Coherent control of excitons in single and coupled quantum wells

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.