sciences Center Pacijk Northwest Laboratory* Richland, Washington 99352 This overview covers progress in the following areas in which Pacific Northwest Laboratory contributes to the CALIOPE Program: (1) Fabrication of electro-optic modulators to generate FM-coding on IR lasers in the 8-12 and 3-5 jt.m regions. (2) IR spectroscopy of signature species, abnormal isotopic distributions, hydrolysis and kinetics of effluents interacting with the atmosphere, and reflectance measurements of natural surfaces. (3) Systems analysis of FM-DIAL concepts, including lateral phase coherence and MTF measurements, and laboratory tests of detector tech- nology and demodulation methods. (4) Field tests of FM-DIAL, covering field validation of portable diode laser concepts, FM-C02 interrogation of Hanford sites, and signal returns from natural speculat surfaces. (5)  Ancillary matters: ground-truthing at Hanford (and RSTR?), countermeasures, and new laser design concepts. ELECTRO-OPTIC MODULATORS Frequency modulation (FM) will be covered extensively by J. F. Kelly in a talk on Thursday and in the poster ses- sion. PNL has been developing FM techniques for remote sensing of weak IR absorptions using FM-coded single- line lasers. Such Fh4 coding offers potentially high common-mode rejection of noise introduced by the effects of propagation through the inhomogeneous atmosphere. We have been investigating FM modulation at both 8-12 pm (for C0,-based FM-DIAL) and 3-5 pm (for tunable solid-state OPOs), using newly-developed high-power tunable semiconductor.diode lasers as seed sources. For gas-discharge lasers, external cavity modulation using bulk transverse CdTe EOMs is the most promising; these can be made with high uniformity and finished and coated to very exacting tolerances. They can also be staged for high efficiency, since the modulation scales as length squared when the RF and optical fields ate correctly phased. For the 3-5 pm region such modulator crystals as KNb03, LiTa03, and KTP have been investigated, but none can now be supplied reliably for the fabrication of high-Q bulk phase modulators. Possible solutions include LiNbO3, and newly-developed high-qudity aIkali-titanyl-arsenate crystals with high damage thresholds and good dielectric loss tangents. INFRARED SPECTROSCOPY Infrared spectroscopy will be discussed in more detail in a talk by S. W. Sharpe on Thursday. PNL has a unique high-resolution infrared spectroscopy laboratory that includes a Bruker IFS 120HR Fourier-transform infrared (FTIR) spectrometer (1-1000 pm, resolution to 0.0017 cm-l'or 50 MHz), two tunable diode laser (TDL) systems (3.3-33 pm, resolution e10 MHz), two beam expansion sources to achieve temperatures of -10 K in gas samples without * Pacific Northwest Laboratory is a multipurpose national laboratory operated for the U.S. Department of Energy by Battelle Memorial Institute under contract DE-AC06-76RLO 1830. condensation, and a complement of gas cells with optical paths of up to 100 m. We have used these facilities to pur- sue several areas of infrared research on high-value effluents and signature species. A signature that may be indicative of certain industrial processes is carbon tetrachloride, which has a rich and com- plex infrared spectrum (due to coupled modes of vibration, a variety of stable isotopomers, and unfavorable vibra- tional and rotational partition functions) that has never been subjected to a full rotation-vibration analysis. We have performed such an analysis of three infrared bands of C35C14: v3 at 799 cm-', v1 + v4 at 774 cm-*, and v4 at 3 16 crn-'. The derived spectroscopic and molecular constants enable us to model accurately the CC14 band contours and absorption intensities under various atmospheric conditions in a plume or stack emission. There is at least one region of overlapping Qbranch lines in an atmospheric window that is suitable as an analytical frequency for sensi- tive remote detection and monitoring. Other possible signature species have been and are being investigated, including certain organophosphates and rare isotopically-substituted species of small molecules. Interest in the latter arises from the fact that photolytically- and thermally-driven dissociation reactions and the formation of small effluent molecules may exhibit kinetic isotope effects that change the natural isotopic abundances enough to be detectable by infrared and Raman spectroscopy. Molecules of special interest in this connection include CO from graphite-moderated reactor operations, NH3 from heavy-water production and processes using nitric-acid baths, nitrogen oxides (NO, NO2, N20, HN03) from nitric- acid baths, O3 from the operation of heavy electrical equipment, and H2S from heavy-water operations. We have also made high-resolution reflectance measurements on the wavelength dependence of albedos of natural surfaces. We will shortly begin high-resolution spectroscopic and kinetic studies of the hydrolysis kinetics of UF6 vapor reacting with the atmosphere. SYSTEMS ANALYSIS OF FM-DIAL CONCEPTS Under conditions of retro-reflection (which might include the clever use of natural or artificial glints) to eliminate speckle and albedo variations, the power received scales, according to the LIDAR equation, as the product of the transmitter, receiver, and reflector areas. Thus lateral phase coherence becomes an important consideration for direct or coherent detection strategies. We have investigated methods of measuring the dimension of the lateral phase coherence (the Fried parameter TO), both by direct imaging to determine the modulation transfer function (MTF) of the turbulent atmosphere, and by experiments on the minimum detectable separation of LEDs. These mea- sures are being correlated with each other and with observed signal degradation. Laboratory tests of detector technology and of direct and coherent detection methods include: *Autodyne detection in laser diodes. *Fast heterodyne detection in extrinsically-doped Ge or Si devices capable of fast response. *Possible use of a fast IR detector as a photomixer. FIELD TESTS Our field efforts in FM-DIAL are concentrated in the three areas of field validation of portable laser diode concepts, FM-COz transception from Rattlesnake Mountain over the Hanford tank farms, and investigation of signal returns from "natural" specular surfaces. The appeal of laser diode techniques is that modulation for 2f detection is easily accomplished, and new develop- ments in these devices may provide sufficient power to probe over distances of some kilometers in the near future. Areas of particular interest include: *HCl at 3.6 pm to check IR transmissiordpropagation issues with an available InSb IR CCD camera. *C-H stretches at 2930 cm-I to study hydrocarbon interferences and detection scaling laws in an atmospheric cut- *NH3 at 1.5 pm: a simple, sensitive detection scheme for ammonia. *HF at 1.3 pm to check effects of water interference on detection scaling laws. off region. Rattlesnake Mountain provides a view over the Hanford Reservation with a slant path to the tank farms of ca. 15 km. We plan to install a stabilized line-tunable CW C02 laser at the Rattlesnake Mountain Observatory to interrogate the atmosphere over the tank farms. All major equipment has been received and most is assembled. Final questions being addressed before fielding this equipment include refinement of the beam steering and correcting systems, and improved vibration isolation. Signal returns from “natural” specular surfaces could reduce albedo variance problems and avoid possible sanction- ing considerations, and are being evaluated using laser-diode-based transceivers to image returns in the near and mid IR. We also intend to use a CO, system with thermal imaging cameras. ANCILLARY MATTERS The IR Sniffer, which uses tunable semiconductor diode lasers and low-pressure sampling for continuous ultrasensi- tive analysis of atmospheric species, has demonstrated routine analytical capabilities for such molecules as N20 and O3 at sub-ppb levels. Grab samples taken downwind from Hanford tank farms for Sniffer analysis in the laboratory have yielded interesting results that are pertinent to questions of possible countermeasures against remote monitor- ing. A field-deployable Sniffer is under development that will provide ultrasensitive real-time analysis of various trace species of interest, and which can be used for ground-truthing at Hanford and similar waste sites, or for rnoni- toring O3 levels at the RSTR. - Finally, we have been exploring new laser concepts of possible interest in CALIOPE operations: alexandrite-based systems with linewidths to 5 MHz that can easily be injection-seeded with laser diodes, and which can drive an OPO for better conversion to 3-5 pm; ring-based IR OPOs; and “high-temperature” IR laser diodes now under develop- ment in several industrial laboratories, which might provide remote detection capabilities over kilometer distances with broad, frequency-agile tuning. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsi- bility for the accuracj, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer- ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom- mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. 

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