Showing papers on "Electromagnetically induced transparency published in 1997"

Electromagnetically Induced Transparency

Abstract: Electromagnetically induced transparency is a technique for eliminating the effect of a medium on a propagating beam of electromagnetic radiation EIT may also be used, but under more limited conditions, to eliminate optical self‐focusing and defocusing and to improve the transmission of laser beams through inhomogeneous refracting gases and metal vapors, as figure 1 illustrates The technique may be used to create large populations of coherently driven uniformly phased atoms, thereby making possible new types of optoelectronic devices

Tunneling induced transparency: Fano interference in intersubband transitions

Abstract: We report the observation of tunneling induced transparency in asymmetric double quantum well structures. Resonant tunneling through a thin barrier is used to coherently couple the two upper states in a three level system of electronic subbands in a GaAs/AlGaAs structure. This creates Fano-type interferences for the collective intersubband excitations in the absorption from the ground state, analogous to electromagnetically induced transparency (EIT) in atomic systems. We observe a 50% reduction in absorption between the subband resonances which can be explained by taking into account the coherent coupling of the upper states. We analyze the bias dependent absorption spectra and determine the relevant lifetime broadening and dephasing rates for the transitions.

Spectroscopy in Dense Coherent Media: Line Narrowing and Interference Effects

Abstract: Spectroscopic properties of coherently prepared, optically dense atomic media are studied experimentally and analyzed theoretically. It is shown that in such media the power broadening of the resonances can be substantially reduced. A density-dependent spectral narrowing of the electromagnetically induced transparency (EIT) window and novel, even narrower, resonances superimposed on the EIT line are observed in dense Rb vapor. A nonlinear two-photon spectroscopic technique based on coherent atomic media and combining high resolution with a large signal-to-noise ratio seems feasible.

Enhanced nondegenerate four-wave mixing owing to electromagnetically induced transparency in a spectral hole-burning crystal

Abstract: We have demonstrated electromagnetically induced transparency (EIT) in an inhomogeneously broadened spectral hole-burning system of Pr(3+)-doped Y(2)SiO(5) at 6 K. We have also shown enhancement of four-wave mixing under conditions of reduced absorption. This demonstration opens the possibilities of pursuing EIT applications such as high-resolution optical image processing and optical data storage in solids.

Frequency-selective time-domain optical data storage by electromagnetically induced transparency in a rare-earth-doped solid

Abstract: We report the experimental observation of optical data storage by frequency-selective stimulated spin echoes based on electromagnetically induced transparency in an inhomogeneously broadened rare-earth-doped solid. We find that the spin dephasing time T2 is almost constant in the range 2–6 K, whereas the optical T2 shortens rapidly above 4 K. This experiment demonstrates the potential of spin echoes excited by electromagnetically induced transparency for higher-capacity optical data storage at higher temperature.

Quantum interference in resonance fluorescence for a driven V atom

Abstract: We investigate the effect of quantum interference between the two transition pathways from the excited doublet to the ground level of a driven V atom on the spectral features of the resonance fluorescence emission. The ultranarrow spectral line at line center, which arises due to quantum interference, occurs over a wide range of parameters. The smaller the ratio of the excited doublet splitting to the effective Rabi frequency, the more pronounced the spectral line narrowing. However, the fluorescence emission is completely quenched when the atomic dipole moments are exactly parallel and the driving field is tuned to the average frequency of the atomic transitions. The narrow line is due to the slow decay rate of one dressed state, while the quenching arises from dressed-state trapping. A finite laser linewidth destroys the spectral narrowing features and the fluorescence quenching.

Electromagnetically Induced Transparency

Abstract: Electromagnetically induced transparency (EIT) is a technique for making an otherwise optically-thick medium transparent to laser radiation.’ The basic idea is to use two lasers or electromagnetic fields whose frequency difference is equal to a Raman (or two-photon) transition of the atom or molecule. We term these fields as the coupling field and the probe field. Figure 1 shows some of the possibilities. Transparency may be created in a (a) three-state system, or (b) in the continuum. Instead, (c) a medium which is already transparent, but is refractively thick (sL » 1), may be made refractively thin (sL « 1).

Atomic coherence effects in four-level systems: Doppler-free absorption within an electromagnetically-induced-transparency window

Abstract: We report here an effect in a four-level ladderlike system, which is in contrast to the usual quantum interference effects such as electromagnetically induced transperency (EIT) or coherent population trapping: we predict the occurrence of a narrow absorption peak within the EIT window when an EIT atomic system interacts with an additional driving rf field. The Doppler-free-central absorption appears when the three-photon resonance condition is satisfied. In the limit of the rf field strength ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{rf}}$\ensuremath{\rightarrow}0, the usual EIT profile is recovered.

Electromagnetically induced transparency in atoms with hyperfine structure

Abstract: Electromagnetically induced transparency ~EIT! is a technique for improving the transmission of laser beams through otherwise absorbing and refracting media. Most often, this is done in an atom that has three states that, at the densitylength product that is to be made transparent, are resolvable. One applies two laser fields and uses either optical pumping ~cw lasers! or adiabatic evolution ~pulsed lasers! to produce a coherent superposition of the probability amplitudes of two states of the same parity, with a near-zero probability amplitude of a third state of opposite parity. Once in this superposition state, the atom does not interact with either of the applied fields @1–3#. Figure 1~a! shows an example of a prototype three-state system. Because the nuclear spin of Pb is zero with linearly polarized light, the J50 and J52 finestructure states of the 6p configuration, together with the J51 state of the 6p7s configuration, form the necessary superposition state @4#. Figure 1~b! shows an energy schematic of Pb. Here, the nuclear spin of I51/2 causes the fine-structure states to split into their hyperfine components, with splittings of a few tenths of a cm. Although at low atom density-length products ~optically thin!, the individual hyperfine components of the u1&→u4& and u1&→u5& transitions are resolvable, in a dense medium, they are not. Even though a particular threestate subsystem may be made transparent, other subsystems will produce a prohibitively large change in the complex refractive index, and the medium will be opaque. The question then arises: How should the lasers be tuned to render an optically thick, hyperfine-split system such as Pb both transparent and nonrefracting? In this paper we show that transparency and a refractive index near unity are attained when the two lasers are tuned to the respective center of gravity of the two transitions. No specific hyperfine state is in Raman resonance and the zero in the real part of the dipole moment results from the interference of the manifold of cooperating m states. At practical Rabi frequencies, the detuning from the individual Starkshifted m states is sufficiently large that the nonzero imaginary part of the dipole moment is not of consequence. We also find, as is the case for the pure three-state system, that self-focusing and defocusing may be eliminated @5#. In related previous work, Ling et al. @6# and Milner et al. @7# have shown how degenerate m states may cooperate to form a population-trapped state. This work is similar to theirs in that we use a multistate interference. It differs from theirs in that the m f states that we use are not degenerate @Fig. 1~b!#. General conditions for obtaining population trap-

Electromagnetically induced transparency with variable coupling-laser linewidth

Abstract: Resonance transmission in a three-level $\ensuremath{\Lambda}$-type system of the rubidium $D1$ line is controlled by adjusting the linewidth of the pumping (coupling) laser. With the change of pumping-laser linewidth from several MHz to about 100 MHz, the absorption reduction degrades from about 70% to less than 15%. The experimentally measured results are in good agreement with a simple theoretical calculation.

Birefringence in electromagnetically induced transparency.

Abstract: He4 2 3S1→2 P3 transitions at 1083 nm were laser probed in the presence of radiation that coupled the 2 P3 level with the 3 3S1 level in a ladder scheme. The metastable helium that was used was produced in a rf discharge. Significant atomic birefringence was detected, in addition to complete electromagnetically induced transparency. A simple theoretical model explains the experimental results.

Nonlinear theory of noninversion lasers of an open three-level system

Abstract: A nonlinear theory of a noninversion laser of an open three-level system based on electromagnetically induced transparency is given. In this noninversion laser model, a nonselective pumping mechanism is used for obtaining lasing gain such that the population in the lower lasing level is always larger than a half of the total population no matter whether the driving field is on or off. In the lasing region, there is no direct pumping to the upper level. The conditions for the existence of a nontrivial and stable laser field are obtained. The dependence of the laser intensity on the intensity of the driving field and the ratio of the two decay rates from the upper level has been obtained, and the ways to obtain a large laser field have been studied.

Coherence and decoherence in the interaction of light with atoms

Abstract: Amplification without population inversion in a resonant V-type atomic medium is analyzed using the theory of quantum trajectories. A global view of the dynamics underlying the amplification is provided by a quantum stochastic process governing an interplay between coherence and decoherence. The quantum trajectories decompose into distinct ``gain cycles'' and ``loss cycles'' which determine, respectively, the emission and absorption spectra that might be calculated from perturbation theory. Two methods for calculating net gain are developed, motivated by complementary views of the exchange of energy between an atom and a probe field. One time averages the energy radiated continuously by the induced dipole, while the other determines probabilities for discontinuous energy exchange through the emission and absorption of individual quanta. In the latter case, the emission and absorption probabilities are evaluated as sums over probabilities for classical records that define the unobservable exchange of a quantum with the probe field in terms of observable scattering events. Quantum trajectories for a V-type medium driven by a coherent field are compared with those for a medium driven incoherently. Two relationships which connect amplification to population inversion in the latter case are shown to be lacking in the former; hence the possibility for amplification without population inversion arises from the following: (1) a decoupling of the rate of gain-cycle (loss-cycle) initiation from the time-averaged population in the initial state for gain (loss), and (2) loss of the symmetry that the final state for emission be the initial state for absorption and vice versa. The specific influences of these general observations vary from model to model. The details are worked out for the resonant V-type medium, where the quantum trajectory analysis sheds light on the meaning of ``without population inversion'' and ``cancellation of absorption by quantum interference.''

Nonlinear generation of extreme-ultraviolet radiation in atomic hydrogen using electromagnetically induced transparency

Abstract: Sum-frequency generation enhanced by electromagnetically induced transparency (EIT) has been extended to the production of extreme ultraviolet (XUV) radiation in the range 97.3\char21{}92.6 nm from $np\ensuremath{-}1s$ transitions $(n=4\char21{}8)$ in atomic hydrogen. Pulsed radiation was generated by strong coupling of the $\mathrm{np}$ and $2s$ levels with laser radiation at Balmer wavelengths, and simultaneously (weaker) coupling of the $2s$ and $1s$ levels by two-photon resonance with 243-nm laser radiation. Investigations were carried out over a range of laser intensities and products of interaction length and atomic density $(\mathrm{NL}).$ As the product $\mathrm{NL}$ increased, the XUV intensities were greatly enhanced by EIT, and at high $\mathrm{NL}$ values, the spectral distributions of some of the generated signals were found to be distorted by the presence of molecular hydrogen. Calculated profiles, modified to incorporate the effects of nearby molecular resonances, were shown to be in good agreement with the observed spectra.

Coherent population trapping on the sodium D 1 line in high magnetic fields

Abstract: We consider the coherent-population-trapping (CPT) phenomenon in a sodium atomic vapor. The experiment leading to the first observation of CPT is revisited with an improved experimental setup and a larger range of magnetic-field strengths. From the analysis of the ground-state hyperfine splitting as a function of the applied magnetic field, we conclude that we have observed the whole spectrum of dark resonances within the D1 line corresponding to the nonabsorbing coherent superposition of two Zeeman sublevels of two different components of the 32S1/2 level. This was not obvious a priori because the transition probabilities at high magnetic-field strengths, as applied in the experiment, have to be taken into account. The differences in the contrast of the various black lines are explained in terms of pumpings outside the interaction scheme preparing the nonabsorbing state. Possible applications of CPT in high magnetic fields are discussed.

Quantum optics: Lasing without inversion and other effects of atomic coherence and interference

Abstract: Quantum coherence and correlations in atomic and radiation physics have led to many interesting and unexpected consequences. For example, an atomic ensemble prepared in a coherent superposition of states yields the Hanle effect, quantum beats, photon echo, self-induced transparency, and coherent Raman beats. In fact, in Section 1.4, we saw that the quantum beat effect provides one of the most compelling reasons for quantizing the radiation field. A further interesting consequence of preparing an atomic system in a coherent superposition of states is that, under certain conditions, it is possible for atomic coherence to cancel absorption. Such atomic states are called trapping states †. The observation of nonabsorbing resonances via atomic coherence and interference impacts on the concepts of lasing without inversion (LWI),‡ enhancement of the index of refraction accompanied by vanishing absorption, and electromagnetically induced transparency. In lasing without inversion, the essential idea is the absorption cancellation by atomic coherence and interference. This phenomenon is also the essence of electromagnetically induced transparency. Usually this is accomplished in three-level atomic systems in which there are two coherent routes for absorption that can destructively interfere, thus leading to the cancellation of absorption. A small population in the excited state can thus lead to net gain. A related phenomenon is that of resonantly enhanced refractive index without absorption in an ensemble of phase-coherent atoms ( phaseonium ). In a phaseonium gas with no population in the excited level, the absorption cancellation always coincides with vanishing refractivity.

Temperature-selective trapping of atoms in a dark state by means of quantum interference.

Abstract: We present a novel type of dark spontaneous-force optical trap The trap is based on a velocity-selective inhibition of repumping light absorption produced by electromagnetically induced transparency Accumulation of cold cesium atoms in a dark state is observed

Counter-counter-intuitive quantum coherence effects

Abstract: The study of an ensemble of phase–coherent atoms has recently lead to interesting theoretical innovations and experimental demonstrations of counter–intuitive effects such as electromagnetically induced transparency (EIT), lasing without inversion (LWI), enhancement of index of refraction and ultra–large nonlinear susceptibility. In the present notes, we report a couple of new effects along these lines. In fact, it would be fair to call them surprises even in the repertoire of ‘counter–intuitive effects’, i.e. ‘counter–counter–intuitive effects’. Specifically, we will show that the LWI concept, which is based on quantum coherence, has a surprising counterpart in the classical physics of free electron laser operation. In other current work, we find that it is possible to ‘lock’ atoms in an excited state via atomic coherence. It is, by now, not surprising that such a phase–coherent ensemble can show holes or dark lines in the emission spectrum. It is surprising that we can lock atoms in an excited (normally decaying) state via atomic coherence and interference. Such a phase–coherent collection of atoms, i.e. ‘phaseonium’, is indeed a novel new state of matter.

Resonant Raman frequency mixing under electromagnetically induced transparency conditions

Abstract: A fully resonant process of Raman mixing of the frequencies of one weak and two strong laser radiations is considered. A study is made of the influence of dynamic (field) splitting of the levels and of quantum interference on nonlinear processes, including the propagation and attenuation of weak pump radiation and of the generated radiation. It is shown that efficient nonlinear frequency mixing is possible in electromagnetically induced transparency regions.

Electromagnetically induced focusing in a Λ-type medium

Abstract: Electromagnetically induced transparency (EIT) in an inhomogenously broadened medium consisting of Λ-type three-level atoms has been analyzed. It is shown that the Λ system can induce a transparency of the medium when the probe laser and the coupling laser have the same frequency detunings (including zero). Across the EIT window, the radial variation of the strong coupling laser radiation may lead to electromagnetically induced focusing or defocusing of the weak probe laser at separate probe frequency detuning points.