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 67th OSU International Symposium on Molecular Spectroscopy – June 22, 2012
Cavity-Enhanced Direct FCS
1. Mode-locked laser (fs
fiber laser)
CE-DFCS
2. Sample interrogation
(high-finesse
enhancement cavity)
3. Dispersive detection
system (VIPA)
M.J. Thorpe et al. Science 311, 1595 (2006).
1. Mode-locked laser
Yb:Fiber Comb Laser
>10 W
110 fs
137 MHz
1070 nm
T.R. Schibli et al. Nat. Photonics 2, 355 (2008).
F. Adler et al. Opt. Lett. 34, 1330 (2009).
1. Mode-locked laser
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
F. Adler et al. Opt. Lett. 34, 1330 (2009).
2. Sample Interrogation
High finesse optical cavity
with intra-cavity gas sample
VIPA spectrometer
Mode-locked laser
99.7% < R < 99.95%
1000 < ℱ < 6000
ROC = 6 m
d = 0.8″
ZnSe substrate
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).
3. Dispersive detector
MIR VIPA
Collectively, these
components create a
in = 99.95%
powerRtool
for the sensitive
R
=
out of98.0%
measurement
absorption spectra
over a broadband on the μs timescale
InSb photodiode array
320 x 256 pixels
LN2 cooled
M.J. Thorpe et al. Science 311, 5767 (2006).
S.A. Diddams et al. Nature 445, 627 (2007).
InSb Camera
M.J. Thorpe et al. Opt. Express 16, 2387 (2008).
M.J. Thorpe and J. Ye, Appl. Phys. B 91, 397 (2008).
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
𝑐
𝐹𝑆𝑅 =
= 𝑛 × 𝑓𝑟𝑒𝑝
2𝐿
𝑓𝑟𝑒𝑝 = 136.6 𝑀𝐻𝑧
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.
S.A. Diddams et al. Nature 445, 627 (2007).
2.05 GHz Filter Cavity
Change in cavity length (L) vs. Change in cavity free spectral range (FSR)
L = c / (2FSR)
At 15 x frep, the comb
line spacing is filtered
to 2.05 GHz
Center point is
14, 15, or 16 x frep
S.A. Diddams et al.
Nature 445, 627 (2007).
Comb Mode Resolution
Detector Image Plane
15°
InSb Camera
pixels
VIPA
Dispersion
pixels
Grating
Dispersion
Observed FWHM = 600 MHz
L. Nugent-Glandorf et al. Opt. Lett., in press (2012). arXiv: 1206.1316
VIPA Performance
Calculate FSR at 25°
𝑐
=
= 60.3 GHz
2𝑛𝑡 cos 𝜃𝑖
Finesse =
𝜋
= 105, assuming R = 0.97, and lossless front face
1−𝑅
𝐹𝑆𝑅
Resolution =
= 60.3 GHz/105 ~ 574 MHz, measured = 600 MHz
ℱ
Measured FSR at 25° = 55 GHz, therefore ℱ = 92 and R = 0.966
S. Xiao et al. IEEE J. Quant. Elec. 40, 420 (2004).
L. Nugent-Glandorf et al. Opt. Lett., in press (2012). arXiv: 1206.1316
Direct FCS Cavity Characterization
ℱ = 2𝜋𝜏0 𝐹𝑆𝑅
𝜋 𝑅
ℱ=
1−𝑅
ℱ𝑚𝑎𝑥 = 1200
𝑅𝑚𝑎𝑥 = 99.74%
𝜆 = 3780 𝑛𝑚
𝜐 = 2645 𝑐𝑚−1
Direct FCS Cavity
N2 reference
0.2% N2O in N2
at 40 torr
Cavity finesse ~1000
Direct FCS Cavity
Experimental Frequency
Axis Calibrated to HITRAN
ax2 + bx +c
VIPA 𝜃𝑖 = 25°
Wavelength (nm)
2,300 comb modes in the
above spectral bandwidth.
1  1 
1  R2 

ln  1 

2 L  R 2  1  I I 0  
Wavelength (nm)
K.C. Cossel et al, Appl. Phys. B, 100, 917 (2010).
L.S. Rothman et al. J. Quant. Spectrosc. Radiat. Transfer 96 139 (2005).
Molecular Gas Dynamics
CH4 gas cell filling dynamics - NIST
Noise
5 x 10-4 noise floor (ms)
1 x 10-8 cm-1 (5 avr., 42 ms,
200 m path length)
640 x 512 pixel camera
120 Hz repetition rate
L. Nugent-Glandorf et al. Opt. Lett., in press (2012). arXiv: 1206.1316
Future: MIR Reaction Dynamics
•
•
•
•
•
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)
Inlet
MIR Comb
Outlet
VIPA and
Camera
Enhancement Cavity
PZT
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
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: 1206.1316
Virtually Imaged Phased Array
M. Shirasaki Fujitsu Sci. Tech J. 35, 113 (1999).
Noise Analysis
Insert Citation Here
Signal Averaging
Single 2ms shot
20 averaged shots
1 FSR
Insert Citation Here
Frequency Comb
Time Domain
Frequency Domain
ADD SINGLE PULSE VS. PULSE
TRAIN IMAGE HERE
Frequency comb structure:
 n  nfr  f o
Cavity mode structure:
FSR  
c
d
2L  c
d
Cavity modes
Frequency comb
Insert Citation Here
1. Mode-locked laser
Yb:fiber mode-locked laser
OPO
>10 W
110 fs
137 MHz
1070 nm
T.R. Schibli et al. Nat. Photonics 2, 355 (2008).
F. Adler et al. Opt. Lett. 34, 1330 (2009).