Search results for "laser"
showing 10 items of 3161 documents
Floating Zone Growth of Silicon
2015
Abstract The floating zone (FZ) technique changed from a crucible-free purification method into a growth technique mainly for high purity silicon crystals. The melt zone is inductively heated by the high frequency magnetic field of a sophisticated one-turn induction coil being the heart of the FZ growth. The needle-eye technique allows for crystals with large diameters beyond the capillary limitations of a cylindrical zone, but both electric breakthrough at the coil slit and bursting of the crystal by thermomechanical stress presently limit the diameter to 200 mm. A novel gFZ concept is depicted that works with granular silicon feedstock instead of expensive feed rods. The automation of the…
Surface acceleration during dry laser cleaning of silicon
1999
We report on measurements of the surface acceleration for the application of dry laser cleaning. For that purpose, industrial silicon samples were irradiated by a frequency-doubled Q-switched Nd:YAG laser. The surface displacement was measured by a heterodyne interferometer and recorded by a digital storage oscilloscope. Several hundreds of shots were averaged to give smooth displacement curves which could be derived numerically. The experiments show that the highest accelerations, which are thought to be responsible for the cleaning, occur on the time scale of the laser pulse. Simple theoretical models are in good agreement with the experimental data. The maximal displacement depends only …
Visible luminescence peculiar to sintered silica nanoparticles: Spectral and decay properties
2015
We report that the sintering at 1000 degrees C of silica nanoparticles (an average diameter of 14 nm) produces a transparent sample that exhibits a bright visible emission under UV excitation. The use of time resolved luminescence spectroscopy and a tunable laser source allows us to single out three contributions centered at 1.96 eV, 2.41 eV and 3.43 eV. The excitation spectra of these emissions evidence bell shaped bands consistent with transitions between localized defects' states. For each emission we study the intensity and the lifetime in the temperature range from 300 K down to 10 K, thus evidencing the competition between radiative and non-radiative processes in the optical cycle of …
Investigations of As-S-Se thin films for use as inorganic photoresist for digital image-matrix holography
2011
AbstractAs-S-Se chalcogenide thin films are successfully employed in classical and dot-matrix holography as inorganic photoresists for obtaining a relief-phase hologram. However using these films for image-matrix hologram recording has not been studied due to some features of image-matrix technology. For the applied research of the optical properties of As-S-Se films an experimental device of digital image-matrix holographic recording based on 100 mW 405 nm semi-conductor laser and Spatial Light Modulator (SLM) has been created. The device has the following main parameters: 140 × 105 µm frame size; laser intensity during exposure 10 W/cm2. With the help of this device diffraction grating an…
First results of cavity ring down signals from exhaled air
2017
In this paper we report first results from the developed cavity ring-down spectrometer for application in human breath analysis for the diagnostics of diabetes and later for early detection of lung cancer. Our cavity ring-down spectrometer works in UV region with pulsed Nd:YAG laser at 266 nm wavelength. First experiments allow us to determine acetone and benzene at the level bellow ppm. In our experiment, first results from breath samples from volunteers after doing different activities were collected and examined. Influence of the smoking on the breath signals also was examined.
Identification Techniques I
2012
Infrared (IR) and Raman spectroscopy have a high potential for characterisation of material. Extensive series of wet chemical analysis may be substituted by a single spectroscopic measurement followed by detailed chemometric data evaluation. Topics of this chapter are: (i) basics of IR and Raman spectroscopy, (ii) the registration of “correct” spectra, and (iii) spectra evaluation. Dedicated applications in the area of conservation science are collected in separate chapters. The infrared (IR) spectrum is often called the fingerprint of a substance. An IR spectrum identifies a substance like a human fingerprint. Due to their origin the features of an IR spectrum are bands, not peaks. They in…
A review of the development of portable laser induced breakdown spectroscopy and its applications
2014
Abstract In this review, we present person-transportable laser induced breakdown spectroscopy (LIBS) devices that have previously been developed and reported in the literature as well as their applications. They are compared with X-ray fluorescent (XRF) devices, which represent their strongest competition. Although LIBS devices have advantages over XRF devices, such as sensitivity to the light elements, high spatial resolution and the possibility to distinguish between different layers of the sample, there are also disadvantages and both are discussed here. Furthermore, the essential portable LIBS instrumentation (laser, spectrograph and detector) is presented, and published results related…
Spin-polarized photoelectrons resonantly excited by circularly polarized light from a fractional Ag film on GaAs(100)
2013
We demonstrate a finite spin polarization of photoelectrons emitted from GaAs(100) covered by a fractional Ag film. The photoemission yield shows a sharp maximum for intermediate coverage and the spin polarization increases with increasing laser intensity. Photoelectrons are excited by circularly polarized 100 fs laser pulses of 800 nm wavelength. We recorded the photoemitted electrons using a photoemission electron microscope combined with a Mott spin polarimeter. The spin polarization is analyzed in dependence on the excitation frequency and intensity and on the average thickness of the silver film. The results are explained by a model combining multiphoton photoemission and optical field…
Generation of broadband THz transients via metallic spintronic emitters driven by 20-fs pulses at 1030 nm
2020
We explore power and bandwidth scaling for the generation of highly-temporally-confined THz transients from spintronic emitters, driven by the 250-fs and 20-fs pulses of a high-power 28-MHz Yb-based laser, spectrally centered at 1030 nm.
Some morphologic changes induced by Nd:YAG laser on the noncoated enamel surface: A scanning electron microscopy study
1992
The enamel surface layer of some human teeth was treated with the low-energy Nd:YAG laser at 8 mJ pulse energy. These samples were previously etched with 0.05 M orthophosphoric acid to reduce the surface reflection. The treated samples, as well as the control samples, were widely studied by scanning electron microscopy, and, in the lased group, significant morphologic changes affecting the enamel surface were observed. Those changes reveal principally the loss of the typical surface structure of the acid-etched enamel. The hydroxyapatite prisms were not discernible, and there was a decrease in the roughness of the lased surface enamel. These laser-induced structural changes may be related t…