Fiber-based Ultrafast sources for Nonlinear Spectroscopy

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1 Fiber-based Ultrafast sources for Nonlinear Spectroscopy Preliminary Exam for Scott R Domingue, PhD candidate Department of Electrical and Computer Engineering Colorado State University

2 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Appropriate Structure for SHG TPEF SHG THG Imaging a follicle through 70 um thick murine ovarian tissue Bartels Group unpublished

3 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contrast mechanism) 900 cm TPEF SHG THG Imaging a follicle through 70 um thick murine ovarian tissue Bartels Group unpublished

4 Nonlinear Imaging Tool Kit Ultrafast Sources Yb:KYW ANDi fiber Laser ANDi seeded MOPA Ti:Saphire Er Fiber Laser Nonlinear Optical Element Normal Dispersion SC SC Seeded Narrow-Band Amp Dual-Band SC Soliton Self Frequency Shifting Rapid Delay Scanner Imaging Modality SHG, THG, TPEF SRS, CARS, Time- Resolved Raman IR / VO Transient Absorption (TAS) 3-Photon Absorption

5 Coherent Raman Excitation Energy CARS Classic Harmonic Oscillator 2 R + γ t2 + Ω νr = 1 2 A t 2M The Frequency Domain representation: D Ω F A t 2 SRS, CARS, Time- Resolved Raman Beating between SC pulse pairs (15fsTL) Alternative: SC and Narrow-Band pulses

6 IR vs. Vibrational Overtone Energy Vibrational Overtone Excitation Shift to Higher frequencies Optics are better (High Resolution Microscope) Potentially simpler sources Weaker absorption crosssections Probe altered Susceptibility: Photothermal Spectroscopy IR / VO Er Fiber Laser Soliton Self Frequency Shifting

7 Pump-Probe Spectroscopy Continue Opening-Up Potential of Pump-Probe Spectroscopy as Imaging Modality Rapid Delay Scanner JW, Wilson et al. Selected Topics in Quantum Electronics, IEEE Journal of 18, no. 1 (2012). Robles, Francisco E., et al. Optics Express (2012): 17082

8 Spectral Targets for Different the Imaging Modalities Imaging Modality Requires Bandwidth Spectral Requisites Nonlinear Optical Element Ultrafast Sources

9 Ultrafast Source Comparison Yb-Doped Ti:Saphire

10 Ultrafast Source Comparison Yb-Doped 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 Ti:Saphire 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

11 Ultrafast Source Comparison Yb-Doped 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 Ti:Saphire 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

12 Our Goals for Yb-Doped Fiber Sources Capitalizing on and Extending these cheap, agile sources 4 ANDi s built and Counting

13 Nonlinear Imaging Tool Kit Ultrafast Sources Yb:KYW ANDi fiber Laser ANDi seeded MOPA Ti:Saphire Er Fiber Laser Nonlinear Optical Element Normal Dispersion SC SC Seeded Narrow-Band Amp Dual-Band SC Soliton Self Frequency Shifting Rapid Delay Scanner Imaging Modality SHG, THG, TPEF SRS, CARS, Time- Resolved Raman IR / VO Transient Absorption (TAS) 3-Photon Absorption

14 Dispersion Regimes for SC generation Yb:KYW Anomalous, PCF Normal, PCF Normal Dispersion SC Normal, UHNA SHG, THG, TPEF SRS, CARS, Time- Resolved Raman Transient Absorption 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

15 Bachler, B. R., et al Optics Express 20.2 (2012): 835 Dudley, J M., et al., Reviews of modern physics 78.4 (2006) Typical SC Generation with Yb-doped Sources in Anomolous Dispersion Fiber Efficient supercontinuum generations in silica suspended core fibers N << 16 => P 0 < 1.6 kw Incoherent SC L D = τ2 β 2 L NN = 1 P 0 γ N 2 = L D L NN Not as simple as shooting pulses into small core fibers nm => L disersion = 4.25 m Peak Power to keep N small, 50 μw => N = 10.2

16 SC Generation in Normal Dispersion Yb:KYW Fiber Normal Dispersion SC Any Applicable Modality N in+1 n! n 2 β n n A T n = i γ A 2 A + i ω 0 A 2 A T R A A 2 SPM Self-Steeping Intrapulse Raman Scattering P UHNA ` P P λ/2 A-λ/2 Time [min]

17 SC Polarization Instability in Weakly N in+1 n! n 2 Birefringent Fiber β n n A T n = i γ A 2 A + i ω 0 A 2 A T R A A 2 The orthogonal E-field polarizations are coupled, giving rise to Polarization Modulation Instability Domingue, Scott R., and Randy A. Bartels. Optics express (2013):

18 SC above Instability Threshold High Correlation in Spectra Changes Mask Spectrally Integrated Noise 375 mw, 330 fs seed pulse RSN λ = σ λ µ(λ) 100 % Φ RSN = σ λ µ(λ)dλ µ 2 λ dλ RSN 100 % Φ RSN De-Polarization ~ 50 % RMS-N = 8% vs. Φ RSN = 20% RMS-N Domingue, Scott R., and Randy A. Bartels. Optics express (2013):

19 SC in Highly Bifrefringent (PM) Nonlinear Fiber 375 mw, 1 m of CorActive PM-HNLF De-Polarization ~ 10 % RMS-N = 0.6% vs. Φ RSN = 0.9% RSN Φ RSN Lower Nonlinearity than UHNA-3 Highly Stable, Efficient generated SC 21 fs Transform Limit RMS-N Domingue, Scott R., and Randy A. Bartels. Optics express (2013):

20 Nonlinear Pulse Compression Yb:KYW Normal Dispersion SC Impulsive Stimulated Raman Scattering Long PM-UHNA fibers = Large GDD and HOD Below: SC with Grating Compressor Only

21 Local Characteristic Lengths Local Characteristic Lengths taken from evolving pulse properties, local in the fiber Model L NL z = 1 P(z)γ 0 ~1m WB ~10mm L D (z) = τ TL z 2 χ i z = 0 z β 2 Accumulated Dispersion and Nonlinear Lengths akin to B-Integral dz L i z Domingue, Scott R., and Randy A. Bartels. Optics express (2013):

22 Accumulated Dispersion/ Nonlinearity Model χ D ~1, L D ~ 10mm Nonlinear Pulse Compression: Pulse Shaper (Transform Limit) Simple Compressor (GDD compensation) Domingue, Scott R., and Randy A. Bartels. Optics express (2013):

23 Nonlinear Pulse Compression SC compression with Grating Compressor and Pulse Shaper [fs] Wavelength Transform Limit dropped from 21 to 36 fs, due to non-optimal pulse shaper: visible SLM, 4λ SLM Wavefront Error, Spherical Abberation Domingue, Scott R., and Randy A. Bartels. Optics express (2013):

24 Nonlinear Imaging Tool Kit Ultrafast Sources Yb:KYW ANDi fiber Laser ANDi seeded MOPA Ti:Saphire Er Fiber Laser Nonlinear Optical Element Normal Dispersion SC SC Seeded Narrow-Band Amp Dual-Band SC Soliton Self Frequency Shifting Rapid Delay Scanner Imaging Modality SHG, THG, TPEF SRS, CARS, Time- Resolved Raman IR / VO Transient Absorption (TAS) 3-Photon Absorption

25 Narrow Band Pulse Generation Yb-doped SC Seeded Narrow-Band Amp SRS, CARS, TAS λ/2 A-λ/2 DM 1020-LP PM-UHNA FBG PM-passive, delay 25 db gain λ/2 WDM PM Low Yb-doped FBG Narrow Band Amplifier 915 nm diode

26 Narrow Band Pulse Generation Yb-doped SC Seeded Narrow-Band Amp SRS, CARS, 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

27 Nonlinear Imaging Tool Kit Ultrafast Sources Nonlinear Optical Element Imaging Modality Yb:KYW Normal Dispersion SC SHG, THG, TPEF ANDi fiber Laser SC Seeded Narrow-Band Amp SRS, CARS, Time- Resolved Raman ANDi seeded MOPA Ti:Saphire Er Fiber Laser? Dual-Band SC Soliton Self Frequency Shifting Rapid Delay Scanner IR / VO Transient Absorption (TAS) 3-Photon Absorption

28 All Normal Dispersion (ANDi) Fiber ANDi Lasers Normal Dispersion SC Any Applicable Modality Different Modelocking mechanism (nonlinear polarization evolution) and wildly different dispersion profiles different SC characteristics? CMS Yb DC PC λ/4 λ/2 BF FI λ/2 λ/4 976 nm diode ~ 500 mw ~100 fs FWHM TL

29 ANDi Spectral Noise and Pulse Compression CMS Yb DC PC λ/4 λ/2 BF FI λ/2 λ/4 976 nm diode Φ RSN = 0.6% RMS-N = 0.4%

30 Cascaded Nonlinearity Results in Significant Noise Generation + Φ RSN = 0.6% RMS-N = 0.4% Φ RSN = 3.6% RMS-N = 0.4% Wavelength [nm] Domingue, Scott R., and Randy A. Bartels. Optics express (2013):

31 ANDi Pulse Compression τ FWHM = 177 fs 130% of TL FWHM 58% TL Peak Power

32 ANDi Pulse Compression τ FWHM = 163 fs 120% of TL FWHM 73% TL Peak Power w/ 87% of the Energy Cubic Aberration maps to TOD 92% of Appodized TL

33 ANDi Seeded SC Improvement with Compression Φ RSN reduced by ~½ BUT, Bandwidth (Power) limited Φ RSN = 1.5% RMS-N = 0.2% Φ RSN = 3.6% RMS-N = 0.4%

34 Nonlinear Imaging Tool Kit Ultrafast Sources Nonlinear Optical Element Imaging Modality Yb:KYW Normal Dispersion SC SHG, THG, TPEF ANDi fiber Laser SC Seeded Narrow-Band Amp SRS, CARS, Time- Resolved Raman ANDi seeded MOPA Ti:Saphire Er Fiber Laser? Dual-Band SC Soliton Self Frequency Shifting Rapid Delay Scanner IR VO Transient Absorption (TAS) 3-Photon Absorption

35 Master Oscillator Power Amplifier (MOPA) ANDi Nonlinear Broadening in Amp NLO Applicable Modality Expectations: Minimize Noise Amplify and Broaden Simultaneously More Power! Unexpected Benefits: Cleaner Chirp Fine Control over Power Spectrum

36 Master Oscillator Power Amplifier (MOPA) 1000 l/mm ` λ/2 CMS PM DC- Yb

37 MOPA Pulse Evolution 5.2nm => 56 fs TL Min TL 56fs WB Side lobe WB SPM How compressible are these pulses??

38 MOPA Compression, SPM 1.8 nm Seed Bandwidth 10 nm 27 nj (1.7 W at 63 MHz) 144 fs FWHM, 180 kw peak power. 95% of TL peak power (135 fs FWHM) 3 rd order correction unnecessary for SPM pulses

39 MOPA Compression, WB 3.5 nm Seed Bandwidth W/ out 3 rd order correction (green): 39% TL PP On-Axis 10 nm Off-Axis Peak Power Estimates for Equal Average Power (reasonable for microscope applications)

40 MOPA Compression, WB 3.5 nm Seed Bandwidth 10 nm 3 rd order correction costs spectral appodization for large Δλ W/ 3 rd order correction (black) 80 fs FWHM 70% TL PP(60 fs FWHM) 20.5 nj, 215 kw W/ out 3 rd order correction (green): 39% TL PP 29 nj Peak Power Estimates for Equal Average Power

41 MOPA Seeded SC ANDi Nonlinear Broadening in Amp Normal Dispersion SC Is SC seeded from the MOPA stable? 20 nm MOPA Stability 2.5x increase in Φ RSN 155x Gain (22dB) 10x Δλ (from seed) SC Stability Increase in RMS-N likely due to Collimator Heating Φ RSN = 0.6% RMS-N = 0.4% Φ RSN = 1.6% RMS-N = 0.2% Φ RSN = 1.9% RMS-N = 1% SC nearly maintains seed Φ RSN

42 MOPA Seeded SC ANDi Nonlinear Broadening in Amp Normal Dispersion SC Applicable Modality

43 MOPA Seeded SC ANDi Nonlinear Broadening in Amp SC Seeded Narrow-Band Amp Normal Dispersion SC and Amplified 980 NB pulses SRS, CARS, Spontaneous cm -1 = the largest vibrational mode excitable Enough bandwidth to excite target Raman Vibrations

44 Nonlinear Imaging Tool Kit Ultrafast Sources Yb:KYW ANDi fiber Laser ANDi seeded MOPA Ti:Saphire Er Fiber Laser Nonlinear Optical Element Normal Dispersion SC SC Seeded Narrow-Band Amp Dual-Band SC Soliton Self Frequency Shifting Rapid Delay Scanner Imaging Modality SHG, THG, TPEF SRS, CARS, Time- Resolved Raman IR / VO Transient Absorption (TAS) 3-Photon Absorption

45 Wang, Hui, and Andrew M. Rollins. Applied optics46.10 (2007): MOPA Seeded Dual-Band SC ANDi Nonlinear Broadening in Amp Dual-Band SC Applicable Modality

46 MOPA Seeded Dual-Band SC ` Our Model using a Split-Step Propagator: MOPA: 130fs pulse 300 mw

47 Yb-doped Fiber Laser Pathway through the Nonlinear Imaging Tool Kit ANDi Nonlinear Broadening in Amp NLO Applicable Modality SPM-Pulses SRS, CARS, TAS ` WB-Pulses SHG, THG, TPEF

48 Nonlinear Imaging Tool Kit Ultrafast Sources Yb:KYW ANDi fiber Laser ANDi seeded MOPA Ti:Saphire Er Fiber Laser Nonlinear Optical Element Normal Dispersion SC SC Seeded Narrow-Band Amp Dual-Band SC Soliton Self Frequency Shifting Rapid Delay Scanner Imaging Modality SHG, THG, TPEF SRS, CARS, Time- Resolved Raman IR / VO Transient Absorption (TAS) 3-Photon Absorption

49 Nonlinear Imaging Tool Kit Ultrafast Sources Yb:KYW ANDi fiber Laser ANDi seeded MOPA Ti:Saphire Er Fiber Laser Nonlinear Optical Element Normal Dispersion SC SC Seeded Narrow-Band Amp Dual-Band SC Soliton Self Frequency Shifting Rapid Delay Scanner Imaging Modality SHG, THG, TPEF SRS, CARS, Time- Resolved Raman IR / VO Transient Absorption (TAS) 3-Photon Absorption

50 General Source τ θ i Rapid Delay Scanner = 2dn g c Rapid Delay Scanner n g + cos θ t cos θ i θ t n g cos θ t SRS, CARS, Time- Resolved Raman Transient Absorption θ t d θ i BS BK7 λ/2 BK7 τ delay (θ i )

51 Time Resolved Raman Spectroscopy Ti:Saphire Rapid Delay Scanner ISRS and Time- Resolved Raman NF B-PD BS BK7 WP BGO GL τ 2 pump-probe delay scans per ½ rev. 4 pump-probe delay scans per rev. ISRS and short probe pulse E t, τ = E 0 A t e i(ωω a sin Ω ντ ) For A(t) 2 shorter than 1/Ω ν E t, Ω ν τ = 0 E 0 A t e i(ωω aa)

52 Time Resolved Raman Spectroscopy NF B- PD BK7 BS WP Nearly parabolic delay-to-angle (accelerating delay rate) = detector gain bandwidth limitations GL τ BGO Increased Lighthouse speed from 15 => 175 Hz Currently, XPM peaks needed to temporally synch individual scans

53 Time Resolved Raman Spectroscopy Reduction in Noise by Scan Averaging Neat CCl 4 10x reduction in Raman Spectrum Background 500 scans 1 scan

54 Time Resolved Raman Spectroscopy 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 CdWO 4, respectively.

55 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

56 Nonlinear Imaging Tool Kit Ultrafast Sources Yb:KYW ANDi fiber Laser ANDi seeded MOPA Ti:Saphire Er Fiber Laser Nonlinear Optical Element Normal Dispersion SC SC Seeded Narrow-Band Amp Dual-Band SC Soliton Self Frequency Shifting Rapid Delay Scanner Imaging Modality SHG, THG, TPEF SRS, CARS, Time- Resolved Raman IR / VO Transient Absorption (TAS) 3-Photon Absorption

57 Photothermal Spectroscopy in μm Butter Fat (lipid) => CH 2 Type I Collagen (protein) => CH 3 Wang, Pu, et al. Journal of Biophotonics 5.1 (2012): 25.

58 Generating Light at μm Modelocked Er-Doped Laser (1550 nm) Soliton Self-Frequency Shift in anomalous fiber Challenge: Balancing Non-linearity and Soliton Order. Linear db 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%

59 Signal Estimates for CH 2 stretch s t = nnnne 0lz 1 ππc p 1 a 2 + 8DD 2 ρ = (kg/m 3 ) D = x 10-6 (m 2 /s) Cp = 4.18x 10 3 (J/kg-K) dn/dt = 8 x 10-5 (K -1 ) αe 0 a, w 0 = λ πππ μ ω S ω dd, NA = 0.3 l, z 1 = z R = πw2 λ Newport Nirvana Gain = 5.2x10 5 (V/W) NEP = 3 (pw/ HZ) Vyas, R., et al, Applied Optics 27, (1988): RICARD-LESPADE, L., et al, Chemical Physics 111, (1990): 245.

60 Spectral Sensitivity Estimates for CH 2 stretch Overtone

61 Modular Pathways through the Nonlinear Tool Kit ANDi MOPA Clean Pulse Compression Normal Dispersion SC SC seeded Narrow-Band Amp Lighthouse Delay Scanner Microscope `

62 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