Search results for "WAVELENGTH"
showing 10 items of 741 documents
High frequency microwave signal generation using dual-wavelength emission of cascaded DFB fiber lasers with wavelength spacing tunability
2010
[EN] A dual wavelength fiber laser source based on two cascaded phase-shifted fiber Bragg gratings is presented The gratings are written in an erbium-doped fiber each configuring the cavity of a distributed feedback fiber laser The spacing between lasing modes is controlled dynamically by the use of piezoelectric actuators A continuous tuning range of 5-724 pm of the wavelength difference which is equivalent to a photodetected 072-92 GHz range is obtained Efficient generation from the L to the W microwave and millimeter bands has been achieved by heterodyne photodetection of the dual-wavelength optical signal (C) 2010 Elsevier BV All rights reserved
Plano-concave microlenses with epsilon-near-zero surface-relief coatings for efficient shaping of nonparaxial optical beams
2017
Abstract Epsilon-near-zero (ENZ) materials, including artificial metamaterials, have been advanced to mold laser beams and antenna-mediated radiated waves. Here we propose an efficient method to control Ohmic losses inherent to natural ENZ materials by the assembly of subwavelength structures in a nonperiodic matrix constituting an ENZ metacoating. Implemented over plano-concave transparent substrates whose radius can be of only a few wavelengths, ENZ surface-relief elements demonstrate to adequately shape a plane wave into highly localized fields. Furthermore, our proposal provides an energy efficiency even higher than an ideally-lossless all-ENZ plano-concave lens. Our procedure is satisf…
Creating Defined 3-D Defects Inside an Opaline Ormocer® Matrix with Two-Photon Lithography
2007
The creation of defined structures inside a synthetic opal is a key step toward applications in optics, where control of the propagation of light inside a photonic crystal is necessary. In a previous paper, we described the nanostructuring of Ormocer® to form inverse opals (Lange et al., Macromol. Rapid Commun. 2006, 27, 1746). Here, we report an application for this robust replica process in which defects can be directly produced within the PC by two-photon lithography. The holes of an inverse opal structure are first filled with a resin of similar refractive index. In this transparent material, polymerization can be initiated at defined places via two-photon lithography. After removal of …
Nd:KGW Laser under Flashlamp-pumping at Repetition Rate up to 50 Hz and Average Power of 70 W (free-lasing and Q-switched mode)
1997
The laser performance of Nd:KGd(WO4)2 crystal or Nd:KGW has been studied under flashlamp-pumping in the free-running and Q-switched mode (with active or passive Q-switching) at repetition rate up to 50 Hz. Maximum output powers respectively of 70 and 30 W were achieved at 1.06 pm with a maximum efficiency of 6%. Free-running emission was also obtained at 1.35 pm with a maximum average power of 24 W and a total efficiency of 2.9% at this wavelength. A comparison with a similar Nd:YAG crystal is given showing a noticeable advantage for Nd:KGW.
Evaluation of the influence of light-curing units on the degree of conversion in depth of a bulk-fill resin.
2020
Background It is known that bulk-fill have been widely studied and used by dentists in the clinic. However, the use of light-curing units that do not have the ability to adequately light-cure these materials at the appropriate depth can affect their clinical performance. The aim of this study was evaluating the influence of 5 different light curing units (LCUs) on the degree of conversion (DC) of a bulk-fill resin at depths of 0 to 4 mm and determined the effect of using 20s exposure and 40s. Material and methods Cylinders of composite were made in a stainless steel matrix (n=10). The specimens were exposed from the top surface using 5 LCUs: Valo® Cordless (VA); Radii Plus (RA); Emitter.D (…
Heavy Metals in Mollusc Shells: A Quick Method for their Detection
2015
It is known for a long time that calcified tissues secreted by aquatic or terrestrial invertebrates – such as mollusc shells – have the ability to concentrate large amounts of pollutants, in particular heavy metals. In the present paper, we have found an extremely rapid and easy procedure to qualitatively detect the putative presence of heavy metals in shells, without having to use sophisticated techniques such as Wavelength Dispersive Spectroscopy, atomic adsorption spectroscopy or ICP-MS. Our method rests on the capacity of the silver enhancement chemicals that are traditionally used in immunogold localization experiments to increase the size of heavy metal nanoparticles, whatever the che…
Thermal effects of continuous laser treatment on Ti-6 Al(wt%)-4V(wt%) titanium alloy
2008
A titanium alloy Ti-6 Al(wt%)-4V(wt%) was treated in air by Nd:YAG laser radiation (wavelength of 1.064 %m) in continuous mode. Targets were irradiated globally with different levels of energy (accumulated fluence) at constant power. Different focal lengths and beam displacement velocities were used. Cross section microstructural observations were carried out by scanning electron microscopy. Backscattered electron imaging reveals microstructural modifications in samples. A structural phase transformation of beta (bcc) to alpha prime (hcp) phase was observed. The depth of the transformed zone observed by phase transformation is dependent on the treatment parameters. Conformity between micros…
Polarization insensitive wavelength conversion of 40 Gb/s DPSK signals in a silicon germanium waveguide
2015
We demonstrate polarization insensitive FWM-based wavelength conversion of 40Gb/s DPSK signals in a SiGe waveguide, with 0.42-dB polarization-dependent loss. A 1.5-dB Dower nenaltv was measured at a BER of 10−9.
Holographic Recording of Surface Relief Gratings on As40S60-xSex Thin Films
2015
The studies of direct holographic recording of the surface relief gratings on amorphous As40S60−xSex thin films are presented. These gratings were created upon exposure to polarized laser beams of various wavelengths (λ = 473 – 650 nm). The orthogonally ±45° linearly polarized light beams were used for recording. The surface structure of the relief gratings was investigated by atomic force microscopy. The influence of laser beam wavelength and spatial frequency of the gratings recorded (grating period ?) on the surface relief gratings formation for every composition was examined.
Impact of pump wavelength on terahertz emission of a cavity-enhanced spintronic trilayer
2018
We systematically study the pump-wavelength dependence of terahertz pulse generation in thin-film spintronic THz emitters composed of a ferromagnetic Fe layer between adjacent nonmagnetic W and Pt layers. We find that the efficiency of THz generation is essentially at for excitation by 150 fs pulses with center wavelengths ranging from 900 to 1500 nm, demonstrating that the spin current does not depend strongly on the pump photon energy. We show that the inclusion of dielectric overlayers of TiO2 and SiO2, designed for a particular excitation wavelength, can enhance the terahertz emission by a factor of of up to two in field.