Summary form only given.We report on a general approach to coherent control in semiconductors, based on optical waveforms with synthesized intensity and phase versus time. This technique is limited only by the bandwidth of the initial laser pulses and the spectral resolution of the pulse-shaping apparatus. It is therefore especially suitable to investigate effects such as off-resonant Rabi oscillations and polaritons in multiple quantum wells. Experiments were performed in four-wave mixing (FWM) and differential reflection geometry based on a mode-locked Ti:sapphire laser emitting 100-fs pulses.
Summary form only given.We report on a general approach to coherent control in semiconductors, based on optical waveforms with synthesized intensity and phase versus time. This technique is limited only by the bandwidth of the initial laser pulses and the spectral resolution of the pulse-shaping apparatus. It is therefore especially suitable to investigate effects such as off-resonant Rabi oscillations and polaritons in multiple quantum wells. Experiments were performed in four-wave mixing (FWM) and differential reflection geometry based on a mode-locked Ti:sapphire laser emitting 100-fs pulses.
Summary form only given. The developments with coherent control (CC) techniques in optical spectroscopy have recently demonstrated population control and coherence manipulations when the induced optical phase is explored with phase-locked laser pulses. These and other developments have been guiding the new research field of quantum control including the recent applications to semiconductors and nanostructures. We study the influence of inhomogeneous broadening in semiconductors on CC results. Photoluminescence (PL) and the coherent emission in four-wave mixing (FWM) is recorded after resonant excitation with phase-locked laser pulses. The sample is a narrow GaAs single quantum well.
In this paper, we report on the ultrafast coherent control of excitons in quantum wells using a phase-locked pulse sequence generated by pulse-shaping techniques. The pulse-shaping system with a double liquid-crystal spatial light modulator (SLM), and a Ti3+-sapphire laser is used to generate phase-locked pulses. The ultrafast coherent control of the exciton population and polarization is demonstrated by the observation of the reflectivity change in the pump-probe and the diffracted power in the degenerate-four-wave-mixing (DFWM) measurements. In single quantum wells, good coherent control characteristics with 87% coherent carrier destruction are demonstrated at the low excitation power of 0.15 mW (∼1.1×1010 photons/cm2). In addition, the preliminary manipulation of the exciton population is demonstrated by the phase-locked triple pulses. In the case of coupled quantum wells, the modulation of the SLM is carefully controlled and the coherent control of both the exciton population and the polarization is demonstrated in the two different coupled quantum-well samples.
Summary form only given. The coherence decay of optically excited electronic systems provides one of the most powerful tools to investigate interaction processes of excited states. In semiconductors, the optical coherence phenomena are usually investigated by nonlinear techniques such as four wave mixing (FWM), photon echo, or reflectivity experiments. Exciton-phonon, exciton-exciton, or exciton-free carriers scattering processes have been explored in recent years with these techniques. As demonstrated recently, a direct measurement of the optical dephasing time can be obtained through the temporal coherent control of electronic excitations. In these experiments, the emission following the excitation by an ultrashort optical pulse sequence, is detected in a non-specular direction (secondary emission). This provides an alternative approach to FWM techniques, which allows us to analyse the scattering processes either with phonons or due to mutual collisions. Using the coherent control technique monitored through the secondary emission (SE), we report on the coherent dynamics of excitons in bare quantum wells (QW) and compare it to that of exciton-polaritons in microcavity (MC) embedded quantum wells.
The four-wave mixing produced with two ultrashort phase-locked !-3! laser pulses propagating coherently in a two-level system in the infrared spectral region is shown to depend on the pulses relative phase. The Maxwell-Bloch equations are solved beyond the rotating-wave approximation to account for field frequencies which are largely detuned from the atomic resonance. The relative phase dominating the efficiency of the coupling to the 5! anti-Stokes Raman component is determined by sign of the total ac Stark shift induced in the system, in such a way that the phase influence disappears precisely where the ac Stark effect due to both pulses is compensated. This fundamental quantum interference effect can be the basis for nonlinear ultrafast optical spectroscopy techniques. Phenomena arising from the coherent control of nonlinear interactions are of importance in fields as diverse as optoelectronics and materials research, in high harmonic generation, in photoionization or molecular dissociation, and in biological applications such as spectroscopy and imaging, among others [1, 2, 3, 4, 5, 6, 7]. Optical quantum coherent control is based on the fact that the phases of interfering transition amplitudes in light-matter interactions can be controlled through the optical phase of coherent light sources that drive the interaction, in such a way that the transition rates to final states and the dynamics at various stages of the process can be modified [1]. In a recent paper [8], a theoretical investigation on the quantum coherent control of the optical transient four-wave mixing of two intense phase-locked femtosecond laser pulses of central angular frequencies ω and 3ω propagating in a two-level atom (TLA) was reported. It was shown how the nonlinear (χ (3) ) coupling to the antiStokes Raman field at frequency 5ω depends critically on the initial relative phase φ of the propagating pulses. In Ref. [8], the study was centered to intense pulses in the visible and ultraviolet spectral regions, with frequencies at resonance or lower than the atomic transition. The phenomena observed in [8], however, can be scaled to various laser and material parameters. In the infrared spectral range, for instance, experiments on ultrafast molecular dynamics are frequently performed by help of twocolor pump probe nonlinear spectroscopy techniques. In this type of studies, due to the high intensities inherent to ultrashort (subpicosecond) pulses, nonlinear effects such as stimulated Raman processes may become important and are often utilized as a complementary tool to gain information [9]. In this Letter, we address the conditions for quantum coherent control of transient four-wave mixing interactions with two phase-locked ω-3ω femtosecond laser pulses in the mid-IR spectral region. Our purpose is to reveal the basic physics for a strict two-level medium and to this end the Maxwell-Bloch TLA will be considered. We will study pulses with a duration of 300 fs (with a w 5w
In this paper, we report the manipulation of coherent exciton in single- and coupled-quantum-wells using phase locked pulses generated by pulse shaping techniques instead of Michelson interferometer. The pulse shaping system with double liquid crystal spatial light modulator, and the Ti3+-sapphire laser with pulse width of about 120 fs are used to generate phase-locked pulses. GaAs/AlGaAs quantum-wells (exciton energy: E0 equals 1.5470 eV) and asymmetric double coupled quantum-well structures (exciton energy: E1 equals 1.5348 eV, E2 equals 1.5422 eV) are used in the experiments. Manipulation of coherent exciton are demonstrated by observation of both the reflectivity-change in the pump-probe and the diffracted power in the degenerate-four-wave-mixing (DFWM) measurements using phase- locked twin-pulse (k1) and single-pulse (k2). Coherent destruction in single quantum-well is observed by the rapid decrease of reflectivity-change after the arrival of the second pulse (pulse interval: 500 fs) and good coherent control with 87% of coherent carrier destruction is demonstrated at low excitation power of 0.15 mW. In case of coupled quantum-wells, the modulation of SLM is carefully set to the twin-pulse having the spectrum with a minimum at both exciton wavelengths for destructive condition. After arrival of the second pulse, coherent control of the quantum beats are observed in DFWM signal.
Summary form only given. Ultrafast coherent control of excitons in semiconductors have been reported using Michelson interferometer with precise control of the pulse interval in time domain. In order to improve the phase controllability and realize arbitrary manipulation, the pulse shaping technique is a more attractive candidate. In this paper, we report very fine phase control of coherent, excitons in GaAs/AlGaAs single quantum wells using phase-locked pulses prepared by pulse shaping technique.