Absorption Of Probe Field Research Articles

Slow and fast light propagation in a triple quantum well nanostructure

In this paper, we investigate the absorption and dispersion properties of a weak probe field in a triple quantum well nanostructure by using the incoherent pumping fields. A deep 7.1 nm-thick GaAs well is coupled, on one side, to two shallow 6.8 nm-thick Al0.2Ga0.8As wells by a 2.5 nm-thick Al0.4Ga0.6As barrier. The two shallow wells are separated by a 2.0 nm-thick Al0.4Ga0.8As barrier. Both sides of quantum well contact with 36 nm Al0.4Ga0.6As. Therefore, this type of triple quantum well nanostructure can be used as a suitable medium for studying the effect of spontaneously generated coherence (SGC) and interference between incoherent pumping fields on absorption and dispersion properties of weak probe light. We find that the interferences from spontaneous emission and incoherent pumping processes can change the slope of dispersion and group velocity of the probe light from slow to fast or vice versa. Moreover, it is demonstrated that the group velocity of the light pulse can be controlled with the rates of incoherent pumping fields.

Roles of Atomic Injection Rate and External Magnetic Field on Optical Properties of Elliptical Polarized Probe Light

In this paper we investigate the optical properties of an open four-level tripod atomic system driven by an elliptically polarized probe field in the presence of the external magnetic field and compare its properties with the corresponding closed system. Our result reveals that absorption, dispersion and group velocity of probe field can be manipulated by adjusting the phase difference between the two circularly polarized components of a single coherent field, magnetic field and cavity parameters i.e. the atomic exit rate from cavity and atomic injection rates. We show that the system can exhibit multiple electromagnetically induced transparency windows in the presence of the external magnetic field. The numerical result shows that the probe field in the open system can be amplified by appropriate choice of cavity parameters, while in the closed system with introduce appropriate phase difference between fields the probe field can be enhanced. Also it is shown that the group velocity of light pulse can be controlled by external magnetic field, relative phase of applied fields and cavity parameters. By changing the parameters the group velocity of light pulse changes from subluminal to superluminal light propagation and vice versa.

Effect of electron-spin relaxation on optical bistability and lasing without population inversion in a three-level V type quantum system

Abstract We have discussed effect of electron spin relaxation on optical bistability behavior and lasing without inversion in a three level V-type quantum system. A reasonable range for electron spin relaxation value is chosen to investigate the phenomena previously mentioned. It has been showed that for different values of electron spin relaxation of the system, the bistable threshold intensity and width of hysteresis loop changes dramatically. Following we showed that how one can manipulate the absorption of probe field by variation of electron spin relaxation and achieve laser without inversion in the absence of incoherent field.

Realization of position-dependent absorption based on biexciton coherence in a Quantum Dot Nanostructure

In this letter, the two-dimensional (2D) spatial-dependent of probe absorption based on biexciton coherence is investigated by monitoring the probe absorption spectra in a Quantum Dot (QD) Nanostructure. We find that due to the quantum interference which is set up by two control pulses that couples to a resonance of the biexciton, the 2D spatial distribution of probe absorption spectrum can be controlled via adjusting the system parameters. We study the effect of controlling parameters of the QD system on spatial distribution of the probe field absorption for two different cases in which the QD interacts with the standing-wave laser fields; first, when two laser fields which couple to a biexciton state, correspond to the two orthogonal standing-wave fields and couple the different transitions. Second, when only one of laser fields correspond to the combination of two orthogonal standing-wave fields, while the other one corresponds to a traveling-wave field. Results exhibit different interesting 2D absorption patterns.

Phase control of Goos–Hänchen shift via biexciton coherence in a multiple quantum well

The behavior of the Goos–Hänchen (GH) shifts of the reflected and transmitted probe and signal pulses through a cavity containing four-level GaAs/AlGaAs multiple quantum wells with 15 periods of 17.5nm GaAs wells and 15-nm Al0.3Ga0.7As barriers is theoretically discussed. The biexciton coherence set up by two coupling fields can induce the destructive interference to control the absorption and gain properties of probe field under appropriate conditions. It is realized that for the specific values of the intensities and the relative phase of applied fields, the simultaneous negative or positive GH shift in the transmitted and reflected light beam can be obtained via amplification in a probe light. It is found that by adjusting the controllable parameters, the GH shifts can be switched between the large positive and negative values in the medium. Moreover, the effect of exciton spin relaxation on the GH shift has also been discussed. We find that the exciton spin relaxation can manipulate the behavior of GH shift in the reflected and transmitted probe beam through the cavity. We show that by controlling the incident angles of probe beam and under certain conditions, the GH shifts in the reflected and transmitted probe beams can become either negative or positive corresponding to the superluminal or subluminal light propagation. Our proposed model may supply a new prospect in technological applications for the light amplification in optical sensors working on quantum coherence impacts in solid-state systems.

Two-dimensional atom localization via phase-sensitive absorption-gain spectra in five-level hyper inverted-Y atomic systems

A scheme for realizing two-dimensional atom localization in the sub-wavelength domain is proposed in a microwave-driven five-level hyper inverted-Y atomic system in which the atom interacts with a weak probe field, two control fields together with two orthogonal standing-wave fields. Because of the spatially dependent atom-field interaction, the information about the position of the atom can be extracted directly from the absorption and gain spectra of a weak probe field. It has been found that the probe detuning, the intensities of two control fields, and the relative phase of the driving fields can significantly improve the localization precision. Moreover, the maximal probability of finding the atom at an expected position in the sub-wavelength domain of the standing-wave field can reach unity via properly adjusting the system parameters.

Superposition of Stationary Wave Fields Via Atom Microscopy

We investigate one-dimensional position microscopy of a three-level atom moving through a stationary wave region under the condition of electromagnetically induced transparency. The precise position information of an atom is observed on the resonance absorption and dispersion distribution spectrum of a weak probe field. Single and multiple localization peaks are observed in specific directions of the corresponding wave numbers and phase of the standing wave fields. The strength of space-independent Rabi frequency reduces the position uncertainty in the localized peaks without disturbing the probability of the atom. In a hot atomic medium the localized probability of an atom is reduced which depends upon the temperature of that medium. Our results provide useful applications in the development of laser cooling, atom nanolithography and Bose–Einstein condensation.

Phase Control of Transient Optical Properties of Quantum-Dot Nanostructure via Terahertz Signal Radiation

We theoretically analyze the transient properties of a probe field absorption dispersion in a quantum-dot nanostructure driven by terahertz signal radiation. Here a four-level quantum-dot nanostructure is designed numerically by Schrödinger and Poisson's equations. We show that in the presence of the THz signal, the medium becomes phase dependent and the absorption dispersion can be dramatically influenced by the relative phase between applied fields.

Controlling the optical bistability in a Λ-type atomic system via incoherent pump field

We investigated optical bistability (OB) and the absorption properties of a weak probe field in a three-level Λ-type atomic system confined in a unidirectional ring cavity via incoherent pump field. We found that the threshold of OB and the probe field absorption can be controlled by the rate of incoherent pump field. No laser field was used in the pumping processes.

Er3+ ion concentration effect on transient and steady-state behavior in Er3+:YAG crystal

The effect of Er3+ ion concentration on transient and steady-state behavior in 45-nm Er3+:YAG crystal is investigated. It is shown that by changing the signal field, the coherent field and the concentration of Er3+ ions in the crystal, the absorption, dispersion, and group index of the weak probe field can be adjusted. Also, it is found that the probe absorption occurs in the presence of population inversion and probe amplification is obtained in the absence of population inversion.

Two-dimensional sub-wavelength atom localization in an electromagnetically induced transparency atomic system

We propose a scheme for high-precision two-dimensional (2D) sub-wavelength atom localization in a tripod-type atomic system. The position information of a moving atom can be obtained by measuring the probe field absorption when the atom interacts with a weak probe field and two orthogonal standing-wave fields. It is found that sub-wavelength atom localization can be obtained under the condition of two-photon resonance. Remarkably, the localization precision can be significantly improved by changing the strength of the coherent coupling fields in the presence of superposition of coherent coupling field and standing-wave field.

Comparison of optical properties between ladder and lambda-type EIT medium with Er3+ ion concentration in Er3+:YAG crystal

The effect of Er3+ doped ion concentration on optical properties of two type three-level schemes in 35 nm Er3+:YAG (yttrium aluminum garnet) crystal is studied. It is found that intensity threshold of optical bistability and multistability can be changed by Er3+ doped ion concentration. Moreover, switching from optical multistability to optical bistability can be done differently by Er3+ concentration in two types of three-level schemes. The steady-state and transient behaviors of absorption, dispersion and group index of weak probe field in two schemes are also discussed. In this study, we will report an initial study on optical properties in Er3+:YAG crystal and propose a basis for selecting the suitable concentration to carry out experimental investigations in the future.

Electronic properties of hemispherical quantum dot/wetting layer with and without hydrogenic donor impurity

We obtain the electronic structure of an InAs hemispherical quantum dot with a wetting layer embedded in a GaAs barrier, with and without hydrogenic impurity located at the origin, using finite element method in the effective mass approximation. The binding energy is calculated as a function of the shape and size of the dot. The system is considered to interact with a weak, pulsed probe field and a strong continuous-wave control field. We obtain the expressions for the linear and nonlinear absorptions and dispersions of the probe pulse. According to results, applying the control field results in the reduction of the probe field absorption and group velocity at transparency window. Results show that as the dot size increases, the absorptions and dispersions increase and exhibit red shifts. Adding impurity to the system results in the blue shifts and the reduction of the absorptions and dispersions.

Double-electromagnetically induced transparency in a Y-type atomic system

We study the absorption and dispersion properties of a weak tunable probe field in a four-level Y-type atomic system driven by two strong laser (coupling) fields within the framework of density matrix formalism. It is found that the probe absorption profile displays double-electromagnetically induced transparency (double-EIT) and it is shown how to control it by changing the Rabi frequencies as well as the atom field detuning of the coupling fields.

Infrared and terahertz signal detection in a quantum Dot nanostructure

In this paper an all-optical method for infrared (IR) and terahertz (TH) signals detection in quantum dot nanostructure is proposed. In our model, incoming IR or TH signals do not directly excite electrons and thus thermionic dark current cancels out. Core of detector is made of four-level quantum dot nanostructure which is designed numerically by the Schrödinger and Poisson's equations. By size control of quantum dot and external voltage, one can design a four level quantum dot with appropriate energy levels which can be suitable for IR or TH signals detections. In this case, a probe and a control field simultaneously interact by four-level quantum dot for creation of coherent population trapping. An IR or TH signal can influence the electron population in dark and bright levels, therefore absorption and transmission spectrum of probe field in the medium can be altered. Thus, one can by studying of probe absorption, easily guesstimate the existence of IR or TH signals in the medium.

CROSSOVER FROM SPONTANEOUSLY GENERATED COHERENCE TO AUTLER–TOWNES SPLITTING IN THREE-LEVEL ATOMIC SYSTEMS

We investigate spontaneously generated coherence (SGC) and Autler–Townes Splitting (ATS) in various three-level systems. Through detailed analytical calculations on absorption spectrum of probe laser field, we show that in V-type system the SGC can completely eliminate the absorption of the probe field and at the same time significantly reduce the group velocity. By using residue theorem and spectrum decomposition method, we prove that there exists a crossover from SGC to ATS for both cold and warm atoms when the magnitude of SGC is changed. Different contributions of SGC and ATS to probe-field absorption spectrum are clearly clarified in different parameter regions. In addition, our results show that there is no SGC and hence no SGC-ATS crossover in Λ- and Ξ-type systems.

Tunneling-induced enhancement of self-Kerr nonlinearity in asymmetric quantum wells

Abstract We propose an asymmetric AlGaAs/GaAs double quantum wells (QWs) structure for realizing the enhancement of self-Kerr nonlinearity. It is found, with resonant tunneling, that the self-Kerr nonlinearity can be clearly enhanced, while the absorption of probe field is very small and can be safely neglected. We attribute the enhancement of self-Kerr nonlinearity mainly to the constructive interference induced by resonant tunneling.

High-temperature all-optical intersubband quantum well Terahertz switch

In this article an asymmetric intersubband quantum well structure as a high temperature terahertz (THz) optical switch is proposed. In our proposed structure the incoming low power energy photon (THz control signal) causes an optical switching. In this structure we introduce an optical terahertz switch based on coherent population trapping (CPT) phenomena. In the presence of electromagnetic THz field, quantum interference between the terahertz control field and short-wavelength probe field under appropriate condition, the medium becomes transparent (zero absorption) for the probe field. So the absorption and refraction characteristic of optical probe field can be modified with THz radiation. Therefore this idea is suitable for all – optical terahertz switching.

Sub-half-wavelength atom localization of a V-type three-level atom via relative phase

Coherent interaction of an atom with a position-dependent standing-wave cavity field can impart position information of a moving atom through the cavity leading to subwavelength atom localization. We show that the position of the atom along the standing-wave field is determined when the probe-field absorption is measured. We find out that absorption of the weak probe field at a certain frequency leads to subwavelength localization of the atom in either of the two half-wavelength regions of the cavity field by appropriate choice of the system parameters. In addition, we demonstrate that the position information of a three-level V-shaped moving atom strongly depends on the relative phase of applied fields. By appropriate choice of the relative phase, it is shown that the scheme can be used for localizing an atom flying through the standing-wave field to the sub-half-wavelength domain.

LASING WITH AND WITHOUT POPULATION INVERSION IN A QUANTUM DOT NANOSTRUCTURE VIA AN INCOHERENT PUMPING FIELD

The effect of incoherent pumping field on absorption spectrum and population inversion in a four-level quantum dot nanostructure are investigated. It is found that with incoherent pumping field the probe field absorption can be converted to probe field gain. Also, it is found that with combine effect of incoherent pumping field and electron tunneling the lasing can be obtained in the absence or presence of population inversion.