Generation of an ultrastable 578 nm laser for Yb lattice clock

In this paper we described the development and the characterization of a 578 nm laser source to be the clock laser for an Ytterbium Lattice Optical clock. Two independent laser sources have been realized and the characterization of the stability with a beat note technique is presente

High-performing vapor-cell frequency standards

Many nowadays scientific and technological applications need very precise time and frequency reference signals. Very often, only atomic clocks can guarantee the high level of accuracy and stability required by these signals. In the current scenario of atomic frequency standards, vapor-cell clocks are particularly suited to be employed in those activities that demand good frequency stability performances joined to compactness, reliability and low power consumption. Recently, due to better-performing laser sources and to innovative techniques to prepare and detect the atoms, several cell-based prototypes exhibiting unprecedented frequency stability have been developed. We review advances in the field of laser-pumped vapor-cell clocks and we provide an overview of the techniques that allowed to achieve frequency stabilities in the order of 1×10^−13 at 1 s (short term) and in the range of 10^−15 for the medium-long term. These stabilities are two orders of magnitude better than current commercial Rb clocks. We also prospect the possibility of further improving these results.Many nowadays scientific and technological applications need very precise time and frequency reference signals. Very often, only atomic clocks can guarantee the high level of accuracy and stability required by these signals. In the current scenario of atomic frequency standards, vapor-cell clocks are particularly suited to be employed in those activities that demand good frequency stability performances joined to compactness, reliability and low power consumption. Recently, due to better-performing laser sources and to innovative techniques to prepare and detect the atoms, several cell-based prototypes exhibiting unprecedented frequency stability have been developed. We review advances in the field of laser-pumped vapor-cell clocks and we provide an overview of the techniques that allowed to achieve frequency stabilities in the order of 1 x 10(-13) at is (short term) and in the range of 10(-15) for the medium-long term. These stabilities are two orders of magnitude better than current commercial Rb clocks. We also prospect the possibility of further improving these results

Generation of continuous-wave THz radiation by use of quantum interference

We propose a scheme for generation of continuous-wave THz radiation. The scheme requires a medium where three discrete states in a $\Lambda$ configuration can be selected, with the THz-frequency transition between the two lower metastable states. We consider the propagation of three-frequency continuous-wave electromagnetic (e.m.) radiation through a $\Lambda$ medium. Under resonant excitation, the medium absorption can be strongly reduced due to quantum interference of transitions, while the nonlinear susceptibility is enhanced. This leads to very efficient energy transfer between the e.m. waves providing a possibility for THz generation. We demonstrate that the photon conversion efficiency is approaching unity in this technique.Comment: 18 pages, 4 figure

Beyond the fundamental noise limit in coherent optical fiber links

It is well known that temperature variations and acoustic noise affect ultrastable frequency dissemination along optical fiber. Active stabilization techniques are in general adopted to compensate for the fiber-induced phase noise. However, despite this compensation, the ultimate link performances remain limited by the so called delay-unsuppressed fiber noise that is related to the propagation delay of the light in the fiber. In this paper, we demonstrate a data post-processing approach which enables us to overcome this limit. We implement a subtraction algorithm between the optical signal delivered at the remote link end and the round-trip signal. In this way, a 6 dB improvement beyond the fundamental limit imposed by delay-unsuppressed noise is obtained. This result enhances the resolution of possible comparisons between remote optical clocks by a factor of 2. We confirm the theoretical prediction with experimental data obtained on a 47 km metropolitan fiber link, and propose how to extend this method for frequency dissemination purposes as well

Measurement of the Blackbody Radiation Shift of the 133Cs Hyperfine Transition in an Atomic Fountain

We used a Cs atomic fountain frequency standard to measure the Stark shift on the ground state hyperfine transiton frequency in cesium (9.2 GHz) due to the electric field generated by the blackbody radiation. The measures relative shift at 300 K is -1.43(11)e-14 and agrees with our theoretical evaluation -1.49(07)e-14. This value differs from the currently accepted one -1.69(04)e-14. The difference has a significant implication on the accuracy of frequency standards, in clocks comparison, and in a variety of high precision physics tests such as the time stability of fundamental constants.Comment: 4 pages, 2 figures, 2 table

Frequency transfer via a two-way optical phase comparison on a multiplexed fiber network

We performed a two-way remote optical phase comparison on optical fiber. Two optical frequency signals were launched in opposite directions in an optical fiber and their phases were simultaneously measured at the other end. In this technique, the fiber noise was passively cancelled, and we compared two optical frequencies at the ultimate 1E-21 stability level. The experiment was performed on a 47 km fiber that is part of the metropolitan network for Internet traffic. The technique relies on the synchronous measurement of the optical phases at the two ends of the link, that is made possible by the use of digital electronics. This scheme offers several advantages with respect to active noise cancellation, and can be upgraded to perform more complex tasks

A pulsed-Laser Rb atomic frequency standard for GNSS applications

We present the results of 10 years of research related to the development of a Rubidium vapor cell clock based on the principle of pulsed optical pumping (POP). Since in the pulsed approach, the clock operation phases take place at different times, this technique demonstrated to be very effective in curing several issues affecting traditional Rb clocks working in a continuous regime, like light shift, with a consequent improvement of the frequency stability performances. We describe two laboratory prototypes of POP clock, both developed at INRIM. The first one achieved the best results in terms of frequency stability: an Allan deviation of σy(τ) = 1.7 × 10−13 τ−1/2, being τ the averaging time, has been measured. In the prospect of a space application, we show preliminary results obtained with a second more recent prototype based on a loaded cavity-cell arrangement. This clock has a reduced size and exhibited an Allan deviation of σy(τ) = 6 × 10−13 τ−1/2, still a remarkable result for a vapor cell device. In parallel, an ongoing activity performed in collaboration with Leonardo S.p.A. and aimed at developing an engineered space prototype of the POP clock is finally mentioned. Possible issues related to space implementation are also briefly discussed. On the basis of the achieved results, the POP clock represents a promising technology for future GNSSs

Realization of an Ultrastable 578-nm Laser for an Yb Lattice Clock

In this paper, we describe the development of an ultrastable laser source at 578 nm, realized using frequency sum generation. This source will be used to excite the clock transition 1S0-3P0 in an ytterbium optical lattice clock experiment. Two independent ultrastable lasers have been realized, and the laser frequency noise and stability have been characterize

On the unique possibility to increase significantly the contrast of dark resonances on D1 line of 87^{87}Rb

We propose and study, theoretically and experimentally, a new scheme of excitation of a coherent population trapping resonance for D1 line of alakli atoms with nuclear spin $I=3/2$ by bichromatic linearly polarized light ({\em lin}$||${\em lin} field) at the conditions of spectral resolution of the excited state. The unique properties of this scheme result in a high contrast of dark resonance for D1 line of $^{87}$Rb.Comment: 9 pages, 7 figures. This material has been partially presented on ICONO-2005, 14 May 2005, St. Petersburg, Russia. v2 references added; text is changed a bi