temperature measurements in flames at 1000 hz using femtosecond coherent anti-stokes raman...

Temperature Measurements in Flames at 1000 Hz Using Femtosecond Coherent Anti-Stokes Raman

Spectroscopy

Temperature Measurements in Flames at 1000 Hz Using Femtosecond Coherent Anti-Stokes Raman

Spectroscopy

Daniel R. Richardson and Robert P. Lucht Purdue University, West Lafayette, Indiana 47907

Waruna D. Kulatilaka and Sukesh RoySpectral Energies, LLC, 2513 Pierce Avenue, Ames, IA 50010

James R. GordAir Force Research Laboratory, Propulsion Directorate, Wright-

Patterson AFB, Ohio 45433

AIAA Aerospace Sciences Meeting Orlando, FL January 7, 2010

AcknowledgmentsAcknowledgments

• Funding for this research was provided by the Air Force Office of Scientific Research (Dr. Julian Tishkoff, Program Manager), and by the Air Force Research Laboratory, Propulsion Directorate, Wright-Patterson Air Force Base, under Contract No. F33615-03-D-2329, by the National Science Foundation, Combustion and Plasmas Program under Award Number 0413623-CTS, and by the U.S. Department of Energy, Division of Chemical Sciences, Geosciences and Biosciences, under Grant No. DE-FG02-03ER15391.

• Excellent technical assistance from Kyle Frisch at WPAFB.

Outline of the Presentation Outline of the Presentation

• Introduction and Motivation

• Fs CARS Measurements of Temperature in Flames: Frequency-Spread Dephasing Decay of the Initial Raman Coherence

• Impulsive Interaction of the fs Pump and Stokes Beams to Create Giant Raman Coherence at t=0

• Used of Chirped Probe to Map Temporal Domain into Frequency Domain: Single-Shot Temperature Measurements

• Conclusions and Future Work

Ns CARS for Gas-Phase Diagnostics Ns CARS for Gas-Phase Diagnostics


Ground Electronic Level

v" = 0, J

v" = 1, J

v" = 2

Frequency

Broadband Dye LaserSpectrum

Single-Shot Multiplex CARS Spectrum

• Nonintrusive

• Coherent Laser-Like Signal

• Spatially and Temporally Resolved

• Excellent Gas-Temperature Measurement Technique

• Nonresonant Background

• Collisional/Linewidth Effects

• Data-Acquisition Rates: No Correlation Between Laser Shots at 10 Hz

• Broadband Dye Laser Mode Noise


Good Bad

Fs CARS for Gas-Phase Diagnostics Fs CARS for Gas-Phase Diagnostics

• Nanosecond CARS using (typically) a Q-switched Nd:YAG laser and broadband dye laser is a well-established technique for combustion and plasma diagnostics

• Fs lasers have much higher repetition rates than ns Q-switched Nd:YAG lasers: > 1 kHz versus ~10 Hz

Fsec CARS for Gas-Phase Diagnostics Fsec CARS for Gas-Phase Diagnostics

• For application as a diagnostic probe for turbulent flames, signal levels must be high enough to extract data on a single laser shot from a probe volume with maximum dimension ~ 1mm.

• How effectively can Raman transitions with line width ~ 0.1 cm-1 line width be excited by the fs pump and Stokes beams (200 cm-1 bandwidth)? Answer: very effectively.

• How do we extract temperature and concentration from the measured single-shot fs CARS signals?

Ultrafast Laser System for Fs CARSUltrafast Laser System for Fs CARS

Optical System for Fs CARS with Mechanically Scanned Probe

Optical System for Fs CARS with Mechanically Scanned Probe

Calculated Time Dependence of CARS Intensity with Time-Delayed Probe Beam


10-34

10-33

10-32

10-31

10-30

10-29

10-28

10-27

0 50 100 150 200

CA

RS

Inte

nsity

Time (psec)

T = 300 KAt t = 0 psec, all Raman transitions oscillate in phase = giant coherence

At t > 20 psec, Raman transitions oscillate with essentially random phases



0.0001

0.001

0.01

0.1

1

10

0 5 10 15

300 K500 K

1000 K2000 K

CA

RS

Inte

nsi

ty (

arb

. un

its)

Time (psec)

(a)100

1000

104

105

106

2250 2265 2280 2295 2310 2325 2340

300 K

2000 K (x 100)

CA

RS

Int

ensi

ty (

arb.

un

its)

Raman Shift (cm-1)

(b)

Calculated Time Dependence of CARS Intensity with Time-Delayed Probe BeamCalculated Time Dependence of CARS

Intensity with Time-Delayed Probe Beam

0.01

0.1

1

0 0.5 1 1.5 2 2.5 3

300 K

500 K

1000 K

2000 K

CA

RS

Int

ensi

ty (

Nor

m.)

Time (psec)

(c) Temperature can be determined from the decay of the initial Raman coherence due to frequency-spread dephasing – Raman transitions oscillate with different frequencies.

Theory for Fitting Time-Delayed Probe Fs CARS Data

Theory for Fitting Time-Delayed Probe Fs CARS Data

cos expt

res p s i i ii i

dP t E t E t dt N t t

d

nres p sP t E t E t

2

pr res nresS I t P t P t dt

Input parameters from spectroscopic databaseFitting parameters

R. P. Lucht et al., Appl. Phys. Lett. 89, 251112 (2006).

Fs CARS Experimental Results: Flame Temperatures

Fs CARS Experimental Results: Flame Temperatures

S. Roy et al.,Opt. Commun. 281, 319-325 (2008).

Raman Excitation for Fs Pump and Stokes Pulses

Raman Excitation for Fs Pump and Stokes Pulses

• There is a drastic difference in laser bandwidth (150-200 cm-1) and Raman line width (0.05 cm-1) for 100-fs pump and Stokes laser pulses.

• How effectively do the laser couple with the narrow Raman transitions?

• Can single-laser-shot fs CARS signals be obtained from flames? (The answer is yes)

Coupling of 70-Fs Pump and Stokes Pulses with the Raman Coherence

Coupling of 70-Fs Pump and Stokes Pulses with the Raman Coherence

Numerical Model of fs CARS in N2Numerical Model of fs CARS in N2

• A model of the CARS process in nitrogen based on direct numerical integration of the time-dependent density matrix equations has been developed [Lucht et al., Journal of Chemical Physics, 127, 044316 (2007)].

• Model is nonperturbative and is based on direct numerical integration of the time-dependent density matrix equations.

Single-Laser-Shot Fs CARS Measurements

Single-Laser-Shot Fs CARS Measurements

• Most significant difference for fs CARS compared to ns CARS is the potential for data rates of 1-100 kHz as compared to 10-30 Hz for ns CARS.

Optical System for Single-Pulse fs CARS with Chirped Probe Pulse


Stokes Beam - 2780 nm, 70 fsec

Pump Beam - 1660 nm, 70 fsec

Probe Beam - 3660 nm, 70 fsec

Delay Linefor Probe

CARS Signal Beam - 4Turbulent Flame

or Gas Cell

Chirped Probe Pulse2-3 psec

Raman Coherence

t

DispersiveRod

60 cm SF11

To Spectrometerand EMCCD

Lang and Motzkus, JOSA B 19, 340-344 (2002).

Single-Shot CPP fs CARSSingle-Shot CPP fs CARS

10-5

10-4

10-3

10-2

10-1

-2 -1 0 1 2 3 4 5

500K600K800KC

AR

S In

tens

ity

Probe Delay Time (ps)

+2 ps Probe Delay

4 Single-Shots with Chirped Probe Pulse4 Single-Shots with Chirped Probe Pulse

Probe Delay = +2 ps300 K

900 K

Theory for CPP fs CARSTheory for CPP fs CARS

cos expt

res p s i i ii i

dP t E t E t dt N t t

d

nres p sP t E t E t

2

pr res nresS I t P t P t dt

Input parameters from spectroscopic database

Fitting parameters

2

00

2

0 0 0

exp

cos

prpr pr

pr

pr pr pr pr pr

t tE t E

t

t t t t

Linear chirp parameter

Envelope function


Source: Swamp Optics website


nonres pr nonres

pr p s

E t E t P t

E t E t E t

res pr resE t E t P t

Calculate time-dependent nonresonant signal:

Calculate time-dependent resonant signal:

cos

sin

real nonres res

imag nonres res

E E t E t t dt

E E t E t t dt

2 2real imagS E E


Fourier transform time-dependent CARS signal:

CPP fs CARS Spectrum in Room Temp Air

CPP fs CARS Spectrum in Room Temp Air

0

5 102

1 103

1.5 103

2 103

2.5 103

3 103

3.5 103

4 103

0

5 1011

1 1012

1.5 1012

16920 17040 17160 17280 17400

Experiment Theory

N2 C

AR

S S

ign

al (

arb

. uni

ts) N

2 CA

RS

Sign

al (arb. u

nits)

CARS Signal Frequency (cm -1)

CPP fs CARS Spectrum at +2 ps Delay for 500 K


0

2 102

4 102

6 102

8 102

1 103

1.2 103

0

2 1011

4 1011

6 1011

8 1011

1 1012

1.2 1012

1.4 1012

16920 17040 17160 17280 17400

Experiment TheoryN

2 C

AR

S S

ign

al (

arb

. uni

ts) N

2 CA

RS

Sign

al (arb. u

nits)


Theoretical fit parameters same as for 300 K spectra




0

2 102

4 102

6 102

8 102

1 103

1.2 103

0

2 1011

4 1011

6 1011

8 1011

1 1012

1.2 1012

16920 17040 17160 17280 17400

Experiment TheoryN

2 C

AR

S S

igna

l (ar

b. u

nits

) N2 C

AR

S S

igna

l (arb. u

nits)





0

2 102

4 102

6 102

8 102

1 103

1.2 103

0

2 1011

4 1011

6 1011

8 1011

1 1012

16920 17040 17160 17280 17400

Experiment TheoryN

2 C

AR

S S

igna

l (ar

b. u

nits

) N2 C

AR

S S

igna

l (arb. u

nits)


CPP fs CARS Spectra at +2 ps DelayCPP fs CARS Spectra at +2 ps Delay

0

5 1011

1 1012

1.5 1012

16950 17100 17250 17400

300 K

500 K

700 K

900 K

S(

) (a

rb.

units

)

Signal Frequency (cm -1)

Chirped Probe Delay Time = +2 ps

Temperature Histograms from Single-Shot fs CARS

Temperature Histograms from Single-Shot fs CARS

Temperature Histograms from Single-Shot fs CARS from Flames

Temperature Histograms from Single-Shot fs CARS from Flames

1 kHz Temperature Data from Flame with a 10 Hz Driven Pulsation

1 kHz Temperature Data from Flame with a 10 Hz Driven Pulsation

1 kHz Temperature Excursion Data from Flame with a 10 Hz Driven Pulsation

1 kHz Temperature Excursion Data from Flame with a 10 Hz Driven Pulsation

0

100

200

300

400

500

600

700

50 100 150 200

363-1670K365-1620K366-1568K368-1545K369-1601K370-1674K377-1772K

CA

RS

Sig

nal

(a

.u.)

Pixel

Laser Shot Number - Fit Temperature (K)

1 kHz Temperature Excursion Data from a Turbulent Bunsen Burner Flame


0

400

800

1200

1600

2000

2400

2800

3200

100 200 300 400 500 600

100101102103104

CA

RS

Sig

nal

(a

.u.)

Pixel

Laser Shot Number



0

0.2

0.4

0.6

0.8

1

100 200 300 400 500 600

100101102103104

CA

RS

Sig

nal

(a

.u.)

Pixel

Laser Shot Number

ConclusionsConclusions

• Single-shot fs CARS spectra from N2 recorded at 1000 Hz from atmospheric pressure air at temperatures of 300, 500, 700, and 900 K, and from laminar, unsteady, and turbulent flames.

• Signals are very strong and reproducible from shot to shot. Precision and accuracy comparble to best single-shot ns CARS.

• Theoretical model developed to fit CPP fs CARS spectra temperature. Agreement is excellent for +2 ps probe delay at all temperatures. Other probe delays also show promise.

Future Work: fs CARSFuture Work: fs CARS

• Analyze recent single-shot data acquired in a turbulent flame at a data rate of 1 kHz. Signals were excellent but data has a long tail to the high-frequency side due to probe spectrum, complicating data analysis.

• Implement better characterization/phase control of the laser beams. Pulse shaping/control for the pump and Stokes beams may also be quite useful for suppressing nonresonant background.

• Develop strategies for optimal strategies for temperature and concentration measurements.


• New laser system from Coherent ordered (AFOSR DURIP Program).

• Laser rep rate of either 5 kHz with 3 mJ per pulse or 10 kHz with 1.2 mJ per pulse.

• Nominal pulse durations of either 90 fs or 40 fs.

• Pulse shaper integrated into the system between the oscillator and amplifier.

Potential Advantages of fs CARSPotential Advantages of fs CARS

• Data rate of 1-100 kHz would allow true time resolution, study of turbulent fluctuations and of transient combustion events.

• Data rate of 1-100 kHz as opposed to 10 Hz would decrease test time considerably in practical applications.

• Fs CARS, unlike ns CARS, is insensitive to collision rates even up to pressure > 10 bars (fs CARS signal increases with square of pressure).


• Fs laser pulses are near-Fourier-transform limited, noise decreased significantly for single-shot measurements.

• Because collisions do not influence the spectrum, no Raman linewidths are needed for temperature fitting code.

Chirped Probe Pulse Cross-Correlation with Fundamental Beam

Chirped Probe Pulse Cross-Correlation with Fundamental Beam

Single-Shot CPP fs CARSSingle-Shot CPP fs CARS

10-5

10-4

10-3

10-2

10-1

-2 -1 0 1 2 3 4 5

500K600K800KC

AR

S In

tens

ity


+2 ps Probe Delay

ConclusionsConclusions

• Single-shot fs CARS spectra from N2 recorded at 1000 Hz from atmospheric pressure air at temperatures of 300, 500, 700, and 900 K, and from flames. Signals are very strong and reproducible from shot to shot.

• Theoretical model developed to calculate synthetic CPP fs CARS spectra for comparison with experiment. Agreement is excellent for latest set of data at +2 ps probe delay at all temperatures.


• Implement least-squares fitting routine to obtain quantitative agreement between theory and experiment.

• Implement better characterization/phase control of the laser beams.

• Develop strategies for optimal strategies for temperature and concentration measurements.


• Fs lasers with mJ output and rep rates of up to 100 kHz will be available soon, use of these fs laser systems has the potential to revolutionize diagnostic measurements in reacting flows – data rate increase of 2-3 orders of magnitude.

• New methods will be required for signal generation and analysis. Pulse shaping/control for the pump and Stokes beams may be quite useful for suppressing nonresonant background. Pulse shaping/control for the probe beam may be useful for extracting temperatures and concentrations.


• Data rate of 1-100 kHz would allow true time resolution, study of turbulent fluctuations and of transient combustion events

• Data rate of 1-100 kHz as opposed to 10 Hz would decrease test time considerably in practical applications

• Fs CARS, unlike ns CARS, is insensitive to collision rates even up to pressure > 10 bars (fs CARS signal increases with square of pressure)

• Fs laser pulses are near-Fourier-transform limited, noise may be decreased significantly for single-shot measurements

Chirped Probe Pulse (CPP) fs CARS in Argon Chirped Probe Pulse (CPP) fs CARS in Argon

-2 ps Probe Delay +5 ps Probe Delay

0 ps Probe Delay

-3 -2 -1 0 1 2 3 4 5

[EPu

(t) ESt

(t)]2


Temperature Measurements in FlamesTemperature Measurements in Flames

0

2 1011

4 1011

6 1011

8 1011

1 1012

1.2 1012

1.4 1012

16950 17100 17250 17400

500 K1000 K1500 K2000 K

S(

) (a

rb. u

nits

)

Signal Frequency (cm-1)

Chirped Probe Delay Time = 2 ps

Temperature Measurements in FlamesTemperature Measurements in Flames

109

1010

1011

1012

1013

16950 17100 17250 17400

500 K1000 K1500 K2000 K

S(

) (a

rb. u

nits

)

Signal Frequency (cm-1)

Chirped Probe Delay Time = 2 ps

temperature measurements in flames at 1000 hz using femtosecond coherent anti-stokes raman...

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