نتایج جستجو برای: ultrafast phenomenon
تعداد نتایج: 170044 فیلتر نتایج به سال:
The transition between different states in manganites can be driven by various external stimuli. Controlling these transitions with light opens the possibility to investigate the microscopic path through which they evolve. We performed femtosecond (fs) transmission electron microscopy on a bi-layered manganite to study its response to ultrafast photoexcitation. We show that a photoinduced tempe...
Conjoined twinning is a rare abnormality and cephalopagus is a very rare form of conjoined twins. We report a case of cephalopagus conjoined twins with encephalocele and omphalocele which diagnosed by ultrasonography and ultrafast magnetic resonance (MR) imaging at 24 weeks of the gestation. Ultrafast MR imaging can provide image quality superior to two dimensional ultrasonography and should be...
1. A.M. Weiner, and A.M. Kan'an, "Femtosecond pulse shaping for synthesis, processing, and time-to-space conversion of ultrafast optical waveforms," IEEE J. of Selec. Top. in Quant. Electron., 4, 317 (1998). 2. M.A. Krurnbügel et al., "Ultrafast optical switching by use of fully phase-matched cascaded second-order nonlinearities in a polarization-gate geometery," Opt. Lett., 22, 245 (1997). 3. ...
A vortex is a flow phenomenon that is very commonly observed in nature. More than a century, a vortex ring that forms during drop splashing has caught the attention of many scientists due to its importance in understanding fluid mixing and mass transport processes. However, the origin of the vortices and their dynamics remain unclear, mostly due to the lack of appropriate visualization methods....
Saturation of carrier occupation in optically excited materials is a well-established phenomenon. However, so far, the observed saturation effects have always occurred in the strong-excitation regime and have been explained by Pauli blocking of the optically filled quantum states. On the basis of microscopic theory combined with ultrafast pump-probe experiments, we reveal a new low-intensity sa...
High-frequency surface acoustic waves can be generated by ultrafast laser excitation of nanoscale patterned surfaces. Here we study this phenomenon in the hypersonic frequency limit. By modeling the thermomechanics from first-principles, we calculate the system's initial heat-driven impulsive response and follow its time evolution. A scheme is introduced to quantitatively access frequencies and...
Topological insulators (TIs) are interesting quantum matters that have a narrow bandgap for bulk and a Dirac-cone-like conducting surface state (SS). The recent discovered second Dirac surface state (SS) and bulk bands (BBs) located ~1.5 eV above the first SS are important for optical coupling in TIs. Here, we report on the time-domain measurements of THz radiation generated from TIs n-type Cu(...
Selective optical excitation of a substrate lattice can drive phase changes across heterointerfaces. This phenomenon is a nonequilibrium analogue of static strain control in heterostructures and may lead to new applications in optically controlled phase change devices. Here, we make use of time-resolved nonresonant and resonant x-ray diffraction to clarify the underlying physics and to separate...
The transient behavior of the optical susceptibility of polydiacetylene induced by an ultrafast pump field is investigated. Within a two-level model which includes phonon effects phenomenologically, an analytical expression for the nonlinear susceptibility is obtained. In addition to spectral hole burning, the novel phenomenon of optical nutation is found. Both this nutation and the shape of th...
The development of ultrashort pulse laser technology will have a strong impact on the advancement of laser machining. Ultrashort laser pulses can reduce the heat-affected zone and the shock-affected zone, resulting in much cleaner cuts, and therefore higher precision. Also, ultrashort laser pulses have shown remarkable promise for processing transparent materials such as glass, fused silica, an...
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