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Microwave and optical oscillators both based on cryogenic sapphire resonators offer advantageous frequency stabilities over time intervals ranging from 0.1 to 10000 seconds. We present progress on the development of a combined optical-and-microwave oscillator, whose component optical and microwave resonators form the same physical package and, furthermore, whose resonance frequencies are defined by...
In this article we report on the first use of degenerate Raman sideband cooling for the collimation of a continuous beam of cold cesium atoms in a fountain geometry. Using this cooling technique we have reduced the atomic beam transverse temperature from 60 µK to 1.6 µK in a few milliseconds. We present experimental results and future directions that we will investigate.
Using Precise Point Positioning (PPP) we show the potential for comparing frequency standards with time stabilities of under 300 ps in flicker phase noise for time periods of 1 to 10 d. This leads to comparisons at 1 part in 1015 or better at 10 d. We compare short baseline PPP results with 2 hour data from the NIST Measurements System. We compare results from the NIST - USNO baseline with hourly...
Most of the GPS links between timing laboratories that contribute to TAI are performed by single channel GPS timing receivers. These are based in the original NBS and JPL designs, and can perform and store 48 tracks per day.
The GPS has provided a model for precise time dissemination in the environment of the Earth. In the future, principles analogous to those now used in the GPS will need to be applied to space missions beyond the Earth. This paper presents some of the theoretical and technical issues that will be important for time synchronization among atomic clocks on Earth, on the surface of Mars, and on satellites...
Applications including : coherently arrayed antennas, radio and radar astronomy, very long baseline interferometry and geodynamic measurement require an ultra stable frequency and distribution system. Phase stable and low noise optical distribution systems would be very useful in the metrological domain. Indeed the opportunity to compare clocks when laboratories are in a range of 100 km or more would...
This paper reports on progress at NPL in extending the range and utility of optical frequency combs. To enable measurements to be made at locations other than our own laboratory, a transportable comb system is being built whilst to extend the spectral range to cover the telecommunications bands we are also building a comb based on a Cr:forsterite laser.
In the process of designing resonant temperature sensors, getting minimal dimensions is required to decrease calorific capacity and response time. In this view, we investigated new shapes of sensing elements essentially obtained by modifying an initial resonator's design. This design consists in plane parallel circular disk plates in NLC-cut for energy trapping by electrodes mass loading. Then, the...
A generalized noise model is discussed of a crystal oscillator, in which the resonator equivalent parameters of the fundamental modes, overtones, and anharmonic branches are assumed to be drive level dependent (DLD) and flicker-noisy. An additive thermal noise of the resonator losses is also taken into account. A feedback amplifier is presented by the generalized nonlinear noise model, in which the...
An approach to PM and AM noise calculation in oscillator with voltage controlled oscillations frequency (VCO) is developed. It is based on quasi-steady state equations of the oscillator. Both wideband and 1/f noise sources are taken into consideration. Under several assumptions simple formula for PM noise in VCO is obtained and discussed. An influence of feedback through unbypassed emitter resistance...
PM and AM noise analysis in voltage controlled phase shifter, consisting of two amplifiers with voltage controlled gain, phase splitter and summing amplifier, is presented. It is based on the theory of PM and AM noise in bipolar junction transistor (BJT) amplifiers. Both 1/f and wideband noise sources in BJT amplifiers are taken into consideration. It is shown that conversion of AM noises of the amplifiers...
In this paper the noise characterization of the GPS receivers (both timing and geodetic) hosted at the Time and Frequency Laboratory of the Istituto Elettrotecnico Nazionale (IEN) “Galileo Ferraris” was taken into account. In particular, a specific algorithm as well as two different approaches (a classical GPS “common view” technique and a geodetic-based Precise Point Positioning, PPP) employed to...
This paper presents the performances of GPS on board clocks computed by the International GPS Service (IGS) [1]. Using recently developed IGS combined clock products referenced to IGST, the identified GPS on board clocks have no longer day boundaries discontinuities, allowing extensive analysis on large integration times. The aim of this paper is to compare the performances of the GPS on board clocks...
Since 1991, most time and frequency laboratories perform standard time dissemination via telephone lines using commercial modems. The time information generated by this system is referenced to the national time standard by direct telephone line and it is accessible to anyone who uses an external modem.
In order to understand the atomistic origin of the inverse piezoelectric effect in α-SiO2 and α-GaPO4 we have measured the changes of integrated X-ray intensities of selected Bragg reflection under influence of an external high electric field up to 8 kV/mm. To do this 300 µm thick samples were sandwiched between metallic contacts and the X-ray intensities were recorded with and without the applied...
A technique used in meteor synchronization equipment constructed in Kazan State University includes transmission of time marks on several carrier frequencies. Time shift between stations is calculated on secondary station by getting the differences between phases of signal carrier waves corresponding to phases of imaginary differential frequencies and resolving their ambiguity. Phase ambiguity resolution...
For a long time, one of the main limitations of cesium atomic fountains has been the cold collision frequency shift [2, 7, 10, 11]. By using a method based on a transfer of population by adiabatic passage (AP) [12, 16, 18] allowing to prepare cold atomic samples with a well defined ratio of atomic density as well as atom number we have a better measurement of this effect. By improving the method we...
This paper reports a review of the Blackbody Radiation (BBR) shift theory for the Cs atom hyperfine clock transition, together with a measurement of the Blackbody Radiation shift in an atomic cesium fountain.
The linewidth of CPT atomic resonances observed in a vapor cell are usually limited by optical saturation and collisions due to buffer gas. We have applied here the Ramsey method with optical CPT pulses generated by a phase-locked device. Fringes are then produced giving narrow atomic signals only dependent on interrogation time between the two pulses. The possibility to obtain narrow fringe widths...
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