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

Combs from chirped waveforms T 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).

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

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

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).

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

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 = 766.7 nm D1 = 770.1 nm 55.55 MHz 461.7 MHz

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

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

Coherent pump-probe

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

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 = −461.724(2) MHz

Free induction decays: Evacuated cell Drive with single tone at 461.7 MHz Can clearly see the FID due to the long lifetime This is the average of 20,000 acquisitions Lifetime of 0.25 μs

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

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

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