Direct Frequency Comb Spectroscopy for the Study of Molecular Dynamics in

the Infrared Fingerprint Region

Adam J. Fleisher, Bryce Bjork, Kevin C. Cossel, Jun YeJILA|NIST and University of Colorado - Boulder

Lora Nugent-Glandorf, Florian Adler, Tyler Neely, Scott A. DiddamsNational Institute of Standards and Technology

Tim DinneenPrecision Photonics

FA 11The 67th OSU International Symposium on Molecular Spectroscopy – June 22, 2012

Cavity-Enhanced Direct FCS

1. Mode-locked laser (fs fiber laser)

2. Sample interrogation (high-finesse enhancement cavity)

3. Dispersive detection system (VIPA)

M.J. Thorpe et al. Science 311, 1595 (2006).

CE-DFCS

1. Mode-locked laser

T.R. Schibli et al. Nat. Photonics 2, 355 (2008).F. Adler et al. Opt. Lett. 34, 1330 (2009).

>10 W110 fs

137 MHz1070 nm

Yb:Fiber Comb Laser

1. Mode-locked laser

F. Adler et al. Opt. Lett. 34, 1330 (2009).

Optical parametric oscillatorTunable from 2.8 – 4.8 μm

(2000 – 3500 cm-1)

150 nm bandwidth at 3.75 μm(100 cm-1 fwhm)

> 1 W power from 3.0 – 4.0 μm

2. Sample Interrogation

M.J. Thorpe et al. Opt. Express 16, 2387 (2008).A. Foltynowicz et al. Appl. Phys. B. doi:10.1007/s00340-012-5024-7(2012).

Mode-locked laser VIPA spectrometer

High finesse optical cavitywith intra-cavity gas sample

99.7% < R < 99.95% 1000 < < 6000

ROC = 6 md = 0.8″

ZnSe substrate

3. Dispersive detector

InSb Camera

M.J. Thorpe et al. Opt. Express 16, 2387 (2008).M.J. Thorpe and J. Ye, Appl. Phys. B 91, 397 (2008).

M.J. Thorpe et al. Science 311, 5767 (2006).S.A. Diddams et al. Nature 445, 627 (2007).

MIR VIPARin = 99.95%Rout = 98.0%

InSb photodiode array320 x 256 pixels

LN2 cooled

Collectively, these components create a power tool for the sensitive

measurement of absorption spectra over a broadband on the μs timescale

VIPA Characterization and Spectroscopy

• Measure the VIPA spectrometer resolution and free spectral range– Fabry-Perot Comb Filter Cavity with FSR = 2.0 GHz– Spectroscopy Cavity with FSR = 546 MHz and

Finesse = 1200

• Record broadband molecular spectra on the millisecond (ms) timescale– 100 ppm CH4 in N2 at a total pressure of 30 Torr

Comb-Cavity Coupling

F. Adler et al. Annu. Rev. Anal. Chem. 3, 175 (2010)

Construction of Filter Cavity

S.A. Diddams et al. Nature 445, 627 (2007).

n FSR (GHz) L (cm)

14 1.91 7.8

15 2.05 7.3

16 2.19 6.9

Exact n value must be know to precisely determine the filtered comb mode spacing required for VIPA calibration.

2.05 GHz Filter Cavity

S.A. Diddams et al. Nature 445, 627 (2007).

Change in cavity length (L) vs. Change in cavity free spectral range (FSR)

Center point is14, 15, or 16 x frep

L = c / (2FSR)

At 15 x frep, the comb line spacing is filtered

to 2.05 GHz

Comb Mode Resolution

L. Nugent-Glandorf et al. Opt. Lett., in press (2012). arXiv: 1206.1316

pixe

ls

pixels

Detector Image Plane

Grating Dispersion

VIPADispersion

InSb Camera

Observed FWHM = 600 MHz

15°

VIPA Performance

S. Xiao et al. IEEE J. Quant. Elec. 40, 420 (2004).L. Nugent-Glandorf et al. Opt. Lett., in press (2012). arXiv: 1206.1316

Measured FSR at 25° = 55 GHz, therefore = 92 and R = 0.966

Calculate FSR at 25°

= = 60.3 GHz

Finesse = = 105, assuming R = 0.97, and lossless front face

Resolution = = 60.3 GHz/105 ~ 574 MHz, measured = 600 MHz

d

Direct FCS Cavity Characterization

Direct FCS Cavity

N2 reference0.2% N2O in N2

at 40 torrCavity finesse ~1000

Direct FCS Cavity

K.C. Cossel et al, Appl. Phys. B, 100, 917 (2010).L.S. Rothman et al. J. Quant. Spectrosc. Radiat. Transfer 96 139 (2005).

Wavelength (nm)

2,300 comb modes in the above spectral bandwidth.

Wavelength (nm)

Experimental Frequency Axis Calibrated to HITRAN

ax2 + bx +c

VIPA = 25°

2

20

1 1 1ln 1

2 1

R

L R I I

Molecular Gas Dynamics

L. Nugent-Glandorf et al. Opt. Lett., in press (2012). arXiv: 1206.1316

Noise5 x 10-4 noise floor (ms)

1 x 10-8 cm-1 (5 avr., 42 ms, 200 m path length)

640 x 512 pixel camera120 Hz repetition rate

CH4 gas cell filling dynamics - NIST

Future: MIR Reaction Dynamics

A. Foltynowicz et al. Appl. Phys. B. doi:10.1007/s00340-012-5024-7(2012).L. Nugent-Glandorf et al. Opt. Lett., in press (2012). arXiv: 1206.1316

• Enhancement factor of ≥ 300 leads to mW/mode of intracavity power• 5,000 lasers available for cavity-enhanced spectroscopy• 100 cm-1 simultaneous bandwidth• Integration time as low as 10 μs (camera limit)• Experimental repetition rate of up to 400 Hz (camera limit)

MIR Comb VIPA and Camera

Inlet

Enhancement Cavity

PZT

Outlet

AcknowledgementsBryce Bjork, Kevin C. Cossel, Jun Ye

JILA|NIST and CULora Nugent-Glandorf, Florian Adler, Tyler Neely, Scott A. Diddams

National Institute of Standards and TechnologyTim Dinneen

Precision Photonics

L. Nugent-Glandorf et al. Optics Letters (2012).

arXiv: 1206.1316

Virtually Imaged Phased Array

M. Shirasaki Fujitsu Sci. Tech J. 35, 113 (1999).

Noise Analysis

Insert Citation Here

Signal Averaging

Insert Citation Here

1 FSR

Single 2ms shot 20 averaged shots

Frequency Comb

Insert Citation Here

Frequency Domain

Frequency comb

Cavity modes

ddcL

cFSR

2

Cavity mode structure:Frequency comb structure:

orn fnf

Time Domain ADD SINGLE PULSE VS. PULSE TRAIN IMAGE HERE

1. Mode-locked laser

T.R. Schibli et al. Nat. Photonics 2, 355 (2008).F. Adler et al. Opt. Lett. 34, 1330 (2009).

Yb:fiber mode-locked laser

>10 W110 fs

137 MHz1070 nm

OPO