Jelena Dimitrijević

Enhancement of electromagnetically induced absorption with elliptically polarized light - laser intensity dependent coherence effect

Using the (2)S(1/2)F(g) = 2 --> (2)P(3/2)F(e) = 3 transition in (87)Rb vapor at room temperature, we study effect of the laser light polarization on the electromagnetically induced absorption (EIA). This work extends the recent study of the behavior of the EIA as a function of the laser ellipticity (Brazhnikov et. al., JETP Lett. 83, 64, 2006). We have shown that such behavior strongly depends on the laser power. For the low laser power EIA amplitude has maximum for linearly polarized light, while for high laser power elliptically polarized light of ellipticity 15-20 degrees generates maximum of the EIA amplitude. EIA width varies slowly with the laser ellipticity at lower laser power, and much stronger at higher laser power. Through our theoretical model we attributed observed results to combined effect of the laser ellipticity and power on the population of ground state Zeeman sublevels.

On non-vanishing amplitude of Hanle electromagnetically induced absorption in Rb.

Amplitude and linewidts of the Hanle EIA, obtained from transmission of the laser locked to closed F(g) ? F(e) = F(g) +1 transitions in (85)Rb and(87)Rb, have maximum values at few mW/cm2. Amplitude of the EIA reaches steady value different from zero for higher laser intensities, even for laser intensities of 40 mW/cm(2). Theoretical model of EIA, for the same atomic system as in the experiment, show that the laser intensity, at which maximum of amplitudes and widths occur, depends on the laser detuning. For smaller laser detuning of a few tens of MHz, EIA has a maximum and then vanishes at higher laser intensities. For larger laser detuning of the order of hundreds MHz (but still in the range of Doppler broadening) amplitude of the EIA has very broad maximum and remains above zero for intensities above 40 mW/cm(2). Such theoretical results indicate that Hanle absorption peak remains in the experimental results, regardless of the laser intensities, due to Doppler effect.

Continuous reversal of Hanle resonances of a counter-propagating pulse and continuous-wave field

In this work we study propagation dynamics of two counter-propagating lasers, a continuous-wave (CW) laser and the pulse of another laser, when both lasers are tuned to the Fg = 2 → Fe = 1 transition in 87Rb, and can therefore develop Hanle electromagnetically induced transparency (EIT) in Rb vapor. We calculate the transmission of both lasers as a function of applied magnetic field, and investigate how the propagation of the pulse affects the transmission of the CW laser. Vice versa, we have found conditions when the Gaussian pulse can either pass unchanged, or be significantly absorbed in the vacuum Rb cell. This configuration is therefore suitable for convenient control of the pulse propagation and the system is of interest for optically switching the laser pulses. In terms of the corresponding shapes of the coherent Hanle resonances, this is equivalent to turning the coherent resonance from Hanle EIT into an electromagnetically induced absorption (EIA) peak. There is a range of intensities of both the CW laser and the laser pulse when strong drives of atomic coherences allow the two lasers to interact with each other through atomic coherence and can simultaneously reverse the signs of the Hanle resonances of both.

Comparison of a double-Λ atomic scheme with single- and two-fold coupled transitions

A four-level double-Λ atomic scheme, i.e. two Λ systems sharing the same two ground levels, that interacts with four laser light fields is studied theoretically. The peculiarity is that each of the two ground states can be coupled to each excited state by two laser light fields. A certain energy difference exists between excited-state levels. We consider this energy small enough so that a laser resonant to either transition can also couple the other transition. We test whether coupling of the more detuned laser is not non-negligible. Multiply connected states were also recently analyzed (and a comparison with experiment was presented), but for the simpler, two- and three-level atomic schemes (Stacey et al 2008 J. Phys. B: At. Mol. Opt. Phys. 41 085502). Theoretical treatment of the double-Λ atomic scheme is commonly done by solving optical Bloch equations (OBEs). When the rotating-wave approximation (RWA) is applied, OBEs become, by their form, a set of linear differential equations with constant coefficients. Theoretical treatment of the interaction scheme treated here leads to OBEs with coefficients that are not constant, but oscillate with time, even after RWA is applied. Under certain assumptions, the approximation can be used where the time-dependent coefficients are averaged over their periods. The method yields a new system of equations (similar to standard OBEs), but with more independent variables, and can also be solved in the usual way. The results presented here analyze the validity of this approximation by comparing the results for the double-Λ atomic scheme with single- and two-fold coupled transitions. We test whether in the limit of large-energy splitting between excited-state levels both approaches lead to similar results.

Using Genetics for Enhancement (Liberal Eugenics)

Abstract The fascinating progress of genetics has led to great achievements in the modern, medical, and nonmedical sciences. Genetic engineering is used in many fields, among which human enhancement is one of the most controversial. Most bioethicists agree on the definition of human enhancement as a physical, cognitive, or moral improvement. Genetic enhancement refers to the introduction of the changes into a genome or epigenome intended to improve nonpathological human traits. It is expected that implementation of genetic enhancement will be reached through the discovery of markers in enhancement related genes, such as athletic performance- or aging-related genes, but also through the development of approaches characteristic for personalized medicine, such as gene enhancement, molecular-targeted enhancement, and cellular enhancement. However, we should be aware that genetic enhancement creates significant ethical and regulatory challenges. Prompt and thorough discussion between liberal eugenicists and bioconservatives is indispensable, because genetics is moving extremely fast toward human genetic enhancement.

Pulse propagation dynamics in the presence of a continuous-wave field

We present theoretical results for the propagation dynamics of an electromagnetic field pulse through rubidium vapor, while another field, a continuous-wave electromagnetic field, is present. The frequencies of both electromagnetic fields are resonant with the transition between the ground and excited state hyperfine levels of Rb, Fg → Fe = Fg ± 1. Detuning from resonance is done by the magnetic field oriented along the light propagation direction (Hanle configuration). When both the electromagnetic fields are simultaneously interacting with Rb atoms, either electromagnetically induced transparency or absorption is induced. Propagation dynamics was obtained solving the set of Maxwell–Bloch equations for the interacting atoms with two electromagnetic fields. Motivated by recent results (Brazhnikov et al 2011 Eur. Phys. J. D 63 315–25; Brazhnikov et al 2010 JETP Lett. 91 625–9; Kou et al 2011 Phys. Rev. A 84 063807), we have analyzed the influence of experimental parameters, laser polarization, and mutual phases between lasers, which can lead to optical switching, i.e. the transformation from electromagnetically induced absorption to transparency and vice versa.

Emergence of electromagnetically induced absorption in a perturbation solution of optical Bloch equations

We study phenomenon of electromagnetically induced absorption (EIA) in the Hanle configuration by applying a perturbative method to solve linear system of optical Bloch equations (OBEs) for the case of closed Fg = 1 → Fe = 2 transition. The method is applied assuming stationary case and a weak laser fields (Ω ≪ Γ, i.e., Rabi frequency small compared to spontaneous emission rate). This way, we calculate (both numerically and analytically) higher order corrections to density matrix. Odd corrections give contributions to optical coherences, while even corrections contribute to populations and Zeeman coherences. The method gives insight into mechanism of transfer of coherences and transfer of populations between Zeeman sublevels. We have found that the ground-state coherences (2nd correction to coherences) are crucial for the 4th correction to the change of populations which brings EIA type behavior of the Hanle spectrum. Using exact analytical expressions we further discuss further the role of decoherence of the ground-state sublevels when forming EIA.

Absorption of elliptically polarized light in closed transitions of Rb vapor

We have studied experimentally and theoretically Hanle EIA on the closed Fg = 3 goes to Fe = 4 D2 transition of 85Rb. Atoms were excited by the laser light with different polarization, from linear to circular. Results of the theoretical calculations of the laser transmission, based on optical Bloch equations for density matrix elements for the same atomic system, show important effects of magnetic field transverse to the laser light. We were not able to control transverse magnetic field in the experiment but the theoretical results are still applicable to our experimental data due the presence of laboratory stray magnetic field in the vicinity of the Rb cell, occurring because of imperfect magnetic shielding.