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

0

5000

10000

15000

0 200 400 600 800 1000 1200 1400 1600

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

0

5000

10000

15000

0 200 400 600 800 1000 1200 1400 1600

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

0

20000

40000

60000

80000

200 400 600 800 1000 1200 1400 1600 1800 2000

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

0

5000

10000

15000

20000

25000

200 400 600 800 1000 1200 1400 1600

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

0

50000

100000

150000

200000

500 1000 1500 2000 2500

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

0

10000

20000

30000

40000

200 400 600 800 1000 1200 Raman Shift (cm-1)

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

0

20000

40000

60000

100 200 300 400 500 600 700 800 900 1000

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

0

500000

1000000

1500000

0 200 400 600 800 1000 1200 1400 1600 1800

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

0

200000

400000

600000

800000

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Acetone

Water

2-propanol

Raman Shift (cm-1)

Inte

nsity

(a.u

.)

10 s

0

500000

1000000

1500000

2000000

2500000

3000000

0 500 1000 1500 2000 2500 3000 3500 4000

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

0

200000

400000

600000

800000

0 500 1000 1500 2000 2500 3000 3500 4000 4500

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

*

0

1000000

2000000

3000000

4000000

5000000

6000000

7000000

500 1000 1500 2000 2500

Ammonium Nitrate

Raman Shift (cm-1)

Inte

nsity

(a.u

.)

5” System

8” System

50 m

•Signal is proportional to size of collection optics

0

20000

40000

60000

80000

100000

120000

200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400

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

0

2000

4000

6000

8000

10000

500 1000 1500 2000 2500

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

0

20000

40000

60000

80000

200 400 600 800 1000 1200 1400 1600 1800 2000

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