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2010, Optics Letters
We theoretically study the stacked optical transients generated from a series of square pulses passing through a cold atomic ensemble. Using the hybrid analysis and fast Fourier transform, we identify the stacked coherent transients [Europhys. Lett. 4, 47 (1987)] as optical precursors. With slow-light and electromagnetically induced transparency, we obtain nearly 700% transmitted intensity at the transient spikes resulting from the interference between the delayed main field and the stacked optical precursors.
Journal of The Optical Society of America B-optical Physics, 2008
We discuss the transient effects associated with short-pulse propagation in a linearly dispersive medium by comparing optical precursors with 0 pulses. The classical and quantum effects were, in the past, treated independently due to the different time scales. Using results from recent studies [Phys. Rev. Lett. 96, 143901 (2006)] as well as the discussions by Varoquaux et al. [Phys. Rev. B. 34, 7617 (1989)] and Bürck [Hyperfine Interact. 123, 483 (1999)], we show analytically that precursors and 0 pulses describe the same physical phenomenon. We also show that most published results of transient pulse propagation can be expressed using one overarching equation. Finally, we give a physical interpretation of the analogy between precursors and 0 pulses as a medium-impulse response using a Green's function.
Journal of the Optical Society of America B, 2008
We discuss the transient effects associated with short-pulse propagation in a linearly dispersive medium by comparing optical precursors with 0 pulses. The classical and quantum effects were, in the past, treated independently due to the different time scales. Using results from recent studies [Phys. Rev. Lett. 96, 143901 (2006)] as well as the discussions by Varoquaux et al. [Phys. Rev. B. 34, 7617 (1989)] and Bürck [Hyperfine Interact. 123, 483 (1999)], we show analytically that precursors and 0 pulses describe the same physical phenomenon. We also show that most published results of transient pulse propagation can be expressed using one overarching equation. Finally, we give a physical interpretation of the analogy between precursors and 0 pulses as a medium-impulse response using a Green's function.
Physical Review A, 1990
Physical Review A, 2007
We consider a duplicated two-level system where each two-level subsystem is driven by a strong resonant femtosecond pulse and a weak resonant femtosecond pulse connects cross transitions. Strong interference effects are induced in such a configuration leading to a modulation of the medium gain as a function of the relative phase between the pulses ͓J. C. Delagnes and M. A. Bouchene, Phys. Rev. Lett. 98, 053602 ͑2007͔͒. We study here the influence of the temporal overlap between the pulses on the dynamics of the system and the medium gain. We show that the dynamics is dominated by two competing phenomena: Light shifts ͑LS͒ induced by the driving pulse that prevails for small delays and free induction decay ͑FID͒ that prevails for large delays. LS enhance the medium gain for = / 2 and reduce it for = 0, whereas FID always leads to a decrease of the medium gain.
Physical Review A, 2014
We have studied stationary and quasi-stationary signal light pulses in cold -type atomic media driven by counterpropagating control laser fields at the condition of electromagnetically induced transparency. By deriving a dispersion relation we present spectral and temporal properties of the signal light pulse and a significant influence of atomic decoherence on the coupled stationary light pulses for spatial splitting. Finally we discuss quasi-stationary light pulse evolution characterized by frozen spatial spreading for a robust coherent control of slow light pulses.
A three-level atom interacting with classical electromagnetic fields is coherently excited by a two-photon transition near resonance and subsequently makes a second transition driven at resonance by a weak ir field at the noise level. Our calculation predicts generation of an electromagnetic field at a third frequency in the uv from zero field. Calculations show a gain of the uv radiation with propagation through the medium, though the populations of the two levels involved are never inverted. Other calculations produce a pulsed amplifier, two-photon optical nutation, and free induction memory. An effective susceptibility is defined and its imaginary part is found to be a good indicator of mode specific absorption and emission by the atomic state, and its real part a good indicator of dispersion. These calculations exemplify the possibility of coherent control over an atomic vapor and the production of a superradient macroscopic ensemble of states in the retarded frame for realistic parameters. S1050-29479808808-8
Chemical Physics Letters, 2000
We study spontaneous fluorescence excited by a series of phase-controlled femtosecond pulses in an inhomogeneously broadened medium containing a frequency comb of sharp spectral holes. We show that evolution of the spontaneous fluorescence on picosecond time scale is sensitive to interference between the excitation pulses and that varying the relative phase between the excitation pulses changes the time evolution of the fluorescence. q 2000 Elsevier Science B.V. All rights reserved.
An iterative predictor-corrector finite-difference time-domain method is used to solve the semiclassical Maxwell-Bloch system numerically without invoking any of the standard approximations such as the rotating-wave approximation. This approach permits a more exact study of self-induced transparency effects in a two-level atom. In addition to recovering the standard results, for instance, for vr, 2~, and 4m pulses, several. features in the results appear at the zeros of the driving pulse, where its time derivatives are maximum. Several ultrafast-pulse examples demonstrate that time-derivative-driven nonlinearities have a significant impact on the time evolution of a two-level atom system. Moreover, typical small-signal gain results are also obtained with our Maxwell-Bloch simulator. We illustrate that these time-derivative effects can be used to design an ultrafast, single-cycle pump pulse that completely inverts the two-level atom population. A pump-probe signal set is then used to illustrate gain in the probe signal.
In this study, we control a three-level atomic system using a typical strong control field with a modified quotient double exponential form (modified QEXP). The considered atomic configuration is a V-type three-level system in which QEXP is applied between the ground and excited states. Atomic population inversion can be achieved by selecting specific shaped pulses. In addition, we control the temporal atomic coherence of the system for a spectrum of waveforms and derive both absorption and dispersion spectra. Compared to a continuous wave control field, the proposed modified QEXP pulse achieves an electromagnetically induced transparency window in the absorption spectrum.
Physical Review Letters, 2013
We investigate the interaction between a single atom and optical pulses in a coherent state with a controlled temporal envelope. In a comparison between a rising exponential and a square envelope, we show that the rising exponential envelope leads to a higher excitation probability for fixed low average photon numbers, in accordance to a time-reversed Weisskopf-Wigner model. We characterize the atomic transition dynamics for a wide range of the average photon numbers, and are able to saturate the optical transition of a single atom with ≈50 photons in a pulse by a strong focusing technique. For photon numbers of ≈1000 in a 15 ns long pulse, we clearly observe Rabi oscillations.
Physical Review Letters, 2009
We report the observation of Sommerfeld-Brillouin optical precursors generated from a long squaremodulated laser pulse propagating through a cold atomic ensemble with electromagnetically induced transparency. The optical depth (0 L) of the medium can be varied from 0 up to 50. We demonstrated that the step-on rising and step-off falling edges propagate with the speed of light in vacuum without a slow light effect. At high 0 L, the precursor is separated from the delayed main pulse at the rising edge, while at the falling edge, we observe damped oscillatory structures resulting from the interference between the precursor and main field.
Physical Review Letters, 2010
We report the generation of stacked optical precursors from a laser beam whose amplitude or phase is modulated by sequenced on-off step waveforms. Making use of the constructive interference between the precursors produced from different steps, as well as the main field, we generate optical transient pulses having peak powers of eight times the input power with electromagnetically induced transparency in lasercooled atoms.
Physical Review A, 2009
We study theoretically the propagation of a step-modulated optical field as it passes through a dispersive dielectric made up of a dilute collection of oscillators characterized by a single narrowband resonance. The propagated field is given in terms of an integral of a Fourier type, which cannot be evaluated even for simple models of the dispersive dielectric. The fact that the oscillators have a low number density (dilute medium) and have a narrow-band resonance allows us to simplify the integrand. In this case, the integral can be evaluated exactly, although it is not possible using this method to separate out the transient part of the propagated field known as optical precursors. We also use an asymptotic method (saddle-point method) to evaluate the integral. The contributions to the integral related to the saddle-points of the integrand give rise to the optical precursors. We obtain analytic expressions for the precursor fields and the domain over which the asymptotic method is valid. When combined to obtain the total transient field, we find that the agreement between the solutions obtained by the asymptotic and the exact methods is excellent. Our results demonstrate that precursors can persist for many nanoseconds and the chirp in the instantaneous frequency of the precursors can manifest itself in beats in the transmitted intensity. Our work strongly suggests that precursors have been observed in many previous experiments.
Physical Review A, 2011
Providing a femtosecond optical pulse with a proper transverse spatial profile represents a fast and relatively simple method to force a quantum system to follow a prescribed temporal evolution. In the present work, we show that the quantum system presents a surprisingly high sensitivity with respect to the spatial shape of the pulse. We discuss an explicit example where differences on the order of a few nanometers in the initial pulse's spot size induce completely different responses in the system under study.
Optics Letters, 2005
We study the influence of shaping the phase of the optical field when time-delayed femtosecond pulse pairs excite a sequential two-photon transition in rubidium atoms. Propagation through this optically dense medium modifies the pulse profile. When an external phase is introduced into one of the pulses, partial cancellation of the two-photon absorption signal is observed for temporal delays much greater than the pulse duration. This behavior is qualitatively explained in terms of a negative group delay.
Journal of the Optical Society of America B, 2014
Simultaneous propagation of two probe pulses in a medium of four-level atoms irradiated by three control fields is studied. The double Λ configuration has been closed by a fifth field, coupling the lower levels. It is shown that the propagation can be described in terms of four modes characterized by particular effective susceptibilities, which have absorption or gain peaks and transparency windows. For incoming one-peak pulses, multipeak spectra are built during the propagation including a few components of well-defined frequencies. They evolve along the sample with some of their spectral components being transmitted, absorbed, or amplified.
Photonics Letters of Poland, 2016
We study the propagation dynamics of a single pair of probe and coupling laser pulses in a three-level cascade atomic medium by numerical solving the Maxwell-Bloch equations for atoms and fields. There are investigated influences of pulse duration, intensity and pulse area of a coupling laser on probe laser propagation. We found the conditions when the undistorted probe pulse in such a medium, i.e., the EIT effect, is established. Under EIT conditions, the ground state population is trapped in a dark state.
Physical Review A, 2006
We report experimental evidence that light storage, understood as the controlled release of a light pulse by an atomic sample dependent on the past presence of a writing pulse, is not restricted to small-group-velocity media but can also occur in a negative-group-velocity ...
Conference on Lasers and Electro-Optics (CLEO 2000). Technical Digest. Postconference Edition. TOPS Vol.39 (IEEE Cat. No.00CH37088), 2000
Atomic coherence-state phase conjugation is studied via optical coherent transient phenomena, in Tm+3: YAG. The theoretical framework is a semi-classical perturbative approach to time-domain wave mixing in an inhomogeneously broadened two-level atomic system. Phase conjugation occurs between coherence-state pathways associated with the stimulated photon echo and the so-called 'virtual' echo.
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