Atomic Sodium Vapor Research Articles

Two Step Excitation in Hot Atomic Sodium Vapor

A two step excitation scheme in hot atomic sodium vapor is experimentally investigated. The observed effects reflect a coupling between the 32S, 32P and the 32D states. We present the relative dependence on detuning of the two utilized lasers around λ = 589 nm and 819 nm. Unlike expected, we achieve a higher detuning dependence of the probe and the coupling laser by a factor of approximately three. The presented work aimed for a Rydberg excitation and quantum light storage. Such schemes are usually implemented with a red laser on the D-line transition and a coupling laser of shorter (typically blue) wavelength. Due to the fact that higher P-Rydberg states are approximately two times higher in energy than the 32D state, a two photon transition from the atomic excited 32P state to a Rydberg P state is feasible. This might circumvent laser frequency doubling whereby only two lasers might mediate a three photon process. The scheme of adding three k-vectors allows for electromagnetically induced transparency experiments in which the resulting k-vector can be effectively reduced to zero. By measurements utilizing electric fields and an analysis of the emission spectrum of the atomic vapor, we can exclude the excitation of the P-P two photon transition.

Noise correlations controlled by dressed suppression and enhancement

The intensity noise correlations between anti-Stokes and Stokes fields, generated from spontaneous parametric four-wave mixing (SP-FWM) process have been investigated in a ladder-type three-level system of sodium atomic vapor. By introduction of an external dressing field, the strengthened (weakened) correlations are obtained under enhancement (suppression) condition of SP-FWM. Besides, sharp correlations have been obtained as attributed to a pair of non-classical beams generated from amplified spontaneous emission.

An atomic spectrum recorded with a single-molecule light source

A single molecule under cryogenic conditions allows one to realize an extremely bright and simultaneously narrow-band single-photon source. We present a review on the different excitation schemes of a single molecule and present the corresponding single-photon nature of the emitted light. Single-molecule spectroscopy has been recently interlinked with atomic spectroscopy. This optical interconnect among the different quantum systems might be enhanced by a so-called Faraday anomalous dispersion optical filter—an ideal tool for many experiments in quantum optics. We introduce our theoretical and experimental approach on these filters which are based on hot atomic sodium vapor. The electrical tunability together with the brightness of a single molecule allows us to record a full atomic spectrum of this filter with the single photons originating from a single-molecular emitter.

Interference between electromagnetically induced transparency and N-type resonances in Na vapor

We show theoretically and experimentally that the line shapes observed in ordinary electromagnetically induced transparency (EIT) experiments in sodium atomic vapor can be explained by the superposition of two processes, EIT and N-type resonances (NTR). When the higher frequency side of the Doppler absorption profile is excited, EIT is dominant, whereas, for the lower frequency side, NTR is dominant, and, in between, interference between EIT and NTR takes place. Theoretical simulations, based on a perturbative approach, agreed reasonably well with the experimental observations. The signal behavior concerning ac Stark shifts has also been studied for EIT and NTR; it was found that, although the signal peak always shifts toward the higher frequency in the case of EIT, for NTR, the shift can be nullified by adjusting the power balance of the two incident beams.

Pulsed cooperative backward emissions from non-degenerate atomic transitions in sodium

We study backward cooperative emissions from a dense sodium atomic vapor. Ultrashort pulses produced from a conventional amplified femtosecond laser system with an optical parametric amplifier are used to excite sodium atoms resonantly on the two-photon 3S–4S transition. Backward superfluorescent emissions (BSFEs), both on the 4S–3P and 4S–3P transitions, are observed. The picosecond temporal characteristics of the BSFE are observed using an ultrafast streak camera. The power laws for the dependencies of the average time delay and the intensity of the BSFEs on input power are analyzed in the sense of cooperative emission from nonidentical atomic species. As a result, an absolute (rather than relative) time delay and its fluctuations (free of any possible external noise) are determined experimentally. The possibility of a backward swept-gain superfluorescence as an artificial laser guide star in the sodium layer in the mesosphere is also discussed.

Electromagnetically induced transparency in a V-type multilevel system of Na vapor

We have theoretically and experimentally investigated the V-type three-level system in hot sodium atomic vapor interacting with two optical waves: probe, resonant to the D1 line, and coupling, the D2 line. Theoretically, probe transmission spectra are simulated by using a perturbative treatment including eight hyperfine levels (multilevel system) in the 3S1/2, 3P1/2, and 3P3/2 states. The spectra are composed of linear absorption, saturated absorption, and electromagnetically induced transparency (EIT) signals. By comparing this simulation with the experimental results, we concluded that we have indeed observed EIT signals when the coupling beam is resonant to the D2-line closed transition.

Molecular photons interfaced with alkali atoms.

Future quantum communication will rely on the integration of single-photon sources, quantum memories and systems with strong single-photon nonlinearities. Two key parameters are crucial for the single-photon source: a high photon flux with a very small bandwidth, and a spectral match to other components of the system. Atoms or ions may act as single-photon sources--owing to their narrowband emission and their intrinsic spectral match to other atomic systems--and can serve as quantum nonlinear elements. Unfortunately, their emission rates are still limited, even for highly efficient cavity designs. Single solid-state emitters such as single organic dye molecules are significantly brighter and allow for narrowband photons; they have shown potential in a variety of quantum optical experiments but have yet to be interfaced with other components such as stationary memory qubits. Here we describe the optical interaction between Fourier-limited photons from a single organic molecule and atomic alkali vapours, which can constitute an efficient quantum memory. Single-photon emission rates reach up to several hundred thousand counts per second and show a high spectral brightness of 30,000 detectable photons per second per megahertz of bandwidth. The molecular emission is robust and we demonstrate perfect tuning to the spectral transitions of the sodium D line and efficient filtering, even for emitters at ambient conditions. In addition, we achieve storage of molecular photons originating from a single dibenzanthanthrene molecule in atomic sodium vapour. Given the large set of molecular emission lines matching to atomic transitions, our results enable the combination of almost ideal single-photon sources with various atomic vapours, such that experiments with giant single-photon nonlinearities, mediated, for example, by Rydberg atoms, become feasible.

Numerical Investigation of the Tri-Atomic Ions Formation during Laser Ionization Based on Resonance Saturation

We present a theoretical investigation of plasma generation in sodium vapor induced by laser radiation tuned to the first resonance line (3S-3P) at λ = 589 ns. A set of rate equations that describe the rate of change of the ground and excited states population as well as the temporal variation of the electron energy distribution function (EEDF), beside the formed atomic ion Na+, molecular ion and tri-atomic ions are solved numerically. The calculations are carried out at different laser energy and different sodium atomic vapor densities under the experimental conditions of Tapalian and Smith (1993) to test the existence of the formed tri-atomic ions. The numerical calculations of the electron energy distribution function (EEDF) show that a deviation from the Maxwellian distribution due to the super elastic collisions effect. In addition to the competition between associative ionization (3P-3P), associative ionization (3P-3D) and Molnar-Horn- beck ionization processes for producing , the calculations have also shown that the atomic ions Na+ are formed through the Penning ionization and photoionization processes. These results are found to be consistent with the experimental observations.

Dressed Four-Wave Mixing From Upper Branch in a Sodium Atomic Vapor

With electromagnetically induced transparency-assisted configuration, a four-wave mixing (FWM) process generated from the upper branch of a cascade-type three-level atomic system is studied both theoretically and experimentally. Through the advantage of neglecting the absorption of a FWM signal due to a much smaller transition probability of a two-photon process, we easily observe the Autler-Townes effect altering the energy levels in such FWM processes. Meanwhile, the multiplied line shapes of a FWM spectrum are investigated by varying the frequency detuning. By applying external field, such FWM processes can be manipulated through modulating the dark state. Finally, conversion efficiency is considered by changing the temperature of oven, which shows a threshold temperature point. Theoretical interpretations correspond well with the experimental data.

Electromagnetically induced polarization rotation in Na vapor

In a hot sodium atomic vapor, we report the observation of electromagnetically induced polarization rotation (EIPR) in the 3S1/2-3P1/2-4D3/2 and 3S1/2-3P3/2-4D3/2,5/2 three-level ladder transitions, where a weak probe beam and a strong coupling beam are resonant to the lower and the upper transition, respectively. The EIPR spectra exhibited a unique double-dispersion feature, which was more pronounced for the higher coupling powers. The maximum rotation angle was 18 deg. Optical switch experiment based on EIPR gave a fast response time of less than 100 ns.

Kinetics of plasma formation in sodium vapor excited by nanosecond resonant laser pulses

We have studied theoretically formation of molecular ion Na-2 (+) and the atomic ion Na+ which are created in laser excited sodium vapor at the first resonance transition, 3S(1/2)-3P(1/2). A set of rate equations, which describe the temporal variation of the electron energy distribution function (EEDF), the electron density, the population density of the excited states as well as the atomic Na+ and molecular ion Na-2 (+), are solved numerically. The calculations are carried out at different laser energy and different sodium atomic vapor densities. The numerical calculations of the EEDF show that a deviation from the Maxwellian distribution due to the superelastic collisions effect. In addition to the competition between associative ionization (3P-3P), associative ionization (3P-3D) and Molnar-Hornbeck ionization processes for producing Na-2 (+), the calculations have also shown that the atomic ions Na+ are formed through the Penning ionization and photoionization processes. These results are found to be consistent with the experimental observations.

Coherent pump-probe spectroscopy in sodium vapor: From electromagnetically induced transparency to parametric amplification

We have theoretically and experimentally investigated coherent pump-probe spectra for the $3{S}_{1/2}$-$3{P}_{1/2}$ $D1$ transition of sodium atomic vapor. Probe transmission spectra in the presence of a coupling beam exhibit dramatic changes depending on experimental conditions. In the weak-excitation, low-atomic-density limit, the spectra are mainly characterized by electromagnetically induced transparency (EIT) and saturated absorption, but for the strong-excitation, high-density case, parametric amplification (PA) is dominant, featuring high probe gain and Stokes-wave generation. We have developed a theory that can explain these two seemingly totally different phenomena (EIT and PA) within the same theoretical framework by manipulating a few experimentally controllable parameters, and have successfully reproduced the observed spectra. Other than the main spectral features, many other interesting physical processes have been predicted and observed.

Interference between electromagnetically induced transparency and two-step excitation in three-level ladder systems

We have performed electromagnetically induced transparency (EIT) and two-photon absorption experiments in ladder-type three-level systems in a hot sodium atomic vapor, using the 3S1/2-3P1/2-4D3/2, 3S1/2-3P3/2-4D3/2,5/2, 3S1/2-3P1/2-5S1/2, and 3S1/2-3P3/2-5S1/2 transitions. In particular, in the most pronounced 3S1/2-3P1/2-4D3/2 system, we have observed quite unique spectral line shapes that are superpositions of sharp dips and peaks, in contrast to ordinary EIT spectra. The peaks and dips have apparently different physical origins, and the line shape can be interpreted as the interference between EIT and two-step excitation.

Parametric oscillation in sodium vapor by using an external cavity

We report on parametric oscillation in sodium atomic vapor by using an external cavity. Output powers of approximately 56 mW are obtained for both the signal and idler waves with the input coupling power of 290 mW, resulting in a conversion efficiency of 39%. The signal and idler frequencies are either upshifted or downshifted from the coupling frequency by the amount of the Na hyperfine splitting frequency, and the two waves are found to be strongly temporally correlated.

Non-linear stability analyses of optical pattern formation in an atomic sodium vapour ring cavity

The development of spontaneous stationary equilibrium patterns induced by the injection of a laser pump field into a purely absorptive two-level atomic sodium vapour ring cavity is investigated by means of various weakly non-linear stability analyses applied to the appropriate governing evolution equation for this optical phenomenon. In the quasi-equilibrium limit for its atomic variables, the mathematical system modelling that phenomenon can be reduced to a single modified Swift-Hohenberg non-linear partial differential time-evolution equation describing the intracavity field on an unbounded 2D spatial domain. Diffraction of radiation can induce transverse patterns consisting of stripes, squares and hexagonal arrays of bright spots or honeycombs in an initially uniform plane-wave configuration. Then, these theoretical predictions are compared with both relevant experimental evidence and existing numerical simulations from some recent non-linear optical pattern formation studies.

Four-wave parametric oscillation: theory and observations

We present theoretically and experimentally a novel type of parametric fluorescence and oscillation in which four optical waves in off-axis, diagonal directions simultaneously build up under resonant counterpropagating pump-laser excitation in atomic sodium vapor. Two of the four are anti-Stokes shifted and the other two are Stokes shifted, and they are strongly coupled owing to electromagnetically induced diffraction. Theoretically, the Liouville-Maxwell equations are solved to derive four-wave propagation equations. Experimentally, we have observed four-wave parametric oscillation when a weak off-axis seed beam is introduced into otherwise axially symmetric parametric fluorescence patterns. Temporal waveforms are also analyzed, and strong correlations between any pairs of the four emissions are identified.

Four-wave parametric oscillation in sodium vapor by electromagnetically induced diffraction

We have observed a novel type of parametric oscillation in sodium atomic vapor where four off-axis signal waves simultaneously build up under resonant and counterpropagating pump beams with elliptical beam profiles. The four waves, two of them Stokes shifted and the other two anti-Stokes shifted, have similar output powers of up to 10 mW with a conversion efficiency of 30% and are parametrically coupled by electromagnetically induced diffraction.

Comments on the problem of anomalous fluorescence of atomic sodium vapor at a wavelength of 589.6 nm

The problem of the laser-induced fluorescence of sodium vapor at a wavelength of 589.6 nm in the case of photoexcitation of a small volume of the medium by a laser beam has been solved numerically. The photon transfer from the zone of excitation to the periphery in the direction perpendicular to the direction of propagation of the laser radiation leads to a significant extension of the volume with a high density of excited atoms. The influence of this factor on the formation of the resonance fluorescence of sodium vapor is discussed.

Experimental constraints of using slow-light in sodium vapor for light-drag enhanced relative rotation sensing

We report on experimental observation of electromagnetically induced transparency and slow-light (vg≈c/607) in atomic sodium vapor, as a potential medium for a recently proposed experiment on slow-light enhanced relative rotation sensing [Shahriar et al. Phys. Rev. Lett. (submitted for publication), http://arxiv.org/abs/quant-ph/0505192.]. We have performed an interferometric measurement of the index variation associated with a two-photon resonance to estimate the dispersion characteristics of the medium that are relevant to the slow-light based rotation sensing scheme. We also show that the presence of counter-propagating pump beams in an optical Sagnac loop produces a backward optical phase conjugation beam that can generate spurious signals, which may complicate the measurement of small rotations in the slow-light enhanced gyroscope. We identify techniques for overcoming this constraint. Conclusions reached from the results presented here will pave the way for designing and carrying out an experiment that will demonstrate the slow-light induced enhancement of rotation sensing.

Competition between electromagnetically induced transparency and stimulated Raman scattering

We claim that the concept of electromagnetically induced transparency is only valid for low atomic densities, and for high densities stimulated Raman scattering is totally dominant, where the incident probe wave is not transmitted but is converted to the Stokes wave. This behavior can be explained by the large difference in linear absorption coefficients between the probe and the Stokes waves. We have verified this claim by the experiments using sodium atomic vapor samples with and without a buffer gas. Theoretical analyses using the Liouville-Maxwell equations and numerical simulations also supported our observations.