Rubidium Cell Research Articles

High-resolution spectroscopy of liquid water with dispersive atomic vapor prism cell

This article presents an experimental demonstration of a spectroscopic method based on the dispersion of the scattering spectrum from laser-illuminated liquid water collected through a rubidium atomic vapor prism cell. Resonant absorption at 780 nm suppresses Mie/Rayleigh scattering and the steep gradients in refractive index near the 780 nm absorption lines separate Brillouin scattering from Raman scattering in liquid water. The opposing spatial displacements of the Stokes and Anti-Stokes shifted Brillouin peaks yield a measurement of their spectral shifts and thus the temperature or salinity of the water. Performance of the prism cell was mapped with a frequency tunable laser for frequency offsets from the center of the rubidium absorption feature of between −15 GHz and 15 GHz and at rubidium cell temperatures between 148 °C and 177 °C. The experimental results are compared with a numerical model and show good agreement with the scattering peak displacements within experimental uncertainties of probe frequency and cell temperature. In the present configuration, the minimum detectable frequency shift is estimated to be 15.5 MHz. Experiments were conducted in water demonstrating the utility of this method for the measurement of water temperature. Liquid water LiDAR was suggested as one of the possible applications for this method and several ways to improve the experimental setup and cell temperature stability were identified.

Photonic integrated beam delivery for a rubidium 3D magneto-optical trap

Cold atoms are important for precision atomic applications including timekeeping and sensing. The 3D magneto-optical trap (3D-MOT), used to produce cold atoms, will benefit from photonic integration to improve reliability and reduce size, weight, and cost. These traps require the delivery of multiple, large area, collimated laser beams to an atomic vacuum cell. Yet, to date, beam delivery using an integrated waveguide approach has remained elusive. Here we report the demonstration of a 87Rb 3D-MOT using a fiber-coupled photonic integrated circuit to deliver all beams to cool and trap > 1 ×106 atoms to near 200 μK. The silicon nitride photonic circuit transforms fiber-coupled 780 nm cooling and repump light via waveguides to three mm-width non-diverging free-space cooling and repump beams directly to the rubidium cell. This planar, CMOS foundry-compatible integrated beam delivery is compatible with other components, such as lasers and modulators, promising system-on-chip solutions for cold atom applications.

A Compact Laser System for the Pulsed Optically Pumped Rubidium Cell Atomic Clock

We describe the design and implementation of a compact laser system for the pulsed optically pumped (POP) rubidium (Rb) cell atomic clock. The laser system includes packaged optics for sub-Doppler absorption, acousto-optic modulation and light beam expansion, and dedicated electronics for laser diode reliable single-mode operation and laser frequency stabilization. With beat measurements between two identical laser systems, the laser frequency stability was found to be 3.0×10-12 for averaging times from 1 to 60 s and it reached 3.5×10-12 at 10 000 s averaging time. Based on the compact laser system, the short-term stability of the Rb cell atomic clock in pulsed regime was approximately [Formula: see text], which is in reasonable agreement with the estimated [Formula: see text]. The compact laser system is significant in terms of the development of transportable and high-performance Rb atomic clock prototypes.

Comparison of Gravitational and Light Frequency Shifts in Rubidium Atomic Clock

The article presents the results of an experimental study of the external magnetic field orientation and magnitude influence on the rubidium atomic clock, simulating the influence of the geomagnetic field on the onboard rubidium atomic clock of navigation satellites. The tensor component value of the atomic clock frequency light shift on the rubidium cell was obtained, and this value was ~2 Hz. The comparability of the relative light shift (~10−9) and the regular gravitational correction (4×10−10) to the frequency of the rubidium atomic clock was shown. The experimental results to determine the orientational shift influence on the rubidium atomic clock frequency were presented. A significant effect on the relative frequency instability of a rubidium atomic clock at a level of 10−12(10−13) for rotating external magnetic field amplitudes of 1.5 A/m and 3 A/m was demonstrated. This magnitude corresponds to the geomagnetic field in the orbit of navigation satellites. The necessity of taking into account various factors (satellite orbit parameters and atomic clock characteristics) is substantiated for correct comparison of corrections to the rubidium onboard atomic clock frequency associated with the Earth’s gravitational field action and the satellite orientation in the geomagnetic field.

The zero-field resonance in optical pumping experiments

It is common for senior physics students at many universities to perform optical pumping experiments using a rubidium cell in an integrated apparatus. Such experiments provide an encounter with atomic structure in the context of a standard technique of modern atomic physics. Typically, students investigate radiofrequency resonances between Zeeman levels and measure hyperfine splitting. Despite its pivotal role in aligning the apparatus the so-called zero-field resonance is usually not investigated in such experiments. However it is instructive to look more closely at this phenomenon. We show that it is a consequence of a residual transverse magnetic field that is the result of the inability to align precisely the optical axis of the apparatus in the local N–S direction. The measured width and depth of the resonance-like minimum in transmission is found to be consistent with a very small relaxation rate for the rubidium atoms. In an appendix we show further that the measurements compare well with theory for the Hanle effect in the ground state for an arbitrary magnetic field direction relative to the optical axis of the experiment.

Diode Pumped Rubidium Laser Based on Etalon Effects of Alkali Cell Windows**Supported by the National Natural Science Foundation of China under Grant Nos. 61875198 and 61775215, and the Foundation of Military Commission of Science and Technology of China under Grant No. 61404140107.

We demonstrate that the etalon effects of alkali cells can be used as the output coupler of an alkali laser. Based on a rubidium cell with highly parallelized windows, a 2.7 W rubidium laser with optical efficiency of 20.9% and slope efficiency of 31.8% is obtained by adopting unconventional output couplers. Since it has compact configuration and the inner surface of the rubidium cell is uncoated, this may be used in high power laser systems with long lifetimes.

Self-induced-transparency mode locking in a Ti:sapphire laser with an intracavity rubidium cell

In a Ti:Sa laser with an absorbing with Rb vapor cell stable self-starting passive mode-locking is demonstrated. We show that the mode-locking appears due to self-induced transparency (SIT) in the Rb cell, that is, the pulse in the Rb cell is a 2pi SIT pulse. For the best of our knowledge, in these experiments we present the first time demonstration of SIT mode-locking in laser systems, which was discussed only theoretical before.

Nonlinear frequency conversion of vector beams with four wave mixing in atomic vapor

We experimentally investigate the frequency conversion of vector beams with four-wave-mixing (FWM) in rubidium vapor. The conversion of vector beams from the probe beam to the conjugate beam is realized. In FWM experiments, the pump and the probe beam have orthogonal polarizations because of the polarization sensitivity of the FWM process and detection convenience. In order to satisfy the polarization sensitive phase matching condition and realize the nonlinear frequency conversion of vector beams, a Sagnac interferometer is used to form two FWM processes in the same rubidium cell, and two generated conjugate beams are combined with a polarizing beam splitter to form a conjugate vector beam. The experimental results agree well with our theoretical simulation. Compared with nonlinear optical crystals, the atomic vapor provides another platform to control and manipulate the vector beams nonlinearly.

Intelligent and automatic laser frequency locking system using pattern recognition technology

This paper reports on an experimental realization of an automatic laser locking scheme using the artificial intelligence algorithm. We design a classifier based on the support vector machine to recognize the pattern of the saturated absorption spectroscopy signal of a laser and to locate its lockable points. We experimentally investigated our intelligent locking scheme on an external-cavity-diode-laser (ECDL) at 780 nm through the rubidium (Rb) cell and Rb saturated absorption lines. Test results show that the laser frequency can be automatically locked or relocked to the desired point within 11.6 s, either from free running state or from unlocked state, where the entire locking and relocking process is managed by the machine itself rather than human operations. The intelligent method reported in this paper provides a robust and smart solution for laser locking in unmanned conditions, e.g., space-borne experiments.

Magnetic Field Measurement Using Peak-Locked Zeeman Coherent Population Trapping Resonance in Rubidium Vapor

A sensor for magnetic field measurement is developed using a small (centimeter size) rubidium cell. A high contrast Zeeman coherent population trapping (CPT) resonance is produced by the magnetic dither in the sensor solenoid, and a peak-locked servo is implemented for magnetic field measurement. Sensitivity close to $\text{110 pT}/\sqrt {\text{Hz}} $ has been achieved in axial field measurement. The CPT-based magnetic sensor is capable of measuring sub-nanotesla level magnetic field variations at high (microtesla) field strength. We discussed possible sources of noise and broadening which are affecting the performance of the sensor, and suggest changes that will further improve the performance of the sensor.

CPT atomic clock with cold-technology-based vapour cell

Alkali-metal vapour cells are the core of coherent population trapping (CPT) atomic clocks, devices with a multitude of applications. These cells ensure high clock stability due to an atomic reference resonance. The contemporary technologies of alkali-metal vapour cells for atomic clocks compatible with mass production are relatively complicated and require special materials, as well as sub-technologies. The present work for the first time studies atomic CPT cocks with rubidium miniature cells fabricated with a simpler direct optical bonding technology, which has never hitherto been used for this purpose. The proposed technology can be implemented both in industrial and in laboratory setting. The measured stability of CPT atomic clock with rubidium cells fabricated with this technology amounted to 4 × 10–11 over 1 s and 1.3 × 10–12 over 103 s. The generated results indicate that the direct optical bonding technology can be successfully utilised for fabrication of compact cells with alkali-metal vapours for metrological and sensor applications.

Raman − Ramsey pulsed excitation of coherent population trapping resonances in a 87Rb cell with a buffer gas

We report the results of experimental investigation of the Raman – Ramsey method of pulsed excitation of coherent population trapping (CPT) resonances in a rubidium vapour cell filled with a mixture of Ar and Ne buffer gases. For the development of compact quantum microwave frequency standards, this method is an alternative to the pulsed optical pumping method recently implemented using the same rubidium cell. Both methods have advantages over the traditional double radio-optical resonance technique, the main of which is the substantial suppression of the light shift of the clock transition frequency, since the evolution of the coherence of atomic states forming the clock transition occurs in the absence of laser radiation in the cell. The narrow (110 – 240 Hz) Raman – Ramsey resonances are obtained using the scheme of pulsed excitation of CPT resonances on the D1 lines of the 87Rb atom with the same linear (lin||lin) polarisations of the bichromatic laser radiation components. The process of optimising the central fringe linewidth, its contrast, and the linewidth-to-contrast ratio is described. The magnetic dependence of the Raman – Ramsey line central fringe linewidth is experimentally investigated.

Microwave oscillator using piezoelectric thin-film resonator aiming for ultraminiaturization of atomic clock.

We developed a microwave oscillator and a micro electromechanical systems-based rubidium cell for the miniaturization of atomic clocks. A thin-film bulk acoustic resonator (FBAR) having a resonant frequency of the fundamental mode in the 3.5 GHz band was employed instead of a crystal resonator. It delivers a clock transition frequency of Rb atoms of 3.417 GHz without the need for a complicated frequency multiplication using a phase-locked loop. This topology considerably reduces the system scale and power consumption. For downsizing the atomic clock system toward the chip level as well as mass production, a microfabricated gas cell containing Rb and N2 gases was also developed. These microcomponents were incorporated into an atomic clock test bench, resulting in a clock operation with a short-term frequency instability of 2.1 × 10-11 at 1 s. To the best of our knowledge, this is the first report of a coherent population trapping clock operation using an FBAR-based microwave oscillator as well as a microfabricated gas cell.

Paraffin coated rubidium cell with an internal atomic vapor source

We present the results of a study on relaxation and diffusion processes of rubidium atoms in a rubidium cell with an internal vapor source. The cell is an evacuated glass bulb, which is characterized in that the source of atomic vapors in the form of a metal film Rb is evenly distributed throughout the inner surface of the bulb, and the paraffin film is uniformly distributed over the entire area and over the metal surface. By using laser optical pumping, we performed measurements of the relaxation time and the average number of bounces of optical pumped rubidium atoms in the bulb. We have measured the adsorption time of rubidium atoms by paraffin coating and rubidium atoms diffusion coefficient in paraffin used. A simple model of the pumping and atomic diffusion processes in the cell is discussed as well.

Technique of pulsed optical pumping and pulsed excitation of microwave resonances using the Ramsey scheme in a 87Rb cell with a buffer gas

A laboratory prototype of a compact quantum frequency standard based on a rubidium vapour cell with pulsed laser pumping is developed. With significantly smaller overall dimensions (a volume of ∼10 L and a mass of ∼10 kg), the frequency standard is expected to have the short-term instability comparable with that of the commercial passive hydrogen masers and even the laboratory fountain-type atomic clocks based on cold atoms. The advantages of the technique of pulsed optical pumping and pulsed excitation of microwave resonances over the traditional techniques of double radio-optical resonance detection are substantiated. The results of the experimental study of pulsed optical pumping of a rubidium cell with a mixture of buffer Ar – Ne gases implemented at the VNIIFTRI are presented, the Ramsey resonances are obtained, and the process of optimising the contrast of the central resonance peak is described.

Experimental and theoretical comparison of different optical excitation schemes for a compact coherent population trapping Rb vapor clock

We have investigated, theoretically as well as experimentally, the relative merits and demerits of using three different optical configurations for a compact coherent population trapping (CPT) vapor clock using 87Rb. These correspond to the following choices of polarizations for the two Raman beams: , (), and push–pull optical pumping (PPOP), applied on the D1 manifold. We have used a multi-level atomic model to study the dependence of the CPT spectrum on axial as well as transverse magnetic fields for these three schemes. Corresponding experimental studies have been performed using a laboratory scale CPT clock employing a two cm long, isotopically pure rubidium cell, loaded with a buffer gas. We observed a CPT contrast close to 20% with a sub-kilohertz linewidth by adopting the PPOP scheme. We discuss the strengths and weaknesses of each of the three optical excitation schemes, and present frequency-stability measurement data for the prototype clock.

Recent improvements on the pulsed optically pumped rubidium clock at SIOM

We report the recent progress of our pulsed optically pumped (POP) vapor cell rubidium clock with dispersive detection. A new compact physics package is made. A rubidium cell with a high precision buffer gases mixing ratio is obtained, and the temperature controlling system is renovated to reduce fractional frequency sensitivity to temperature variation. The resolution of the servo control voltage is also optimized. With these improvements, a clock frequency stability of 3.53×10?13 at 1 s is obtained, and a fractional frequency stability of 4.91×10?15 is achieved at an average time of τ=2000 s.

Optical cavity for enhanced parametric four-wave mixing in rubidium

We demonstrate the implementation of a ring cavity to enhance the efficiency of parametric four-wave mixing in rubidium. Using an input coupler with 95% reflectance, a finesse of 19.6$\pm$0.5 is achieved with a rubidium cell inside. This increases the circulating intensity by a factor of 5.6$\pm$0.5, and through two-photon excitation on the $5s_{1/2}\rightarrow5d_{5/2}$ transition with a single excitation laser, up to 1.9$\pm$0.3 mW of power at 420 nm is generated, 50 times what was previously generated with this scheme. The dependence of the output on Rb density and input power has been explored, suggesting the process may be approaching saturation. The blue output of the cavity also shows greatly improved spatial quality, combining to make this a promising source of 420 nm light for future experiments.

Frequency characteristics of far-detuned parametric four-wave mixing in Rb.

We have investigated the frequency characteristics of the coherent 420 nm beam generated via parametric four-wave mixing (FWM). A single, high-power 778 nm laser is directed through a high-density rubidium cell with a detuning of 1 THz from the intermediate state, generating fields at 420 nm and 5.23 μm through FWM. The frequency of the 420 nm light has been found to shift as the excitation laser is tuned. The measured frequency shift ratio of 1.87±0.04 corresponds with the selection of a different velocity class at each excitation frequency, implying that the 5.23 μm beam frequency is correspondingly shifted. The 420 nm light has been tuned over a range of 1 GHz. This parametric FWM process has potential application as a tunable photon source at novel wavelengths.

Observation of the5p3/2→6p3/2electric-dipole-forbidden transition in atomic rubidium using optical-optical double-resonance spectroscopy

Direct evidence of excitation of the 5p3/2 -> 6p3/2 electric dipole forbidden transition in atomic rubidium is presented. The experiments were performed in a room temperature rubidium cell with continuous wave extended cavity diode lasers. Optical-optical double resonance spectroscopy with counterpropagating beams allows the detection of the non-dipole transition free of Doppler broadening. The 5p3/2 state is prepared by excitation with a laser locked to the maximum F cyclic transition of the D2 line, and the forbidden transition is produced by excitation with a 911 nm laser. Production of the forbidden transition is monitored by detection of the 420 nm fluorescence that results from decay of the 6p3/2 state. Spectra with three narrow lines (~ 13 MHz FWHM) with the characteristic F - 1, F and F + 1 splitting of the 6p3/2 hyperfine structure in both rubidium isotopes were obtained. The results are in very good agreement with a direct calculation that takes into account the 5s -> 5p3/2 preparation dynamics, the 5p3/2 -> 6p3/2 non-dipole excitation geometry and the 6p3/2 -> 5s1/2 decay. The comparison also shows that the electric dipole forbidden transition is a very sensitive probe of the preparation dynamics.