Optical Pumping Effects Research Articles

Cavity linewidth narrowing by optical pumping-assisted electromagnetically induced transparency in V-type rubidium at room temperature

A detailed experimental investigation is made in the intracavity V-type electromagnetically induced transparency (EIT) of the Rb atomic medium at room temperature. The optical pumping effect will increase the transparency for the V-type EIT at room temperature and therefore the cavity linewidth can be narrowed apparently. For the seven EITs observed in our previous study, cavity linewidth narrowing is observed in all of them. More importantly, we find that the cavity linewidth can keep at 1.2 MHz over a wide frequency range of 100 MHz by utilizing the central double-peak-structure EIT. This property provides a novel way for constructing a high resolution tunable frequency reference via the intracavity EIT.

Effect of optical pump on the dielectric properties of SrTiO3 in terahertz range

Tuning the dielectric permittivity spectra of strontium titanate (SrTiO3) single crystals in an external optical field is investigated at room temperature by means of terahertz time-domain spectroscopy. The application of the optical field leads to an appreciable tuning of the permittivity, reaching up to 2.8%, with the dielectric loss changing about 3%. The observed behavior is interpreted in terms of soft-mode hardening due to the anharmonic character of its potential. We also find that the change of the refractive index responds linearly to the applied light power. These findings are attributed to a linear electro-optical effect of the internal space charge field of the crystal.

Influence of interaction time and population redistribution on the localization of atomic excitation through electromagnetically induced transparency

We study numerically the localization of atomic excitation based on the dark states formed through electromagnetically induced transparency using interfering coupling beams. In particular, we examine the formation of dark states in a system exhibiting hyperfine splitting, including the effects of optical pumping in this multilevel system, laser polarization, and finite interaction time, and explore the conditions that lead to optimal spatial resolution of the excitation. We find that optimal localization requires long interaction times, due to the slow approach of the atomic system to steady state near the nodes of the standing wave pattern.

Effect of optical pumping on the momentum relaxation time of graphene in the terahertz range

The momentum relaxation time of a photoexcited graphene in the THz frequency range has been studied by using terahertz time domain spectroscopy under optical pumping at room temperature. It is found that the momentum relaxation time of the graphene as a function of the optical pumping intensity exhibits a threshold behavior. The features of the momentum relaxation time as a function of the optical pumping intensity are also investigated. The results are useful for understanding the basic underlying physics of graphene scattering as well as finding the possible applications in carbon-based electronics.

Effects of optical pumping in the photo-excitation of organic triplet states

Upon the application of laser and microwave pulses, non-zero magnetic moment of a photo-excited triplet state of organic molecules is generated in zero-field (ZF). The time evolution of the transient magnetic moments can be measured by free induction decay (FID) in ZF. The observed ZF spectra become broadened and ZF transition shifted to lower frequencies when the repetition rate of laser excitation is increased, which are attributed to the optical pumping of nuclear polarization (ONP) effect and the associated nuclear spin lattice relaxation processes. The observed ONP effect is discussed in terms of the local field effect and spin diffusion processes in optical pumping.

Ladder-type electromagnetically induced transparency with optical pumping effect

This paper thoroughly elucidates the relative intensities of the probe transmission in a ladder-type electromagnetically induced transparency (EIT) system by considering the optical pumping effect. The observed EIT spectra reveal a different probe or coupling power dependence for various transmission peaks. In addition to causing quantum interference, the probe and coupling laser fields realign the population of Zeeman sublevels in the ground state through optical pumping. Analytical results indicate that the re-distribution levels, failing to contribute to the EIT peaks, either out of transition path or zero transition probability, significantly affect the transmission intensity.

Enhanced Squeezing of a Collective Spin via Control of Its Qudit Subsystems

Unitary control of qudits can improve the collective spin squeezing of an atomic ensemble. Preparing the atoms in a state with large quantum fluctuations in magnetization strengthens the entangling Faraday interaction. The resulting increase in interatomic entanglement can be converted into metrologically useful spin squeezing. Further control can squeeze the internal atomic spin without compromising entanglement, providing an overall multiplicative factor in the collective squeezing. We model the effects of optical pumping and study the tradeoffs between enhanced entanglement and decoherence. For realistic parameters we see improvements of ~10 dB.

Coexisting four-wave mixing and six-wave mixing in three-level atomic system

We demonstrate the coexisting four-wave mixing (FWM) signal and six-wave mixing (SWM) signal which can be enhanced both by electromagnetically induced transparency (EIT) and optical pumping effect in a common three-level and open four-level inverted-Y type systems of 85Rb. We also analyze the effect of optical pumping in different energy level systems by arranging laser beams and comparing the strength of the increased and reduced absorption caused by optical pumping.

Optically controlled spin-dependent Andreev reflection and spin accumulation in a quantum dot

We theoretically investigate the Andreev reflection and the spin accumulation in a quantum dot subjected to a continuous circularly polarized optical irradiation. Due to the optical pumping effects, electrons having a certain spin experience the Rabi oscillation and their energy levels are shifted by the Rabi frequency. Correspondingly, only electrons with certain spin can contribute to the current by adjusting the dot level and the bias voltage. The Andreev reflection current thus becomes spin dependent and exhibits a tunable spin polarization. Furthermore, the electron occupation number in the quantum dot also becomes spin dependent and exhibits a strong spin accumulation. The magnitude and direction of the spin accumulation in the quantum dot can be easily controlled by tuning the dot level and the bias voltage. This provides an efficient mechanism to control the Andreev reflection and spin accumulation in the quantum dot.

Collimated blue light enhancement in velocity-selective pumped Rb vapour

The effect of hyperfine optical pumping on the parametric four-wave mixing process responsible for the generation of collimated blue light (CBL) in alkali atoms is explored. Over a wide range of atomic densities (4.5 × 1010 cm−3 ⩽ N ⩽ 1.4 × 1011 cm−3), a more than ten-fold enhancement of CBL is obtained from optical pumping produced by an additional laser. Pulsed optical pumping has been applied to investigate the temporal characteristics of CBL generation. It is shown that optical pumping offers efficient control of the mixing process and the collimated light generation that may be useful for probing a small number of atoms.

Effect of optical pumping on the refractive index and temperature in the core of active fibre

This paper examines the refractive index change (RIC) induced in the core of Yb3+-doped active silica fibres by pulsed pumping. RIC kinetic measurements with a Mach — Zehnder interferometer make it possible to separately assess the contributions of the electronic and thermal mechanisms to the RIC and evaluate temperature nonuniformities in the fibre.

Nonlinear resonances caused by coherent, optical pumping and saturating effects in the presence of three laser fields for the 85Rb-D2 line

Atomic coherence resonances such as electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) signals are observed in a Doppler broadened multi-level system for the D2 line of 85Rb atoms in a vapour cell considering different types of atom–laser coupling schemes. Besides the coherence resonances, the nonlinear resonances like velocity selective optical pumping (VSOP) dips and velocity selective resonances (VSR) are also observed for the non-zero velocity selective groups of atoms. In the presence of pump, control and probe laser fields, we observe two EIT signals in a double Λ-type system and two EIA signals in a double V-type system. We are able to see the EIA signal for the non-zero velocity group of atoms when the pump laser is locked with an open transition by a small red detuning. We also report the experimental observation of simultaneous EIT and EIA signals in a (Λ+V)-type system. The effect of frequency tuning of the control laser is also studied in the presence of the frequency locked pump laser. A simple theoretical analysis explains the experimental results.

Double-resonance optical-pumping effect and ladder-type electromagnetically induced transparency signal without Doppler background in cesium atomic vapour cell

In a Doppler-broadened ladder-type cesium atomic system (6S1/2-6P3/2-8S1/2), this paper characterizes electromagnetically induced transparency (EIT) in two different experimental arrangements, and investigates the influence of the double-resonance optical-pumping (DROP) effect on EIT in both arrangements. When the probe laser is weak, DROP is explicitly suppressed. When the probe laser is moderate, population of the intermediate level (6P3/2 F′ = 5) is remarkable, therefore DROP is mixed with EIT. An interesting bimodal spectrum with the broad component due to DROP and the narrow part due to EIT has been clearly observed in cesium 6S1/2 F = 4−6P3/2 F′ = 5−8S1/2 F″ = 4 transitions.

Quantitative atomic spectroscopy for primary thermometry

Quantitative spectroscopy has been used to measure accurately the Doppler-broadening of atomic transitions in $^{85}$Rb vapor. By using a conventional platinum resistance thermometer and the Doppler thermometry technique, we were able to determine $k_B$ with a relative uncertainty of $4.1\times 10^{-4}$, and with a deviation of $2.7\times 10^{-4}$ from the expected value. Our experiment, using an effusive vapour, departs significantly from other Doppler-broadened thermometry (DBT) techniques, which rely on weakly absorbing molecules in a diffusive regime. In these circumstances, very different systematic effects such as magnetic sensitivity and optical pumping are dominant. Using the model developed recently by Stace and Luiten, we estimate the perturbation due to optical pumping of the measured $k_B$ value was less than $4\times 10^{-6}$. The effects of optical pumping on atomic and molecular DBT experiments is mapped over a wide range of beam size and saturation intensity, indicating possible avenues for improvement. We also compare the line-broadening mechanisms, windows of operation and detection limits of some recent DBT experiments.

Optical pumping effects in ladder-type electromagnetically induced transparency of 5S1/2–5P3/2–5D3/2 transition of 87Rb atoms

We have investigated the optical pumping effects of single-resonance optical pumping (SROP) and double-resonance optical pumping (DROP) in the ladder-type electromagnetically induced transparency (EIT) of the 5S1/2–5P3/2–5D3/2 transition of 87Rb atoms. In the 5S1/2(F = 2)–5P3/2(F′ = 3)–5D3/2(F″ = 2, 3) transition with the single-resonance cycling 5S1/2(F = 2)–5P3/2(F′ = 3) transition, we observed the transmittance spectrum due to DROP and EIT. Based on our experimental results investigated according to the laser power (the probe and the coupling) and the coupling laser detuning, we revealed that DROP was significant for the transmittance spectrum. Particularly, in the 5S1/2(F = 2)–5P3/2(F′ = 1, 2)–5D3/2(F″ = 1) transition without a cycling transition, we observed the two-photon absorption due to two-photon atomic coherence, when the probe laser power was weak and the coupling laser power was strong.

Discrimination of the effects of saturation and optical pumping in velocity-dependent pump-probe spectroscopy of rubidium: A simple analytical study

This paper presents a simple analytical theory for the velocity-dependent pump-probe laser spectroscopy of $^{87}\mathrm{Rb}$ and $^{85}\mathrm{Rb}$ atoms where the pump and the probe beams are circularly or linearly polarized. The analytical solutions of the line shapes of the velocity-selective optical pumping spectroscopy [G. Moon and H. R. Noh, Phys. Rev. A 78, 032506 (2008)] and saturated absorption spectroscopy [G. Moon and H. R. Noh, J. Opt. Soc. Am. B 25, 701 (2008); 27, 1741 (2010)] obtained in the previous reports, expressed as a sum of several Lorentzian functions, could be approximated as one (or in some cases, two) Lorentzian function(s). In particular, the contributions of the saturation and optical pumping effects could be discriminated explicitly in these simple analytical solutions, which is not possible in existing theories such as Nakayama's model. The simple analytical results for the saturation spectroscopy were compared with experimental results, and good agreement between them was observed.

Pulsed Nuclear Pumping and Spin Diffusion in a Single Charged Quantum Dot

We report the observation of a feedback process between the nuclear spins in a single charged quantum dot under coherently pulsed optical excitation and its trion transition. The optical pulse sequence intersperses resonant narrow-band pumping for spin initialization with off-resonant ultrafast pulses for coherent electron-spin rotation. A hysteretic sawtooth pattern in the free-induction decay of the single electron spin is observed; a mathematical model indicates a competition between optical nuclear pumping and nuclear spin-diffusion. This effect allows dynamic tuning of the electron Larmor frequency to a value determined by the pulse timing, potentially allowing more complex coherent control operations.

Analytic solutions of the susceptibility for Doppler-broadened two-level atoms

We derive the rigorous analytic solutions for the susceptibility of Doppler-broadened two-level atoms, valid for arbitrary laser intensities. As is usually the case with real atoms, we observe that, when the homogeneous linewidth is much narrower than the Doppler width, the real part of the susceptibility is given by the product of an imaginary error function and a Gaussian, whereas the imaginary part consists simply of a Gaussian function. By employing the analytic results, in particular, we study the effects of optical pumping and saturation on the atomic susceptibility. We also find that the real (imaginary) part of the susceptibility is weakly (strongly) dependent on such parameters as the laser intensity or the optical pumping rate. The availability of analytic solutions for the simple laser-atom interaction may provide convenient tools for its understanding as well as application to more general and realistic situations.

A NON-LOCAL THERMODYNAMIC EQUILIBRIUM ANALYSIS OF BORON ABUNDANCES IN METAL-POOR STARS

The non-local thermodynamic equilibrium (NLTE) line formation of neutral boron in the atmospheres of cool stars are investigated. Our results confirm that NLTE effects for the B I resonance lines, which are due to a combination of overionization and optical pumping effects, are most important for hot, metalpoor, and low-gravity stars; however, the amplitude of departures from LTE found by this work are smaller than that of previous studies. In addition, our calculation shows that the line formation of B I will get closer to LTE if the strength of collisions with neutral hydrogen increases, which is contrary to the result of previous studies. The NLTE line formation results are applied to the determination of boron abundances for a sample of 16 metal-poor stars with the method of spectrum synthesis of the B I 2497 A resonance lines using the archived HST/GHRS spectra. Beryllium and oxygen abundances are also determined for these stars. The abundances of the nine stars which are not depleted in Be or B show that, no matter the strength of collisions with neutral hydrogen may be, both Be and B increase with O quasi-linearly in the logarithmic plane, which confirms the conclusions that Be and B are mainly produced by primary process in the early Galaxy. The most noteworthy result of this work is that B increases with Fe or O at a very similar speed as, or a bit faster than Be does, which is in accord with the theoretical models. The B/Be ratios remain almost constant over the metallicity range investigated here. Our average B/Be ratio falls in the interval [13+-4, 17+-4], which is consistent with the predictions of spallation process. The contribution of B from the nu-process may be required if the 11B/10B isotopic ratios in metal-poor stars are the same as the meteoric value.

Transient response of nonlinear magneto-optic rotation in a paraffin-coated Rb vapor cell

We study resonant nonlinear magneto-optic rotation (NMOR) in a paraffin-coated Rb vapor cell as the magnetic field is swept. At low sweep rates, the nonlinear rotation appears as a narrow resonance signal with a linewidth of about ``300 mu G''(2 pi x 420 Hz). At high sweep rates, the signal shows transient response with an oscillatory decay. The decay time constant is of order 100 ms. The behavior is different for transitions starting from the lower or the upper hyperfine level of the ground state because of optical pumping effects.