Topic
Femtosecond
About: Femtosecond is a research topic. Over the lifetime, 35106 publications have been published within this topic receiving 691405 citations. The topic is also known as: 1 E-15 s & fs.
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TL;DR: The fabrication of symmetric waveguides in bulk poly(methyl methacrylate) (PMMA) by femtosecond laser pulses and a waveguide with a circular transverse profile can be obtained by using a slit beam shaping method.
Abstract: We report on the fabrication of symmetric waveguides in bulk poly(methyl methacrylate) (PMMA) by femtosecond laser pulses. A waveguide with a circular transverse profile can be obtained by using a slit beam shaping method. The refractive index in the core increases by up to 4.6 x 10(-4) and the waveguide works as single-mode waveguide at a wavelength of 632.8 nm. This writing technique is applied to the fabrication of a directional coupler to split a coupled beam with a 1:1 splitting ratio at 632.8 nm.
145 citations
TL;DR: For the first time to the authors' knowledge, transient oscillations were observed in DPS and the spectral shift of a probe pulse was time resolved together with the rise in DPS, which is clear evidence for induced phase modulation in absorptive materials.
Abstract: A new femtosecond time-resolved interferometer was developed that utilizes interference fringes in the frequency domain to obtain simultaneously difference phase spectra (DPS) and difference transmission spectra with a multichannel spectrometer. For the first time to our knowledge, transient oscillations were observed in DPS and the spectral shift of a probe pulse was time resolved together with the rise in DPS, which is clear evidence for induced phase modulation in absorptive materials.
145 citations
TL;DR: It is shown that electron-magnon excitation does not affect the overall magnetization even though it is an efficient spin-flip channel on the sub-200 fs time scale, and experimental evidence is found for the relevance of Elliott-Yafet-type spin-Flip processes for the ultrafast demagnetization taking place on a time scale of 300 fs.
Abstract: The femtosecond magnetization dynamics of a thin cobalt film excited with ultrashort laser pulses has been studied using two complementary pump-probe techniques, namely, spin-, energy-, and time-resolved photoemission and the time-resolved magneto-optical Kerr effect. Combining the two methods, it is possible to identify the microscopic electron spin-flip mechanisms responsible for the ultrafast macroscopic magnetization dynamics of the cobalt film. In particular, we show that electron-magnon excitation does not affect the overall magnetization even though it is an efficient spin-flip channel on the sub-200 fs time scale. Instead, we find experimental evidence for the relevance of Elliott-Yafet-type spin-flip processes for the ultrafast demagnetization taking place on a time scale of 300 fs.
145 citations
TL;DR: In this article, a femtosecond distributed soliton spectrum with τ ≳ 100 fsec covering a wide spectral range between 1.55 < λ < 1.85 μm is presented.
Abstract: By pumping a fiber in the anomalous group-velocity dispersion regime with a color-center laser, we generate a femtosecond distributed soliton spectrum with τ ≳ 100 fsec covering a wide spectral range between 1.55 < λ < 1.85 μm. We present a theory to explain the spectrum and use autocorrelations and cross correlations to verify the results experimentally. Modulation instability and the soliton self-frequency shift effect initiate a multisoliton collision process that results in narrow, high-intensity solitons. An ensemble average over these solitons, which start from noise and frequency shift by different amounts, yields the observed broad spectra. We use the fiber output in pump–probe experiments, measuring the exciton ionization time in InGaAs/InP multiple quantum wells for the first time to our knowledge.
145 citations
TL;DR: In this paper, the authors studied the ultrafast evolution of the surface electronic structure of the topological insulator Bi(2)Te(3) following femtosecond laser excitation.
Abstract: We discuss the ultrafast evolution of the surface electronic structure of the topological insulator Bi(2)Te(3) following a femtosecond laser excitation. Using time and angle-resolved photoelectron spectroscopy, we provide a direct real-time visualization of the transient carrier population of both the surface states and the bulk conduction band. We find that the thermalization of the surface states is initially determined by interband scattering from the bulk conduction band, lasting for about 0.5 ps; subsequently, few picoseconds are necessary for the Dirac cone nonequilibrium electrons to recover a Fermi-Dirac distribution, while their relaxation extends over more than 10 ps. The surface sensitivity of our measurements makes it possible to estimate the range of the bulk-surface interband scattering channel, indicating that the process is effective over a distance of 5 nm or less. This establishes a correlation between the nanoscale thickness of the bulk charge reservoir and the evolution of the ultrafast carrier dynamics in the surface Dirac cone.
145 citations