Absolute frequency measurement of the 6s21S0 → 6s6p3P1F = 3/2 → F' = 5/2 201Hg transition with background-free saturation spectroscopy.

We report the development of a method for eliminating background-induced systematic shifts affecting precise measurements of saturation absorption signals. With this technique, we measured the absolute frequency of the 6s21S0 → 6s6p3P1 transition in 201aHg (F = 3/2 → F' = 5/2) to be 1181541111051(83) kHz. The measurement was referenced with an optical frequency comb synchronized to the frequency of the local representation of the UTC. This specific atomic line is situated on the steep slope of the Doppler background at room temperature, which results in a frequency systematic shift. We determined the dependence of this shift on the properties of both the spectral line and the background of the measured signal.

Response of an optical cavity to phase-controlled incomplete power switching of nearly resonant incident light.

The response of an optical cavity to incomplete extinction of nearly resonant incident light was experimentally examined. Measurements were performed using a Pound-Drever-Hall-locked frequency-stabilized cavity ring-down spectrometer (CRDS) that allowed the laser frequency detuning from the cavity resonance center to be controlled at Hz-level resolution. It is shown that an insufficient laser light extinction ratio combined with a phase shift and frequency detuning may lead to non-exponential cavity pumping and decay signals. The experimental results can be explained with a simple analytical model. The non-exponential decay can lead to a systematic shift as high as 0.5% in the ring-down time constants, dependent on the laser frequency detuning from the cavity mode center and on the extinction ratio. This can lead to appreciable systematic errors in the absorption coefficients determined with the CRDS technique.

Dual Hg-Rb magneto-optical trap.

We present a two-species laser cooling apparatus capable of simultaneously collecting Rb and Hg atomic gases into a magneto-optical trap (MOT). The atomic sources, laser system, and vacuum set-up are described. While there is a loss of Rb atoms in the MOT due to photoionization by the Hg cooling laser, we show that it does not prevent simultaneous trapping of Rb and Hg. We also demonstrate interspecies collision-induced losses in the 87Rb-202Hg system.

Cavity mode-width spectroscopy with widely tunable ultra narrow laser.

We explore a cavity-enhanced spectroscopic technique based on determination of the absorbtion coefficient from direct measurement of spectral width of the mode of the optical cavity filled with absorbing medium. This technique called here the cavity mode-width spectroscopy (CMWS) is complementary to the cavity ring-down spectroscopy (CRDS). While both these techniques use information on interaction time of the light with the cavity to determine absorption coefficient, the CMWS does not require to measure very fast signals at high absorption conditions. Instead the CMWS method require a very narrow line width laser with precise frequency control. As an example a spectral line shape of P7 Q6 O2 line from the B-band was measured with use of an ultra narrow laser system based on two phase-locked external cavity diode lasers (ECDL) having tunability of ± 20 GHz at wavelength range of 687 to 693 nm.

Absolute frequency measurement of rubidium 5S-7S two-photon transitions.

We report the absolute frequency measurements of rubidium 5S-7S two-photon transitions with a cw laser digitally locked to an atomic transition and referenced to an optical frequency comb. The narrow, two-photon transition, 5S-7S (760 nm), insensitive to first-order in a magnetic field, is a promising candidate for frequency reference. The performed tests yielded more accurate transition frequencies than previously reported.

Absolute measurement of the 1S0 - 3P0 clock transition in neutral 88Sr over the 330 km-long stabilized fibre optic link.

We report a stability below 7 × 10(-17) of two independent optical lattice clocks operating with bosonic (88)Sr isotope. The value (429 228 066 418 008.3(1.9)(syst) (0.9)(stat) Hz) of the absolute frequency of the (1)S(0) - (3)P(0) transition was measured with an optical frequency comb referenced to the local representation of the UTC by the 330 km-long stabilized fibre optical link. The result was verified by series of measurements on two independent optical lattice clocks and agrees with recommendation of Bureau International des Poids et Mesures.