1. Multiplexed saturation spectroscopy with electro-optic frequency combs
D.A. Long, A.J. Fleisher, D.F Plusquellic, J.T. Hodges
National Institute of Standards and Technology

2. Combs from chirped waveformsT
Chirps from f0 to f1
time
carrier frequency (fc)
frequency
fc + f0
fc + f1
1/T
comb teeth
D. A. Long, et al., Phys. Rev. A, (2016).

3. Ultranarrowly spaced optical frequency combs
10,000 comb teeth at a 200 kHz spacing
D. A. Long, et al., Phys. Rev. A, (2016).

4. Self-heterodyne spectroscopy
Radio Frequency LO
Absorption Cell
Detector
Probe comb
Laser PM
AOM
Optical Frequency
Optical Frequency
Optical Frequency

5. The need for coherent averaging
Interferograms often recorded in 5 µs
Given a digitization rate of 1.5 GS/s this leads to 8 TB/h of data!
Very difficult to do FFT at these data rates without dead time
So we need to average the time-domain data.
This is very demanding as we need the time-domain data to remain coherent over long time scales.
A. J. Fleisher, et al., Opt. Express, (2016).

6. Reduction in RF linewidth
A. J. Fleisher, et al., Opt. Express, (2016).

7. 39K energy levels 4 2P3/2 4 2P1/2 4 2S1/2 33.77 MHz D2 = 766.7 nm D2
F = 3
4 2S1/2
4 2P1/2
4 2P3/2
F = 2
F = 1
F = 0 D2 D1
33.77 MHz
D2 = nm
D1 = nm
55.55 MHz
461.7 MHz

8. Doppler-broadened spectra
D. A. Long, et al., Phys. Rev. A, (2016).

9. Sub-Doppler spectra: counter-propagating
D. A. Long, et al., Phys. Rev. A, (2016).

10. Coherent pump-probe

11. Sub-Doppler spectra: co-propagating
T = 34 °C
Cell placed in triply-shielded magnetic chamber HP HP HP
41K EIT
EIT

12. Sub-Doppler spectra: Buffer gas cell
T = 35 °C
Cell contains 20 Torr of Ar buffer gas to reduce transit time broadening
Collisions with Ar do not dephase
20 kHz spaced comb allows us to see this feature with a FWHM of only 33(5) kHz
Center frequency = − (2) MHz

13. Free induction decays: Evacuated cell
Drive with single tone at MHz
Can clearly see the FID due to the long lifetime
This is the average of 20,000 acquisitions
Lifetime of 0.25 μs

14. Fourier-transform chirped pulse optical
Drive with a chirped pulse from one at 400 to 650 MHz
FFT of the decay reveals the EIT feature when the laser is tuned on to the Doppler profile
Pulse duration of 500 ns
Average of 20,000 time domain signals

15. Conclusions
Driving electro-optic modulators allows for agile and flat optical frequency combs
The strong carrier tone can be used as a pump to allow for multiplexed sub-Doppler spectroscopy
Hole burning, hyperfine pumping, and electromagnetically induced transparency (EIT) have been simultaneously observed in 39K
The long lifetime of the EIT features allows for observation of free induction decays and chirped pulse spectra

16. NIST Greenhouse Gas Measurements and Climate Research Program
Acknowledgements
NIST Greenhouse Gas Measurements and Climate Research Program