This work presents an experimental and theoretical study of the 6s21S0→6s6p3P10 (791 nm) and 5s5d3D2→6s5f3F20 (355 nm) transitions within a low vapor pressure barium vapor in the absence of a buffer gas. To the authors’ knowledge, this is the first measurement of the latter absorption feature. The study is motivated by the development of an optically controlled atomic vapor notch filter functioning at the third harmonic of the commonly used Nd:YAG laser at 355 nm. The low-pressure environment within the vapor source has enabled a deeper understanding of barium vapor collisional and velocity changing properties with a simple pump-probe spectroscopy measurement. The results demonstrate depletion of the ground state and subsequent population of the 5s5d3D2 level. Most notably, the 5s5d3D2→6s5f3F20 transition displays a non-thermal, cusped absorption curve. An analysis of this line shape in the context of existing analytical collisional kernels is presented. Additionally, a six-level kinetic model of the low-lying energy levels, incorporating spatial diffusion and collisional and radiative transitions, is introduced and compared to the measured level populations for the barium ground state and excited 5s5d3D2 state.
This work presents an experimental and theoretical study of the 6s21S0→6s6p3P10 (791 nm) and 5s5d3D2→6s5f3F20 (355 nm) transitions within a low vapor pressure barium vapor in the absence of a buffer gas. To the authors’ knowledge, this is the first measurement of the latter absorption feature. The study is motivated by the development of an optically controlled atomic vapor notch filter functioning at the third harmonic of the commonly used Nd:YAG laser at 355 nm. The low-pressure environment within the vapor source has enabled a deeper understanding of barium vapor collisional and velocity changing properties with a simple pump-probe spectroscopy measurement. The results demonstrate depletion of the ground state and subsequent population of the 5s5d3D2 level. Most notably, the 5s5d3D2→6s5f3F20 transition displays a non-thermal, cusped absorption curve. An analysis of this line shape in the context of existing analytical collisional kernels is presented. Additionally, a six-level kinetic model of the low-lying energy levels, incorporating spatial diffusion and collisional and radiative transitions, is introduced and compared to the measured level populations for the barium ground state and excited 5s5d3D2 state.
View Video Presentation: https://doi.org/10.2514/6.2021-3107.vid This work is a portion of a combined theoretical and experimental effort to develop a controllable excited state barium vapor source to be used as a notch filter. The energy pooling properties of the low-lying levels of barium, which make it ideal for this application, have been the subject of several past kinetics studies. This work was utilized to develop a 6-level kinetics model, incorporating collisional and radiative decay and, most critically, diffusional quenching. This model demonstrates efficient pumping of the metastable manifold in the 6s5d 3DJ levels, particularly the 6s5d 3D2 level which will be utilized by the proposed filter. A vacuum vapor cell and its implementation into a counter-propagating, optically pumped absorption spectroscopy arrangement are also described. Measurements of the optically pumping transition (6s2 1S0-- 6s6p 3P01, 791 nm) and the proposed filtering transition (6s5d 3D2 -- 6s5f 3F02, 355 nm) have been performed with this system. To our knowledge, these are the first measurements of this 355 nm filtering transition. These measurements demonstrate a non-Maxwellian lineshape, suggesting a non-thermalized metastable 6s5d 3D2 level. The measured ground state depletion and 3D2 population agree with the model trends but show quantitative discrepancies which require further study. A detailed theoretical analysis of the effects on filter performance of incorporating an argon buffer gas into the vapor source is also presented. This work shows promise for creating a narrowband absorption feature with increased optical depth.
We describe a set of experiments that investigate diffusion of barium 6s5d3DJ metastable level and 6s21S0 ground-state atoms through the noble gases: He, Ne, Ar, Kr, and Xe. The barium metastable levels were populated through optical pumping of the 6s21S0\ensuremath{\rightarrow}6s6p3P1o intercombination transition with a pulsed laser, followed by spontaneous or stimulated emission into the 6s5d3D1,2 levels. Collisional mixing then distributed population throughout the 6s5d3DJ levels. A weak narrow-band cw laser was tuned to appropriate transitions to probe the spatial distribution of metastable level atoms, as well as the hole created in the ground-state spatial distribution, by the pulsed laser. Time-dependent absorption coefficients were obtained by measuring the transmission of the probe laser at several different pump-probe spatial separations. From these absorption data, spatial number density profiles were mapped out for various times following the firing of the pump laser. These density profiles were used to determine the diffusion coefficient for each state at a particular buffer-gas pressure and temperature. From these pressure- and temperature-dependent diffusion coefficients D, we determined the thermally averaged diffusion cross sections ${\mathrm{\ensuremath{\sigma}}}_{\mathit{D}}$(6s5d3DJ) and ${\mathrm{\ensuremath{\sigma}}}_{\mathit{D}}$(6s21S0) for the metastable and ground-state atoms diffusing through the noble gases, respectively. We also report values for the scaled standard diffusion coefficients D0. Our experimental values of the thermally averaged diffusion cross sections ${\mathrm{\ensuremath{\sigma}}}_{\mathit{D}}$(6s5d3DJ) and ${\mathrm{\ensuremath{\sigma}}}_{\mathit{D}}$(6s21S0) for the barium-helium system are compared with values calculated from published, theoretical barium-helium potentials and the agreement is excellent. \textcopyright{} 1996 The American Physical Society.
Optical quantum memory describes the process of on-demand storage and retrieval of single photon-level quantum states, and is a critical enabling technology for many quantum applications. Memory bandwidth plays an important role in these applications, as it determines the pulse durations compatible with the memory and places an upper bound on the clock rate and processing speed of a quantum device. Here we present experimental results of an atomic barium quantum memory that enables storage and retrieval of ultra-broadband(>800GHz) signal photons with high storage efficiency [95.6(3)%] and low noise [3.8(6)×10−5noise photons]. Experimental Results.- The quantum memory operation is based on the ground(6s21S0), excited(6s6p1P1), and metastable(6s5d1D2)orbital states of atomic barium in aΛ-type configuration. The barium vapor is created in an 800–900 °C barium heat pipe oven with 0–1000 torr tunable argon buffer gas pressure. The ground-excited transition at 553.5 nm features large and tunable homogeneous collisional broadening due to the argon buffer gas and a peak optical depth ofd=50. The memory operates in the so-called absorb-then-transfer (ATT) regime, in which the signal field is linearly absorbed along the ground-excited transition, whose collisionally broadened lineshape enables efficient absorption of ultra-broadband photons; the resulting atomic polarization is transferred into a so-called spin wave by application of a strong[O(10uJ),100fs]control pulse along the excited-metastable transition at 1500 nm. The storage state has a 0(0.1) second coherence lifetime in the bare atom [1], but this is reduced to theO(ns)level due to motional dephasing [0.49(1) ns measured memory lifetime]. The memory experiment is repeated at a repetition rate of 1 kHz. The total end-to-end efficiency of the memory at 900°C is 31(1)%, which is limited by available control field power.
Abstract Optical spectroscopy of atoms and molecules is a field where one usually operates very far from thermal equilibrium conditions. A prominent example is spectroscopy of thin vapors, where the pump irradiation leads to a non-equilibrium distribution within the electronic structure that is well shielded from the environment. Here we describe experimental work investigating absorption and emission lines of rubidium vapor subject to a noble buffer gas environment with pressure 100–200 bar, a regime interpolating between usual gas phase and liquid/solid state conditions. Frequent elastic collisions in the dense buffer gas sample cause a large coupling to the environment. We give a detailed account of recent observations of the Kennard–Stepanov scaling, a Boltzmann-like thermodynamic frequency scaling between absorption and emission profiles, for both atomic and molecular rubidium species in the gaseous environment. Our observations are interpreted as due to the thermalization of alkali-noble gas submanifolds in both ground and electronically excited states respectively. Both pressure broadening and shift of the high pressure buffer gas D -lines system are determined. We also discuss some prospects, including possible advances in collisional laser cooling and optical thermometry.
Energy-pooling collisions between low-lying excited states of Ba have been studied. We have used a CW dye laser to excite the level in Ba. Radiative decay and collisions with Ba or buffer-gas atoms (Ar, He) populate also the , and metastable levels. The spatial density distributions of these excited levels were measured by the absorption of lines from a Ba hollow-cathode lamp as a function of laser frequency. When the laser was on the exact atomic resonance we observed fluorescence from the , , , , , , and states populated by energy-pooling collisions of Ba( , ). By changing the buffer gas pressure the fluorescence intensity ratio between - and - transitions changes dramatically. This is found to be due to redistribution of population among metastable levels, both in magnitude and space. In addition, we have found that the and metastable levels are also populated when the laser is tuned to the blue from the 553.5 nm line under which conditions a pronounced red-shifted light cone (cone emission) is observed.
Atomic line filters take advantage of the sharp spectral features offered by electronic transitions in free atoms. The basic idea is to convert a narrow atomic absorption profile into an equally narrow optical transmission filter by detecting the fluorescence radiation that is emitted after a photon has been absorbed. We developed the metastable thallium atomic line filter from the basic physical idea to a laboratory prototype in order to evaluate the usefulness of the technology for satellite borne backscatter LIDARs. Atomic thallium provides for an unsurpassed combination of features for this purpose. The input wavelength of the filter is 535 nm, which matches the frequency doubled Nd:BEL laser. The filter is an active device, it upconverts the 535 nm input into 378 nm output that is detected by a PMT. The experimental results were as expected concerning the characteristics directly related to atomic properties, i.e. the filter has only 10 ns response time, its optical bandwidth is 0.004 nm, and its acceptance angle is only limited by the device geometry. An optimized setup, with the size constraints of a space-borne system, displays a total quantum efficiency of 2%, i.e. from input photons to detected output photons. This constitutes a remarkable and unsurpassed value for atomic line filters but is too low for the application in mind. (A ground-based, scaled-up version of our prototype would reach about 10% quantum efficiency). In addition, the 500 degree(s)C operating temperature of the vapor cell requires sophisticated thermal layout and thermal shielding, which means a lot of added mass and volume. In summary, we found that atomic line filters can be built that offer characteristics not found with other technologies, but their applicability for space borne systems is questionable.