No Slide Title
Final Report Performance of a cryogenic multipath Herriott cell
Vacuum coupled to the Bruker 125HR system at JPLArlan W. Mantz1,
Keeyoon Sung2, Tim J. Crawford2, Linda R. Brown2, Mary Ann H.
Smith3, V. Malathy Devi4, D. Chris Benner41Dept. of Physics,
Astronomy and Geophysics, Connecticut College, New London, CT2Jet
Propulsion Laboratory/California Institute of Technology, Pasadena,
CA3Science Directorate, NASA Langley Research Center, Hampton,
VA4Dept. of Physics, The College of William and Mary, Williamsburg,
VA 23187
69th Meeting - June 16-20, 2014 - Champaign-Urbana, IL TI07
#/13JPLAdvantages of FT-IR + Herriott cellFT-IR with a white
lightBroad-band spectroscopy securing high level of consistency
(frequency, line to line, band to band intensity, etc.)Multiplex
advantage leading to high S/NRadiometric stability enabling long
integrationHerriott cellVirtually everything is in one
materialSimpler and robust design (over White cell) - Two mirrors
onlyLess susceptible to opto-mechanical disturbance alignment
preservesAll materials are identical - uniform coolingCompact
design saving space/sample gas - efficient coolingShortcoming over
White-type cellAbsorption path length is fixed.Beam alignment is
difficult for a converging beam (e.g. sharing one hole).FT-IR +
Herriott cell Ideal for spectroscopy at cold temperaturesStudy of
temperature-dependent molecular line parameters
69th Meeting - June 16-20, 2014 - Champaign-Urbana, IL TI07
#/13JPLHerriott cell in a simple designMirror distance, dTwo
concave spherical mirrors, focal length = fCurvature, RrMirror
separated by distance, dEntrance hole ( in dia.) at r away from the
centerFocal length, f = R/2Ang. Dist. each pass, Closure
constraints cos = 1 d/2f N = 2 k Total path inside the cell L = Nd
+ Nr4/(8df 2)69th Meeting - June 16-20, 2014 - Champaign-Urbana,
Illinois 3/12 F
Herriott cellCNot to scale
69th Meeting - June 16-20, 2014 - Champaign-Urbana, IL TI07
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Herriott Cell InstallationHyperboloid
Beam spots simulatedHerriott cell parameters# of passes N 62
Focal length125 mm Center-to-center distance337.031mmEntrance/Exit
hole diameter4 mmExtra path due to window22.25 mmTotal path at 293
K, L293K20.941 mTotal path at 100 K, L100K20.882 mTwisting angle
per pass, 110.37closure constraint and offset = N = k 2,(k
=19)6842.94 = 2.94
Movie from Wikipedia
69th Meeting - June 16-20, 2014 - Champaign-Urbana, IL TI07
#/13JPLEntrance hole () size (in ) 9.02 Hyperboloid of one sheet,
x2/a2 + y2/b2 z2/c2 = 1
From the topFrom the side[Not to scale]
Ray tracing and beam couplingCoupler vacuum tankBruker sample
compartmentThe Herriott cellInterferometerThe Herriott cell
installed
69th Meeting - June 16-20, 2014 - Champaign-Urbana, IL TI07
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Pathlength validation(using single spectrum fit, fov = 1.244
mrad) Experimental inputs in common: L = 21.005 m (assumed)12CO
(99.999%)P = 28.33 TorrT = 297.1 KRes.=0.012 cm-1 Absorption
pathlength = 21.005 * (1. 0.008) = 20.837 ( 0.147) m %discrepancy =
-0.5 ( 0.7) % from the optically determined L = 20.941 m12CO
(99.999%)P = 28.33 TorrT = 297.1 KRes.=0.012 cm-1
69th Meeting - June 16-20, 2014 - Champaign-Urbana, IL TI07
#/13JPLTemperature control of the cellBodyOxygen Free High
Conductivity copper#Volume3.23 L (Cavity)0.008 L (inlet
tube)MirrorsBare gold (4 in. dia.); R = 0.99Cell Window CaF2
(wedged, 30, Qty. = 1)Vacuum boxCaF2 (wedged, 30, Qty. = 1)Cooling
systemCTI Cryogenics9600 He-compressor; 1020 CP CryopumpRefrig.
agentHelium (99.9999%)Heater capacity25 W 2Temp. sensorsilicon
diode (accuracy of 0.125K)Temp. achieved75 250 K and 296 KTemp.
control$< 0.05 K for days#Thermal conductivity, among the best
in the range 70 < T < 300 (better than Al and Au)$Achieved by
PID (Proportional, Integrate and Differentiate) temperature control
loop adopted in a Model 331 temperature controller supplied by
Lakeshore Cryotronics, Inc.
Excellent temperature stability0.05 K / days
Compressor and chiller
69th Meeting - June 16-20, 2014 - Champaign-Urbana, IL TI07
#/13JPLMake the font bigger in the green boxAssumption: Cell T =
Gas T Investigated four cases between 300 and 79 K
Ratio of line intensity at two different temperaturesSubscript R
for Reference data set Subscript X for Measurement data set
SX/SR = QR/QX exp{c2 E" (1/TX 1/TR)} [1 exp(-c2 v/TX)]/[1exp(-c2
v/TR)]
Solve for Rotational temperature, TX, iteratively log(SX/SR)
log(QR/QX) c2E"(1/TX 1/TR)
Validation of the temperature assumption
69th Meeting - June 16-20, 2014 - Champaign-Urbana, IL TI07
#/13JPLKin.TRad.TRot.TVib.TTDE.T
8
Validation of the gas temperaturesGas temperature offsets for
CO
Effective gas temperature Higher by ~0.5 K at room Temperature
Lower by ~0.4 K at T ~ 80 K Other experimental factors Sensor
location / cooling time / sample gas/pressure / cryodeposits
etc.Temp. ReadingsRot.Temp(CO)Rot.Temp(CO2)Offsets(CO;
CO2)300.4(0.1)301.2(1.4)300.6(1.4) 0.8;
0.2250.0(0.1)250.1(0.2)249.9(0.2) 0.1;
-0.1179.3(0.1)179.0(0.2)179.1(0.1) - 0.3; 0.1 78.8(0.1) 78.2(0.2)
78.6(0.2) - 0.6; -0.2Rot.Temp Temp.Readings!! Agree within ~ 0.5 K
!!
69th Meeting - June 16-20, 2014 - Champaign-Urbana, IL TI07
#/13JPLNOTE: These are not the 13CH4 runs: should indicate this in
words.9Sample spectrum ICold 12CO2/Air for the OCO-2 mission
L = 20.941 m
69th Meeting - June 16-20, 2014 - Champaign-Urbana, IL TI07
#/13JPLSample spectrum IIStudy of weak bands of CH4
Transition with higher ETransition with lower E
69th Meeting - June 16-20, 2014 - Champaign-Urbana, IL TI07
#/13JPLSummary and future workHerriott cell developed and
integrated to FT-IRDeveloped and installedCharacterized to be L =
20.941 m, T = 296, 250 75 K (or colder)Excellent radiometric
stability (Througtput =~ 50 %; S/N =300 :1; vibrational
perturbation mitigated)Report results (Mantz, et al., Submitted to
JMS)
Data acquisition at JPLAir-broadened cold CO2 and CO2
isotopesAir-broadened cold O2Air-broadened cold CH4 and isotopes,
etc.
Future workEnabling cryogenic spectroscopy in the
near-infraredCollisional cooling studyCollision-induced
absorption
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The team and Acknowledgements
AcknowledgementsResearch described in this talk was performed at
Connecticut College, the College of William and Mary, NASA Langley
Research Center and the Jet Propulsion Laboratory, California
Institute of Technology, under contracts and cooperative agreements
with the National Aeronautics and Space
Administration.KeeyoonLindaTimArlanMary Ann
ChrisMalathy
69th Meeting - June 16-20, 2014 - Champaign-Urbana, IL TI07
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