1,720,991 research outputs found
Wavelength flipping in laser emission driven by a switchable holographic grating
No full textWe report lasing from a simple wafer structure made of a thin layer of rhodamine 6G as active material and of a switchable holographic mirror, based on a reflection grating made of polymer dispersed liquid crystals. It is shown that switching-off the mirror reflectivity by application of a suitable voltage allows wavelength flipping of the laser emission by 10 nm
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Large scale indium tin oxide (ITO) one dimensional gratings for ultrafast signal modulation in the visible spectral region
Full text linkIndium tin oxide (ITO) is a heavily doped semiconductor with a plasmonic response in the near infrared region. When exposed to light, the distribution of conduction band electron induces a change in the real and imaginary parts of the dielectric permittivity. The coupling of the electromagnetic waves with the electrons in the conduction band of metallic nanostructures with ultrashort light pulses results in a nonlinear plasmonic response. Such optical modulation occurring on ultrafast time scales, e.g. picosecond response times, can be exploited and used to create integrated optical components with terahertz modulation speed. Here, we present a photophysical study on a one dimensional ITO grating, realized using a femtosecond micromachining process, a very industrially accessible technology. The geometries, dimensions and pitch of the various gratings analyzed are obtained by means of direct ablation in a controlled atmosphere of a homogeneous thin layer of ITO deposited on a glass substrate. The pitch has been selected in order to obtain a higher order of the photonic band gap in the visible spectral region. Femtosecond micromachining technology guarantees precision, repeatability and extreme manufacturing flexibility. By means of ultrafast pump-probe spectroscopy, we characterize both the plasmon and inter-band temporal dynamics. We observe a large optical nonlinearity of the ITO grating in the visible range, where the photonic band gap occurs, when pumped at the surface plasmon resonance in the near infrared (1500 nm) region. All together, we show the possibility of all-optical signal modulation with heavily doped semiconductors in their transparency window with a picosecond response time through the formation of ITO grating structures
Holographic polymeric materials for optical processing: Microlasers, data storage and all optical switching
No full textWe report on recent research in the field of optical processing with microlasers, high density optical storage media and all-optical switching devices. By combining different materials and optical holography some devices which show attractive optical properties and interesting wide range of potential applications will be presented
Detailed investigation of high-resolution reflection gratings through angular-selectivity measurements
No full textWe performed an investigation on Bragg reflection gratings recorded in blue-sensitive holographic polymer dispersed liquid crystals. The use of a position-sensitive detector allows selective measurements of the reflected light, never before reported in these materials, to our knowledge. We can show that by using this experimental technique it is possible to detect the formation of multiple gratings, even when the transmission spectrum does not show multiple peaks. The results are discussed in the frame of existing coupled-wave theory for anisotropic materials, allowing us to obtain the optical characterization of the gratings
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