Fiber-based Ultrafast sources for Nonlinear Spectroscopy€¦ · • Fiber Lasers and Amps have HOD...

Fiber-based Ultrafast sources for Nonlinear Spectroscopy

Preliminary Exam for Scott R Domingue, PhD candidate

Department of Electrical and Computer Engineering Colorado State University

Nonlinear Interactions for Label-Free Chemical Imaging

The best parts of Multiphoton laser scanning microscopy:

• High Resolution (submicron) • Optical Sectioning • Imaging Through Scattering

media • Non-Invasive

BUT • Require tags/labels • Limited to Endogenous 2-Photon

Fluorescence • Appropriate Structure for SHG

SHG

TPEF

THG

Bartels Group unpublished

Imaging a follicle through 70 um thick murine ovarian tissue

Nonlinear Interactions for Label-Free Chemical Imaging

Keep the best parts of Multiphoton laser scanning microscopy:

• High Resolution (submicron) • Optical Sectioning • Imaging Through Scattering media

(maybe extend this) • Non-Invasive

BUT • Interrogate Atomic and Molecular

arrangements (label-free) • IR Spectroscopy (stronger but

sub-optimal sources • Coherent Raman (weaker but

“better” sources • Transient Absorption (leverage

any/all endogenous contrast mechanism)

Bartels Group unpublished

Imaging a follicle through 70 um thick murine ovarian tissue

900 cm-1

1150

1230

SHG

TPEF

THG

Nonlinear Imaging Tool Kit Imaging Modality Nonlinear Optical

Element Ultrafast Sources

SC Seeded Narrow-Band Amp

Soliton Self Frequency Shifting

Dual-Band SC

Er Fiber Laser

Normal Dispersion SC

ANDi fiber Laser

ANDi seeded MOPA

Ti:Saphire

SHG, THG, TPEF

SRS, CARS, Time-Resolved Raman

Transient Absorption (TAS)

IR / VO

3-Photon Absorption Rapid Delay

Scanner

Yb:KYW

Coherent Raman Excitation


Ener

gy

CARS 𝜕2𝑅𝜕𝑡2

+ 𝛾𝜕𝑅𝜕𝑡

+ Ω𝜈𝑅 =12𝑀

𝜕𝜕𝜕𝑅

𝐴 𝑡 2

The Frequency Domain representation: 𝐷 Ω ∝ ℱ 𝐴 𝑡 2

Beating between SC pulse pairs (15fsTL) Alternative: SC and Narrow-Band pulses

Classic Harmonic Oscillator

IR vs. Vibrational Overtone

IR / VO

Ener

gy

Vibrational Overtone Excitation

Shift to Higher frequencies • Optics are better (High

Resolution Microscope) • Potentially simpler sources • Weaker absorption cross-

sections


Er Fiber Laser

Probe altered Susceptibility: Photothermal Spectroscopy

Pump-Probe Spectroscopy

JW, Wilson et al. Selected Topics in Quantum Electronics, IEEE Journal of 18, no. 1 (2012). Robles, Francisco E., et al. Optics Express 20.15 (2012): 17082

Continue Opening-Up Potential of Pump-Probe Spectroscopy as Imaging Modality

Rapid Delay Scanner

Spectral Targets for Different the Imaging Modalities

Imaging Modality

Ultrafast Sources

Nonlinear Optical Element

Requires Bandwidth

Spectral Requisites

Ultrafast Source Comparison

Yb-Doped

Ti:Saphire

Ultrafast Source Comparison

Yb-Doped

Ti:Saphire

Pros • Cheaper: ANDi = $12k • Simple fiber Amplifiers ($10k) • Longer Wavelength: 1/3

scattering, deeper penetration in tissue

• SHG, THG, TPEF microscopy ready

Cons • Narrower bandwidth: 130 fs

pulses • Fiber Lasers and Amps have

HOD compression constraints

Pros • Broadbandwidth: <30 fs pulses • SHG, THG, TPEF microscopy

ready • Also ready limited versions of

CARS and OCT • Pumping OPO’s Cons • Not Cheap: $150k oscillators • No simple amplifiers • Often coupled to OPO’s: another

$150k • More Dispersion in typical

Optical Media

Our Goals for Yb-Doped Fiber Sources Capitalizing on and Extending these cheap, agile

sources

4 ANDi’s built and Counting…





Dual-Band SC

Er Fiber Laser


ANDi fiber Laser

ANDi seeded MOPA

Ti:Saphire

SHG, THG, TPEF



IR / VO


Scanner

Yb:KYW

Dispersion Regimes for SC generation

Anomalous, PCF

Normal, PCF

Normal, UHNA

Photonic Crystal Fiber (PCF) • Tunable Dispersion • Tight Mode-field Confinement • Need to seal the ends, tricky to

splice Ultra-high Numerical Aperture (UHNA) • Tight Modefield Confinement • Highly dispersive (~4x that of

normal fiber) • High Germanium content,

reducing the damage threshold


SHG, THG, TPEF


Transient Absorption

Yb:KYW

Bachler, B. R., et al Optics Express 20.2 (2012): 835 Dudley, J M., et al., Reviews of modern physics 78.4 (2006)

“Efficient supercontinuum generations in silica

suspended core fibers” N << 16 => P0 < 1.6 kW

Incoherent SC

Not as simple as shooting pulses into small core fibers 350 fs @ 1042 nm => Ldisersion = 4.25 m

Peak Power to keep N small, 50 μW => N = 10.2

𝐿𝐷 = τ2

β2 𝐿𝑁𝑁 =

1𝑃0γ

𝑁2 = 𝐿𝐷𝐿𝑁𝑁

Typical SC Generation with Yb-doped Sources in Anomolous Dispersion Fiber

SC Generation in Normal Dispersion Fiber

𝜕𝜕𝜕𝜕

− �in+1

n! βn

𝜕n𝜕𝜕Tn

N

n ≥2

= i γ 𝜕 2𝜕 + iω0

𝜕𝜕𝜕

𝜕 2𝜕 − TR𝜕𝜕 𝜕 2

𝜕𝜕

SPM Self-Steeping Intrapulse Raman Scattering

P║ P

║

P┴

λ/2 A-λ/2

UHNA `

Time [min]


Any Applicable Modality Yb:KYW

SC Polarization Instability in Weakly Birefringent Fiber

𝜕𝜕𝜕𝜕

− �in+1

n! βn

𝜕n𝜕𝜕Tn

N

n ≥2

= i γ 𝜕 2𝜕 + iω0

𝜕𝜕𝜕

𝜕 2𝜕 − TR𝜕𝜕 𝜕 2

𝜕𝜕

Domingue, Scott R., and Randy A. Bartels. Optics express 21.11 (2013): 13305.

The orthogonal E-field polarizations are coupled, giving rise to Polarization Modulation Instability

SC above Instability Threshold

High Correlation in Spectra Changes Mask Spectrally Integrated Noise

De-Polarization ~ 50 % RMS-N = 8% vs. ΦRSN = 20%

ΦRSN

RMS-N

RSN


ΦRSN = ∫σ λ µ(λ)dλ∫ µ2 λ dλ

∙ 100 %

RSN λ =σ λµ(λ)

⋅ 100 % 375 mW, 330 fs seed pulse

SC in Highly Bifrefringent (PM) Nonlinear Fiber

375 mW, 1 m of CorActive PM-HNLF

• Lower Nonlinearity than UHNA-3 • Highly Stable, Efficient generated SC • 21 fs Transform Limit

ΦRSN

RMS-N

RSN


De-Polarization ~ 10 % RMS-N = 0.6% vs. ΦRSN = 0.9%

Nonlinear Pulse Compression

Long PM-UHNA fibers = Large GDD and HOD Below: SC with Grating Compressor Only


Impulsive Stimulated Raman Scattering Yb:KYW

Local Characteristic Lengths Local Characteristic Lengths taken from evolving pulse

properties, local in the fiber

LD(𝜕) =τTL 𝜕 2

β2

LNL 𝜕 =1

P(𝜕)γ0

~1m

~10mm

WB

χi 𝜕 = �d𝜕′

Li 𝜕′z

0

Accumulated Dispersion and Nonlinear Lengths akin to B-Integral


Model

Accumulated Dispersion/ Nonlinearity

χD~1, LD ~ 10mm

Nonlinear Pulse Compression: • Pulse Shaper

(Transform Limit) • “Simple

Compressor” (GDD compensation)


Model

SC compression with Grating Compressor and Pulse Shaper

Nonlinear Pulse Compression

[fs]


Transform Limit dropped from 21 to 36 fs, due to non-optimal pulse shaper: visible SLM, 4λ SLM Wavefront Error, Spherical Abberation

Wavelength





Dual-Band SC

Er Fiber Laser


ANDi fiber Laser

ANDi seeded MOPA

Ti:Saphire

SHG, THG, TPEF



IR / VO


Scanner

Yb:KYW

Narrow Band Pulse Generation

A-λ/2

PM-UHNA

λ/2

1020-LP

FBG

PM-passive, delay

FBG

WDM

PM Low Yb-doped

915 nm diode

DM

λ/2

Narrow Band Amplifier

25 dB gain


SRS, CARS, … Yb-doped

TAS

Narrow Band Pulse Generation SC Seeded

Narrow-Band Amp SRS, CARS,

Yb-doped TAS

Successful Proof-of-Concept ~20 dB gain 200 μW Seed => 17.5 mW

Comparison: 300 Δλ square spectrum w/ 500 mW => ~2mW/nm 10x the power spectral density in our 980 pump

Consideration: Maintaining PM





Dual-Band SC

Er Fiber Laser


ANDi fiber Laser

ANDi seeded MOPA

Ti:Saphire

SHG, THG, TPEF



IR / VO


Scanner

Yb:KYW

?

Different Modelocking mechanism (nonlinear polarization evolution) and wildly different dispersion profiles… different SC characteristics?


Any Applicable Modality ANDi

λ/2 λ/4 λ/4

CMS Yb DC

FI

PC

BF λ/2

976

nm

diod

e

• ~ 500 mW • ~100 fs FWHM TL

All Normal Dispersion (ANDi) Fiber Lasers

λ/2 λ/4 λ/4

CMS Yb DC

FI

PC

BF λ/2

976

nm

diod

e

ANDi Spectral Noise and Pulse Compression

ΦRSN = 0.6% RMS-N = 0.4%

Cascaded Nonlinearity Results in Significant Noise Generation

+

Wavelength [nm]

= Domingue, Scott R., and Randy A. Bartels. Optics express 21.11 (2013): 13305.

ΦRSN = 3.6% RMS-N = 0.4%

ΦRSN = 0.6% RMS-N = 0.4%

ANDi Pulse Compression

• τFWHM = 177 fs • 130% of TL FWHM • 58% TL Peak Power

ANDi Pulse Compression

• τFWHM = 163 fs • 120% of TL FWHM • 73% TL Peak Power

w/ 87% of the Energy

92% of Appodized TL Cubic Aberration maps to TOD

ANDi Seeded SC Improvement with Compression

ΦRSN reduced by ~½ BUT, Bandwidth (Power) limited

ΦRSN = 1.5% RMS-N = 0.2%

ΦRSN = 3.6% RMS-N = 0.4%





Dual-Band SC

Er Fiber Laser


ANDi fiber Laser

ANDi seeded MOPA

Ti:Saphire

SHG, THG, TPEF



IR VO


Scanner

Yb:KYW

?

Master Oscillator Power Amplifier (MOPA)

Expectations: • Minimize Noise • Amplify and Broaden

Simultaneously • More Power!

Unexpected Benefits: • Cleaner Chirp • Fine Control over

Power Spectrum

Nonlinear Broadening in Amp

Applicable Modality ANDi

NLO

Master Oscillator Power Amplifier (MOPA)

`

1000 l/mm

CMS

PM DC-Yb

λ/2

MOPA Pulse Evolution

Min TL 56fs

WB

SPM

WB

Sid

e lo

be

5.2nm => 56 fs TL

How compressible are these pulses??

MOPA Compression, SPM

3rd order correction unnecessary for “SPM” pulses

• 27 nJ (1.7 W at 63 MHz)

• 144 fs FWHM, 180 kW peak power.

• 95% of TL peak power (135 fs FWHM)

1.8 nm Seed Bandwidth

10 n

m

MOPA Compression, WB W/ out 3rd

order correction (green): • 39% TL PP

3.5 nm Seed Bandwidth On-Axis

Off-Axis

Peak Power Estimates for Equal Average Power (reasonable for microscope

applications)

10 n

m

MOPA Compression, WB

W/ 3rd order correction (black) • 80 fs FWHM • 70% TL PP(60 fs

FWHM) • 20.5 nJ, 215 kW

W/ out 3rd

order correction (green): • 39% TL PP • 29 nJ

3rd order correction costs spectral appodization for large Δλ

3.5 nm Seed Bandwidth

Peak Power Estimates for Equal Average Power

10 n

m

MOPA Seeded SC Nonlinear

Broadening in Amp ANDi Normal Dispersion SC

Is SC seeded from the MOPA stable?

20 nm

MOPA Stability 2.5x increase in ΦRSN • 155x Gain (22dB) • 10x Δλ (from seed)

SC Stability • Increase in RMS-N

likely due to Collimator Heating

SC nearly maintains seed ΦRSN ΦRSN = 0.6%

RMS-N = 0.4% ΦRSN = 1.6%

RMS-N = 0.2% ΦRSN = 1.9% RMS-N = 1%

MOPA Seeded SC


Applicable Modality ANDi Normal

Dispersion SC

MOPA Seeded SC


SRS, CARS, Spontaneous.. ANDi

SC Seeded Narrow-Band

Amp

2000 cm-1 = the largest vibrational mode excitable Enough bandwidth to excite target Raman Vibrations

Normal Dispersion SC and Amplified 980 NB pulses

Nonlinear Imaging Tool Kit

Imaging Modality Nonlinear Optical Element Ultrafast Sources



Dual-Band SC

Er Fiber Laser


ANDi fiber Laser

ANDi seeded MOPA

Ti:Saphire

SHG, THG, TPEF



IR / VO


Scanner

Yb:KYW

MOPA Seeded Dual-Band SC

http://www.nktphotonics.com/files/files/NL-1050-ZERO-2.pdf Wang, Hui, and Andrew M. Rollins. Applied optics46.10 (2007): 1787.


Applicable Modality ANDi Dual-Band SC

http://www.nktphotonics.com/files/files/NL-1050-ZERO-2.pdf

MOPA Seeded Dual-Band SC ` Our Model using a Split-Step

Propagator: MOPA: 130fs pulse 300 mW

Yb-doped Fiber Laser Pathway through the Nonlinear Imaging Tool Kit

` Nonlinear

Broadening in Amp Applicable Modality ANDi

NLO

SRS, CARS, …

TAS

SHG, THG, TPEF

SPM-Pulses

WB-Pulses





Dual-Band SC

Er Fiber Laser


ANDi fiber Laser

ANDi seeded MOPA

Ti:Saphire

SHG, THG, TPEF



IR / VO


Scanner

Yb:KYW

Rapid Delay Scanner

𝜏 𝜃𝑖 = −2𝑑𝑛𝑔𝑐

𝑛𝑔 + cos 𝜃𝑡 − cos 𝜃𝑖 − 𝜃𝑡𝑛𝑔 cos 𝜃𝑡

SRS, CARS, Time-Resolved Raman Rapid Delay

Scanner Transient

Absorption

BK7

BK7

BS

d

θi

θt

τdelay(θi)

λ/2

General Source

Time Resolved Raman Spectroscopy

B-PD

τ

NF

GL

WP

BK7

BS

2 pump-probe delay scans per ½ rev. 4 pump-probe delay scans per rev.

ISRS and Time-Resolved Raman

Rapid Delay Scanner Ti:Saphire

𝐸 𝑡, 𝜏 = 𝐸0𝐴 𝑡 𝑒−𝑖(𝜔𝑡−a sin Ω𝜈𝜏 )

BGO

𝐸 𝑡,Ω𝜈𝜏 = 0 ≈ 𝐸0𝐴 𝑡 𝑒−𝑖(𝜔𝑡−𝑎𝜏) For |A(t)|2 shorter than 1/Ων

ISRS and short probe pulse

Time Resolved Raman Spectroscopy B-PD

τ

NF

GL

WP

BK7

BS

• Increased Lighthouse speed from 15 => 175 Hz

• Currently, XPM peaks needed to temporally synch individual scans

Nearly parabolic delay-to-angle (accelerating delay rate) = detector gain bandwidth limitations

BGO


Reduction in Noise by Scan Averaging

10x reduction in Raman Spectrum Background

500 scans 1 scan

Neat CCl4


Chemical Imaging

“Crude” discrimination based on peak/valley comparison Principal Component Analysis would improve discrimination among target species 30 and 15 dB discrimination between BGO and CdWO4, respectively.

Rapid(er) Delay Scanner

• 12 kHz Resonant Galvo Mirror (RM)

• 24 kHz pump-probe delay scan rate

• Successful Proof-of-Concept Experiment

Issues to Resolve • Switch to window with Isotropic

Optical Response • Align with window at a high angle to

“amplify” the delay range Potential Use: • Generate Modulation signal by

dithering vibrational Excitation





Dual-Band SC

Er Fiber Laser


ANDi fiber Laser

ANDi seeded MOPA

Ti:Saphire

SHG, THG, TPEF



IR / VO


Scanner

Yb:KYW

Photothermal Spectroscopy in 1.6-1.85 μm

Wang, Pu, et al. Journal of Biophotonics 5.1 (2012): 25.

Butter Fat (lipid) => CH2 Type I Collagen (protein) => CH3

• 80 fs FWHM seed pulse • ~100 mW (37MHz) available • Reduced to ~60 mW for 1730nm

(and 10 cm fiber) • N ~ 5.2 • Efficiency of Conversion ~ 85%

Generating Light at 1.6-1.85 μm • Modelocked Er-Doped Laser (1550 nm) • Soliton Self-Frequency Shift in

anomalous fiber • Challenge: Balancing Non-linearity and

Soliton Order. dB Linear

Vyas, R., et al, Applied Optics 27, (1988): 4701. RICARD-LESPADE, L., et al, Chemical Physics 𝟏𝟏𝟏, (1990): 245.

Signal Estimates for CH2 stretch

𝑠 𝑡 =𝑛𝑛𝑛𝜕𝐸0𝑙𝑧1𝜋𝜋𝐶𝑝

𝜕𝑛𝜕𝜕

1𝑎2 + 8𝐷𝑡 2

• ρ = 998.2 (kg/m3) • D = 0.143 x 10-6 (m2/s) • Cp = 4.18x 103 (J/kg-K) • dn/dt = 8 x 10-5 (K-1)

𝜕𝐸0 → � 𝜇 𝜔 𝑆 𝜔 𝑑𝜔

∞

−∞

𝑙, 𝑧1 = 𝑧𝑅 =𝜋𝑤2

𝜆

𝑎,𝑤0 = 𝜆𝜋𝑁𝜋

, NA = 0.3

Newport Nirvana • Gain = 5.2x105 (V/W) • NEP = 3 (pW/√HZ)

Spectral Sensitivity Estimates for CH2 stretch Overtone

Modular Pathways through the Nonlinear Tool Kit

`

AN

Di

MO

PA

Cle

an P

ulse

C

ompr

essi

on

Nor

mal

D

ispe

rsio

n SC

SC se

eded

N

arro

w-B

and

Am

p

Ligh

thou

se

Del

ay S

cann

er

Mic

rosc

ope

Special Thanks The Bartels Ultrafast Lab Randy Bartels Philip Schlup Jeff Field David Winters David Kupka David Smith Keith Wernsing

Committee Members Amber Krummel Diego Krapf Mario Marconi Funding Sources Department of Energy National Institute of Health The Keck Foundation

Fiber-based Ultrafast sources for Nonlinear Spectroscopy€¦ · • Fiber Lasers and Amps have HOD...

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Transcript of Fiber-based Ultrafast sources for Nonlinear Spectroscopy€¦ · • Fiber Lasers and Amps have HOD...