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Probe Pulses (probe + pulse)
Selected AbstractsCoherent acoustic phonons in a thin gold film probed by femtosecond surface plasmon resonanceJOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2008Shoichi Yamaguchi Abstract We report on coherent phonon detection in a thin gold film by a new femtosecond pump-probe surface plasmon resonance (SPR) technique. Acoustic coherent phonons are generated impulsively in the gold film on a prism, and they are detected in the time domain through the reflectivity modulation for probe pulses that satisfy the SPR condition. We observed not only the fundamental vibration of a longitudinal acoustic phonon but also the overtones up to the fourth. Copyright © 2008 John Wiley & Sons, Ltd. [source] Four-wave mixing characteristics in SOAs with optimum time-delays between pump and probe pulsesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2007Narottam Kumar Das Abstract We have analyzed the four-wave mixing (FWM) characteristics in semiconductor optical amplifiers (SOAs) with optimum time-delays between pump and probe pulses by the finite-difference beam propagation method. This study is very important to achieve the high FWM conversion efficiency and to clarify the timing jitter. From the simulations, we have clarified that the FWM conversion efficiency increases with optimum time-delays between pump and probe pulses in SOA for short optical pulses. In the experiment, we have found the similar tendency. Therefore, we have obtained an excellent agreement between the simulation and experimental results of high FWM conversion efficiency in SOAs with optimum time-delays between pulses. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1182,1185, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22389 [source] Coherence control of electron spin currents in semiconductorsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2006Henry M. van Driel Abstract We provide an overview of some of our recent work on the use of one color and two color optical techniques to generate and control electronic spin currents in semiconductors for which a spin,orbit interaction exists. The generation process relies on the quantum interference between different absorption pathways, such as that between single and two photon absorption or those involving different polarization states of a monochromatic beam. For different crystal orientations and/or beam polarizations it is possible to generate a spin current with or without an electric current, and an electrical current with or without a spin current. In our experiments, which are conducted either at 80 K or 295 K, we typically employ nominally 100 fs pulses centered near 1500 and 750 nm. The currents generated are quasi-ballistic and the carriers typically move distances of ,1,10 nm, determined by the momentum relaxation time, which is of the order of 100 fs. The transient characteristics of spin-polarized electrical currents generated in strained GaAs at room temperature by ,100 fs pulses is detected by the emitted THz radiation. Pure spin currents can be detected by taking advantage of the accumulation of up and down spins on opposite sides of tightly focused pump beams. The spin states are detected through differential transmission measurements of tightly focused right and left circularly polarized, near-band-edge probe pulses, delayed by several picoseconds from the pump pulses to allow carrier thermalization to occur. By spatial scanning across the differential spin profiles and determining the amplitude of the response we are able to translate this into nm spatial resolution of spin displacement. Finally, the ability to generate ballistic currents using purely optical techniques allows us to generate transverse Hall-like currents, with transverse charge currents generated from pure spin currents and transverse spin currents generated from pure charge currents. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nonlinear optical microscopy of a single self-assembled InGaAs quantum dotPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2006M. Wesseli Abstract Carrier dynamics in InGaAs/GaAs quantum dots is analyzed with highly sensitive two-color femtosecond transmission spectroscopy. Especially, a single artificial atom is addressed in the optical near-field of a nanometer scale shadow mask. Resonantly exciting the wetting layer beneath the nanoisland, we detect transmission changes of the quantum dot with narrowband femtojoule probe pulses. We find bleaching signals in the order of 10,5 that arise from individual interband transitions. Moreover, the nonlinear optical response reveals a picosecond dynamics associated with carrier relaxation in the quantum dot. As a result, we have demonstrated an ultrafast optical tool for both manipulation and read-out of a single self-assembled quantum dot. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Excited-state molecular structures captured by X-ray transient absorption spectroscopy: a decade and beyondACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2010Lin X. Chen Transient molecular structures along chemical reaction pathways are important for predicting molecular reactivity, understanding reaction mechanisms, as well as controlling reaction pathways. During the past decade, X-ray transient absorption spectroscopy (XTA, or LITR-XAS, laser-initiated X-ray absorption spectroscopy), analogous to the commonly used optical transient absorption spectroscopy, has been developed. XTA uses a laser pulse to trigger a fundamental chemical process, and an X-ray pulse(s) to probe transient structures as a function of the time delay between the pump and probe pulses. Using X-ray pulses with high photon flux from synchrotron sources, transient electronic and molecular structures of metal complexes have been studied in disordered media from homogeneous solutions to heterogeneous solution,solid interfaces. Several examples from the studies at the Advanced Photon Source in Argonne National Laboratory are summarized, including excited-state metalloporphyrins, metal-to-ligand charge transfer (MLCT) states of transition metal complexes, and charge transfer states of metal complexes at the interface with semiconductor nanoparticles. Recent developments of the method are briefly described followed by a future prospective of XTA. It is envisioned that concurrent developments in X-ray free-electron lasers and synchrotron X-ray facilities as well as other table-top laser-driven femtosecond X-ray sources will make many breakthroughs and realise dreams of visualizing molecular movies and snapshots, which ultimately enable chemical reaction pathways to be controlled. [source] Polarization control of ultrashort mid-IR laser pulses for transient vibrational circular dichroism measurements,CHIRALITY, Issue 1E 2009Mathias Bonmarin Abstract Linear dichroism and birefringence artifacts are a major source of concern in transient circular dichroism measurements. They mainly arise from interaction of an imperfectly circular polarized probe beam with a nonisotropic sample. We present in this article a procedure to generate mid-IR pulses of highly symmetric left and right handed circular or elliptical polarization states for transient VCD measurements. An infrared femtosecond laser source is synchronized to the natural frequency of a photo elastic modulator. Residual static birefringence of the modulator and the sample cell can be largely compensated by carefully controlling the arrival time of the ultrashort probe pulses at the modulator. Chirality 21:E298,E306, 2009. © 2009 Wiley-Liss, Inc. [source] | |||||||||||||