Photonic-crystal ﬁber based CARS microspectroscopypotma/UCI2006.pdf · Photonic-crystal ﬁber based CARS microspectroscopy UCI 2006 Esben Ravn Andresen, Henrik Nørgaard Paulsen,

UCI 3 March 2006 PCF-based CARS microspectroscopy - p. 1/??

Photonic-crystal fiber based CARSmicrospectroscopy

UCI 2006

Esben Ravn Andresen, Henrik Nørgaard Paulsen, Victoria Birkedal,Jan Thøgersen, and Søren Rud KeidingDept. of Physics and Astronomy and Dept. of Chemistry

University of Aarhus

Femtolab: www.femtolab.au.dk

Introduction

● Motivation

● Multiplex CARS

● The optimal light source for

MCARS● Photonic-crystal fibers

Spectral Compression

Continuum generation

Soliton generation

CARS microspectroscopy

Conclusion and Outlook


Introduction

Introduction

● Motivation

● Multiplex CARS





Soliton generation




Motivation

■ Coherent anti-Stokes Raman Scattering (CARS)microspectroscopy◆ First realization in 2002 (Muller et al., Cheng et al.)◆ Contrast arises from the Raman spectrum of the sample.◆ Microscopic image with spectral information in every pixel.

Introduction

● Motivation

● Multiplex CARS





Soliton generation




Motivation


■ Can be realized with two inter-locked lasers.

Introduction

● Motivation

● Multiplex CARS





Soliton generation




Motivation


■ Can be realized with two inter-locked lasers.■ Can we realize a simpler implementation?

◆ Femtosecond (fs) laser oscillator (Mira).◆ Frequency conversion in photonic-crystal fibres (PCF).

Introduction

● Motivation

● Multiplex CARS





Soliton generation




Multiplex CARS

■ Multiplex CARS

Introduction

● Motivation

● Multiplex CARS





Soliton generation




Multiplex CARS

■ Multiplex CARS◆ P spectrally narrow

(spectral resolution); Sspectrally broad (widthof probed spectralregion).

Introduction

● Motivation

● Multiplex CARS





Soliton generation




Multiplex CARS



◆ Excitation of 2.-orderpolarization.

Introduction

● Motivation

● Multiplex CARS





Soliton generation




Multiplex CARS





Introduction

● Motivation

● Multiplex CARS





Soliton generation




Multiplex CARS





◆ The anti-Stokesspectrum.

Raman (Stokes) CARS (anti−Stokes)Pumpe

FrekvensIn

tens

itet

Introduction

● Motivation

● Multiplex CARS





Soliton generation




The optimal light source for MCARS

■ We have◆ Mira fs laser oscillator◆ Pave = 500 mW; Epulse = 5 nJ; ν0 = 12500cm−1;

∆ν = 300cm−1; τ0 = 40fs; νrep = 76MHz.

Introduction

● Motivation

● Multiplex CARS





Soliton generation






∆ν = 300cm−1; τ0 = 40fs; νrep = 76MHz.■ We want

◆ Pump pulse: ∆ν ≈ 10 cm−1; Pave ≈ 20 mW.◆ Stokes pulse: ∆ν ≈ 300 cm−1; Pave ≈ 20 mW; ν0 must be

tunable from 12500 cm−1 to 9000 cm−1.

Introduction

● Motivation

● Multiplex CARS





Soliton generation








tunable from 12500 cm−1 to 9000 cm−1.■ What dælen do we do?

Introduction

● Motivation

● Multiplex CARS





Soliton generation









◆ Two interlocked lasers? Too expensive.

Introduction

● Motivation

● Multiplex CARS





Soliton generation









◆ Two interlocked lasers? Too expensive.◆ Parametric conversion? Not enough laser power.

Introduction

● Motivation

● Multiplex CARS





Soliton generation









◆ Two interlocked lasers? Too expensive.◆ Parametric conversion? Not enough laser power.◆ Photonic-crystal fibers!

Introduction

● Motivation

● Multiplex CARS





Soliton generation




Photonic-crystal fibers

■ PCF: microstuctured fiber◆ Very small core (high

nonlinearity (frequencyconversion))

◆ Novel dispersionproperties

600 800 1000 1200 1400

−2

0

2

4

6

8

10x 10

4

β 2 /

fs2 /

m

λ / nm

Fiber1

Fiber2

Introduction

● Motivation

● Multiplex CARS





Soliton generation




Photonic-crystal fibers

■ PCF: microstuctured fiber◆ Very small core (high

nonlinearity (frequencyconversion))

◆ Novel dispersionproperties

◆ New nonlinearphenomena becomepossible at ν0 = 12500cm−1:■ Spectral compression■ Continuum generation

by four-wave mixing■ Soliton generation and

soliton self-frequencyshift

■ (...and other veryexotic phenomena)

600 800 1000 1200 1400

−2

0

2

4

6

8

10x 10

4

β 2 /

fs2 /

m

λ / nm

Fiber1

Fiber2

Introduction


● Spectrallyl compressed P

pulse

● Setup

● Results


Soliton generation





Introduction



pulse

● Setup

● Results


Soliton generation




Spectrallyl compressed P pulse

■ Principle◆ Send negatively chirped

pulse through a PCF(large nonlinearity, smallβ2 > 0).

◆ Self-phase modulation(SPM) compensates thechirp.

Tid

Inst

anta

n fr

ekve

ns d

φ / d

t SPM

Input

Output

Introduction



pulse

● Setup

● Results


Soliton generation








◆ Redistribution offrequency components.

Tid

Inst

anta

n fr

ekve

ns d

φ / d

t SPM

Input

Output

Frekvens

Nor

mal

iser

et in

tens

itet

Input

Output

Introduction



pulse

● Setup

● Results


Soliton generation








◆ Redistribution offrequency components.

■ By virtue of the chosenPCF, dispersion can beneglected.

Tid

Inst

anta

n fr

ekve

ns d

φ / d

t SPM

Input

Output

Frekvens

Nor

mal

iser

et in

tens

itet

Input

Output

Introduction



pulse

● Setup

● Results


Soliton generation




Setup

■ Fiber parametersβ2(800nm) = 3400 fs2 / m(v. small); γ = 0.09W−1m−1 (v. large); L = 60cm.

■ Laser parametersνrep = 76 MHz, ∆ν = 300cm−1, τ0 = 50 fs, Epulse ≈ 5nJ.

600 700 800 900 1000 1100 1200 1300−1

0

1

2

3

4

5

6

7x 10

4

β 2 /

fs2 /

m

λ / nm

Introduction



pulse

● Setup

● Results


Soliton generation




Results

■ Best results◆ ∆ν = 14 cm−1.◆ Compression factor =

21.◆ Brightness increase

factor = 5.

0 2000 4000 6000 80000

10

20

30

40

50

60

Længde af chirpet puls (FWHM) / fs

Min

. spe

ktra

l bre

dde

(FW

HM

) / c

m−

1 BeregningMåling

Introduction



pulse

● Setup

● Results


Soliton generation




Results

■ Best results◆ ∆ν = 14 cm−1.◆ Compression factor =

21.◆ Brightness increase

factor = 5.■ Dependency of input pulse

energy (calculated) 0 2000 4000 6000 8000010

20

30

40

50

60

Længde af chirpet puls (FWHM) / fs

Min

. spe

ktra

l bre

dde

(FW

HM

) / c

m−

1 BeregningMåling

01020304050600

0.5

1

1.5

2

2.5

3

3.5

4

Min. spektral bredde (FWHM) / cm−1

Pul

sene

rgi /

nJ

Introduction



● S pulse: Continuum

generation 1


generation 2

Soliton generation





Introduction




generation 1


generation 2

Soliton generation




S pulse: Continuum generation 1

■ Brute force approach.Send high-power (nJ) fspulse through PCF.

800 900 1000 11000

0.2

0.4

0.6

0.8

1

λ / nm

Inte

nsity

/ a.

u.

0 1000 2000 3000 4000

∆E / cm−1

Introduction




generation 1


generation 2

Soliton generation






■ Produces very widespectra, output pulse is stilla fs pulse. 800 900 1000 1100

0

0.2

0.4

0.6

0.8

1

λ / nm

Inte

nsity

/ a.

u.

0 1000 2000 3000 4000

∆E / cm−1

600 700 800 900 10000

0.2

0.4

0.6

0.8

1

λ / nm

Inte

nsity

/ a.

u.600 700 800 900 1000 1100 1200 13000

0.2

0.4

0.6

0.8

1

λ / nm

Inte

nsity

/ a.

u.

Introduction




generation 1


generation 2

Soliton generation






■ Produces very widespectra, output pulse is stilla fs pulse.

■ Can probe wide region ofthe Raman spectrum at thesame time.

800 900 1000 11000

0.2

0.4

0.6

0.8

1

λ / nm

Inte

nsity

/ a.

u.

0 1000 2000 3000 4000

∆E / cm−1

600 700 800 900 10000

0.2

0.4

0.6

0.8

1

λ / nm

Inte

nsity

/ a.

u.600 700 800 900 1000 1100 1200 13000

0.2

0.4

0.6

0.8

1

λ / nm

Inte

nsity

/ a.

u.

Introduction




generation 1


generation 2

Soliton generation






■ Produces very widespectra, output pulse is stilla fs pulse.

■ Can probe wide region ofthe Raman spectrum at thesame time.

■ Fiber parameters:◆ Middle: γ = 0.04

(Wm)−1; L ≈ 5 cm;◆ Bottom: γ = 0.09

(Wm)−1; L ≈ 5 cm;

800 900 1000 11000

0.2

0.4

0.6

0.8

1

λ / nm

Inte

nsity

/ a.

u.

0 1000 2000 3000 4000

∆E / cm−1

600 700 800 900 10000

0.2

0.4

0.6

0.8

1

λ / nm

Inte

nsity

/ a.

u.600 700 800 900 1000 1100 1200 13000

0.2

0.4

0.6

0.8

1

λ / nm

Inte

nsity

/ a.

u.

Introduction




generation 1


generation 2

Soliton generation





■ Advantages:◆ Very simple and compact light source◆ Very wide spectra◆ Generation of hard-to-generate colours◆ Fiber nonlinearity so high that dispersion can almost be

neglected■ Disadvantages:

◆ Low spectral density (wide spectra...)◆ Output spectra are hard to control

Introduction



Soliton generation

● S pulse: Soliton generation 1





Soliton generation

Introduction



Soliton generation






S pulse: Soliton generation 1

■ Soliton◆ A pulse that is unaltered

upon propagation in thefiber.

◆ Input pulse converges toa soliton in certainPCFs.

Introduction



Soliton generation










■ Soliton self-frequency shift:◆ Intrapulse stimulated

Raman scattering =>.◆ Adiabatic frequency shift

of the soliton.

0 2000 40000

50

100

Con

v. /

%

∆ν / cm−1

010002000300040005000

Frequency shift / cm−1

Inte

nsity

/ a.

u.

8009001000110012001300

λ / nm

0 2000 40000

5

10

Pou

t / m

W

Introduction



Soliton generation










■ Soliton self-frequency shift:◆ Intrapulse stimulated

Raman scattering =>.◆ Adiabatic frequency shift

of the soliton.■ Fiber parameters:

◆ γ = 0.09 (Wm)−1; L = 2m

0 2000 40000

50

100

Con

v. /

%

∆ν / cm−1

010002000300040005000

Frequency shift / cm−1

Inte

nsity

/ a.

u.

8009001000110012001300

λ / nm

0 2000 40000

5

10

Pou

t / m

W

Introduction



Soliton generation







■ Advantages◆ Excellent conversion efficiency◆ Frequency shift easily tunable 0-4000 cm−1.◆ Spectral density similar to that obtained by continuum

generation◆ Stokes pulse is transform-limited because of its solitonic

nature■ Downsides

◆ Shift is coupled to input power◆ Soliton energy is intrinsically limited to ≈ 10 pJ.

Introduction



Soliton generation


● Setup

● Results 1

● Results 2




Introduction



Soliton generation


● Setup

● Results 1

● Results 2



Setup

Introduction



Soliton generation


● Setup

● Results 1

● Results 2



Results 1

10 20 30 40

5

10

15

20

25

30

35

40

pixels

pixe

ls

Polystyren5um_3000cm_2

2000 2500 3000 35000

500

1000

1500Active...

νP − ν

S / cm−1

10 20 30 40

5

10

15

20

25

30

35

40

pixels

pixe

ls

Introduction



Soliton generation


● Setup

● Results 1

● Results 2



Results 2

10 20 30 40

5

10

15

20

25

30

35

40

pixels

pixe

ls

polystyren5um_1600cm_2

800 1000 1200 1400 1600 1800 2000 2200165

170

175

180

185

190

195

Active...

νP − ν

S / cm−1

10 20 30 40

5

10

15

20

25

30

35

40

pixels

pixe

ls

Introduction



Soliton generation



● Conclusion

● Outlook

● Publications



Introduction



Soliton generation



● Conclusion

● Outlook

● Publications


Conclusion

■ Presented low-budget, alternative implementations of CARSmicrospectroscopy◆ Spectral compression (pump)◆ Continuum generation (Stokes)◆ Soliton self-frequency shift (Stokes)

Introduction



Soliton generation



● Conclusion

● Outlook

● Publications


Conclusion

■ Presented low-budget, alternative implementations of CARSmicrospectroscopy◆ Spectral compression (pump)◆ Continuum generation (Stokes)◆ Soliton self-frequency shift (Stokes)

■ Discussion◆ Pump pulse is ok - fs pulse -> near-TFL ps pulse (spectral

density ≈ 5 · 10−11 J/cm−1.◆ Difficult to reach high spectral density in Stokes pulse

(≈ 5 · 10−14 J/cm−1).

Introduction



Soliton generation



● Conclusion

● Outlook

● Publications


Outlook

■ Remedy low Stokes spectral density with a fiber amplifier.■ CARS microscopy with chirped pump and chirped Stokes

pulse.■ Replace Mira with (cheap) fiber laser, and entire light source

fits in a shoe box.■ Heterodyne detection with PCF-generated local oscillator.

Introduction



Soliton generation



● Conclusion

● Outlook

● Publications


Publications

Documents

Photonic-crystal ﬁber based CARS microspectroscopypotma/UCI2006.pdf · Photonic-crystal ﬁber based CARS microspectroscopy UCI 2006 Esben Ravn Andresen, Henrik Nørgaard Paulsen,