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Due to the collision-shift effect, helium permeation into the vapor cell causes a time-dependent frequency drift in rubidium atomic clock. To quantify this shift, a cylindrical vapor cell with dimensions of 1.8 cm in diameter, 1.6 cm in height, and 1 mm in thickness, operating at a temperature of 65 ℃, is selected for analysis. Numerical methods are employed to simulate the temporal variation of helium gas pressure within atomic vapor cells composed of Pyrex (Corning 7740) and low helium-permeable aluminosilicate (Corning 1720). The results of the calculations indicate that for Pyrex vapor cells, after 12 years of operation, the drift rate attributable to helium permeation decreases to less than 1.0×10-14/day. In contrast, the frequency drift rate due to helium permeation in aluminosilicate vapor cell rubidium atomical clocks remains below 3.0×10-17/day throughout their operational lifetime, rendering its contribution to the drift rate negligible. This computational approach is also applicable to the investigation of the permeation processes of other gaseous species in various glass materials.

With their high reliability, small size and low power consumption, rubidium atomic clocks are widely used in the fields of navigation, communication, etc. In particular, rubidium atomic clocks for navigation satellites have developed excellent stability. However, their inherent frequency drift characteristics (about E-12 to E-13/day) will deteriorate their long-term performance and affect the autonomous punctual timing of satellites. In this paper, we fully analyzed the frequency data of high-performance rubidium atomic clocks, aiming to figure out the physical mechanism behind the frequency drift. A high-precision frequency drift compensation scheme is proposed and experimentally verified. The results show that the drift rate of high-performance rubidium clock can be maintained in the order of E-15/day within 60 days without external taming, and the day stability can reach the order of E-15 (Allan variance), which greatly improves the autonomous punctual timing ability of rubidium atomic clock．

Rubidium fountain clocks are operated by a control system. In this study, first, the control requirements of a rubidium fountain clock are analyzed; then, a control system is designed and divided into a timing sequence control system, a data acquisition system, and a servo control system. Multiple boards based on PCI extensions for the instrumentation (PXI) bus and Labwindows/CVI software 2019 are adopted. The timing sequence control system outputs 16 transistor–transistor logic (TTL) signals and three arbitrary waveforms. The results show that these signals are synchronized within 380 ns. Moreover, the digital locking frequency of the master laser is triggered by one of the timing signal, sweeping the laser frequency in a wide range during polarization gradient cooling. Two time-of-flight signals are acquired, and Ramsey fringes are scanned using the data acquisition system. An error signal is obtained every two cycles, and it is feed back to the frequency synthesizer and a high resolution offset generator using the servo control system. Then the frequency synthesizer is locked to the Ramsey center resonance. The rubidium atomic fountain clock exhibited a frequency stability of 7.4 × 10−16 at 86,400 s. Moreover, the phase of the Rb fountain clock is compared with that of UTC (NTSC) in real time, demonstrating a frequency drift of 0.00044 ns/day/day. The whole control system is full-featured, robust and flexible, thus satisfying the requirements of rubidium fountain clocks. [ABSTRACT FROM AUTHOR]

The effect of atomic motion on the optical properties of atomic ensembles cooled in special laser traps was analyzed. The possibility was studied to model the continuous displacement of atoms under the assumption of stationary coupled oscillators, in which slow motion is modeled, firstly, by averaging over their random spatial distribution, and, secondly, by introducing a random shift of their frequencies, modeling Doppler effects. A direct comparison of the results obtained taking into account the continuous displacement of atoms with the model ones revealed a very limited range of applicability of the latter. [ABSTRACT FROM AUTHOR]

In technical systems, in addition to mechanical oscillations, it is also worth noting electrical sinusoidal processes in alternating current circuits, in electronic devices, in particular, in the industrial power supply network, oscillatory circuits, signal generators, communication systems, etc. In radar systems, sinusoidal signals with frequency drift can also be observed, for example, linear frequency-modulated or Doppler signal reflected from a maneuvering target, the speed of which has at least one derivative. Among the possible ones, in the future we limit ourselves to comparative studies of two types of SL-oscillations - harmonic (SG) with all constant parameters and sinusoid with linear frequency drift (SD). At the same time, we will consider two types of their mathematical models - trigonometric (T-models) and autoregressive (AR-models). The paper analyzes sine-like trigonometric models and features of their application. The peculiarities of the task of measuring the parameters of the movement of an object with uniform acceleration based on the estimation of the Doppler frequency of the radar probing signal reflected from it are considered. A synthesis of simplified and approximate ARD models was carried out. An important feature of the synthesized ARG model is the fact that only one parameter of the trigonometric model appears in it - the normalized frequency. The main merit of the synthesized simplified and approximate ARD models is their invariance to the amplitude and initial phase of the sinusoidal signal. This reduces the parametric dimension of the estimation problem from four to two parameters, which contributes to a significant improvement in the speed of calculations. Based on mathematical modeling, statistical errors were obtained for different sampling intervals in the triplet and sample size. Based on mathematical modeling, statistical errors were obtained for different sampling intervals in the triplet and sample size. The selection of pairs of triplets was probabilistic. Calculations show that the error of the obtained model does not exceed 8%. [ABSTRACT FROM AUTHOR]

• We improve the ranging accuracy of FMCW systems using the spectral refinement method CZT. • The experimental system constructed improves the ranging stability of the FMCW lidar when performing high-precision ranging. • Accurately measures the speed of target motion using binomial fitting. • The constructed experimental system can determine the direction of motion when measuring the motion state of a moving target. The conventional coherent FMCW lidar system has the problem of frequency drift to meet the high accuracy range. When measuring the moving target, it cannot judge the target motion status in real-time. This paper proposes a high-stability coherent heterodyne FMCW lidar detection method to solve the above-proposed problems. The combined single/double sideband modulation method significantly suppresses the frequency drift and, combined with the spectrum refinement processing method, achieves high stability of laser ranging and speed measurement. The result shows that the target is located at an 8 m distance from the system, the range accuracy is 5 cm, the range error is less than 1.5 cm, and the root mean square(RMS) error is 6.6 × 10-3 m, which is an order of magnitude higher than that of the conventional FMCW laser detection system. We use the binomial fitting method to obtain a measurement speed error of fewer than 1.15 × 10-2 m/s. [ABSTRACT FROM AUTHOR]