Instrumentation for 

Bench- and Large-scale Test FixturesKevin L. McNesbyU. S. Army Research LaboratoryAberdeen Proving Ground, MD.Erik JohnssonNISTGaithersburg, MD

Army Research Laboratory (APG, MD)

Chapter Title:
3.C - Laser-Based Instrumentation for R

In-Situ Measurements of Combustible GCombustion By-Products, & SuppressiConcentrations

Army Research Laboratory (APG, MD)

Project working title:Kevin McNesby, Erik Johnsson, George Mulholland, Reed Skaggs, Andrzej Miziolek, Edwin Lancaster, Robert Daniel,Bill Bolt, Craig Herud, Brian Kennedy
OPTICAL SPECTROSCOPIC TECHNIQU

ARMY APPLICATIONS

Army Research Laboratory (APG, MD)

Working Description:Kevin McNesby, Reed Skaggs, Andrzej Miziolek, Erik Johnsson, George Mulholland, Edwin Lancaster, Robert DaniBill Bolt, Craig Herud, Brian Kennedy, Bill Jackson, Ian McLaren, DSteve Modiano
• joint, effort at ARL (Army Research Labo(Aberdeen Test Center), NIST Using OpticSpectroscopy •(FY97-02)• work focussed on needs pertaining to ar• field-scale to laboratory scale environme

Army Research Laboratory (APG, MD)
Talk Outline

3⁄4 Introduction – Tanks3⁄4 Species (Suppressants; Toxic By-pro

Fuels; Oxidizers)

3⁄4 Fast Vibrational/Visible Spectroscopy3⁄4 Differential Infrared Rapid Agent Conce

Sensor (DIRRACS)

3⁄4 Laser Induced Breakdown Spectroscopy 

Explosive Suppressant Measureme

3⁄4 Diode Laser Spectroscopy for Toxic an

Combustible Gas Measurement

Army Research Laboratory (APG, MD)
Differential Infrared Rapid Agent Conce

Sensor (DIRRACS)3⁄4Measurement of suppressant concentration3⁄4Previous instrument response time ~ 200 ms (viscosity sensor)3⁄41 ms response time3⁄4Infrared absorption3⁄4Insensitivity to vibration

HFC 125

Ins
DIRRACS II Schematic
DIRRACS II Instrument
DIRRACS II Test Rig

Transient Application Recirculating Pool Fire(TARPF) Facility at NIST.
DIRRACS Testing

HFC 125 agent volume fraction versus time for two rHFC-125 in the TARPF facility.

Time ResSensitivit
Suppressant Gas Measure

Laser Induced Breakdown Spectro

• Plasma Formation

– Multiphoton Absorptio– Absorption of Laser R

i.e. Inverse Brehmstra

– Electron Collisions --> 

Breakdown

– Typical Gas Temperat

• Spectrochemical Analysis 

Emission of Atomic and Moafter Plasma Continuum Rusec).

Army Research Laboratory (APG, MD)
LIBS Instrumentation

1064 nm Pulsed Laser Radiation

Spectrograph

Gated Intensified Camera

FocusiLens

Collimator / FibeCoupler

Army Research Laboratory (APG, MD)
LIBS of DMMP

2

0

5000

10000150002000025000

210 220 230 240 250 260 270 

Wavelength (nm)

Signal IntensityP

C

Army Research Laboratory (APG, MD)
LIBS of Fire Suppressa

0

0 2000 4000 6000 8000 10000 

Concentration (ppm)

Signal Intensity (arbitrary units) FM-200 H

Army Research Laboratory (APG, MD)
Toxic and Combustible Gas Measureme

Infrared Tunable Diode Laser (TDL) Spec

HF, O

2 , CO, CH

4, HCl, other small molecules

789

10111213141516

7665.5 7665.51 7665.52 7665.53 7665.54 7665

Wavelength (nm)

Signal at Detector (V)

Wavelength Modulation Spectroscopy

Transmission - no modulation

Transmission - with modulation (note RAM)

Demodulated 
HF Gas Measurement During SupTesting

0

50

100

 5000 

%Transmittance

wa

-200

0

200400600800

100012001400

0 50 100 150 200

Time, seconds

Average HF Concentration, ppm

FE-36FE-36 + 7 % APPFE-36 + 15 % APP

Figure 2

Army Research Laboratory (APG, MD)
Oxygen Measurement Using TDL S

Oxygen Absorption Nea1

Σg

+

↔3

Σg

- )

0.00E+00

1.00E-052.00E-053.00E-054.00E-055.00E-056.00E-057.00E-05

13123.6

13131.4

13139.2

Wave

Intensity

Oxygen Concentration

1012141618202224

0 100 200 300 400 500 600 700 800 900

Time (seconds)

% Oxygen

JP-8 - air fire, inhibition by C3F8 , crew compartment

test fixture, fire extinguished 150 ms after detection.

X .001

Army Research Laboratory (APG, MD)
Laser

LaserLaser

FiberMixer

λ1λ2λ3

Dem

Multiple Species Gas Sensing UDiode Lasers (TDL)

Fiber tofree space

Free spaceto fiber

Mod

1

Mod 2

Mod 3

(lock-inWDM, e
Time Division Multiplexin

Diode laser Detector

A/D D

Semi-conductor diode laser

lens

Fiber optic cab

Fiber optic cable
Spectrum of dry air saturated at 294K with vapor from unlea

gasoline, JP-8, DF2. Spectra offset for clarity. 

0

20406080

100120140160

1.2 1.7 2.2 2.7 3.2 

Wavelength (micrometers)

%

T

r

a

n

s

m

i

s

s

o

i

n

Detection and Measurement of Middle DFuel Vapors Using Tunable Diode Lase
Limitations of TDL Spectroscopy For Measurement of High Molecular Weight 

Absorption features are unstructured.Can’t use traditional wavelength or fremodulation techniques to measure bi(e.g., middle distillate fuels - JP-8, DFUnable to scan on and off resonance DFB laser.Develop a near-infrared diode laser-bsensor capable of measuring hydrocavapor concentrations with a time resoof 10 msec per measurement point; madvantages of WMS.
Measurement Techniq

uses laser diode absorption spectroscopy in the near

microns and 1.71 microns)

Emission intensity from two lasers is varied sinusoidfrom first laser 180 degrees out of phase with emissiMeasurement is made in situ.Phase sensitive detection is used to measure differentwo laser emission wavelengths.10 msec response time
Oscilloscope Lock-in Amplifier

GRIN 

InGaAs Detector

4 m optical cell 

Laser 11.31microns

FunctionGenerator 1

LaserDriver 1

Laser 21.71microns

FunctionGenerator 2

LaserDriver 2

Figure 3: The experimental apparatus used to mvapors from middle distillate fuels.

Laser Mixing Apparatus
-0.1

0

0.10.20.30.4

1.2 1.3 1.4 1.5 1.6 1.7 

Wavelength (micrometers)

Absorbance

Laser 1 Laser 2

Gasoline vapor

JP-8 vapor

DF-2 vapor

Figure 4: shows the vapor phase absorption spectrum 

by vapor at 294K from JP-8, DF-2, and gasoline betwevalues of 1.3 and 1.75 micrometers superimposed upo

from the optical fiber which carries the mixed waveleng

Overlap of Fuel Absorbance Spand Mixed Laser Probe Beam
0

2000400060008000

1000012000

0 100 200 300 40

Time (sec)

Gasoline Vapor (ppm)

gasoline

O

2

Simultaneous measurement of fuel/oxygen concentration (by displacement of contents (dry air) of a 14 liter vessel by air savapor at 294K and 1 atmosphere total pressure. Oxygen sensof Oxigraf, Inc.

Results: Approach to Lower Ex(LEL) in a Gasoline Fuel Tank at 
Results: “Aging” of JP-8 Det

Mixed Laser Sensor

0

500

10001500200025003000

0 1000 2000 3000 

ppm JP-8 Vapor

Time (s)

Fresh samp

Sam
fixm

beam splitter

to detector

from 

For a monochromatic source:

I(σ) = I(ν)cos2πνσ

For a polychromatic source:

I(σ) = ∫ I(ν)cos2πνσ d ν

0∞

σ= mirror positionν = light frequency (cm-1)

I(σ) = intensity at detectorI(ν) = source intensity

FT Diode Laser Spectroscopy
3.22 μ

3.24 μ3.26 μ

3.28 μ

IC, QC laser

lens

Analyte region 

FT Diode Laser Spectro
2.50E-02

2.70E-022.90E-023.10E-023.30E-023.50E-023.70E-023.90E-024.10E-024.30E-024.50E-02

0.00E+00 4.00E-04 

-1.00E+02-9.00E+01-8.00E+01-7.00E+01-6.00E+01-5.00E+01-4.00E+01-3.00E+01

2.00E+04 4.00E+04 6.00E+04 8.00E+04 

Intensity (a.u)

Time (sec)

Intensity (a.u)

Frequency (sec-1)

FT Diode Laser Spectro

Signal at detectorLaser 1 (100 KHz) at 1.31μLaser 2 (110 KHz) at 1.71 μ

Fourier transform ofsignal at detector (res.= 100 Hz)
8.00E-01

8.50E-019.00E-019.50E-01

1.00E+001.05E+001.10E+00

9.50E+04 9.90E+04 1.03E+05 1.07E+05 

0

0.010.020.030.040.050.060.070.080.09

0 500 1000 1500 

Fraction Transmitted

Frequency (sec-1)

Absorbance

Time (sec)

Absorption of laser radiation at 1.71μ as air

in 2m cell is displacedby air saturated withgasoline vapor.

FT Diode Laser Spec

LEL
Conclusions/Successes/Failu

3⁄4Project greatly enhanced knowledge of f

on board combat vehicles.

3⁄4Laser diode systems fielded at ATC/ARL 3⁄4DIRRACS II testing at WPAFB.3⁄4FTLS work continues.3⁄4JP-8 sensor vibration problems3⁄4COF

2 formation documented
Conclusions/Successes/Failures 

3⁄4Lasers outside communication bands sexpensive3⁄4Mid-IR RT CW lasers still unreliable3⁄4Narrow BW, broadly tunable, fast light sunavailablePublications9 open literature, 1 book chapter, 11 Gov
Acknowledgements

Dick Gann, NISTGamboa InternationalLawrence Ash, NAWCOxigraph, Inc.