Direct Frequency Comb Spectroscopy for the Study of Molecular Dynamics in the Infrared Fingerprint Region Adam J. Fleisher, Bryce Bjork, Kevin C. Cossel, Jun Ye JILA|NIST and University of Colorado - Boulder Lora Nugent-Glandorf, Florian Adler, Tyler Neely, Scott A. Diddams National Institute of Standards and Technology Tim Dinneen Precision Photonics FA 11 The 67 th 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 W 110 fs 137 MHz 1070 nm Yb:Fiber Comb Laser

1. Mode-locked laser F. Adler et al. Opt. Lett. 34, 1330 (2009). Optical parametric oscillator Tunable 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: /s (2012). Mode-locked laser VIPA spectrometer High finesse optical cavity with intra-cavity gas sample

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 VIPA R in = 99.95% R out = 98.0% InSb photodiode array 320 x 256 pixels LN 2 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 CH 4 in N 2 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). nFSR (GHz)L (cm) 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 is 14, 15, or 16 x f rep L = c / (2FSR) At 15 x f rep, the comb line spacing is filtered to 2.05 GHz

Comb Mode Resolution L. Nugent-Glandorf et al. Opt. Lett., in press (2012). arXiv: pixels Detector Image Plane Grating Dispersion VIPA Dispersion 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: d

Direct FCS Cavity Characterization

Direct FCS Cavity N 2 reference 0.2% N 2 O in N 2 at 40 torr Cavity 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 (2005). Wavelength (nm) 2,300 comb modes in the above spectral bandwidth. Wavelength (nm)

Molecular Gas Dynamics L. Nugent-Glandorf et al. Opt. Lett., in press (2012). arXiv: Noise 5 x noise floor (ms) 1 x cm -1 (5 avr., 42 ms, 200 m path length) 640 x 512 pixel camera 120 Hz repetition rate CH 4 gas cell filling dynamics - NIST

Future: MIR Reaction Dynamics A. Foltynowicz et al. Appl. Phys. B. doi: /s (2012). L. Nugent-Glandorf et al. Opt. Lett., in press (2012). arXiv: 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 PZT Outlet

Acknowledgements Bryce Bjork, Kevin C. Cossel, Jun Ye JILA|NIST and CU Lora Nugent-Glandorf, Florian Adler, Tyler Neely, Scott A. Diddams National Institute of Standards and Technology Tim Dinneen Precision Photonics L. Nugent-Glandorf et al. Optics Letters (2012). arXiv:

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 shot20 averaged shots

Frequency Comb Insert Citation Here Frequency Domain Frequency comb Cavity modes Cavity mode structure: Frequency comb structure: 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 W 110 fs 137 MHz 1070 nm OPO