PNNL-13501 - Pacific Northwest National Laboratory

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containing nitrous oxide, an optical cavity (with piezo adjustable end mirror), and a digital oscilloscope used for data averaging and export to a computer. Liquid nitrogen cooled HgCdTe photovoltaic detectors are used with custom-built low-noise preamplifiers. The optical cavity used in this work incorporated plano-concave ZnSe mirrors (radius = 100 cm) with a reflectivity of 99.85%. The cavity itself consists of a 40-cm stainless steel tube with vacuum-sealable mirror mounts (incorporating a piezo element used to modify the cavity length). Approximately 4 MW of infrared emission is collimated from the quantum cascade laser, 10% of which is diverted to a reference cell for wavelength calibration prior to the optical cavity. Figure 1. Experimental infrared integrated cavity absorption spectrometer layout Since the cavity length is 40 cm and the radius of curvature of the resonator mirrors is 100 cm, a myriad of longitudinal modes of the cavity are seen (in transmission) as the wavelength of the quantum cascade laser is scanned. Typical scans (accomplished by applying a sawtooth modulation on the injection current) are up to 0.5 cm -1 at a repetition rate of 1 to 10 kHz. At first, this quasi-continuum of transmission modes may seem to be detrimental to the absorption measurement; however, if the optical cavity is being used to increase the effective path length, then the higher number of modes is advantageous. If fact, our apparatus is intentionally misaligned (to reduce back-reflections to the laser) and the spatial mode profile of the quantum cascade laser is non-optimal for coupling to the primary mode of the cavity. These two effects act to increase the number of accessible modes of the cavity. During an experiment, the cavity length is dithered (typically 10 to 100 Hz) using various waveforms that are not synchronized to the wavelength scan of the laser. Therefore, when many cavity transmission scans are averaged on the digital oscilloscope, the resulting spectrum appears as a nearly flat baseline with a small direct current offset, rather than the multitude of sharp cavity resonance peaks. The lower panel in Figure 2 compares a signal-sweep trace and an averaged trace (2500 sweeps) of the cavity transmission with 100 ppmv of nitrous oxide present in cavity. The upper panel in Figure 2 shows an expanded version of the averaged data. Cavity Transmission Single Sweep 2500 averages 1172.1 1172.4 Laser Frequency ν (cm -1 ) Figure 2. Lower panel depicts a comparison of single (gray) and averaged (black) transmission spectra with approximately 100 ppmv of nitrous oxide present in the cell at 25 torr. Upper panel is an expanded version of the averaged trace. As can be seen in the upper panel in Figure 2, the noise floor is very regular and is similar to etaloning commonly seen in laser absorption measurements. In this case, the periodicity of the baseline fluctuations results from an incomplete averaging of clusters of cavity modes. Ideally, the cavity modes would be uniformly spaced in the transmission spectra. Conventional cavity modes calculations support this observation and suggest that this effect can be dramatically reduced using a slightly shorter cavity. The effective path length (i.e., cavity-enhancement factor) of this arrangement was found by multiplying the cavity length by the ratio of cavity-enhanced absorbance to the single-pass absorbance (found by replacing the mirrors with plain windows). The comparison of the cavityenhanced absorption spectrum with the single-pass absorption is shown in Figures 3a and 3b, respectively. The effective path length in the cavity-enhanced case was found to be 38 meters (cavity-enhancement factor of ~90). This initial effective path length can be improved upon with the use of high reflectivity mirrors; a factor of ten improvement would yield path lengths not easily obtained with multi-pass cells. Sensors and Electronics 385
Absorbance 0.006 0.004 0.002 0.000 (a) Cell Length (b) No Cavity = 0.4 meters With Cavity CEF ~ 90 Laser frequency Summary and Conclusions Laser frequency Effective Pathlength = 38 meters Figure 3. Comparison of single-pass (3a) and cavityenhanced (3b) absorption spectra for same nitrous oxide line under the same conditions (100 ppmv in 25 torr air). The cavity-enhancement factor (CEF) is given by the ratio of the two measurements. The first phase of the instrument development has been accomplished and initial results are very encouraging. Technical milestones that have been reached include • integration of infrared system components (quantum cascade laser, detectors, optical cavity) 386 FY 2000 <strong>Laboratory</strong> Directed Research and Development Annual Report 0.5 0.4 0.3 0.2 0.1 0.0 Absorbance • an effective path length of 38 meters has been obtained from a 40-cm cell • cavity mode calculations have identified optimal cavity configurations. Our goal for continuation of this project will be to increase the effective path length of the instrument and to make field atmospheric measurements. References Capasso F, C Gmachl, D Sivco, et al. 1999. “Quantum Cascade Lasers.” Physics World 12:27. Engeln R, G Berden, R Peeters, et al. 1998. “Cavity enhanced absorption and cavity enhanced magnetic rotation spectroscopy.” Review of Scientific Instruments 69(11):3763-9. O’Keefe A, JJ Scherer, and JB Paul. 1999. “CW Integrated Cavity Output Spectroscopy.” Chem. Phys. Lett. 307:343-349.
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Laboratory Directed Research and De
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Laboratory Directed Research and De
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Computational Science and Engineeri
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Policy and Management Sciences Asse
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Introduction Department of Energy O
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5. After reviews by the Technical a
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• The Technical Council peer revi
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methods applicable to combustion, s
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Summary Each national laboratory mu
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Study Control Number: PN0004/1411 A
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Table 1. Positive and negative ions
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m/z Arbitrary Units Figure 1. Mass
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introduce low-volatility compounds
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arrangement, but the charge is reta
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two liquid chromatographic gradient
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Integrated Microfabricated Devices
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Matrix Assisted Laser Desorption/Io
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Molecular Beam Synthesis and Charac
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temperature distribution of the des
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expected to result in significant a
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Study Control Number: PN99069/1397
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Seuss DT and KA Prather. 1999. “M
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Analysis of Receptor-Modulated Ion
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laboratory (Lu and Xie 1997; Lu et
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Automated DNA Fingerprinting Microa
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Comparison of 4 Xanthomonas Isolate
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Approach Hematopoietic (bone marrow
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Anti-Human lgG Human lgG Protein G
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Characterization of Global Gene Reg
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PCR products for immobilization on
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identify novel proteins of importan
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Immunoprecipitaton of tyrosinephosp
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Coupled NMR and Confocal Microscopy
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In the optical microscopy image, th
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Development and Applications of a M
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Figure 3. Hepa-1 cells undergoing a
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cellular processing (such as post-t
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8. Initial demonstration of an off-
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expression systems for several year
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accumulation of protein products, i
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Fungal Conversion of Agricultural W
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Fungal Conversion of Waste Glucose/
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Summary and Conclusions We demonstr
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are shown in Figure 1(a) and 1(b),
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Anchorage-Independent Growth (% con
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selection of seedlings demonstratin
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NMR-Based Structural Genomics Micha
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Solution-State Structure and Fold-C
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Plant Root Exudates and Microbial G
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Summary and Conclusions • The gre
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Jones-Oliveira JB, JS Oliveira, HE
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• securely moves files to a targe
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Plenary invited lecture, “The Ele
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Figure 1. X3DGEN tetrahedral mesh o
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Figure 5a. OSO volume rendering of
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Development of Models of Cell-Signa
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SOS p 23 EGFR Professor Rodland at
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Oliveira JS, JB Jones-Oliveira, and
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Figure 2. Associating a dataset mar
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shown in Figure 1. Simulated result
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HostBuilder: A Tool for the Combina
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Invariant Discretization Methods fo
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Graphics, Inc., workstation. The co
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Mixed Hamiltonian Methods for Geoch
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guyanaite, and grimaldiite (see Fig
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in the Environmental Molecular Scie
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Simulation and Modeling of Electroc
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Summary and Conclusions We implemen
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Since the implementation of the gen
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asis of previous performance, perce
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Bioinformatics for High-Throughput
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Summary and Conclusions In previous
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User Cat - Supervisor (client) Anal
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The second goal was to research way
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Figure 1. A visualization technique
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and interactions. The flexibility o
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Figure 4. A filtered version of Fig
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Development of Modeling Tools for J
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Figure 2. Schematic of experimental
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Integrated Modeling and Simulation
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(a) (b) (c) (d) Figure 1. Results o
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Thurman DA. August 2000. Collaborat
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MARC Input initial m esh and result
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(Johnson 1999; Colligan 1999; Gould
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Modeling of High-Velocity Forming f
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Global divergence error 1 10 -14 0
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that users were unlikely to appreci
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Earth System Science
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the lateral extent of the plume so
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Biogeochemical Processes and Microb
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Analyses of populations of viable a
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The first task was to establish fiv
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purged for 2 minutes. The gas sampl
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developing code architecture to min
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Berkowitz, CM. June 2000. “Atmosp
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environmental monitoring, 2) portab
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corresponded to a current density o
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Enhancing Emissions Pre-Processing
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Environmental Fate and Effects of D
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nitrogen and unpredictable eutrophi
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Figure 1. Ordinary kriging of 2 m d
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precipitation of calcite occurred i
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Interrelationships Between Processe
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phenanthrene resistant fraction con
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injection of an immiscible gas phas
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still some key kinetic issues that
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Application of a Crop Model The res
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The Nature, Occurrence, and Origin
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Particle number concentration, 1/cm
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geometry optimized AlOOH and FeOOH
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allowable parameters using thermody
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TCE + 3H + + 3Fe 2+ Fe)=> acetylene
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Use of Shear-Thinning Fluids for In
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concentration of 0.5% AMX was the m
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Roberts AL, LA Totten, WA Arnold, D
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tetra-scale computing, envisioned a
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Energy Technology and Management
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Figure 2. Setup for the second expe
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phase. The algorithms will be teste
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[Pb-212]/[Pb-212] final 100 10 1 0.
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Plasma Particle Dielectric Fiber El
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(species, sub-species, and sex), sp
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Figure 3. Relative risk of bone and
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Development of a Preliminary Physio
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Development of a Virtual Respirator
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Figure 3. Use of the chest cavity a
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Examination of the Use of Diazolumi
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Indoor Air Pathways to Nuclear, Che
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Source Building Release Observed re
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To illustrate the potential impact
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Non-Invasive Biological Monitoring
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Materials Science and Technology
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Figure 1. (a) - (c) Successive magn
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Component Fabrication and Assembly
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Development of a Low-Cost Photoelec
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elaxations, indicating the adequacy
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Promising chemical durability, as m
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Study Control Number : PN98028/1274
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High Power Density Solid Oxide Fuel
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Hybrid Plasma Process for Vacuum De
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Matson DW, PM Martin, WD Bennett, J
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We showed the proof-of-principle ap
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Figure 1. Thermogravimetric analysi
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Validation and Scale-Up of Monosacc
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Concentration (g/100g solution) Con
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Analysis of High-Volume, Hyper-Dime
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ecent figure of merit values. Shoul
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Probabilistic Methods Development f
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a) Traditional PCA-based process co
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Acronyms and Abbreviations 2-D two-
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