Control Laser Field Research Articles

TRANSIENT AND STEADY-STATE ABSORPTIONS OF A WEAK PROBE FIELD IN A COUPLED DOUBLE QUANTUM-WELL STRUCTURE

We propose and analyze an efficient scheme for suppressing the absorption of a weak probe field based on intersubband transitions in a four-level asymmetric coupled quantum well (CQW) driven coherently by a probe laser field and a control laser field. We study the steady-state process analytically and numerically, and our results show that the probe absorption can be completely eliminated under the condition of Raman resonance (i.e. two-photon detuning is zero). Besides, we can observe one transparency window without requiring one- or two-photon detuning to exactly vanish. This investigation may provide a possible scheme for EIT in solids by using the CQW.

Coherently Controlled Multifunctional Active Optical Filters

In this paper, we propose multifunctional active optical filters using coherent nonlinear effects and quantum interference in quantum-well structures. Based on the application demand, in the absence of a control laser field, these filters can be either completely opaque or transparent. However, in the presence of such a control laser, the filter structure is activated, allowing transmission of a single frequency. We show that the amplitude and linewidth of these filters can be optically controlled, demonstrating various functionalities and performances including attenuation, amplification, and switching processes. We also show that, with proper design of such active filters, one can tune the wavelength of the filtered signal by varying the intensity of the control field.

Slow vector optical solitons in a cold five-level hyper V-type atomic system

A new scheme of five-level hyper V-type atomic system is proposed with the aim of generating slow temporal vector optical solitons. Two transitions in the five-level atomic medium independently interact with the two orthogonally polarized components of a low intensity linear-polarized pulsed probe field, while two other transitions are driven by control laser fields. We demonstrate that various distortion-free slow temporal vector optical solitons, such as bright-bright, bright-dark, dark-bright and dark-dark vector solitons, can be evolved from the probe field. Besides, we also show that the modified Hubbard model that includes the Manakov system may be realized by adjusting the corresponding self- (cross-) phase modulation and dispersion effects of this system.

The effect of controlling laser field on broadband suppercontinuum generation

The effect of controlling laser field on broadband suppercontinuum generation is researched. By adjusting the wavelength of controlling field as much as ±0.2 μm at 1.6 μm, no effect has been found in suppercontinuum obviously, the cut off range and the bandwidth of suppercontinuum both vary less than 5%. With increasing of the intensity of the controlling field, the suppercontinuum is broadened. A 12 fs/800 nm and a 30 fs/1.6 μm pulses are combined to serve as the driving pulse with the relative phase of -0.1π and relative intensity of 20%, the short quantum path is selected and a 105 eV suppercontinuum is obtained.

Coherent control of magneto-optic rotation

We experimentally study the rotation of the plane of polarization of a laser beam passing through room-temperature Rb vapour. The rotation occurs because the medium behaves differently for the two orthogonally-polarized components, displaying what is known as circular birefringence or linear dichroism. The difference is induced either by a control laser applied to an auxiliary transition of a ladder-type system, or by an applied axial magnetic field. In the presence of both control laser and magnetic field, the line shape shows an interesting interplay between the two effects with regions of suppressed and enhanced rotation. The line shapes can be understood qualitatively based on a density-matrix analysis of the system.

Transformable broad-band transparency and amplification in negative-index films

The possibility to produce laser-induced optical transparency of a metamaterial slab through the entire negative-index frequency domain is shown above a certain control laser field intensity threshold.

Collision-assisted electromagnetically induced control of coherent population transfer

The effect of the collisions on the control of coherent population transfer in a closed inverse $Y$-type four-level system driven by three laser fields is investigated with the stimulated Raman adiabatic passage technique. An arbitrary coherent superposition between the initial state and target state can be created either by varying the Rabi frequency of the control laser field or by tuning the one-photon detunings of the pump and Stokes laser fields. When the three laser fields with nearly equal peak Rabi frequencies are each tuned to resonance with the respective transitions, the low transfer efficiency due to the nonadiabatic coupling between two degenerate adiabatic states could be enhanced dramatically with the increase of the collision-induced coherence decay rates to the value nearly comparable to the Rabi frequency of the control field. The enhanced transfer efficiency results from the collision-controlled electromagnetically induced transparency in the $\ensuremath{\Lambda}$-type three-level subsystem and electromagnetically induced absorption in the ladder-type three-level subsystem of the four-level system.

Inversionless distributed feedback semiconductor lasers: Ultranarrow linewidth and immunity against spatial hole burning

We propose and parametrically study an inversionless intrinsically single-mode distributed feedback laser structure. This laser is optically excited by a control laser field that is responsible for transferring a fully transparent waveguide structure into a coherent state, wherein a periodic variation of gain without inversion in the absence of any refractive index perturbation is generated. We show that such a laser can perform under the conditions where its gain is equal or even less than its loss, i.e., zero and negative net gain regimes. The results suggest that, via coherent control of the longitudinal mode intensity profile and standing wave effects, in the negative net gain regime such a laser can be operated at the Bragg wavelength with ultranarrow linewidth and virtual elimination of any sidemode. The inherent resistance of such a laser against spatial hole burning, despite of having strong nonuniform longitudinal mode intensity, and the effects of facet reflectivities are discussed.

Semiconductor quantum templates: bottom-up design of optical devices and photoniccircuits using sub-nanoscale high monolayer features and quantum optics

We propose an alternative bottom-up technique for designing, fabricating andmonolithically integrating optical components, including functional distributed feedbacklasers, modulators, waveguides, etc in a single semiconductor wafer without any need foretching or post-processing epitaxial growth. The proposed technique is based on theformation of semiconductor quantum templates at the well/barrier interfaces of quantumwell structures. Such templates are responsible for changing the thickness of a quantumwell in designated regions by adding one extra monolayer of the well material in thoseregions during the growth process. We show that, using a control laser field, thesetemplates or sub-nanoscale high monolayer features allow us to spatially control theformation of electromagnetically induced transparency, gain without inversion, andcoherent enhancement/suppression of the refractive index along the plane of the quantumwell. We demonstrate that this can lead to bottom-up design capabilities for functionaloptical devices and their monolithic integration using a single epitaxial growth process.

Deflection of slow light by magneto-optically controlled atomic media

We present a semiclassical theory for light deflection by a coherent $\ensuremath{\Lambda}$-type three-level atomic medium in an inhomogeneous magnetic field or an inhomogeneous control laser. When the atomic energy levels (or the Rabi coupling by the control laser) are position-dependent due to the Zeeman effect caused by the inhomogeneous magnetic field (or due to inhomogeneity of the control field profile), the spatial dependence of the refraction index of the atomic medium will result in an observable deflection of slow signal light when the electromagnetically induced transparency cancels medium absorption. Our theoretical approach based on Fermat's principle in geometrical optics not only provides a consistent explanation for the most recent experiment in a straightforward way, but also predicts the two-photon detuning dependent behaviors and larger deflection angles by three orders of magnitude for the slow signal light deflection by the atomic media in an inhomogeneous off-resonant control laser field.

Purely loss-coupled distributed feedback lasers based on electromagnetically induced absorption in active photonic band gaps

We utilize electromagnetically induced absorption (EIA) in a one-dimensional functional (active) photonic band gap structure to propose a coherently generated purely loss-coupled distributed feedback (DFB) laser. Such a laser happens when interaction of the photonic band structure with a control laser field totally removes its refractive index perturbation and replaces it with periodic regions of EIA, forming an optical dark lattice. Such a lattice does not have any stop band, but scatters light coherently at the Bragg wavelength. We also show that before the optical dark lattice happens, the photonic band gap structure can act as a coherently generated partly loss-coupled DFB laser with dominant lasing mode at the longer wavelength side of the stop band. We expect such a distinct feature makes this laser quite stable.

Destruction and enhancement of photonic band gap and coherent localization of optical fields in functional photonic crystals

We use electromagnetically induced transparency combined with coherent enhancement of refractive index in the conduction intersubband transitions of a n-doped quantum well structure to study one-dimensional functional (active) photonic band gap structures. In the absence of a control laser field, such structures act as conventional photonic band gaps created by off-resonant (background) refractive index perturbations. In the presence of the control field, they are transformed into resonant structures with transitions around the Bragg wavelength. We show that this process can be used to (i) destroy the band gap, making the structure fully transparent around the Bragg wavelength, or (ii) coherently tune the band gap while enhancing its width by nearly a factor of 2. Using these phenomena we then study coherent localization of electromagnetic modes in photonic band gap structures without having any structural defects. Such a localization process here happens via partial illumination of such structures by the control field, generating electromagnetically induced optical defects. We show that the phase associated with such defects can be adjusted by the control field, allowing us to generate tunable electromagnetically induced transmission resonances (or photonic electromagnetically induced transparency) within the band gap.

Role of noise operators on two-photon correlations in an extended coherent Raman medium

An extended medium driven in a double Raman configuration generates Stokes and anti-Stokes fields that are described by coupled parametric oscillator equations with solutions that depend on input boundary operators and quantum noise operators. We identify the conditions where the boundary operators can be the substitute to the noise operators for describing two-photon cross correlation in forward and backward geometries. These conditions include short sample and small decoherence between ground states ${\ensuremath{\gamma}}_{bc}$, and they are fulfilled by the spontaneous Raman electromagnetic induced transparency scheme (weak pump with large detuning). We verify the correspondence between the results from boundary and noise operators analytically and show that the correlation due to the boundary operators is typically smaller than that due to the noise operators. In general the noise operators are required to obtain the correct correlation, especially when the control laser field is weak and ${\ensuremath{\gamma}}_{bc}$ is finite. Explanations for the findings are given based on the physics represented by the boundary operators and noise operators. Similar conclusions are obtained for the Stokes and anti-Stokes intensities.

Quenching the collective effects on the two-photon correlation from two double-Raman atoms

We obtain an analytical expression for two-photon correlation ${G}^{(2)}$ from two atoms driven in a double-Raman (or $\ensuremath{\Lambda}$) configuration where collective effects such as superradiant, subradiant, and dipole-dipole interaction are included. It is found that the collective effects on the ${G}^{(2)}$ can be quenched to some extent by a resonant control laser field. The collective effects provide features via ${G}^{(2)}$ that enable the two atoms to be resolved at subwavelength separation. We also identify an effect in the double Raman scheme due to the collective effects and the control field, i.e., the Stokes and anti-Stokes frequencies are increased by fourfold.

Controllable optical bistability in a four-subband semiconductor quantum well system

We study optical bistability (OB) behavior based on intersubband transitions in asymmetric double quantum wells (QWs) where tunneling-induced quantum inference can be observed. The system interacts with a probe-laser field and a control laser field by means of a unidirectional ring cavity. We show that OB can be controlled efficiently by tuning the coupling strength of the tunneling, the Fano-type interference, and the intensity of the control field. The influence of the frequency detuning of the probe and control fields on the electronic OB behavior is also discussed. This investigation can be used for the optimal design of semiconductor QW systems to achieve fast and low-threshold all-optical switches, which is much more practical than that in an atomic system because of its flexible design and the controllable interference strength.

Two-mode single-atom laser as a source of entangled light

A two-mode single-atom laser is considered, with the aim of generating entanglement in macroscopic light. Two transitions in the four-level gain medium atom independently interact with the two cavity modes, while two other transitions are driven by control laser fields. Atomic relaxation as well as cavity losses are taken into account. We show that this system is a source of macroscopic entangled light over a wide range of control parameters and initial states of the cavity field.

Coherent control of optical bistability in tunnel-coupled double quantum wells

We analyze optical bistability (OB) behavior based on intersubband transitions in an asymmetric coupled-quantum well (CQW) driven coherently by a probe laser field and a control laser field by means of a unidirectional ring cavity. We demonstrate that OB can be controlled by tuning the energy splitting between two tunnel-coupled electronic levels, the intensity of the control field, and the frequency detuning of the probe and control fields. The influence of the electronic cooperation parameter on the OB behavior is also discussed. This investigation may be used for optimizing and controlling the optical switching process in the CQW solid-state system, which is much more practical than that in atomic system because of its flexible design and the controllable interference strength.

Tunable Infrared Semiconductor Lasers Based on Electromagnetically Induced Optical Defects

We propose tunable midinfrared laser systems based on dynamic formation of electromagnetically induced optical defect sites. Such defects occur in a waveguide structure having a uniformly corrugated quantum well structure in the absence of any structural defect or phase slip. In the absence of a control laser field, such a corrugated structure causes a uniform perturbation of refractive index along the waveguide. However, when a relatively small region of such a waveguide structure is illuminated from the side by the control laser field, electromagnetically induced transparency occurs in this region while its refractive index corrugation is removed. We also show that such a coherently induced defect can be dynamically moved along the waveguide structure by just steering the control laser beam to illuminate different locations. We utilize the fact that the phase associated with this defect site can be adjusted via changing the length of the illuminated region to present a tunable distributed feedback laser where its lasing wavelength can be continuously varied within the stop-band. We study the case where two coherently induced defect sites happen along the waveguide structure and discuss the impacts of illumination of the whole waveguide structure with the control laser field. We show that the latter can either make the waveguide coherently transparent by destroying its refractive index perturbation and stop-band, or generate a gain-without-inversion grating. Formation of such a grating allows the waveguide to act as a tunable partly gain-coupled distributed feedback laser.

Purely gain-coupled distributed feedback laser via a bright optical lattice

We utilize degeneracy of Bragg resonance and the intersubband transitions in a quantum well bright optical lattice to propose a coherently induced purely gain-coupled distributed feedback laser. The optical lattice is generated via formation of periodic regions of resonant intersubband gain without inversion in the absence of any refractive index perturbation using a control laser field. We show that longitudinal mode intensity profile and standing wave effects of such an intrinsically single-mode intersubband laser can be coherently controlled. These features allow immunity against spatial hole burning and lasing when modal loss is higher than modal gain.

Phase control over decaying molecular states in intense laser pulses

A time-dependent approach to study phase control over molecular photoabsorption, provided by intense laser pulses, is elaborate. The method allows for the decay linewidth of molecular states and frequency bandwidth of the controlling laser field, and can be applied in weak and strong laser fields where the perturbation theory is invalid. It is shown that a frequency mismatch between the fundamental laser wave and its third harmonic can destroy control. For the example of the one-photon versus three-photon control a simple picture of interference from two monochromatic absorption pathways is not enough to explain phase control and one needs to consider a nonlinear temporal interference of multiquantum transitions. In the perturbation-theory limit an elegant generalization of the famous Shapiro-Hepburn-Brumer equation for the one-photon versus three-photon control is derived. Various numerical calculations illustrate the dependence of phase control on molecular linewidth, fundamental laser wavelength, pulse duration, and peak intensity. It is obtained, that the one-photon versus three-photon control is productive if the molecular state populations, individually produced by each laser wave, have beats of approximately the same frequency. The calculations demonstrate that an enough intense optical pulse can suppress molecular decay and may be used in order to keep stable the state population of a decaying molecule for a long time. The available experimental results for the one-photon versus three-photon control over simple and large polyatomic molecules are analyzed and recommendations for the experimental improvement of control are formulated.