Spectroscopy: Lecture 7 - SOEST · 2015. 6. 29. · - UH remote Raman system in field during dust...
Transcript of Spectroscopy: Lecture 7 - SOEST · 2015. 6. 29. · - UH remote Raman system in field during dust...
Anupam K. MisraHIGP, University of Hawaii, Honolulu, USA
Spectroscopy: Lecture 7
Remote Raman Spectroscopy
www.soest.hawaii.edu\~zinin
GG 711: Advanced Techniques in Geophysics and Materials Science
Daytime rapid detection of Minerals and organics
University of Hawaii
* Detection time: 1 Second
Remote Raman Spectroscopy
* Range: Up to 125 m
: some chemicals even with single laser shot.
Raman spectra Vibrational modes of molecules
Incident Light
Energy
Elastic Scattering (Mie-Rayleigh)
Strong Phenomenon
Inelastic scattering(Raman)
Weak Phenomenon
StokesAnti-Stokes
Raman Effect: (Discovered by C. V. Raman 1928 )
Depends on atomic mass, bond lengths, bond strength, configuration, etc…
Unique spectrum for each chemical
Commercial (traditional) Raman system (after 1962)
CW Laser
CCD
Notch/edge Filter
Sample
Beam splitter
Spectrograph
C. V. Raman 1928
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Raman Shift (cm-1)
Inte
nsity
(a.u
.)Typical Raman spectra
801
Cyclohexane C6H12
1085
Calcite CaCO3
Laser at 0 cm-1
Not
ch fi
lter
GeoPhysics (HIGP), Univ. of Hawaii
Daytime conditions
Raman Shift (cm-1)
Inte
nsity
(a.u
.)Issues with daytime Raman spectra
801
Cyclohexane C6H12
1085
Calcite CaCO3
Laser at 0 cm-1
Not
ch fi
lter
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CCD over saturated
1. Background too strong2. Raman signal too weak.
* Kaiser F/1.8 Holospec Spectrometer
* Laser: 532 nm, Nd:YAG, PULSED, 20 Hz, 8 ns
* Telescope = 5” or 8” (Maksutov-Cassegrain, Meade)
* ICCD detector (gated), Princeton Instruments
Remote Raman Instrument What do you need for daytime measurements
Remote Raman System Design
Key components: (1) High power pulse laser(2) Beam expander (3) Telescope(4) Highly efficient Spectrograph (VPG)(5) ICCD (gated detection)
(1)(2)
(4)
(5)
(3)
U. of Hawaii Raman Lab
Lightening Condition
Operating Modes:
* CW (lights on)
* CW (lights off)
* Gated (lights on)
Calciteat 10 m, 1 s.
• Provides High Signal to Background
Pulsed-Laser
Telescope
ICCD
50 m
Laser pulse width = 10 ns (half width)
Time of arrival for first Raman Photon = 100 m ÷ 3x108
= 0.33 µs
Gate Width = 20 ns + τ (Raman) ≈ ( 20+ ) ns
Simplified concept
Background
Pulsed-Laser
Telescope
Spectrograph
ICCD
50 m
Laser pulse rate = 20 HzT = 1s means 20 measurements
In 400 ns all the Raman photons were countedBackground collection time = Gate width *20
≈ ( ) ns
Pulsed-Laser
Telescope
Spectrograph
ICCD
50 m
Laser pulse energy = 20 mJ
Power = Energy/time = 20 mJ x 20 Hz = 0.4 W
!!! Actually very large number of Photonsper pulse (in 20 ns)
• High Signal to Background• Very few cosmic ray peaks
Low Background
Large Signal
Remote Raman Systems developed at UH
• 5” system (532 nm) (fiber optic coupled) (NASA)• 5” system (532 nm) (direct coupled) (NASA)• 8” system (532 nm) (ONR)• 8” UV system (248 nm) (ONR)• 16” UV system (248 nm) (JIEDDO)• 8” Raman+LIBS system (ONR)• 2” system (532 nm) (NASA)
5” Remote Raman System
For Official Use Only
Holmes Hall (128 m)
8” Remote Raman System
Remote Raman ApplicationsCapabilities & data
As recorded data shown without any processing
Raman Shift (cm-1)
1 pulse, 50 m
Inte
nsity
(a.u
.)
1 pulse, 100 m
85
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Single pulse Remote Raman Spectra of Naphthalene C10H8
50 m
100 m
109
390
513
763
947
1021
1147
1165
1382
1465
1578
1631
20 mJ/pulse, 532 nm, 8 ns pulse width, gate width 2 µs, 8” telescope, 100 µm slit
Daytime
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Raman Shift (cm-1)
Nitrobenzene C6H5NO2
X0.2
Daytime Remote Raman spectra from 100 m, 1 sIn
tens
ity (a
.u.)
Nitromethane CH3NO2
O2
1556
483 65
6
917
1033
Met
hano
l
853
1376
1401
1003
1109 13
47
612
39617
8
1524 15
88
20 mJ/pulse, 532 nm, 8 ns pulse width, gate width 2 µs, 8” telescope, 100 µm slit
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Raman Shift (cm-1)
Inte
nsity
(a.u
.) NH4NO3
KClO4
138
168
717
1044
1288
O2
1556
462
630
928
941
1086
1123
N2
2331
O2
N2
Daytime Remote Raman spectra from 100 m, 1 s
20 mJ/pulse, 532 nm, 8 ns pulse width, gate width 2 µs, 8” telescope, 100 µm slit
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Sulfuric acid
Nitric acid
Acids at 50 m , 1sIn
tens
ity (a
.u.)
347
418
557
736
910
977
1046
686 95
5 1044
1304
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Raman Shift (cm-1)
50 m
Single Pulse spectra of Sulfur from 50 and 100 mIn
tens
ity (a
.u.)
100 m
85
153 21
9
473
Application : Geology
2”system using 85 mm camera lens
Detection at 50 m
Detection of home made explosive chemicals
532 nm system, 50 ns gate width, 20 Hz, 30 mJ/pulse
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KClO4
KNO3
NH4NO3
10 s integration
Raman Shift (cm-1)
Inte
nsity
(a.u
.)
2” remote Raman system daytime at 50 m
•Provides clear sharp peaks for chemicalidentification with high SNR
2” remote Raman system daytime at 50 m
•Can measure through plastic and glass bottles
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Acetone
Water
2-propanol
Raman Shift (cm-1)
Inte
nsity
(a.u
.)
10 s
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Benzene
Ethyl benzene
Nitrobenzene N
O
O
Raman Shift (cm-1)
Inte
nsity
(a.u
.)
10 s
2” remote Raman system daytime at 50 m
•Can easily distinguish between very similar chemicals
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Target with atmosphere, 350 ns
Atmosphere before target, 310 ns
Target (Gypsum at 50 m, 10s)
Target, 50 ns
Raman Shift (cm-1)
Inte
nsity
(a.u
.)2” remote Raman system at 50 m
•Can measure target, atmosphere, and both
O2H2O
N2
* Atmospheric Rotational bands
*
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Ammonium Nitrate
Raman Shift (cm-1)
Inte
nsity
(a.u
.)
5” System
8” System
50 m
•Signal is proportional to size of collection optics
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Single Pulse Raman Excitation, 532 nm8% RDX on silica, 9 m
35 mJ
94 mJ
Double 94 mJ
Raman Shift (cm-1)
Inte
nsity
(a.u
.)
885
848
591,
606
464
347
946
1031
226
1216
1274
159414
3513
8813
10
•Signal is proportional to laser pulse power
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Cyclohexane, 50 m
Raman Shift (cm-1)
1 pulse
1 Second
Inte
nsity
(a.u
.)
383 42
6
801
1027
1157
1266
1347
1443
O2 15
56
N2
2331
•Signal is proportional to number of laser pulses
532nm, 20 Hz laser, 1 s = 20 pulses
Raman Shift (cm-1)
1 pulse, 50 m
Inte
nsity
(a.u
.)
1 pulse, 100 m
85
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20000
40000
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Single pulse detection of Naphthalene C10H8
50 m
100 m
109
390
513
763
947
1021
1147
1165
1382
1465
1578
1631
20 mJ/pulse, 532 nm, 8 ns pulse width, 8” telescope
•Signal is inversely proportional to distance
811
1532
1209
1357
1615
1556
(O2)
811
1532
1209
1357
1615
1556
(O2)
811
1532
1209
1357
1615
1556
(O2)
1556
(O2)
885
1216
1275
1310
Raman Shift (cm-1)
1556
(O2)
885
1216
1275
1310 15
56 (O
2)
885
1216
1275
1310
Raman Shift (cm-1)
Successful field test for chemical detection
during dust storm
December 2007 Fort Irwin, Mojave Desert
University of Hawaii Raman Group
Show Video (57 seconds long) of - UH remote Raman system in field during dust storm- Single pulse spectra of gypsum at 50 m
(measurements through two ¼” thick glass windows)
December 2007 Fort Irwin, Mojave Desert
University of Hawaii Raman Group