arXiv:1206.0999 · Physical Review A

Velocity-selective direct frequency-comb spectroscopy of atomic vapors

J. E. Stalnaker, S. L. Chen, Michael Rowan, K. Nguyen, Trinity Pradhananga, Christopher Palm, Derek F. Jackson Kimball

Published Sep 24, 2012• 14 citations

Abstract

We present an experimental and theoretical investigation of two-photon direct frequency-comb spectroscopy performed through velocity-selective excitation. In particular, we explore the effect of repetition rate on the $5{S}_{1/2}\ensuremath{\rightarrow}5{D}_{3/2,5/2}$ two-photon transitions excited in a rubidium atomic vapor cell. The transitions occur via stepwise excitation through the $5{P}_{1/2,3/2}$ states by use of the direct output of an optical frequency comb. Experiments were performed with two different frequency combs, one with a repetition rate of $\ensuremath{\approx}925$ MHz and one with a repetition rate of $\ensuremath{\approx}250$ MHz. The experimental spectra are compared to each other and to a theoretical model.

DOI: 10.1103/physreva.86.033832

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arXiv:1206.0999 · Physical Review A

Velocity-selective direct frequency-comb spectroscopy of atomic vapors

J. E. Stalnaker, S. L. Chen, Michael Rowan, K. Nguyen, Trinity Pradhananga, Christopher Palm, Derek F. Jackson Kimball

Published Sep 24, 2012• 14 citations

arXiv HTML PDF

Abstract

5{S}_{1/2}\ensuremath{\rightarrow}5{D}_{3/2,5/2}

two-photon transitions excited in a rubidium atomic vapor cell. The transitions occur via stepwise excitation through the

5{P}_{1/2,3/2}

states by use of the direct output of an optical frequency comb. Experiments were performed with two different frequency combs, one with a repetition rate of

\ensuremath{\approx}925

MHz and one with a repetition rate of

\ensuremath{\approx}250

MHz. The experimental spectra are compared to each other and to a theoretical model.

DOI: 10.1103/physreva.86.033832

Related papers

Velocity-selective double resonance in Doppler-broadened rubidium vapor

Nataša Vujičić, Ticijana Ban, Gordana Kregar +2 more

We study resonantly enhanced cascaded two-photon transitions in Doppler-broadened rubidium vapor, induced by an optical frequency comb. Cascaded two-step excitation of atoms from the ground state 5 $S$ ${}_{1/2}$ to the final 5 $D$ ${}_{5/2}$ state via an intermediate 5 $P$ ${}_{3/2}$ state as well as the influence of the frequency comb repetition rate on the two-photon fluorescence signal have been investigated. It is shown that the careful choice of ${f}_{R}$ leads to enhancement of the two-photon signal with considerable increase of the final $5{D}_{5/2}$ -state population due to velocity-selective double resonance. Since the double-resonance condition for two different rubidium isotopes is fulfilled for different ${f}_{R}$ , the possibility of isotope-selective two-photon excitation is explored. The dependence of the two-photon signal on external magnetic field values and different repetition rates of the optical frequency comb is also investigated.We study resonantly enhanced cascaded two-photon transitions in Doppler-broadened rubidium vapor, induced by an optical frequency comb. Cascaded two-step excitation of atoms from the ground state 5$S$${}_{1/2}$ to the final 5$D$${}_{5/2}$ state via an intermediate 5$P$${}_{3/2}$ state as well as the influence of the frequency comb repetition rate on the two-photon fluorescence signal have been investigated. It is shown that the careful choice of ${f}_{R}$ leads to enhancement of the two-photon signal with considerable increase of the final $5{D}_{5/2}$-state population due to velocity-selective double resonance. Since the double-resonance condition for two different rubidium isotopes is fulfilled for different ${f}_{R}$, the possibility of isotope-selective two-photon excitation is explored. The dependence of the two-photon signal on external magnetic field values and different repetition rates of the optical frequency comb is also investigated.

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We report on the combined action of a cw diode laser and a train of ultrashort pulses when each of them drives one step of the 5S-5P-5D two-photon transition in rubidium vapor. The fluorescence from the 6P(3/2) state is detected for a fixed repetition rate of the femtosecond laser while the cw-laser frequency is scanned over the rubidium D(2) lines. This scheme allows for a velocity selective spectroscopy in a large spectral range including the 5D(3/2) and 5D(5/2) states. The results are well described in a simplified frequency domain picture, considering the interaction of each velocity group with the cw laser and a single mode of the frequency comb.We report on the combined action of a cw diode laser and a train of ultrashort pulses when each of them drives one step of the 5S-5P-5D two-photon transition in rubidium vapor. The fluorescence from the 6P(3/2) state is detected for a fixed repetition rate of the femtosecond laser while the cw-laser frequency is scanned over the rubidium D(2) lines. This scheme allows for a velocity selective spectroscopy in a large spectral range including the 5D(3/2) and 5D(5/2) states. The results are well described in a simplified frequency domain picture, considering the interaction of each velocity group with the cw laser and a single mode of the frequency comb.

arXiv:1207.3998Optics LettersOct 15, 20128 citations

5{S}_{1/2}\ensuremath{\rightarrow}5{D}_{3/2,5/2}

two-photon transitions excited in a rubidium atomic vapor cell. The transitions occur via stepwise excitation through the

5{P}_{1/2,3/2}

states by use of the direct output of an optical frequency comb. Experiments were performed with two different frequency combs, one with a repetition rate of

\ensuremath{\approx}925

MHz and one with a repetition rate of

\ensuremath{\approx}250

MHz. The experimental spectra are compared to each other and to a theoretical model.

We study resonantly enhanced cascaded two-photon transitions in Doppler-broadened rubidium vapor, induced by an optical frequency comb. Cascaded two-step excitation of atoms from the ground state 5

S

{}_{1/2}

to the final 5

D

{}_{5/2}

state via an intermediate 5

P

{}_{3/2}

state as well as the influence of the frequency comb repetition rate on the two-photon fluorescence signal have been investigated. It is shown that the careful choice of

{f}_{R}

leads to enhancement of the two-photon signal with considerable increase of the final

5{D}_{5/2}

-state population due to velocity-selective double resonance. Since the double-resonance condition for two different rubidium isotopes is fulfilled for different

{f}_{R}

, the possibility of isotope-selective two-photon excitation is explored. The dependence of the two-photon signal on external magnetic field values and different repetition rates of the optical frequency comb is also investigated.

The two-photon transition $5S\ensuremath{-}5P\ensuremath{-}5D$ in rubidium vapor is investigated by detecting the fluorescence from the

6{P}_{3/2}

state when the atomic system is excited by the combined action of a cw diode laser and a frequency comb. The cw laser plays a role as a velocity-selective filter and allows for sub-Doppler spectroscopy over a large spectral range including the

5{D}_{3/2}

and

5{D}_{5/2}

states. For a counterpropagating beam configuration, the response of each atomic velocity group is well characterized within the Doppler profile and the excited hyperfine levels are clearly resolved. The contribution of the optical pumping to the direct two-photon process is also revealed. The results are well described in a frequency domain picture by considering the interaction of each velocity group with the cw laser and the modes of the frequency comb.

The two-photon transition of

{}^{87}

Rb ($5{S}_{1/2}\ensuremath{-}4{D}_{3/2}$, $5{S}_{1/2}\ensuremath{-}4{D}_{5/2}$) in a vapor cell is investigated with direct frequency-comb spectroscopy. When strong chirp is imposed on a frequency comb, it is found that the Doppler-free signal amplitude barely degrades despite a significant reduction in peak intensity. In addition, it is found that the Doppler-broadened signal is strongly dependent on the applied chirp. We present a simple model that explains this counterintuitive behavior based on the elongated spatial extent of chirped pulses. Keeping Doppler-free signals almost constant, Doppler-broadened background signals can be strongly suppressed with chirped-pulse excitations. Consequently, in the case of uniformly distributed target atoms, chirped-pulse direct frequency-comb spectroscopy can be a useful method to improve the signal-to-noise ratio in two-photon direct frequency-comb spectroscopy.