High-resolution Cs-Rb two-photon spectrometer for directly stabilizing a Ti:sapphire comb laser.

In this paper, we present a simple scheme for efficiently removing the residual Doppler background of a comb laser based two-photon spectrometer to be better than 10-3 background-to-signal ratio. We applied this scheme to stabilize the frequencies of a mode-locked Ti:sapphire laser directly referring to the cesium 6S-8S transition and rubidium 5S-5D transition. We suggest a standard operation procedure (SOP) for the fully direct comb laser stabilization and evaluate the frequency of two spectral lines at a certain temperature, by which we demonstrate an all-atomic-transition-based Ti:sapphire comb laser merely via a 6-cm glass cell.

Measurement of the 5S1/2 to 5D5/2 two-photon clock transition frequency of rubidium-85 in high vacuum.

We present a scheme to precisely resolve the unperturbed line shape of an optical rubidium clock transition in a high vacuum, by which we avoided the systematic errors of "collision shift" and "modulation shift." The spectral resolution resolved by this scheme is significantly improved such that we can use "Zeeman broadening" to inspect the stray magnetic field, through which we were able to compensate the magnetic field inside the Rb cells to be below 10-3 Gauss. We thus update the absolute frequency of the clock transition and propose a standard operation procedure (SOP) for the clock self-calibration.

Influence of atmospheric helium on secondary clocks.

Glass-cell-based secondary clocks, including coherent population trapping (CPT) clocks, are the most used clocks in modern laboratories and in industry. However, the reported frequency accuracies of those secondary clocks were always much worse than expected, though all error sources have been previously discussed. In this report, a high-precision measurement on the spectral frequency-linewidth relation (FL-R) is first used for revealing a new error source in secondary clocks by which we answer the puzzle raised in Opt. Lett.38, 3186 (2013)10.1364/OL.38.003186.

Absolute frequency of cesium 6S1/2-6D3/2 hyperfine transition with a precision to nuclear magnetic octupole interaction.

We have determined the fundamental frequency of the cesium atom 6S1/2-6D3/2 two-photon transition, for the first time, to our knowledge. Moreover, our high-resolution scheme made it possible to address the influence of the nuclear magnetic octupole on the hyperfine structure. We found that the octupole-interaction hyperfine constant deduced from the cesium 6D-level has a value nearly eight times larger than what has been deduced from the 6P-level.

Robust sub-millihertz-level offset locking for transferring optical frequency accuracy and for atomic two-photon spectroscopy.

Robust sub-millihertz-level offset locking was achieved with a simple scheme, by which we were able to transfer the laser frequency stability and accuracy from either cesium-stabilized diode laser or comb laser to the other diode lasers who had serious frequency jitter previously. The offset lock developed in this paper played an important role in atomic two-photon spectroscopy with which record resolution and new determination on the hyperfine constants of cesium atom were achieved. A quantum-interference experiment was performed to show the improvement of light coherence as an extended design was implemented.

Absolute frequency of cesium 6S-8S 822 nm two-photon transition by a high-resolution scheme.

We present an alternative scheme for determining the frequencies of cesium (Cs) atom 6S-8S Doppler-free transitions. With the use of a single electro-optical crystal, we simultaneously narrow the laser linewidth, lock the laser frequency, and resolve a narrow spectrum point by point. The error budget for this scheme is presented, and we prove that the transition frequency obtained from the Cs cell at room temperature and with one-layer µ-metal shielding is already very near that for the condition of zero collision and zero magnetic field. We point out that a sophisticated linewidth measurement could be a good guidance for choosing a suitable Cs cell for better frequency accuracy.

High-resolution 133Cs 6S-6D, 6S-8S two-photon spectroscopy using an intracavity scheme.

This Letter presents an intracavity scheme for diode laser based two-photon spectroscopy. To demonstrate generality, three (133)Cs hyperfine transition groups of different wavelengths are shown. For the 6S-6D transitions, we achieved a 10(2) times better signal-to-noise ratio than in previous work [J. Phys. Soc. Jpn. 74, 2487 (2005)] with 10(-3) times less laser power, revealing some previously vague and unobserved spectra. Possible mutual influences between the two-photon absorber and laser cavity were investigated for the first time to our knowledge, which leads to the application of a reliable hand-sized optical frequency reference. Our approach is applicable for most of the two-photon spectroscopy of alkali atoms.

Cesium 6S(1/2) --> 8S(1/2) two-photon-transition-stabilized 822.5 nm diode laser.

A cesium 6S(1/2) --> 8S(1/2) two-photon-transition (TPT)-stabilized 822.5 nm diode laser is reported for the first time to our knowledge. Allan deviation of 4.4 x 10(-13) (60 s) was achieved, and the possible systematic errors were evaluated as smaller than 2 kHz. We demonstrate that the cesium TPT-stabilized diode laser could be a reliable frequency reference at 822.5 nm wavelength.

Iodine stabilization of a diode laser in the optical communication band.

The iodine molecule has frequently been used as a frequency reference from the green to the near-infrared wavelength region (500-900 nm). We describe the frequency locking of the second-harmonic signal of a 197.2-THz (1520.25-nm) distributed-feedback diode laser to the absorption lines of the iodine hyperfine structure; a frequency jitter below 0.1 MHz was achieved at a 300-ms time constant. This scheme provides a simple, compact, and high-performance frequency reference in the optical communication band.

Sub-Doppler molecular-iodine transitions near the dissociation limit (523-498 nm).

A widely tunable and high-resolution spectrometer based on a frequency-doubled Ti:sapphire laser was used to explore sub-Doppler transitions of iodine molecules in the wavelength range 523-498 nm. The wavelength dependence of the hyperfine transition linewidth of iodine was mapped out in this region, and the narrowest linewidth was ~4 kHz near 508 nm. The hyperfine-resolved patterns were found to be largely modified toward the dissociation limit. The observed excellent signal-to-noise ratio should lead to high-quality optical frequency standards that are better than those of the popular 532-nm system.