Alkali Vapor Research Articles

Measurement on Gas Number Density Distribution by Tunable Diode Laser Absorption Spectroscopy

An experimental technique was designed to measure the gas number density distribution of alkali vapor by tunable diode laser absorption spectroscopy. The measurement method was developed by scanning multiple gas absorption lines and fitting the experiment data with Lorentz profile to obtain the density. A discretization strategy of the equation for absorption lines is also present here as well as a constrained liner least-square fitting method. A simulation model was set up to reconstruct the two-dimensional distribution of number density and the feasibility of the reconstruction was verified. In the end, this work demonstrates the calculation error of the acquired number density and the distribution. The results indicated that the error would be no more than 5% if the measurement error is less than 9%.

Modeling of a Diode Side Pumped Cesium Vapor Laser MOPA System

A physical model is established to describe the kinetic process and the laser amplification mechanism of a diode side pumped alkali vapor laser MOPA system. The pump energy distribution inside the vapor cell is displayed. Taking into consideration the amplification saturation effect, the influences of the parameters, such as the temperature, cell length, and pump power on the output performance, are simulated and analyzed. The gain saturation effect in the direction of cell axis is also discussed. The calculations have a good agreement with observations, which shows the validity of this model. A group of optimal parameters is obtained for further improving the output characteristics of a cesium laser MOPA system.

Optical pumping in a microfabricated Rb vapor cell using a microfabricated Rb discharge light source

Miniature (<few cm3) vapor-cell based devices using optical pumping of alkali atoms, such as atomic clocks and magnetometers, today mostly employ vertical-cavity surface-emitting lasers as pump light sources. Here, we report on the demonstration of optical pumping in a microfabricated alkali vapor resonance cell using (1) a microfabricated Rb discharge lamp light source, as well as (2) a conventional glass-blown Rb discharge lamp. The microfabricated Rb lamp cell is a dielectric barrier discharge (DBD) light source, having the same inner cell volume of around 40 mm3 as that of the resonance cell, both filled with suitable buffer gases. A miniature (∼2 cm3 volume) test setup based on the Mz magnetometer interrogation technique was used for observation of optical-radiofrequency double-resonance signals, proving the suitability of the microfabricated discharge lamp to introduce efficient optical pumping. The pumping ability of this light source was found to be comparable to or even better than that of a conventional glass-blown lamp. The reported results indicate that the micro-fabricated DBD discharge lamp has a high potential for the development of a new class of miniature atomic clocks, magnetometers, and quantum sensors.

100 GHz光谱扫描测量碱金属蒸气激光器增益介质浓度

100 GHz光谱扫描测量碱金属蒸气激光器增益介质浓度

基于受抑全反射的碱金属气室镀膜厚度测量

基于受抑全反射的碱金属气室镀膜厚度测量

Analysis on threshold characteristics of a diode-pumped Cs vapor laser

A rate equation model is established to describe the threshold characteristics of a diode-pumped Cs vapor laser in this paper. With the help of the numerical solution for the model, the influences of several parameters (waist position and waist radius of pump laser, length of vapor cell, and operating temperature) on the threshold pump power are analyzed. Results show that there are optimal values of the pump waist position and radius, vapor cell length and operating temperature to ensure a lowest threshold pump power. Besides, the decrease of divergence angle can reduce threshold pump power effectively. Simulation results are in good agreement with the experimental data. It is shown that the model can be used to reveal the threshold characteristics of diode-pumped alkali vapor laser and may serve as a theoretical guidance for the optimization design of this laser.

Comparative study of diode-pumped hydrocarbon free Rb and K vapor lasers

Based on the kinetic model of diode-pumped alkali vapor lasers, operation parameters including helium pressure, temperature and output mirror reflectivity are optimized for hydrocarbon free Rb laser and K laser. A comparative study on the output characteristics of hydrocarbon free Rb laser and K laser is also carried out. Results show that a better capability is presented in hydrocarbon free K laser instead of hydrocarbon free Rb laser, such as lower pump threshold, higher laser gain and optical-to-optical efficiency. The performance difference between K and Rb laser is mainly induced by the difference of helium pressure, which results in an evident difference on the absorption cross section and emission cross section. (C) 2013 Elsevier Ltd. All rights reserved.

Production of magnesium during carbothermal reduction of magnesium oxide by differential condensation of magnesium and alkali vapours

Most of researchers believed that the developments on the condensation of magnesium produced by carbothermic reduction just concentrated on two process routes: the “quench” route and the “solvent” route. But this paper will briefly analyzes the major challenges in magnesium vapor condensation during the vacuum carbothermic reduction of calcined dolomite, on equipment upgrade, heat transfers alter, to achieve condensation control and production collection. Solutions are then proposed using theoretical calculations and experiment results. Comparative analysis of the experiment results shows that the burning and even explosion of condensation products during the vacuum carbothermic reduction of calcined dolomite are mainly due to the burning of crystallized powder magnesium, which results from the self-ignition of alkali metals. Finally, this paper proposes a multistage condensation solution to improve traditional vacuum condensation equipment. And result show that the condensation equipment can effectively mitigate the burning and loss during condensation, also the morphology of the condensation products clearly improved, the grain size increased, and the oxidation rate decreased. The potassium/sodium vapor and the magnesium vapor were separately condensed.

Inorganic constituents formed during small-scale gasification of poultry litter: A model based study

Europe's vast poultry industry requires a proper waste management in order to comply with environmental regulations. As a result, poultry litter represents a potential fuel candidate for thermal conversion technologies since it is an available source. Therefore, a process simulation for the gasification of poultry litter is examined in this study. This process integrates a fluidised bed gasifier with a gas turbine with the aim of generating combustibles gases for energy production. The system allows the treatment of waste with the additional benefit of energy generation. A small-scale system (200 kWe) installed on-site the biomass source shows to be suitable for a poultry farm to avoid the litter transportation to centralised plants. Among the by-products generated during gasification, such as NOx, SO2, and tar, ash represents a potential risk since bed agglomerates can lead to loss of fluidisation and alkali vapours in the product gases can increase rates of hot corrosion on turbine surfaces. This work presents the partition of the most problematic inorganic species in order to assess the feasibility of the system and identify the optimum parameters to minimise the vaporisation of inorganics. It was found that low ER values produced low HCl emissions and good process efficiencies but released very high SO2 emissions.

Nonlinear Elimination of Spin-Exchange Relaxation of High Magnetic Moments

Relaxation of the Larmor magnetic moment by spin-exchange collisions has been shown to diminish for high alkali densities, resulting from the linear part of the collisional interaction. In contrast, we demonstrate both experimentally and theoretically the elimination of spin-exchange relaxation of high magnetic moments (birefringence) in alkali vapor. This elimination originates from the nonlinear part of the spin-exchange interaction, as a scattering process of the Larmor magnetic moment. We find counterintuitively that the threshold magnetic field is the same as in the Larmor case, despite the fact that the precession frequency is twice as large.

Review on diode-pumped alkali vapor laser

Diode-pumped alkali vapor lasers (DPAL) are attracted much attention during recent years for its numerous potential applications. Development of DPAL is reviewed in this paper. The key techniques of DPAL are summarized and analyzed in detail, including the interactions between buffer gas and alkali vapor, pumping structure and power scaling magnification. Novel techniques used in DPAL are discussed, such as hydrocarbon-free DPAL and unstable cavity with transverse pumping. Blue-violet lasers by frequency doubling of DPAL are also introduced specifically. In addition, potential applications and the prospects of DPAL are concluded briefly.

Optical switching in a Ξ system: A comparative study on DROP and EIT

In this experimental work we address the issue of optical switching through pump induced atomic coherence in pump-probe spectroscopy of Doppler broadened medium of Rubidium atoms. Here a cascade system 5S → 5P → 5D is chosen as the medium for optical switching. The merit of using this level scheme for current study lies in the fact that two photon spectroscopy conducted in the above-mentioned manifold results into a combination of double resonance optical pumping (DROP) and electromagnetically induced transparency (EIT) signals. Within an intensity modulation frequency range of 10 Hz → 10 MHz, DROP and EIT behave differently. This fact may be attributed to the distinctive difference in mechanisms giving rise to DROP and EIT signals. Though both DROP and EIT stem from two photon spectroscopy, unlike DROP, which arises due to population transfer between dipole forbidden 5S → 5D levels, EIT originates from destructive quantum interference mechanism. This subtle difference is well evidenced when optical switching is conducted through the coherently prepared alkali vapour sample. The EIT is found to be more agile towards faster optical switching while DROP acts as an over damped medium for the same. A simple qualitative discussion is included to explain our results on optical switching.

Nanoscale light–matter interactions in atomic cladding waveguides

Alkali vapours, such as rubidium, are being used extensively in several important fields of research such as slow and stored light nonlinear optics quantum computation, atomic clocks and magnetometers. Recently, there is a growing effort towards miniaturizing traditional centimetre-size vapour cells. Owing to the significant reduction in device dimensions, light–matter interactions are greatly enhanced, enabling new functionalities due to the low power threshold needed for nonlinear interactions. Here, taking advantage of the mature platform of silicon photonics, we construct an efficient and flexible platform for tailored light–vapour interactions on a chip. Specifically, we demonstrate light–matter interactions in an atomic cladding waveguide, consisting of a silicon nitride nano-waveguide core with a rubidium vapour cladding. We observe the efficient interaction of the electromagnetic guided mode with the rubidium cladding and show that due to the high confinement of the optical mode, the rubidium absorption saturates at powers in the nanowatt regime.

A Linearly-Polarized Rubidium Vapor Laser Pumped by a Tunable Laser Diode Array with an External Cavity of a Temperature-Controlled Volume Bragg Grating

A diode pumped alkali vapor laser has advantages in high quantum efficiency, excellent beam quality, and low thermal effect. We obtain a laser diode array (LDA) with linewidth of 0.20 nm and an external cavity of volume Bragg grating (VBG). Its central wavelength can be tuned from 779.30nm to 780.10nm by changing the VBG's temperature. Pumped by this LDA, a 2.1 W rubidium vapor laser is achieved with optical efficiency of 10.5% and slope efficiency of 22.7%.

Lifetime improvement of micro-fabricated alkali vapor cells by atomic layer deposited wall coatings

Alumina (Al2O3), silicon dioxide (SiO2) and titanium dioxide (TiO2) films were examined for their suitability as a protection coating for micro-fabricated cesium vapor cells. The layers were deposited by atomic layer deposition (ALD). This technique enables the deposition of pinhole-free passivation layers with a low roughness, a high conformality and a high homogeneity, even at three-dimensional surfaces. It is shown that Al2O3 and SiO2 films, in contrast to TiO2 films, do not hamper anodic bonding up to thicknesses of 20nm. The resistance enhancement of the vapor cells by means of the implementation of the ALD films is demonstrated by absorption measurements of the cesium D1 line. SiO2 coatings showed no effects on the resistance of the vapor cells against the reducing behavior of cesium. In contrast, Al2O3 coatings improved the resistance of the vapor cells by a factor of ~100.

Low-temperature indium-bonded alkali vapor cell for chip-scale atomic clocks

A low-temperature sealing technique for micro-fabricated alkali vapor cells for chip-scale atomic clock applications is developed and evaluated. A thin-film indium bonding technique was used for sealing the cells at temperatures of ≤140 °C. These sealing temperatures are much lower than those reported for other approaches, and make the technique highly interesting for future micro-fabricated cells, using anti-relaxation wall coatings. Optical and microwave spectroscopy performed on first indium-bonded cells without wall coatings are used to evaluate the cleanliness of the process as well as a potential leak rate of the cells. Both measurements confirm a stable pressure inside the cell and therefore an excellent hermeticity of the indium bonding. The double-resonance measurements performed over several months show an upper limit for the leak rate of 1.5 × 10−13 mbar·l/s. This is in agreement with additional leak-rate measurements using a membrane deflection method on indium-bonded test structures.

Fouling Intensity of Three Indian Coals

Ash particles can arrive at heat-transfer surfaces either in solid (solidified) state or in molten state, depending on the factors such as location inside the boiler, temperature, and residence time. In this study, arrival of ash particles in solid state, which can occur in the convective section of the boiler, was considered. Apart from the inertial force that drives particles \>10 µm to the surface, the low-melting inorganic alkali vapors play a vital role in deposit formation by promoting sticking. Chemical equilibrium calculations were performed to calculate the equilibrium composition of flue gas, as well as the amount of condensable inorganic alkali vapors at any particular temperature. Condensed alkali liquids act as \glue in holding together impacting fly ash particles. Eutectic formation between alkali salts was considered to accurately predict the condensation onset temperature. Using the glue volume fraction obtained as a function of temperature, we adopted a self-regulated deposit growth model to predict deposit growth rate. The uniqueness of the model is that it simultaneously incorporates sticking and particle-particle erosion, where both are dependent on available liquid fraction, to predict fouling intensity. The deposit growth rate of three Indian coals was simulated and compared with coal having lower ash content.

半导体泵浦铷蒸气激光器出光实验

A chopper was used to change a diode bar with a center wavelength of 780 nm from continuous laser to pulsed laser, and a Littrow external cavity was build with a 2400 l/mm plane grating to narrow the linewidth of the diode laser to less than 0.2 nm. Then the diode laser was shaped by a lens group. After the linewidth narrowing and beam shaping, the laser was focused to a Rb vapor cell with a length of 8 mm. In that diode pumped alkali vapor laser system, a linearly polarized fundamental mode Rb laser with a peak power of 17.5 mW was obtained. In the latest experiment, we obtained a 2.8 W Rb laser in the improved diode pumped rubidium vapor laser system.

Characterization and modelling of low-pressure rf discharges at 2–500 MHz for miniature alkali vapour dielectric barrier discharge lamps

Low-pressure dielectric barrier discharge (DBD) alkali vapour lamps are of particular interest for portable atomic clocks because they (1) could enable low-power operation, (2) generate the precise required wavelength, (3) are planar simplifying chip-level integration and (4) use external electrodes, which increases the lifetime. Given the stringent requirements on lamps for atomic clocks, it is important to identify the parameters that can be optimized to meet these performance requirements (size, power consumption, stability, reliability). We report on the electrical and optical characteristics of dielectric barrier plasma discharges observed in two configurations: (1) in a vacuum chamber over a wide low-pressure range (2–100 mbar) for three different buffer gases (He, Ar, N2) driven at different frequencies between 2 and 500 MHz and (2) on microfabricated hermetically sealed Rb vapour cells filled with 30 and 70 mbar of Ar. We discuss the optimum conditions for a low-power and stable operation of a Rb vapour DBD lamp, aimed at chip-scale atomic clocks. We also present the electrical modelling of the discharge parameters to understand the power distribution mechanisms and the input power to discharge power coupling efficiency.

Review of alkali laser research and development

In this review we present an analysis of optically pumped alkali laser research and development from the first proposal in 1958 by Schawlow and Townes to the current state. In spite of the long history, real interest in alkali vapor lasers has appeared in the past decade, after the demonstration of really efficient lasing in Rb and Cs vapors in 2003 and the first successful power scaling experiments. This interest was stimulated by the possibility of using efficient diode lasers for optical pumping of the alkali lasers and by the fact that these lasers can produce a high quality and high power output beam from a single aperture. We present a review of the most important achievements in high power alkali laser research and development, discuss some problems existing in this field, and provide future perspectives in diode pumped alkali laser development.