Laser-Based Instrumentation for Real-Time, In-Situ 

Measurements of Combustible Gases, Combustion 

By-Products, and Suppression 

Concentrations During Fire Suppression

by Kevin L. McNesby, Ph.D., R. Reed Skaggs, Ph.D., 

and Andrzej W. Miziolek, Ph.D. 

ARL-TR-3004 July 2003 

Approved for public release; distribution is unlimited. 
NOTICES 

Disclaimers 

The findings in this report are not to be construed as an official Department of the Army position unless 

so designated by other authorized documents. 

Citation of manufacturer’s or trade names does not constitute an official endorsement or approval of the 

use thereof. 

Destroy this report when it is no longer needed. Do not return it to the originator. 
Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5066 

ARL-TR-3004 July 2003 

Laser-Based Instrumentation for Real-Time, In-Situ 

Measurements of Combustible Gases, Combustion 

By-Products, and Suppression 

Concentrations During Fire Suppression 

Kevin L. McNesby, Ph.D., R. Reed Skaggs, Ph.D., 

and Andrzej W. Miziolek, Ph.D. 

Weapons and Materials Research Directorate, ARL 

Approved for public release; distribution is unlimited. 
ii

Report Documentation Page Form Approved 

OMB No. 0704-0188

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering 

and maintaining the data needed, and completing and reviewing the collection information. Send comments regarding this burden estimate or any other aspect of this collection of 

information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 

1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty 

for failing to comply with a collection of information if it does not display a currently valid OMB control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 

1. REPORT DATE (DD-MM-YYYY)

July 2003 

2. REPORT TYPE 

Final 

3. DATES COVERED (From - To) 

October 1997–October 2000 

5a. CONTRACT NUMBER 

5b. GRANT NUMBER 

4. TITLE AND SUBTITLE 

Laser-Based Instrumentation for Real-Time, In-Situ Measurements of Combustible 

Gases, Combustion By-Products, and Suppression Concentrations During Fire 

Suppression 

5c. PROGRAM ELEMENT NUMBER 

5d. PROJECT NUMBER 

622618H8000 

5e. TASK NUMBER 

6. AUTHOR(S) 

Kevin L. McNesby, Ph.D., R. Reed Skaggs, Ph.D., and Andrzej W. Miziolek, Ph.D. 

5f. WORK UNIT NUMBER 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 

U.S. Army Research Laboratory 

ATTN: AMSRL-WM-BD 

Aberdeen Proving Ground, MD 21005-5066 

8. PERFORMING ORGANIZATION 

 REPORT NUMBER 

ARL-TR-3004 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S) 

Strategic Environmental Research and Development Program 

901 North Stuart St., Suite 303 

Arlington, VA 22203 

11. SPONSOR/MONITOR'S REPORT 

 NUMBER(S) 

12. DISTRIBUTION/AVAILABILITY STATEMENT 

Approved for public release; distribution is unlimited. 

13. SUPPLEMENTARY NOTES 

14. ABSTRACT 

This report describes results of a 3-year program to investigate applications of laser-based instrumentation to real-time 

measurements of combustible gases, combustion by-products, and suppression concentrations during suppression of fires and 

explosions. This program was sponsored by the Department of Defense Strategic Environmental Research and Development 

Program. 

15. SUBJECT TERMS

laser-based measurements, fire suppression, diode lasers, Halons, fuel vapors 

16. SECURITY CLASSIFICATION OF: 

19a. NAME OF RESPONSIBLE PERSON

Kevin L. McNesby 

a. REPORT 

UNCLASSIFIED 

b. ABSTRACT 

UNCLASSIFIED

c. THIS PAGE 

UNCLASSIFIED

17. LIMITATION 

OF ABSTRACT 

UL 

18. NUMBER 

OF PAGES 

40 19b. TELEPHONE NUMBER (Include area code) 

(410) 306-0715 

Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18
iii

Contents 

List of Figures v

List of Tables vi

1. Summary of Task Objectives 1

1.1 FY97–FY98.....................................................................................................................1 

1.2 FY99–FY00.....................................................................................................................1 

1.4 General Methodology......................................................................................................3 

1.5 Technical Results ............................................................................................................3 

2. Detailed Description of Project 4

2.1 Species of Interest: LOD ................................................................................................4 

2.2 LIBS ................................................................................................................................4 

2.3 2F Tunable Diode Laser Absorption Spectroscopy (TDLAS)........................................5 

2.3.1 Stand-Alone Spectrometer System for HF Gas Measurement..............................5 

2.3.2 Results of HF Measurement Using Single Gas Stand-Alone Spectrometer 

System 7 

2.3.3 Multiposition, Multigas Spectrometer System......................................................8 

2.3.4 Results Using the Multiposition, Multigas Spectrometer System.........................9 

2.4 Real-Time Fuel/Oxygen Sensor ....................................................................................10 

2.4.1 Background .........................................................................................................11 

2.4.2 Measuring Broad Band Absorbers With Narrow Band Lasers ...........................12 

2.4.3 Experimental Apparatus......................................................................................14 

2.4.4 Results .................................................................................................................15 

2.5 Second Generation Sensor Development ........................................................................18 

2.5.1 Results of Prototype Testing of Second-Generation Sensor System ..................19 

2.5.2 Sensitivity............................................................................................................21 

2.5.3 Future Developments ..........................................................................................21 

3. Technical Problems 22

4. Conclusion 23
iv

5. Milestones 23

5.1 FY 97.............................................................................................................................23 

5.2 FY 98–99.......................................................................................................................24 

6. Significant Project Results: Discussion and Recommendations 26

7. References 28

Bibliography 31
v

List of Figures 

Figure 1. A schematic of a TDLAS measurement of gases produced during fire suppression 

on board Army vehicles.............................................................................................................2 

Figure 2. A schematic of a LIBS measurement for gas measurement during fire suppression 

on board Army vehicles.............................................................................................................2 

Figure 3. LIBS of several fluorinated fire suppressants, measured in the vapor phase. The 

signal intensity is the peak F emission near 400 nm..................................................................5 

Figure 4. The signals produced at the detector as slow and fast laser modulations combined 

and the 2f signal produced by the lock-in amplifier, for a typical TDLAS measurement of 

HF gas. .......................................................................................................................................6 

Figure 5. HF gas produced during suppression of heptane pan fires by FE-36 with and 

without the addition of APP.......................................................................................................9 

Figure 6. Oxygen concentration measured within the crew compartment of a BFV during 

suppression (by C3F8) of a spark-initiated JP-8 spray fire.......................................................10 

Figure 7. FTIR spectra of dry air saturated at 294 K with vapor from unleaded gasoline, JP8, and DF2. Spectra are offset for clarity. Structured absorptions near 1.9 and 2.7 μm are 

from water vapor......................................................................................................................12 

Figure 8. A diagram of the laser mixing apparatus used to measure fuel vapor 

concentrations. .........................................................................................................................15 

Figure 9. The vapor phase absorption spectrum of air saturated by vapor at 294 K from JP-8, 

DF-2, and gasoline between wavelengths of 1.3 and 1.75 μm superimposed upon the 

emission from the optical fiber carrying the mixed wavelength laser beam. ..........................16 

Figure 10. Gasoline vapor concentration (measured using the mixed laser sensor) as dry air 

saturated by gasoline vapor slowly displaces (several hundred cm3/min) the dry air in a 

13.7-L volume optical cell. Also shown in this figure is the change in oxygen 

concentration that occurs during the displacement (DFB laser-based oxygen sensor, 

courtesy of Oxigraf, Inc., Mountain View, CA)......................................................................17 

Figure 11. Aging of JP-8 (loss of lighter hydrocarbons) caused by repeated fills of the 

optical cell used for testing the mixed laser fuel vapor sensor. ...............................................17 

Figure 12. The two-laser interferogram measured at the detector for the second-generation 

fuel vapor sensor......................................................................................................................19 

Figure 13. A schematic of the experimental apparatus used for FT-LS. ......................................20 

Figure 14. Absorption of laser radiation at 1.71 μm as air in 2-m cell is displaced by air 

saturated with gasoline vapor. For the absorbance calculation, the background was the 

demodulated signal for each laser prior to the onset of fuel vapor flow..................................20 

Figure 15. Schematic of a 10-laser FT-LS source in the near infrared (under development), 

providing reasonable coverage of the full overtone C-H absorption envelope for 

hydrocarbon vapors..................................................................................................................22 
vi

List of Tables 

Table 1. LOD using TDLAS and LIBS for various vapors. ...........................................................4 
1

1. Summary of Task Objectives 

This final report summarizes results of a multi-year project, the purpose of which was to 

implement laser-based instrumentation for real-time, in-situ measurements of combustible gases, 

combustion by-products, and suppression concentrations during suppression of flames and 

explosions on board U.S. Army combat vehicles. This effort directly addresses the statement of 

need for element 3.c of the Next Generation Fire Suppression Technology Program, administered 

by the Department of Defense Strategic Environmental Research and Development Program. The 

nominal project duration was from fiscal year 1997 (FY97) through FY99, although delays in 

accomplishing the goals set for the final year of the project required a no-cost extension through 

FY00. 

1.1 FY97–FY98 

The first two years of the project (FY97–FY98) focused on adaptation of near-infrared tunable 

diode laser absorption spectroscopy (TDLAS) for measurement of by-products produced during 

chemical flame suppression (e.g., hydrogen fluoride [HF]) over a 250-ms fire suppression period, 

such as experienced in crew compartments of military vehicles. Part of the testing program 

involved evaluating rugged, low-cost fiber-optics and couplings for transporting the near-infrared 

laser radiation from the diode laser (located at a safe distance from the measurement location) to 

the measurement location, and retrieving the signal. An additional part of the program for the first 

2 years involved the adaptation of laser induced breakdown spectroscopy (LIBS) for measuring 

suppression agent concentrations, starting with halogenated suppressants, and then using LIBS for 

measurement of oxygen concentrations. 

Following laboratory characterization, these diagnostics would be installed in the crew 

compartment test fixture at the U.S. Army Aberdeen Test Center (ATC) for full-scale fire 

suppressant testing. The ultimate goals of the first 2 years of the program were to understand why 

a suppressant is behaving well or poorly in full-scale suppression tests, for determining the 

repeatability of the tests, and for guiding optimization of agent distribution and dispersion. A 

simple schematic showing implementation of TDLAS and LIBS for gas measurement is shown in 

Figures 1 and 2. 

1.2 FY99–FY00 

The final year of the project (including the no-cost extension) concentrated on the development of 

a multipoint, field worthy, fiber-coupled, near-infrared tunable diode laser-based sensor for 

measurement and detection of combustible mixtures of oxygen and hydrocarbon fuels (heptane and 

JP-8). The goal of the project during this time was to build a sensor capable of quantitative 

measurement of fuel/oxygen concentrations before (minimum five data points prior to agent 

release), during, and after the suppression event (nominal event time equal to 250 ms) with a time 
2

Figure 1. A schematic of a TDLAS measurement of gases produced during fire suppression on 

board Army vehicles. 

1064 nm 

Pulsed Laser 

Radiation

Spectrograph

Gated Intensified 

Camera

Laser induced plasm a 

w ithin m easurem ent 

region

Focusing 

Lens

Collim ator / Fiber 

Coupler

Figure 2. A schematic of a LIBS measurement for gas measurement during fire 

suppression on board Army vehicles. 

resolution better than 10 ms. Detection of fuel and oxygen concentration is especially important 

after the suppression event in order to predict the possibility of reignition. Minimum acceptable 

detection limits for fuel/oxygen mixtures are ~600 ppm fuel (0.06%) and ~3000 ppm oxygen 

(0.3%), for a 10-cm path length at room temperature.

Laptop

Computer Oscilloscope Lock-inAmplifier

Gradient Index

(GRIN) Lens

InGaAs Detector

Tunable

Diode

Laser

Function

Generator 

Laser

Driver 

Fiber Optic

Measurement Region

(Light into free space)

(Light collection)
3

1.3 Technical Challenges 

The technical challenges faced during the first 2 years of the project were grouped into two broad 

categories. First, several challenges needed to be overcome relating to the ability to measure and 

store data continuously with a new data point acquired every 10 ms. Second, it was unclear how 

the sensor equipment would perform in the harsh environment for field testing, in which the 

sensor assembly in the vehicle was subjected to shock (explosion) and heat (fire). For the third 

year of the project, the main challenge was developing a method that enabled the narrow band 

light source (the diode laser) to measure a broadband absorber (JP-8 vapor), while maintaining 

the signal to noise enhancement achievable with phase sensitive detection (1, 2). 

1.4 General Methodology 

For the first 2 years of the project, the measurement techniques using near-infrared tunable diode 

lasers were based on well-established techniques (2, 3) for phase sensitive detection of gases that 

exhibit well-resolved rovibrational spectra. Typically, the protocol was measurement and 

calibration of a system (e.g., HF gas measurement by near-infrared TDLAS near a wavelength of 

1.31 μm, using 2f detection) in lab, followed by reinstallation of this system at the measurement 

site. During this time, LIBS experiments were carried out in the laboratory to determine 

measurement linearity and limits of detection for gaseous fire suppressants. For the third year of 

the program, most of the effort was devoted to method development within the laboratory 

(measurement of fuel vapors using distributed feedback diode lasers), with minimum time being 

spent at full-scale testing ranges. 

1.5 Technical Results 

A brief summary of technical results (excluding publications describing this work, which are 

listed separately) follows: 

• Four-position near-infrared tunable diode laser spectroscopy (NIR-TDLAS) system 

installed at ATC. 

• Tunable diode laser system for HF detection installed, calibrated, and tested in field and 

laboratory applications. 

• Comparative testing to determine limits of detection (LOD) of HF detection using NIRTDLAS, Fourier transform infrared spectroscopy (FTIR), and ion-selective electrode 

completed. 

• Laboratory measurement of LIBS spectra of CF3Br and FM-200 completed. 

• Measurement of near-infrared spectra of mixtures of methane and FM-200 for single laser 

detection completed. 

• Field worthy, mobile tunable diode laser system, with fieldable calibration system, 

completed, tested for HF measurement.
4

• Initial tunable diode laser-based oxygen measurements during crew compartment fire 

suppression system testing completed. 

• Time resolved measurements of HF dissipation during scavenging testing completed for 

FE-36 and FM-200. 

• Laboratory measurement of pyridine vapor using distributed feedback laser. 

• Simultaneous measurement of fuel/oxygen concentrations (100 ms/point) using distributed 

feedback diode laser for gasoline, DF-2, and JP-8. 

• Prototype Fourier transform laser spectrometer used to measure gasoline vapor 

concentrations. 

2. Detailed Description of Project 

In general, the first 2 years of the project involved transitioning proven laboratory-based methods 

(TDLAS employing phase-sensitive detection, LIBS) from the lab at the U.S. Army Research 

Laboratory (ARL) to the crew compartment fire test facility at ATC. 

2.1 Species of Interest: LOD 

LOD using TDLAS and LIBS for various vapors are listed in Table 1. All LOD values listed are 

(to our knowledge) best achievable laboratory values. In our experience, LODs in field 

measurement are always at least 1 order of magnitude worse than lab measurements. 

Table 1. LOD using TDLAS and LIBS for various vapors. 

Method Molecule Wavelength 

(μm) 

Approximate LOD 

TDLAS (4, 5) HF 1.31 0.04 ppm-m 

TDLAS (4, 5) O2 0.76 100 ppm-m 

TDLAS (4, 5) CH4 1.65 0.6 ppm-m 

TDLAS (4, 5) CO 1.55 5 ppm-m 

TDLAS (6) JP-8 1.71 100 ppm-m 

LIBS (7, 8) O2, CF3Br, CF3H Emission 1000 ppm-v 

Notes: ppm-m = parts per million-meters. 

ppm-v = parts per million-volume. 

2.2 LIBS 

A schematic showing the application of LIBS to gas measurement was shown in Figure 2. 

Briefly, a pulsed laser (typically Nd: YAG, pulse energy > 50 mJ) is brought to a focus in free 

space such that a breakdown occurs. The breakdown is believed to occur as follows. Initially, in 

the focal volume of the laser, the high electric field causes an ionization of a small number of gas 
5

molecules (usually air). Free electrons within this plasma may then absorb laser radiation 

(inverse Brehmstrahlung [9]) resulting in further ionization accompanied by collisional heating. 

Temperatures within the laser focal volume may reach 20000 K, resulting in atomization of any 

molecules within the focal volume (7, 8). After the laser pulse, rapid deceleration of the 

electrons within the plasma leads to an initial emission of broadband radiation (Brehmstrahlung 

[9]) lasting tens to hundreds of nanoseconds, followed by emission of discrete wavelengths of 

light as the atomic species present in the plasma return to their ground states (tens to hundreds of 

microseconds). 

The application of LIBS focused along two areas. First, the technique was used for measurement 

of linearity and determination of limits of detection for halogenated fire suppressants (7, 8). 

Figure 3 shows the LIBS spectra of several fluorinated fire suppressants, measured in the gas 

phase. The limits of detection for each gas, using LIBS, was ~1000 parts per million (ppmvolume). Figure 3 shows that the intensity of F emission measured using LIBS is nearly directly 

proportional to vapor concentration. 

LIBS of Fire Suppressants

0

0 2000 4000 6000 8000 10000 12000 14000 16000

Concentration (ppm)

Signal Intensity (arbitrary units)

FM-200

Halon-1301

Halon-14

HFC134a

Figure 3. LIBS of several fluorinated fire suppressants, measured in the vapor phase. 

The signal intensity is the peak F emission near 400 nm.

2.3 2F Tunable Diode Laser Absorption Spectroscopy (TDLAS) 

2.3.1 Stand-Alone Spectrometer System for HF Gas Measurement 

The TDLAS effort was focused in two areas. The first of these was an effort designed to 

measure HF concentrations during fire suppression testing, using a stand-alone spectrometer 

system assembled at the ARL. This system used a single distributed feedback (DFB) tunable 
6

diode laser emitting near-infrared radiation at a wavelength near 1.31 μm. This wavelength 

coincides with the P2 line of the first overtone absorption of HF gas, and is free of overlap by 

water lines present in most combustion environments (10). Typically, the laser was modulated 

(wavelength tuned) at 100 Hz for a range of ~0.5 cm!1

, such that the center of this tuning range 

coincided with the center of the absorption by the P2 transition in HF gas (absorption line width 

~0.1 cm!1

). Superimposed upon this “slow” modulation was a fast (50–100 KHz) sinusoidal 

wavelength modulation. The wavelength range of the fast modulation was adjusted so that it was 

a small (<0.25) fraction of the absorption line width of the P2 transition (first overtone) in HF 

gas. This dual modulated light beam was then launched onto an optical fiber and the fiber used 

to transmit the beam from a control room (located a safe distance from the measurement site) to 

the measurement site. For fieldwork, this usually meant the beam was transported ~100 m to the 

measurement site. At the measurement site, the fiber was terminated with a gradient index 

(GRIN) lens, causing the light beam to be collimated while it passed through free space (the 

measurement region). After passing through free space for ~10–15 cm, the modulated light 

beam impinged upon a semiconductor, room temperature operation light detector (typically 

InGaAs). The signal from the biased (12-V) photodetector was returned to the control room via 

a BNC cable, demodulated using a lock-in amplifier, and recorded on a laptop computer running 

LabView* software. The amplitude (height) of the second derivative-like signal output by the 

lock-in amplifier was proportional to the amount of light-absorbing gas (HF) present in the 

measurement region. The steps involved in laser modulation and demodulation are shown in 

Figure 4. 

7

8

9

10

11

12

13

14

15

16

7665.5 7665.51 7665.52 7665.53 7665.54 7665.55 7665.56

Wavenumbers (cm-1)

Signal at Detector (V)

0

0.01

0.02

0.03

0.04

0.05

0.06

Lock-in Signal Intensity (a.u.)

Signal at detector without

fast modulation

Signal at detector with 

fast modulation

2f signal from 

lock-in

Figure 4. The signals produced at the detector as slow and fast laser modulations 

combined and the 2f signal produced by the lock-in amplifier, for a typical 

TDLAS measurement of HF gas.

 *

 LabView is a registered trademark of National Instruments. 
7

The experimental protocol, lab results, field results, and data analysis methods are detailed in 

several publications (6, 10–18) from our research group. Early in the experimental cycle, an 

effort was made to use a second optical fiber to capture the light after it had passed through the 

measurement region, allowing the photodetector to remain in the control room. However, it was 

found that the alignment of the two optical fibers for the “pitch and catch” setup at the 

measurement site (typically, the crew compartment of a Bradley Fighting Vehicle [BFV]) was 

extremely sensitive. So, it was decided to place the photodetector at the measurement site, since 

tests showed that small misalignments in the open path fiber-to-detector line of sight were less 

important than small misalignments in open path fiber-to-fiber line of sight. Additionally, the 

costs associated with replacing either the fiber-to-detector or fiber-to-fiber setup within the 

vehicle were similar (hundreds of dollars). Using this system, measurement duration was 10 ms 

(100 scans/s); however, the time between measurements was ~100 ms, caused by the delay in 

transferring information from the lock-in amplifier to an oscilloscope, and from the oscilloscope 

to the laptop computer running LabView software. 

2.3.2 Results of HF Measurement Using Single Gas Stand-Alone Spectrometer System 

The single gas stand-alone spectrometer system for HF gas measurement was used for three 

types of testing. Results from each type of testing have been reported in the open literature (10, 

11, 15, 17). Briefly, the three tests were (1) suppression of spark and ballistically initiated JP-8 

fires (CF3Br, FM-200) in the crew compartment of a BFV hull, (2) suppression of JP-8 pool fires 

(using a handheld extinguisher charged with FM-200), and (3) suppression of heptane pan fires 

(using a mechanically actuated bottle charged with a series of fluorinated propanes). For the 

tests conducted in the crew compartment of the Bradley hull, measurements of HF gas (and other 

combustion products) were also measured using extractive FTIR spectroscopy. 

For these tests, the HF measurement location approximated the seating location of a passenger 

within the vehicle. Production of HF gas ranged from hundreds to thousands of parts per 

million-meters depending on how quickly the fire was extinguished. For successful tests (fires 

extinguished with 250 ms of the suppressant being deployed, HF levels were typically in the 

hundreds of parts per million range. For tests where the fire was not extinguished or suppression 

was not complete after 250 ms (resulting in suppressant being burned), the HF levels were often 

beyond the measurement range of both instruments (usually 5000 ppm for TDLAS). For the 

JP-8 pool fire measurements, the main goal was to obtain a measurement of the approximate 

exposure to HF experienced by a firefighter while suppressing the fire using a handheld 

extinguisher. For these tests, the HF measurement location was ~5 m from the pool fire, 

allowing the firefighter full access to the pool fire, as he was attempting to extinguish the fire as 

rapidly as possible. For these tests, the HF gas concentration that was measured ranged from 

0 to ~1000 ppm. As only one measurement site was used, the measurement was largely a 

function of wind direction, although the time-averaged exposure was always beyond acceptable 

levels. 
8

For the heptane pan fires, an attempt was made to understand the temporal behavior of HF gas 

concentration following an initial release of the commercial suppressant FE-36 

(hexafluoropropane), with and without the addition of an acid gas scavenging agent that may 

also act as a flame suppressant (ammonium polyphosphate [APP]). The two mechanisms by 

which HF gas concentrations can be decreased during and following fire extinguishment by 

FE-36 or FM-200 are by reducing the time required to extinguish the fire, thereby minimizing 

the time that the fluorine-containing suppressant is exposed to flame temperatures or releasing a 

scavenging agent in conjunction with the fire suppressant chemical to remove HF after it is 

produced. A potential chemical scavenging agent of gaseous HF is APP, which is a 

commercially available chemical (Phos-Chek*

) with fire retardant properties. One of the 

drawbacks to the release of a powder agent in an occupied space is the possibility of reduced 

visibility. 

HF was produced in the full-scale tests from a series of enclosed heptane/air pan fires 

extinguished by either FE-36 (C3F6H2), FM-200 (C3F7H), FE-36 plus APP, or FM-200 plus APP. 

By measuring how much the HF concentrations were reduced in fires extinguished with 

FE-36/APP or FM-200/APP mixtures compared to fires extinguished by FE-36 or FM-200 alone, 

the effectiveness of APP as a HF reduction and potential scavenging agent was demonstrated. In 

addition, spectroscopic measurements of the amount of light attenuation (obscuration) that 

occurs as a handheld fire extinguisher containing powder fire fighting agent is released in the 

crew space of a M1 land combat vehicle were performed. 

Results (17) from the full-scale tests indicate that HF concentrations produced from fires 

extinguished by FE-36 plus APP and FM-200 plus APP were reduced in the test facility and that 

the presence of APP accelerated the reductions. It has been concluded that the combination of 

APP in an extinguisher containing FE-36 or FM-200 appears to reduce HF levels. Visibility 

reduction during extinguisher deployment was measured inside an actual combat vehicle for 

extinguishers containing FE-36 plus APP and NaHCO3 plus N2. 

Some results of these tests are shown in Figure 5. Measurements suggest that by following the 

temporal evolution of HF gas during fire suppression, it would be possible to determine whether 

the decrease in observed HF gas levels was due to acid gas scavenging or the fire being 

extinguished more rapidly because of the presence of the additional suppressant. 

2.3.3 Multiposition, Multigas Spectrometer System 

The second area of investigation involved the use of a fully automated, multiposition, multilaser 

instrument housed in a small trailer adjacent to the control room at the measurement site. This 

instrument, built for the Army by Southwest Sciences, Inc. (Santa Fe, NM), was originally 

designed to measure concentrations of CO, O2, HF, and NO2 at four different locations within the 

 *

 Phos-Chek is a registered trademark of Astaris LLC. 
9

-200

0

200

400

600

800

1000

1200

1400

0 50 100 150 200

Time, seconds

Average HF Concentration, ppm-m

FE-36

FE-36 + 7 % APP

FE-36 + 15 % APP

-200

0

200

400

600

800

1000

1200

1400

0 50 100 150 200

Time, seconds

Average HF Concentration, ppm-m

FE-36

FE-36 + 7 % APP

FE-36 + 15 % APP

Figure 5. HF gas produced during suppression of heptane pan 

fires by FE-36 with and without the addition of APP. 

crew compartment of the BFV, achieving continuous measurement with data points every 10 ms. 

This instrument used the same technique of dual modulation spectroscopy employed by the 

stand-alone HF measurement system described earlier, but used a 10-KHz ramp for the “slow” 

modulation and a 1-MHz sine wave for the “fast” modulation. During the course of development 

of this instrument, it was decided to focus exclusively on measuring HF and O2 within the BFV 

hull, during suppression by FM-200 of spark- and ballistically initiated JP-8 fires. 

2.3.4 Results Using the Multiposition, Multigas Spectrometer System 

Results using this system have been reported (10), but were limited to oxygen and HF 

measurements during chemical suppression of spark-initiated P-8 fires. For these fires, a heated 

(~70 °C) spray of JP-8 liquid was begun within the crew compartment of the BFV hull (fuel 

nozzles located along one interior wall), and 1s later this fuel spray was ignited by a series of 

spark plugs located along the wall of the interior of the vehicle. Approximately 1s after ignition, 

the two onboard bottles containing the pressurized suppressant—FE-36 (C3F6H), FM-200 

(C3F7H), C3F8—were released. At the crew seating location, a sharp drop in O2 concentration 

occurred during the fire and suppression event. Following suppression, O2 levels returned to 

ambient in a few seconds. It was not clear whether the decrease in O2 levels during the fire and 

suppression event was due to combustion of oxygen or displacement of oxygen by the hot fuel 

vapors/expanding FM200 vapor. Results from a typical test measuring oxygen concentration as 

a function of time in the crew compartment of the BFV are shown in Figure 6.
10

O xyg en C o n cen tratio n

1 0

1 2

1 4

1 6

1 8

2 0

2 2

2 4

0 100 200 300 400 500 600 700 800 900

T im e (m illis e c o n d s )

% Oxygen

Figure 6. Oxygen concentration measured within the crew compartment of a 

BFV during suppression (by C3F8) of a spark-initiated JP-8 spray 

fire. 

2.4 Real-Time Fuel/Oxygen Sensor 

The last year of the funded project (FY99), plus almost a year (FY00) of additional work 

resulting from a no-cost extension, concentrated on measurement of fuel/air mixtures using 

“real” fuels, e.g., JP-8 turbine fuel. Specifically, the work concentrated on development, within 

an initial 1-year period, of a multipoint, field worthy, fiber-coupled, near-infrared tunable diode 

laser-based sensor for measurement and detection of combustible mixtures of oxygen and 

hydrocarbon fuels (heptane and JP-8). The goal of this work was to provide quantitative 

measurement of fuel/oxygen concentrations before (minimum five data points prior to agent 

release), during, and after the suppression event (nominal event time equal to 250 ms) with a 

time resolution better than 10 ms. Detection of fuel and oxygen concentration is especially 

important after the suppression event in order to predict the possibility of reignition. The goal 

for the system was a LOD for fuel vapors of ~600 ppm fuel (0.06%) and ~3000 ppm oxygen 

(0.3%), for a 10-cm path length at room temperature. 

The desired LOD for O2 gas was routinely achievable using the TDLAS techniques described 

previously. The main challenge for the remaining year was the measurement of fuel vapors. 
11

2.4.1 Background 

Field worthy detectors for hydrocarbon vapor measurements typically rely upon infrared 

absorption (differential optical absorption spectrometry [DOAS] and FTIR emission/absorption) 

(19, 20) or electrochemical/electrothermal techniques (21). These methods give good results, but 

have found limited use for measurements in fires. FTIR and DOAS spectrometers are usually 

bulky and expensive, and measurements require placement/alignment of interferometer/source 

optics and detector or retroreflector and are generally limited to a single line of sight. Placement 

of the instrument within the test environment (crew compartment) is not feasible (potential 

damage); looking across the entire measurement space does not isolate the region of interest, and 

although extractive sampling has been shown to be useful (22), it does not provide necessary 

temporal information. Additionally, the interferometer temporal resolution is limited by the 

mirror scan speed (although some new designs are approaching scan rates near 1 KHz) (23). 

Nevertheless, use of FTIR and DOAS for measurement of the fundamental C-H stretch in 

hydrocarbon fuels near 3.4 μm can yield sensitivities in the parts per billion (ppb) range, and 

because the full spectrum may be measured (when using FTIR), it is often possible to determine 

species of hydrocarbons present in a simple mixture. For stable, relatively safe sampling sites 

with an accessible line of sight, incoherent infrared absorption techniques (FTIR, DOAS) are 

often the techniques of choice. Electrothermal/electrochemical detectors are generally 

inexpensive ($2000–$5000), are often one-man portable, and have sensitivities (approximately 

hundreds of parts per million) well below lower explosion limits for most hydrocarbon vapors 

(24). Time sensitivity is typically from 1 to 15 s. Some units may have accuracy problems when 

used in the presence of methane gas and may be less sensitive to heavier hydrocarbon vapors 

(21). For measurement sites requiring full portable instrumentation with time resolution from 

one to tens of seconds, these instruments can also provide excellent results. 

Gas detection methods using near-infrared tunable diode lasers can use optical fibers and 

relatively inexpensive (room temperature operation) semiconductor detectors to separate 

electronics and laser sources from hazardous testing locations. Using modulation techniques and 

phase sensitive detection methods, temporal resolution routinely exceeds 1 ms/measurement. As 

previously mentioned, detection methods employed (typically wavelength modulation 

spectroscopy [WMS] and balanced ratiometric detection [BRD] techniques) (2, 3) give good 

results for gas phase concentration measurements of small molecules with well-resolved 

rovibrational absorption lines, such as hydrogen fluoride, methane, carbon monoxide, water, etc. 

(25). However, large and/or heavy molecules may not posses well-resolved rovibrational 

absorption bands because of overlap between fundamental, combination, and/or overtone 

vibrations, and because of rotational constants which may be less than typical gas phase 

linewidths (26). For mixtures of heavy molecules (e.g., the middle distillate fuels), the spectra 

may be even less structured. Figure 7 shows the near-infrared gas phase absorption spectrum of 
12

0

20

40

60

80

100

120

140

160

1.2 1.7 2.2 2.7 3.2 3.7

Unleaded

Gasoline

(regular)

JP-8

DF2

Wavelength (micrometers)

%

Tra

n

s

mis

s

oi n

Figure 7. FTIR spectra of dry air saturated at 294 K with vapor from unleaded gasoline, JP-8, and DF2. 

Spectra are offset for clarity. Structured absorptions near 1.9 and 2.7 μm are from water vapor. 

dry air saturated at 294 K by the hydrocarbon fuels JP-8, DF-2, and gasoline (0.75-m optical 

path), measured using a FTIR spectrometer. 

As suggested by the spectra shown in Figure 7, the vapors from each fuel fit criteria (27) to be 

classified as a gas having unstructured absorption spectra (often called a “broad band absorber”). 

Both WMS and BRD, as usually employed, are not suitable for gases that exhibit broad, 

unstructured absorption spectra (2, 3, 25). For both techniques, the main limitation for fuel 

sensing is the narrow tuning range of the diode laser. Because the tuning range of the DFB 

lasers is usually several orders of magnitude smaller than the width of the spectral feature in 

broad band absorbers (0.4 cm!1

 vs. >100 cm!1), it is not possible using commercially available 

DFB lasers to tune from the region of maximum absorption to a region of zero absorption. A 

main goal of the project was to overcome this limitation for measurement of such molecules, 

while approaching the sensitivity and time response of WMS and BRD methods.

2.4.2 Measuring Broad Band Absorbers With Narrow Band Lasers 

The initial method developed for the project takes advantage of the residual amplitude 

modulation (RAM) that occurs as the wavelength of a semiconductor tunable diode laser is 

varied by modulating the laser injection current. Typically (for WMS and BRD), RAM is a 

nuisance, and what is important is the wavelength modulation. For this method, the RAM is 

what enables the technique to work, and the (relatively) small variation of wavelength during the 

modulation is largely ignored (but will be commented upon later). For this method, two different 

DFB lasers are driven using a sinusoidally varying injection current. Each laser injection current 
13

is modulated at the same frequency but out of phase by 180° (27). These light output of the two 

lasers is combined to produce the probe beam used for the line-of-sight measurement. When the 

power output amplitudes of each sinusoidally modulated laser are the same, the combined output 

of the two lasers will have an amplitude that is (ideally) invariant with time. The key to the 

method is selection of one laser wavelength coincident with a wavelength absorbed by the gas of 

interest and selection of the second laser wavelength in a region where no absorption is 

anticipated. When the mixed, modulated probe beam is passed through a gas that preferentially 

absorbs the laser radiation from only one of the lasers, the signal at the detector is modulated at 

the injection current modulation frequency and, for small absorptions, has an amplitude whose 

magnitude is proportional to the concentration of absorbing gas. 

The simple mathematical description begins by considering Beer’s law (1) for narrow band laser 

radiation exiting an absorbing sample gas of concentration c molecules per cubed centimeters, 

for a path length of l cm. The absorption coefficient (cm2

/molecule) at the most intense region of 

absorption (the resonant wavelength, λR), is α(λR). I0(λR) is the intensity of the incident 

radiation at the resonant wavelength. I(λR) is the intensity of radiation at the resonant 

wavelength after exiting the sample gas: 

 ) I( ) I ( ) exp( ( )cl λ R = 0 λ R −α λ R . (1) 

If the incident radiation at the resonant wavelength is now power-modulated sinusoidally at 

frequency a, and time t, with depth of modulation DR, the intensity of the radiation at the 

resonant wavelength after exiting the gas becomes 

 ) I( ) I ( )(1 sin(at)) exp( ( )cl λ R = 0 λ R + DR −α λ R . (2) 

To get a measurement of transmission off resonance (important to generate a differential signal 

and to discriminate against scattering by particles such as smoke), we add a second laser source 

at a wavelength not absorbed by the gas, λNR. This nonresonant wavelength is mixed with the 

resonant wavelength, power modulated at the same frequency but 180° out of phase with the 

resonant wavelength modulation, and has a depth of modulation DNR. If the radiation exiting the 

gas is now focused on an (ideally) wavelength-insensitive detector, the power at this detector, 

I(λR +λNR), may be given by 

I( ) [I ( )(1 D sin(at))exp( ( )cl) I ( )(1 D sin(at ))] λ R + λ NR = 0 λ R + R −α λ R + 0 λ NR + NR + π . (3) 

To process this signal, we multiply by a reference sine wave of amplitude p in phase with and at 

the same frequency, a, as the power modulation of the two lasers. We then integrate over C 

periods of power modulation: 

{ } I ( )(1 D ) exp( ( )cl) I ( )(1 D )]sin(at)psin(at) dt C0 ∫ 0 λ R + R −α λ R − 0 λ NR + NR

π 

 )] = (C/2) pπ [I0 (λ R )(1+ DR ) exp(−α(λ R )cl)- I0 (λ NR )(1+ DNR . (4)
14

Rearranging, assuming exp(-α(λR)cl) <<1 and using A (absorbance) = α(λR)cl : 

{ } ∫ 2C I ( )(1+ ) exp(− ( )cl) − I ( )(1+ D )]sin(at)psin(at) dt 0π 0 λ R DR α λ R 0 λ NR NR

 A] Cp [I ( )(1 D ) I ( )(1 D ) I ( )(1 D ) = π 0 λ R + R − 0 λ NR + NR − 0 λ R + R . (5) 

For the special case where the power and depth of modulation of the two lasers are equal, 

equation 5 becomes 

{ } ∫ 2C I ( )(1+ )exp(− ( )cl) − I ( )(1+ D )]sin(at)psin(at) 0π 0 λ R DR α λ R 0 λ NR NR

 A] dt Cp [I ( )(1 D ) = − π 0 λ R + R . (6) 

Equation 6 is just the output of a lock-in amplifier operating on the first harmonic for 

measurement of the amplitude of the sine wave created by the differential absorption (for small 

absorptions) of the mixed laser beam by the gas at concentration c and path length l. This output 

is proportional to the number of periods, C, over which the integration is carried, the amplitude, 

p, of the reference sine wave, the incident power, I0(λR), of the laser at the resonant wavelength, 

and the absorbance, A (and hence gas concentration when pressure broadening of the spectral 

feature is not important). It is worth noting that equation 6 also indicates that lock-in output is 

increased by increasing depth of modulation (DR). As will also be discussed later, equation 5 

shows that it is important that the two laser power amplitudes and depths of modulation are as 

equal as possible, especially for small values of absorbance. As mentioned previously, and 

implied by equation 6, because the measurement relies on differential absorption to quantify gas 

concentrations, division of the raw signal at the detector by the average laser power should 

account for pseudo-wavelength-independent signal intensity extinction from scatterers, such as 

smoke particles. However, it should also be mentioned that decreases in overall signal voltage 

will result in similar decreases in the signal-to-noise ratio of the measurement. 

2.4.3 Experimental Apparatus 

A diagram of the experimental apparatus employing this method is shown in Figure 8. The two 

DFB laser diodes (Sensors Unlimited) used to produce the mixed wavelength probe beam have 

nominal wavelengths of 1.307 and 1.71 μm. The laser diodes are driven using an ILX LDC3900 modular laser diode controller. The variable phase sinusoidal injection currents are 

supplied by two SRS model DS345 function generators operating on a common time base. 

Sinusoidally modulated (100 KHz, modulation depth adjusted to near 100%) laser diode 

radiation from each diode laser is mixed onto a common fiber using a fiber-optic coupler (Gould 

Fiberoptics) and launched into free space using a single mode fiber that is terminated by a GRIN 

lens (Sentech Corp.). The output beam is directed into a variable pathlength gas cell (Laser 

Photonics L5210) set at the minimum setting of 4 m. Radiation exiting the 4-m path length cell 

is detected using a New Focus Model 2034 InGaAs large element photodetector (maximum 

responsivity near 1600 nm). The detector signal is demodulated at the laser injection current
15

Laptop

Computer Oscilloscope Lock-inAmplifier

GRIN Lens 1

InGaAs Detector

4 m optical cell 

Laser 1

1.31

microns

Function

Generator 1

Laser

Driver 1

Laser 2

1.71

microns

Function

Generator 2

Laser

Driver 2

Fiber

optic 

coupler

Laptop

Computer Oscilloscope Lock-inAmplifier

GRIN Lens 1

InGaAs Detector

4 m optical cell 

Laser 1

1.31

microns

Function

Generator 1

Laser

Driver 1

Laser 2

1.71

microns

Function

Generator 2

Laser

Driver 2

Fiber

optic 

coupler

Figure 8. A diagram of the laser mixing apparatus used to measure fuel vapor 

concentrations. 

modulation frequency using a lock-in amplifier (SRS 830), displayed on an oscilloscope (LeCroy 

7200), and recorded on a laptop computer (Dell Latitude) running LabView software (National 

Instruments). JP-8 and DF-2 were in accordance with military specifications and obtained from 

the fuel depot at the Aberdeen Proving Ground. The gasoline was regular grade obtained during 

the summer months at a commercial vendor in Aberdeen, MD. All were used as supplied. Air 

was saturated with fuel vapor using a bubbler apparatus based upon a nitrogen sparger. Airflow 

through the stainless steel frit immersed in the fuel was typically 100–250 cm3

/min. 

Near-infrared spectra shown in Figures 1 and 3 were recorded using a Bomem DA-8 (using a 

liquid nitrogen-cooled InSb detector) interfaced to a Wilkes 0.75-m path length cell. 

2.4.4 Results 

Figure 9 shows the vapor phase absorption spectrum of air saturated by vapor at 294 K from 

JP-8, DF-2, and gasoline between wavelengths of 1.3 and 1.75 μm superimposed upon the 

emission from the optical fiber carrying the mixed wavelength laser beam. Both sets of spectra 

were measured using an FTIR spectrometer (Bomem DA-8). The near-infrared tunable diode 

laser radiation was transported using optical fibers to the external source port on the FTIR 

spectrometer. This figure shows that the emission of the laser at 1.71 μm falls near the most 

intense region of the C-H stretch (first overtone) absorption for the three fuels studied, and that 

the 1.3-μm laser falls in a region where there is no measurable absorption of the laser radiation 

by the fuels studied. Because of the narrow emission linewidth of the lasers, the reported 
16

-0.1

0

0.1

0.2

0.3

0.4

1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

-0.25

0.25

0.75

1.25

Wavelength (micrometers)

Absorbance

Laser Emission (arb. units)

Laser 1 Laser 2

Gasoline vapor

JP-8 vapor

DF-2 vapor

Figure 9. The vapor phase absorption spectrum of air saturated by vapor at 294 K from JP-8, DF2, and gasoline between wavelengths of 1.3 and 1.75 μm superimposed upon the 

emission from the optical fiber carrying the mixed wavelength laser beam. 

lineshape in this figure is just the instrument lineshape (in this case, sinc) of the FTIR 

spectrometer (28). 

Figure 10 shows the gasoline vapor concentration (measured using the mixed laser sensor) as dry 

air saturated by gasoline vapor slowly displaces (several hundred cubic centimeters per minute) 

the dry air in a 13.7-L volume optical cell (4-m path length). Also shown in this figure is the 

change in oxygen concentration that occurs during the displacement (DFB laser-based oxygen 

sensor courtesy of Oxigraf, Inc., Mountain View, CA). This figure shows the sensor response as 

the vapor concentration approaches and exceeds the lower explosive limit (LEL) for most 

hydrocarbon vapors (e.g., for JP-8 the LEL is ~9500 ppm [24, 29]). Each data point is the 

average of the lock-in amplifier output measured over 10 ms. All measurements were made at 

atmospheric pressure. 

Figure 11 shows the measured fuel vapor concentration as the dry air in the 13.7-L volume 

optical cell is displaced by air saturated (at 294 K) by JP-8 vapor. The difference in peak 

hydrocarbon levels between runs shown in Figure 11 is caused by the gradual removal of lighter 

hydrocarbons from the JP-8. For brevity, results on DF2 are not presented, since the results for 

DF-2 were similar to those for JP-8. The partial pressures at atmospheric pressure (measured 

using a capacitance manometer) for gasoline, JP-8, and DF-2 fuels were found to be ~13, 3.5, 

and 1.75 torr (±20%), respectively. We measured the C-H stretch first overtone absorption 

coefficient for the fuel vapors to be ~2.7 (±4) H 10!21 cm2

/molecule, which is in reasonable
17

0

2000

4000

6000

8000

10000

12000

0 100 200 300 400 500

0

0.05

0.1

0.15

0.2

0.25

0.3

Time (sec)

Gasoline Vapor (ppm)

Fraction Oxygen 

gasoline

O2

Figure 10. Gasoline vapor concentration (measured using the mixed laser sensor) as dry air saturated by 

gasoline vapor slowly displaces (several hundred cm3

/min) the dry air in a 13.7-L volume 

optical cell. Also shown in this figure is the change in oxygen concentration that occurs during 

the displacement (DFB laser-based oxygen sensor, courtesy of Oxigraf, Inc., Mountain View, 

CA). 

-0.1

0.4

0.9

1.4

1.9

2.4

2.9

3.4

0 500 1000 1500 2000 2500 3000 3500

Parts-per-million meter JP-8 vapor

 (added to 13.7 liter optical celll)

Instrument Response (arb. units)

Fresh sample

Sample after 5 runs

(added to 13.7 liter optical cell) 

Figure 11. Aging of JP-8 (loss of lighter hydrocarbons) caused by repeated fills of the optical 

cell used for testing the mixed laser fuel vapor sensor. 

agreement to that for the first overtone of the C-H stretch for methane (8.7 H 10!22 cm2/molecule) 

(4). We estimate the limit of detection for each of these fuel vapors, using the mixed laser 

sensor, to be ~100 ppm-m. 
18

Two factors led us to decide that measurement of the full absorption envelope for the C-H 

stretching vibration was necessary, and that our first-generation sensor system was inadequate 

for general fuel vapor sensing. First, careful examination of the C-H overtone bands for each of 

the fuels tested (JP-8, diesel, and gasoline) shows that the contours of the absorption features, 

when normalized to each other, were not superimposable. So, being limited to sampling vapors 

from different fuels using the same single wavelength would be a potential source of error. 

Second, changes in temperature, storage conditions (aging) and changes in fuel composition 

between vendors may cause changes in the contour of the unstructured absorption envelope. 

Therefore, it was necessary to develop a technique with the simplicity of the first generation 

sensor but with the capability of expansion to measure the full C-H absorption envelope of the 

fuel vapor. 

2.5 Second Generation Sensor Development 

Perhaps the best method for detection and measurement of vapor phase broad band absorbers is 

FTIR spectroscopy (28). In conventional Fourier transform spectrometers, each “discrete” 

wavelength of light emitted by the glow bar source (most Fourier transform spectrometers use a 

resistively heated tungsten coil) is power modulated by a Michelson interferometer so that the 

output, as measured at the detector, is cosinusoidal, with a frequency in the kilohertz (acoustic) 

range. The amplitude and frequency of this cosine wave are a function of moving mirror 

displacement and of the wavelength of the incident light. As an example of the relationship 

between spectral resolution and mirror displacement, to resolve the line separation of the 

fundamental rovibrational transition in CO gas, it is necessary to move one of the mirrors in the 

interferometer ~1 cm. Although highly refined, the net effect of this design is to limit the use of 

these instruments mainly to the laboratory, necessitate complicated electromechanical mirror 

transport systems, and limit measurement applications to repeatable or static events. Details of 

FTIR spectroscopy are widely available in several standard texts on the subject (30). 

The approach employed in our second-generation sensor uses an array of addressable 

microphotonic semiconductor lasers, each emitting light at a different wavelength, and power 

modulated at different frequencies (typically between 100 and 150 KHz). When the modulated 

light is combined onto a single path, and the combined beam brought to focus on a detector, the 

signal reported by the detector has the contour of an interferogram. This interferogram is 

analyzed by standard fast Fourier transform (FFT) techniques to yield the amplitudes of the 

individual component cosine waves (31). These amplitudes are proportional to the average 

power of light at each wavelength reaching the detector. Figure 12 shows the interferogram 

generated by a two-laser mixed beam. Laser 1 emits radiation near a wavelength of 1.31 μm and 

was power modulated at 100 KHz, with a depth of modulation near 95%. As with the firstgeneration sensor, this laser wavelength was chosen because it is not absorbed by hydrocarbon 
19

2.50E-02

2.70E-02

2.90E-02

3.10E-02

3.30E-02

3.50E-02

3.70E-02

3.90E-02

4.10E-02

4.30E-02

4.50E-02

0.00E+00 4.00E-04 8.00E-04

Signal at detector

Laser 1 (100 KHz) at 1.31μ

Laser 2 (110 KHz) at 1.71 μ

Intensity (a.u)

Time (sec)

Figure 12. The two-laser interferogram measured at the detector for the second-generation fuel 

vapor sensor. 

vapor or by water vapor. Laser 2 emits laser radiation near a wavelength of 1.71 μm and was 

power modulated at 110 KHz, with a depth of modulation near 95%. Also, as with the firstgeneration sensor, this laser wavelength was chosen because it is approximately at the center of the 

first overtone C-H stretching vibration of most middle distillate fuel vapors. 

The output from each fiber-coupled laser is launched onto a single, common, single-mode optical 

fiber using a commercially available fiber coupler (Gould Fiber Optics). Each laser is power 

modulated, each at a different frequency, using digital function generators (Stanford Research 

Systems DS-345) operating on a common time base. This modulated light beam is passed through 

a GRIN lens into free space and the transmitted light detected using an InGaAS (New Focus model 

2011) detector. The signal at the detector is demodulated (Agilent Infinium Oscilloscope) using an 

FFT, in a manner similar to that of commercially available FTIR spectrometers (31). Time for each 

measurement is user controlled by varying the frequency of power modulation. Resolution is user 

controlled by varying the number of periods of power modulation measured per “scan.” The 

experimental apparatus for the Fourier transform laser spectroscopy (FT-LS) system is described in 

Figure 13. 

2.5.1 Results of Prototype Testing of Second-Generation Sensor System 

As with the first-generation sensor, the second-generation sensor was tested by measuring gasoline 

vapor concentration as dry air saturated by gasoline vapor slowly displaces (several hundred cubic 

centimeters per minute) the dry air in a 13.7-L volume optical cell (4-m path length). Figure 14 
20

Laser 1

Laser 2

Analyte region

InGaAs

detector

FFT

Laser diode controller

Function generators

GRIN

Fiber mixer lens

Fiber optic

Figure 13. A schematic of the experimental apparatus used for FT-LS. 

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0 500 1000 1500 2000 2500

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0 500 1000 1500 2000 2500

Absorbance

Time (sec)

LEL (Lower 

Explosion Limit)

Figure 14. Absorption of laser radiation at 1.71 μm as air in 2-m cell is displaced by air saturated 

with gasoline vapor. For the absorbance calculation, the background was the 

demodulated signal for each laser prior to the onset of fuel vapor flow. 
21

shows the sensor response as the vapor concentration approaches and exceeds the LEL for most 

hydrocarbon vapors (e.g., for JP-8 and most other middle distillate fuels the LEL is ~10,000 ppm 

[24, 29]). For the absorbance measurement, the background for each laser was the demodulated 

signal prior to the onset of fuel vapor flow. The flow apparatus was characterized using our firstgeneration sensor, and using that calibration the absorbance reported here is reasonably linear with 

concentration (within 5%), but was not explicitly measured for these experiments. All of the 

factors that determine quality of conventionally measured FTIR spectra are of importance here 

(modulation depth, apodization, phase, etc. [28]). Most of the efforts for the prototype were 

focused on making sure the lasers were modulated in phase, using a common time base. We did 

not investigate effects of varying the modulation depth or of varying the laser power. Dynamic 

range effects were not investigated, although we anticipate some improvement relative to 

Michelson interferometer-based instruments because the Fourier frequencies for each laser are no 

longer coupled to the laser wavelength. Time for each measurement point was ~1 s. All 

measurements were made at atmospheric pressure. 

2.5.2 Sensitivity 

The absorption coefficients for most volatile organic compounds (VOCs) in the near-infrared 

spectral region (~1- to 2-μm wavelength, 2 (or more) vibrational quanta/transition) are typically 

lower by 1 order of magnitude than for the mid-infrared spectral region (~2- to 30-μm wavelength, 

typically 1 vibrational quantum/transition) (32). In our lab we have measured the near-infrared 

absorption coefficients between wavelengths of 1.0 and 30 μm for several VOCs (Figure 7). For 

the military fuel, JP-8 (a mixture of several hundred hydrocarbons) we have measured (using a 

Bomem DA-8 FTIR spectrometer) the maximum absorption coefficient in the spectral region 

between a wavelength of 1.6 and 1.825 μm to be ~3 H 10!21 cm2

/molecule (4). Using the prototype 

FT-LS instrument previously described (33), we obtained a detection limit of ~200 ppm-m for JP-8 

vapor in air, or ~50 times worse than the detection limit using a commercial FTIR spectrometer. It 

is worth noting that for the prototype sensor described here, we observed that the power modulation 

of each diode laser was not purely cosinusoidal (harmonics in the FFT output), even though the 

driver current was supplied by the SRS DG535 function generators. We anticipate that as the 

number of lasers being power modulated is increased, the contributions to signal from frequencies 

other than driver frequencies may limit resolution. We have considered designing a custom driver 

waveform to give the best cosinusoidal power modulation, but have yet to actually try this. 

2.5.3 Future Developments 

We are presently pursuing development of a 10-laser FT-LS source in the near-infrared, providing 

reasonable coverage of the full overtone C-H absorption envelope for hydrocarbon vapors. The 

basic idea for this sensor is illustrated in Figure 15. Analysis similar to projection to latent 

structure techniques already employed for FTIR spectral data could be used to identify mixture 

components (34). Such an instrument may be readily assembled from commercially available 

tel-com equipment. Here, the main impediment is finding a vendor for the individual laser diodes. 
22

0

0.02

0.04

0.06

0.08

0.1

0.12

1.625 1.675 1.725 1.775 1.825 1.875

Absorbance – air saturated by gasoline vapor1 meter path

Wavelength (micrometers)

Wavelength position of 10 diode laser

addressable source

Figure 15. Schematic of a 10-laser FT-LS source in the near infrared (under development), 

providing reasonable coverage of the full overtone C-H absorption envelope for 

hydrocarbon vapors. 

The problem is that low demand for lasers outside of the fiber windows near 1350 and 1550 nm 

limits availability. 

Provided that the cost of addressable light sources continues to decrease, arrays covering larger 

spectral windows may become available. While several options exist for wavelength separation, 

we believe that the highly developed FTIR market may influence the design of new solid-state 

spectrometers, and that this approach may warrant further consideration. 

3. Technical Problems 

The main technical difficulties associated with this project center on the availability of DFB lasers. 

With the contraction of the tel-com market at the beginning of this century, many fabrication 

facilities discontinued manufacture of lasers at user specified wavelengths, producing lasers only 

within the tel-com bands near 1330 and 1550 nm. Although some of the decrease in availability of 

domestically manufactured near-infrared DFB lasers has been made up by foreign manufacturers 

(in particular, NEC of Japan), obtaining lasers for gas sensing (particularly, O2 near 760 nm) 

remains challenging. The difficulty in obtaining lasers at custom wavelengths exacerbates what we 

perceive to be the main challenge for gas sensing using near-infrared DFB lasers—namely, sensing 

of molecules and mixtures of gases that do not present well-resolved vibrational spectra. We 

believe we have made reasonable efforts towards solving this problem (see sections 2.4 and 2.5), 

but the difficulty in obtaining lasers at custom wavelengths makes full demonstration of a truly 

addressable source difficult. 
23

4. Conclusion 

Gas sensing using near-infrared lasers will probably continue gaining market share, although it 

seems likely that a transition will occur in which a single laser detecting a single gas is replaced 

either by an addressable source or by a single broadly tunable laser. Near-infrared devices for gas 

sensing will likely continue to be used because of the ease of transmission through optical fibers, 

room temperature operation, high signal-to-noise ratio through phase-sensitive detection 

techniques, and because of the large tel-com infrastructure that continues development of 

electronics that may easily be adapted to gas sensing. However, room temperature operation midinfrared lasers (quantum cascade and interband cascade designs) offer all of the advantages of 

phase-sensitive detection available with near-infrared DFBs, with the huge advantage of gas 

sensing using the fundamental vibrational transition. It seems likely that future microphotonic 

sensors will employ suites of arrays of near- and mid-infrared devices, and that these devices will 

gradually displace conventional Michelson interferometer based systems in the laboratory and in 

the field. 

5. Milestones 

5.1 FY 97 

(1) Complete comparison of LIBS vs. near-infrared lasers for oxygen detection. 

Status: Met 

(2) Evaluate LIBS for P, Si, -NHx, and metal-containing suppressants, as well as other new fire 

suppression chemicals of tri-Service interest. 

Status: Met 

(3) Procure near-infrared lasers for two additional gases. 

Status: Met 

(4) Complete installation of additional near-infrared lasers at ATC. 

Status: Met
24

(5) Complete transition of LIBS sensor technology from ARL to ATC. 

Status: Unmet: After testing of LIBS for characterization of suppressants, fuels, and oxidizers, it 

was found that current fiber-coupled laser systems did not meet sufficient durability 

requirements for transmission of laser radiation necessary for air breakdown (~100 mJ/pulse, 

10-ns pulse length). 

5.2 FY 98–99 

(1) Measurement of near-infrared absorption survey spectra (using a Fourier transform nearinfrared [FT-NIR] spectrometer) of heptane and JP-8 at several temperatures. 

Status: Met 

(2) Procurement of laser diodes whose output wavelength is coincident with an absorption 

transition in these gases as determined by the survey spectra. 

Status: Met 

(3) Procurement of fiber signal splitters, GRIN lens-tipped fibers, and InGaAs detectors for 

multipoint detection. 

Status: Met 

(4) Procurement of additional lasers and equipment for multiplexing applications and for 

multipoint measurements. 

Status: Met 

(5) Procurement of additional fibers for multiple point LIBS. 

Status: Unmet. Suitable fibers for transmission of pulsed laser radiation were unavailable 

(6) Complete evaluation of demodulation techniques for multiplex TDLAS. 

Status: Partially met. Modulation techniques for measurement of gases with unstructured 

absorption spectra became a main focus of this project. The work performed in this area 

resulted in three publications (see sections 2.4 and 2.5), although the authors believe the effort 

at measuring broadband absorbers has not been suitably concluded. 

(7) Software development for multiplex spectral measurement, demodulation, and real-time 

display of concentrations of fuel and oxidizer. 

Status: Partially met. See FY98–99 milestone 6. Real-time display used commercial software 

(LabView), employing custom virtual instrument interface programs.
25

(8) Procurement of demodulation electronics. Demonstration of continuous 10-ms time 

resolution, data storage capabilities. 

Status: Met 

(9) Laboratory calibration of diode laser 2f spectra for O2, heptane, and JP-8. 

Status: Partially met. Oxygen calibration was straightforward and was referenced against an 

Oxygraph oxygen meter. Middle distillates and heptane were measured using the “broadband 

absorber” techniques described in section 3 of this document. 

(10) Initial testing of the fuel/oxygen sensor on static heptane/air and JP-8/air mixtures. 

Comparison testing against the National Institute of Standards and Technology (NIST) 

“phi-meter.” 

Status: Partially met. JP-8/air mixtures were successfully measured in lab. Comparison testing 

with NIST phi-meter was never performed. 

(11) Extension of initial sensor to multipoint detection capability. 

Status: Unmet. Use of the splitter required for multipoint detection caused the mixed laser beam 

to lose modulation balance. We were not able to correct this within the project duration. 

(12) Complete initial multipoint measurements of fuel/oxidizer mixtures (laboratory-based) for 

determination of flammable mixture detection. 

Status: Partially met. Single point detection successful. Use of the splitter required for 

multipoint detection caused the mixed laser beam to lose modulation balance. We were not 

able to correct this within the project duration. 

(13) Initial fuel/oxygen sensor installation, testing at ATC facility. Initial LIBS installation, 

testing at ATC facility. 

Status: Partially met. Initial fuel/air testing at ATC successful for single point measurement. 

Multipoint installation failed because splitter required for multipoint detection caused the 

mixed laser beam to lose modulation balance. We were not able to correct this within the 

project duration. 

(14) Initial field testing of LIBS for multipoint measurement of halon alternative compounds. 

Comparison with the differential infrared rapid agent concentration sensor method. 

Status: Unmet. Suitable fibers for transmission of pulsed laser radiation were unavailable. 

(15) Demonstration of multiplex detection of fuel/oxygen mixtures during real-scale fire 

suppression testing. 

Status: Partially met. Single point detection only.
26

(16) Demonstration of LIBS for multiple-point detection of FM-200 in crew compartment. 

Status: Unmet. Suitable fibers for transmission of pulsed laser radiation were unavailable.

6. Significant Project Results: Discussion and Recommendations 

We believe this project to have been successful, although the achieved results differed appreciably 

from those outlined in the initial proposals. The project fell short of initial expectations in that 

diode lasers are currently fielded at ATC only for HF and oxygen measurement. Real-time fuel 

measurement, demonstrated successfully in the laboratory at ARL, has not been successfully 

transitioned to ATC. The reasons for this are twofold. First, although we developed two methods 

for laser-based measurements of “broadband absorbers” (gases with poorly resolved vibrational 

structure), we have been unable to achieve sensitivities for these gases similar to those attainable 

for detection of light hydrocarbons (e.g., methane). Additionally, for multipoint detection, we were 

unable to maintain the modulation balance on which our first technique was dependent. We are 

still engaged in refining our techniques for measuring gases that do not exhibit well-resolved 

vibrational structure. Second, measurement of these heavy hydrocarbon vapors requires nearinfrared DFB lasers near a wavelength of 1.7 μm. These lasers must be custom fabricated. For 

such custom orders, it is necessary to wait until several customers need lasers in this wavelength 

region, making the wafer growth economically feasible. 

LIBS has never been transitioned to field use within armored vehicles at ATC. The main reason for 

this is that optical fibers necessary for delivering pulsed radiation to the measurement site were 

found to be unreliable (failure at <200 shots). It’s worth noting that several manufacturers are now 

offering fibers for delivering pulsed radiation at 1.06 μm. The current highest power delivery fiber 

of which we are aware (3M Powercore fibers, up to 80 mJ/pulse at 10 ns) may enable LIBS of 

gases at remote locations. 

Given these shortcomings, we still believe the project to be successful. First, we demonstrated the 

first measurement of broadband absorbers using phase-sensitive detection. Additionally, the 

project resulted in development of FT-LS, in which an array of lasers is used to create an 

addressable source that mimics the output of a Michelson interferometer, but with no moving parts, 

and with the Fourier frequencies decoupled from the light wavelengths. Second, and perhaps even 

more important, the project has demonstrated the use of LIBS for quantitative measurement of 

gases. The use of LIBS for this project provided much impetus for expanding this technique into 

investigations of detection methods for toxic and explosive materials, including chemical/biological 

agents. 

Third, the project has resulted in a greater understanding of toxic gas formation (specifically HF 

gas) during fire suppression onboard armored vehicles. The combination of diode laser 

measurements and of extractive FTIR measurements during real-scale testing has lent credence to 
27

both methods. Tunable diode laser measurements have shown how the rate of formation of HF gas 

is affected by varying fire suppressants and by chemicals added to decrease HF formation. 

We believe microphotonic sensors, employing tunable diode laser spectroscopy and LIBS, will play 

a major role in the next generation of sensor equipment. Equipment design and experimental 

results from this project have enhanced the effort towards this next generation of sensors. We hope 

to continue our work in tunable diode laser spectroscopy and LIBS and to continue development of 

sensors of use to the Army. 
28

7. References 

1. Reid, J.; Labrie, D. Second-Harmonic Detection With Tunable Diode Lasers—Comparison of 

Experiment and Theory. Applied Physics B 1981, 26, 203–210, 

2. Bomse, D. S.; Stanton, A. C.; Silver, J. A. Frequency Modulation and Wavelength Modulation 

Spectroscopies: Comparison of Experimental Methods Using a Lead-Salt Diode Laser. 

Applied Optics 1992, 31, 718–731. 

3. Hobbs, P. C. D. Ultrasensitive Laser Measurements Without Tears. Applied Optics 1997, 36, 

903–921. 

4. Linnerud, I.; Kaspersen, P.; Jaeger, T. Gas Monitoring in the Process Industry Using Diode 

Laser Spectroscopy. Applied Physics B 1998, 67, 297–305. 

5. Martinelli R.; Menna, R.; Cooper, D.; Carlisle, C.; Riris, H. Near-Infrared InGaAs/InP 

Distributed-Feedback Lasers For Spectroscopic Applications. In Laser Diode Technology and 

Applications XI, P.C. Chen; L. Johnson; H. Tamkin, Eds.; Proc. SPIE 1994, 2148, 292–307. 

6. McNesby, K. L.; Wainner, R. T.; Daniel, R. G.; Skaggs, R. R.; Morris, J. B.; Miziolek, A. W.; 

Jackson, W. M.; McLaren, I. A. Detection and Measurement of Middle-Distillate Fuel Vapors 

by Use of Tunable Diode Lasers. Applied Optics 2001, 40, 840–845. 

7. Lancaster, E. D.; McNesby, K. L.; Daniel, R. G.; Miziolek, A. W. Spectroscopic Analysis of 

Fire Suppressants and Refrigerants by Laser-Induced Breakdown Spectroscopy. Applied 

Optics 1999, 38, 1476. 

8. Williamson, C. K.; McNesby, K. L.; Daniel, R. G.; Miziolek, A. W. Laser-Induced Breakdown 

Spectroscopy for Real-Time Detection of Halon Alternative Agents. Analytical Chemistry

1998, 70, 1186–1191. 

9. Brewster M. Q. Thermal Radiative Transfer and Properties. Wiley Interscience: New York, 

1992; p 253. 

10. McNesby, K. L.; Skaggs, R. R.; Miziolek, A. W.; Clay, M.; Hoke, S.; Miser, C. S. Diode 

Laser-Based Measurements of Hydrogen Fluoride Gas During Chemical Suppression of Fires. 

Applied Physics B 1998, 67, 443. 

11. McNesby, K. L.; Daniel, R. G.; Modiano, S. H.; Miziolek, A. W. Optical Measurement of 

Toxic Gases Produced During Firefighting Using Halons. Applied Spectroscopy 1997, 51, 

678–683.
29

12. McNesby, K. L.; Daniel, R. G.; Miziolek, A. W.; Modiano, S. H. Optical Measurement of 

Toxic Gases Produced During Firefighting Using Halons. ARL-TR-1349; U.S. Army 

Research Laboratory: Aberdeen Proving Ground, MD, April 1997. 

13. McNesby, K. L.; Skaggs, R. R.; Miziolek, A. W.; Daniel, R. G.; Miser, C. S. Near-Infrared 

Tunable Laser Diagnostics in Laboratory Scale Flames. Proceedings of Laser Applications to 

Chemical and Environmental Analysis Topical Meeting, Orlando, FL, March 1998; p 203. 

14. McNesby, K. L.; Skaggs, R. R.; Miziolek, A. W.; Clay, M.; Hoke, S.; Miser, C. S. Diode 

Laser-Based Measurements of Hydrogen Fluoride Gas During Chemical Suppression of Fires. 

ARL-TR-1785; U.S. Army Research Laboratory: Aberdeen Proving Ground, MD, 1998. 

15. Skaggs, R. R.; Daniel, R. G.; Miziolek, A. W.; McNesby, K. L.; Herud, C.; Bolt, W. R.; 

Horton, D. Diode Laser Measurements of HF Concentrations From Heptane/Air Pan Fires 

Extinguished by FE-36 and FE-36 Plus Ammonium Polyphosphate. ARL-TR-2143; U.S. Army 

Research Laboratory: Aberdeen Proving Ground, MD, 2000. 

16. Skaggs, R. R.; Daniel, R. G.; Miziolek, A. W.; McNesby, K. L.; Herud, C.; Bolt, W. R.; 

Horton, D. Diode Laser Measurements of HF Concentrations Produced From Heptane/Air Pan 

Fires Extinguished by FE-36, FM-200, FE-36 Plus APP, or FM-200 Plus APP. Proceedings of 

the 1998 JANNAF Combustion Meeting, 2000; CPIA Publication 685, p 161. 

17. Skaggs, R. R.; Daniel, R. G.; Miziolek, A. W.; McNesby, K. L.; Herud, C.; Bolt, W. R.; 

Horton, D. Diode Laser Measurements of HF Concentrations Produced From Heptane/Air Pan 

Fires Extinguished by FE-36, FM-200, FE-36 Plus APP, or FM-200 Plus APP. Applied 

Spectroscopy 1999, 53, 1143. 

18. Skaggs, R. R.; Daniel, R. G.; Miziolek, A. W.; McNesby, K. L.; Herud, C.; Bolt, W. R.; 

Horton, D. Diode Laser Measurements of HF Concentrations From Heptane/Air Pan Fires 

Extinguished by FE-36 and FE-36 Plus Ammonium Polyphosphate. 1998 Proceedings of the 

International Society for Optical Engineering, 1999. 

19. Wormhoudt, J. Infrared Methods for Gaseous Measurements-Theory and Practice. MarcelDekker: New York, 1985. 

20. Guenther P. L.; Stedman, D. H.; Bishop, G. A.; Beaton, S. P.; Bean, J. H.; Quine, R. W. 

A Hydrocarbon Detector for the Remote Sensing of Vehicle Exhaust Emissions. Review of 

Scientific Instruments 1995, 66, 3024–3029. 

21. Brandt Instruments, Inc. Use of “Propane Equivalent” Calibration Gas Mixtures. 

http://www.brandtinst.com/biosystems/appnotes/equiv3.htm (accessed May 2003). 

22. Modiano S. H.; McNesby, K. L.; Marsh, P. E.; Bolt, W.; Herud, C. Quantitative Measurements 

by Fourier Transform Infrared Spectroscopy of Toxic Gas Production During Inhibition of JP-8 

Fires by CF3Br and C3F7H. Applied Optics 1996, 35, 4004–4008.
30

23. Griffiths, P. R.; Hirsche, B. L.; Manning, C. J. Ultra-Rapid-Scanning Fourier Transform 

Infrared Spectrometry. Vibrational Spectroscopy 1999, 19, 165–176. 

24. Naegeli, D. W.; Childress, K. H. Lower Explosion Limits and Compositions of Middle 

Distillate Fuel Vapors. Proceedings of the Fall Meeting of the Society of Automotive 

Engineers, 1998; SAE paper no. 982485, pp 1–7. 

25. Werle P. A Review of Recent Advances in Semiconductor Laser Based Gas Monitors. 

Spectrochimica Acta Part A 1998, 54, 197–236. 

26. Hertzberg, G. Infrared and Raman Spectra. Van Nostrand Rheinhold Co.: New York, 1945. 

27. McNesby, K. L.; Wainner, R. T.; Daniel, R. G.; Miziolek, A. W.; Jackson, W. M.; 

McLaren, I. A. High-Sensitivity Laser Absorption Measurements of Broadband Absorbers in 

the Near-Infrared Spectral Region. Applied Optics 2000, 39, 5006–5011. 

28. Griffiths, P. R.; de Haseth, J. A. Fourier Transform Infrared Spectrometry. WileyInterscience: New York, 1986. 

29. McNesby, K. L., Wainner, R. T.; Daniel, R. G.; Skaggs, R. R.; Morris, J. B.; Miziolek, A. W.; 

Jackson, W. M.; McLaren, I. A. Detection and Measurement of Middle-Distillate Fuel Vapors 

by Use of Tunable Diode Lasers. Applied Optics 2001, 40, 840–845. 

30. Ferraro, J. R.; Basile, L. J. Fourier Transform Infrared Spectroscopy: Applications to 

Chemical Systems, Vols. 1–3, Academic Press: New York, 1978. 

31. Cooley, J. W.; Tukey, J. W. An Algorithm for the Machine Calculation of Complex Fourier 

Series. Mathematics of Computation 1965, 19, 297. 

32. Rothman, L. S.; Gamache, R. R.; Tipping, R. H.; Rinsland, C. P.; Smith, M. A. H.; Chris, D.; 

Benner, V.; Devi, M.; Flaud, J. M.; Camy-Peyret, C.; Perrin, A.; Goldman, A.; Massie, S. T.; 

Brown, L. R.; Toth, R. A. The Hitran Molecular Database: Editions of 1991 and 1992. 

Journal of Quantitative Spectroscopy and Radiative Transfer 1992, 48, 469. 

33. McNesby, K. L.; Miziolek, A. W. Fourier Transform Laser Spectroscopy. Applied Optics, 

submitted for publication. 

34. Zhu, X.; Cassidy, D. T. Liquid Detection With InGaAsP Semiconductor Lasers Having 

Multiple Short External Cavities. Applied Optics-LP 1996, 35 (24), 4689–4693.
31

Bibliography 

Daniel, R. G.; McNesby, K. L.; Skaggs, R. R.; Sagear, P.; Miziolek, A. W. Spectroscopy of 

Inhibited Counterflow Diffusion Flames. 1997 JANNAF Propellant Development and 

Characterization Subcommittee Meeting, West Palm Beach, FL, 1997. 

Lancaster, E. D.; McNesby, K. L.; Daniel, R. G.; Miziolek, A. W. Spectroscopic Analysis of Fire 

Suppressants and Refrigerants by Laser Induced Breakdown Spectroscopy. Applied Optics

1999, 38, 1476. 

McNesby, K. L. Flame and Temperature Measurement Using Vibrational Spectroscopy. 

Encyclopedia of Spectroscopy and Spectrometry, Academic Press: London, 2000; pp 548–559. 

McNesby, K. L.; Miziolek, A. W. Fourier Transform Laser Spectroscopy. Applied Optics, 

submitted for publication, July 2000. 

McNesby, K. L.; Daniel, R. G.; Miziolek, A. W.; Modiano, S. H. Optical Measurement of Toxic 

Gases Produced During Firefighting Using Halons. ARL-TR-1349, U.S. Army Research 

Laboratory: Aberdeen Proving Ground, MD, April 1997. 

McNesby, K. L.; Daniel, R. G.; Modiano, S. H.; Miziolek, A. W. Optical Measurement of Toxic 

Gases Produced During Firefighting Using Halons. Applied Spectroscopy 1997, 51, 678–683. 

McNesby K. L.; Skaggs, R. R.; Miziolek, A. W.; Clay, M.; Hoke, S.; Miser, C. S. Diode LaserBased Measurements of Hydrogen Fluoride Gas During Chemical Suppression of Fires. 

Applied Physics B 1998, 67, 443. 

McNesby, K. L.; Skaggs, R. R.; Miziolek, A. W.; Clay, M.; Hoke, S.; Miser, C. S. Diode LaserBased Measurements of Hydrogen Fluoride Gas During Chemical Suppression of Fires. 

ARL-TR-1785; U.S. Army Research Laboratory: Aberdeen Proving Ground, MD, 1998. 

McNesby, K. L.; Skaggs, R. R.; Miziolek, A. W.; Daniel, R. G.; Miser, C. S. Near-Infrared 

Tunable Laser Diagnostics In Laboratory Scale Flames. Proceedings of Laser Applications to 

Chemical and Environmental Analysis Topical Meeting, 1998; p 203. 

McNesby, K. L.; Skaggs, R. R.; Miziolek, A. W.; McLaren, I. A. Diode Laser-Based Detector for 

Fast Detection of Binary Gas Mixtures. Proceedings of the 1999 Halon Options Technical 

Working Conference, Albuquerque, NM, 1999. 

McNesby, K. L.; Daniel, R. G.; Miziolek, A. W.; Wainner, R. T.; Jackson, W. M.; McLaren, I. A. 

Measurement of Middle Distillate Fuel Vapor Concentrations Using Diode Laser Spectroscopy. 

Proceedings of Halon Options Technical Working Conference (HOTWC), May 2000. 
32

McNesby, K. L.; Miziolek, A. W.; McLaren, I. A. Rapid High Sensitivity Laser Absorption 

Measurements of Broad Band Absorbers in the Near Infrared Spectral Region. In Laser 

Applications to Chemical and Environmental Analysis, OSA (Optical Society of America) 

Technical Digest, 2000; pp 80–83. 

McNesby, K. L.; Miziolek, A. W.; McLaren, I. A. Rapid High Sensitivity Laser Absorption 

Measurements of Broad Band Absorbers in the Near Infrared Spectral Region. Proceedings of 

Laser Applications to Chemical and Environmental Analysis Topical Meeting, 2000; p 80. 

McNesby, K. L.; Wainner, R. T.; Miziolek, A. W.; Jackson, W. M.; McLaren, I. A. High 

Sensitivity Laser Absorption Measurements of Broad Band Absorbers in the Near-Infrared 

Spectral Region. Applied Optics-LP 2000, 39 (27), 5006–5011. 

McNesby, K. L.; Wainner, R. T.; Daniel, R. G.; Skaggs, R. R.; Morris, J. B.; Miziolek, A. W.; 

Jackson, W. M.; McLaren, I. A. Detection and Measurement of Middle Distillate Fuel Vapors 

Using Tunable Diode Lasers. Applied Optics 2001, 40, 840–845. 

Miziolek A. W.; McNesby, K. L.; Wainner, R. T.; Harmon, R. S.; French, P. D. LIBS: An 

Emerging Chemical Sensor Technology for Field Use in Warfare and Peacetime Applications. 

Army Science Conference, 2000. 

Skaggs, R. R.; Daniel, R. G.; Miziolek, A. W.; McNesby, K. L.; Herud, C.; Bolt, W. R.; 

Horton, D. Diode Laser Measurements of HF Concentrations From Heptane/Air Pan Fires 

Extinguished by FE-36 And FE-36 Plus Ammonium Polyphosphate. 1998 Proceedings of the 

International Society for Optical Engineering, Photonics East Conference, 1999. 

Skaggs, R. R.; Daniel, R. G.; Miziolek, A. W.; McNesby, K. L.; Herud, C.; Bolt, W. R.; 

Horton, D. Diode Laser Measurements of HF Concentrations Produced From Heptane/Air Pan 

Fires Extinguished by FE-36, FM-200, FE-36 Plus APP, or FM-200 Plus APP. Applied 

Spectroscopy 1999, 53, 1143. 

Skaggs, R. R.; Daniel, R. G.; Miziolek, A. W.; McNesby, K. L.; Herud, C.; Bolt, W. R.; 

Horton, D. Diode Laser Measurements of HF Concentrations from Heptane/Air Pan Fires 

Extinguished by FE-36 and FE-36 Plus Ammonium Polyphosphate. ARL-TR-2143; U.S. Army 

Research Laboratory: Aberdeen Proving Ground, MD, January 2000. 

Skaggs, R. R.; Daniel, R. G.; Miziolek, A. W.; McNesby, K. L.; Herud, C.; Bolt, W. R.; 

Horton, D. Diode Laser Measurements of HF Concentrations Produced From Heptane/Air Pan 

Fires Extinguished by FE-36, FM-200, FE-36 Plus APP, or FM-200 Plus APP. Proceedings of 

the 1998 JANNAF Combustion Meeting, 2000; CPIA Publication 685, p 161. 

Williamson, C. K.; McNesby, K. L.; Daniel, R. G.; Miziolek, A. W. Laser-Induced Breakdown 

Spectroscopy for Real-Time Detection of Halon Alternative Agents. Analytical Chemistry 

1998, 70, 1186–1191. 
NO. OF NO. OF 

COPIES ORGANIZATION COPIES ORGANIZATION

1

 2 DEFENSE TECHNICAL 

 INFORMATION CENTER 

 DTIC OCA 

 8725 JOHN J KINGMAN RD 

 STE 0944 

 FT BELVOIR VA 22060-6218 

 1 COMMANDING GENERAL 

 US ARMY MATERIEL CMD 

 AMCRDA TF 

 5001 EISENHOWER AVE 

 ALEXANDRIA VA 22333-0001 

 1 INST FOR ADVNCD TCHNLGY 

 THE UNIV OF TEXAS AT AUSTIN 

 3925 W BRAKER LN STE 400 

 AUSTIN TX 78759-5316 

 1 US MILITARY ACADEMY 

 MATH SCI CTR EXCELLENCE 

 MADN MATH 

 THAYER HALL 

 WEST POINT NY 10996-1786 

 1 DIRECTOR 

 US ARMY RESEARCH LAB 

 AMSRL D 

 DR D SMITH 

 2800 POWDER MILL RD 

 ADELPHI MD 20783-1197 

 1 DIRECTOR 

 US ARMY RESEARCH LAB 

 AMSRL CS IS R 

 2800 POWDER MILL RD 

 ADELPHI MD 20783-1197 

 3 DIRECTOR 

 US ARMY RESEARCH LAB 

 AMSRL CI OK TL 

 2800 POWDER MILL RD 

 ADELPHI MD 20783-1197 

 3 DIRECTOR 

 US ARMY RESEARCH LAB 

 AMSRL CS IS T 

 2800 POWDER MILL RD 

 ADELPHI MD 20783-1197 

ABERDEEN PROVING GROUND

 2 DIR USARL 

 AMSRL CI LP (BLDG 305) 

 AMSRL CI OK TP (BLDG 4600)