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Summary form only given. The optical response of nanostructured semiconductors around the bandgap is dominated by the properties of excitons in interface potentials fluctuating: on a mesoscopic length scale. On this length scale, scanning near-field optical microscopy (SNOM) extents the optical resolution to a fraction of the wavelength of light. The results of a finite difference time domain evaluation...
Summary form only given. The spectroscopy of individual quantum dots (QDs) using optical micro-probing techniques is opening up possibilities of various applications based on the physics of the zero-dimensional (0D) semiconductor structures. Self-assembled quantum dots (SAQDs) are also attractive 0D structures, where strong confinement on a no-meter scale can be realized. Here, we carried out time-correlation...
Summary form only given. Femtosecond differential transmission (DT) spectroscopy of In/sub 0.4/Ga/sub 0.6/ quantum dots (QD) pumped resonantly with a narrow band pulse shows an extremely rapid spreading of the energy spectrum, indicating carrier coupling among dots of different sizes. This rapid spectral spread has been observed and attributed to carrier-carrier scattering in quantum well systems...
Summary form only given. Time-integrated (TI) and time-resolved (TR) four-wave-mixing (FWM) techniques have been employed successfully to study the relaxation dynamics of coherent excited states in semiconductors and semiconductor quantum wells. A large number of experimental and theoretical studies on FWM have been mainly focused on the resonant FWM signals in thin semiconductors with thicknesses...
Summary form only given. Using the density matrix formulation of quantum mechanics, the optically-heterodyne-detected coherent Raman scattering signal in the out-of-phase configuration, under the off-resonant condition, is given.
Summary form only given. We present a near-field optical technique for second harmonic imaging using bare tapered optical fiber tips illuminated with femtosecond laser pulses. We show theoretically and experimentally that under illumination with P-polarized light the local SHG from the sample region under the tip is strongly enhanced even in the case of a dielectric tip. At the same time, the glass...
Summary form only given. Four-wave mixing processes in semiconductor quantum wells have been studied intensively for many years, because they allow for a detailed investigation of ultrafast many-body processes such as quantum correlations and quantum coherences. From a theoretical point of view one can roughly divide the existing approaches into two categories: (i) fully microscopic theories based...
Summary form only given. Recently, non-degenerate inter-level interactions caused by Coulomb correlations have been studied by using partially non-degenerate four-wave mixing. The most important signature of this interaction was the existence of strong coherent emission at the exciton resonance even when the first pulse (/spl omega//sub 1/) excites continuum that is non overlapping to the exciton...
Summary form only given. Coherent dynamics in semiconductors can be strongly affected by interaction between energetically degenerate interband transitions. In this paper, we demonstrate for the first time to our knowledge that this strong interaction can be used to transfer the coherence properties of discrete excitons to continuum transitions and vice versa. This transfer can generate coherent radiation...
Summary form only given. We use spectral interferometry and temporal gating techniques to investigate the time-integrated quantum beats (TI-QBs) involving the light hole (lh) and heavy hole (hh) excitons in GaAs-AlGaAs quantum wells in a geometry that is sensitive both to the nonradiative Raman coherence and to the radiative dipole coherence associated with the dynamic interactions between hh and...
Summary form only given. Two laser beams whose frequency difference is close, but not exactly equal, to that of a Raman resonance in a molecular medium will drive the resonance so as to establish a phased and, in effect, propagating molecular coherence. We discuss the conditions for the existence of Raman eigenvectors. These conditions are: (1) In analogy to electromagnetically induced transparency...
Summary form only given. The reciprocal relationship between time and frequency implies that a single short laser pulse has a broad spectrum. A pulse circulating inside a laser cavity or the periodic pulse train if a mode-locked laser, however, can be described as a coherent superposition of discrete laser modes. This frequency-domain comb of modes is now providing an elegant and universal solution...
Summary form only given. We report an absolute measurement of the optical frequency of a stabilized Nd:YAG laser by measuring the gap between its fundamental f/sub 1064/ and second harmonic 2f/sub 1064/ using a fs laser frequency comb which has been broadened in a silica microstructure fiber. To our knowledge, this is the first ever direct rf to optical frequency measurement using a single optical...
Summary form only given. Ultrashort pulse laser systems are finding increasing application in optical frequency metrology and nonlinear optics which require precise control over the pulse frequency and phase. We show the stabilization of the frequency, phase and repetition rate of an ultrashort pulse train to a Fabry-Perot reference cavity using a unique combination of actuators allowing for sufficient...
Summary form only given. In optical frequency metrology, it is often necessary to precisely bridge THz frequency gaps. Optical frequency combs (OFC) are one technique that have recently attracted interest. Key characteristics of OFCs include consistency of comb line spacing, center wavelength, and comb width. Previous OFCs have been constructed by placing an electro-optic modulator inside a high-finesse...
Summary form only given. Characterization of ultrashort light pulses is a primary concern of the researcher working with mode-locked lasers. Here we present an improved frequency domain phase measurement (FDPM). This configuration employs only linear passive filters with a nonlinear time integrating detector incorporated to measure a phase-dependent signal. In our setup we used a nonlinear detector...
Summary form only given. Two-beam coupling (TBC) with chirped pulses can be used to determine response times shorter than the chirped pulse duration. Here we explore the possibility of a direct determination of the electronic response time through measurements of two-beam coupling with pulses as short as 10 fs. We use fused silica as a model system. In numerical simulations we assume that the pulses...
Summary form only given. We analyze the spatiotemporal waveform evolution of self-focused high power femtosecond pulses with a three dimensional phase-retrieval cross-correlation technique. The FWHM beam diameter evolution for 8l0-nm, 270-fs pulses propagating in sapphire due to self-focusing. Within the experimental power range, the beams shrink on propagation, and no catastrophic beam collapse was...
Summary form only given. When intense TW-fs-laser pulses propagate through the atmosphere, nonlinear effects like self-phase modulation (SPM), self-focusing (SF) or degenerated four-wave mixing (DFWM) cause an immense change of the temporal and spatial profile. The frequency content is changed, too. Depending on the initial beam profile, the pulse duration and other parameters like temporal chirp,...
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