Applied Laser Power Research Articles

A comparative study of natural stone modification by laser

Laser is a new technique for cleaning and decorative machining of natural stone, which is a brittle material. Copper vapour laser (CVL) is a suitable tool for machining without damaging the work material. Thus, this technique is suitable for the machining of different materials such as natural stone, ceramic and wood. In this study, the comparative modification of marble, serpentine, quartzite and granite with CVL technique has been investigated. Encouraging results are obtained with marble in all applied laser power ranges and in serpentine in the low power range.

Photon statistics in single-molecule fluorescence at room temperature

The fluorescence of single terrylene molecules in a crystalline host is investigated at room temperature by scanning confocal optical microscopy. Photon arrival times are analyzed in terms of inter-photon time distribution, second-order correlation function, and Mandel's Q-function. Nonclassical photon statistics is observed and a reverse intersystem crossing is detected that accelerates linearly with the applied laser power. Rate equations for the time evolution of the molecular level populations are shown to be appropriate for the analysis of the observations.

Continuous-wave two-photon excitation of individual CdS nanocrystallites

By use of low-temperature confocal microscopy, continuous-wave two-photon fluorescence images are obtained of individual CdS nanocrystallites embedded in a polymer matrix. The quadratic dependence of the emission rate on the applied laser power proves that the observed fluorescence originates from the simultaneous absorption of two photons. From the experimental data the two-photon absorption cross-section σ(2) could be determined, resulting in a value smaller than that known from literature. The work presented is a first step towards high-resolution fluorescence-excitation spectroscopy on the electronic states in the band edge, inaccessible by conventional one-photon spectroscopy.

Laser annealing of an amorphous NdFeB alloy

Amorphous NdFeB films prepared by sputtering technique were annealed by laser irradiation of a Nd:YAG pulse laser. Laser annealing yielded rapid precipitation of ferromagnetic Nd 2Fe 14B phase from the amorphous matrix. The magnetic properties and the microstructure of the annealed NdFeB materials could be controlled by the applied laser power.

Optical pumping magnetic resonance in high magnetic fields: Characterization of nuclear relaxation during pumping

The polarization of 129Xe gas by spin exchange with optically pumped Rb vapor is investigated in high magnetic field. Operation in a high field provides added spectral dispersion via Zeeman shifts of the electronic transitions. This simplifies the physics of the pumping process in such a way as to make it more amenable to treatment with simple rate theory. A relationship between the steady state 129Xe polarization and the applied laser power is derived which agrees with experimental results. This theory serves as a guide to the manufacture of very high polarizations of 129Xe gas.

Laser writing on gold-containing hydrocarbon films

Conducting metal tracings have been realized on gold-containing hydrocarbon matrix films deposited on glass by a technique combining cathodic sputtering with RF glow discharge. The metal tracings were formed as a consequence of laser irradiation of the films, based on an anomalous optical absorption property of the films at a particular laser wavelength, which generated a localized heating that decomposed the hydrocarbon matrix. The tracings were found to be continuous at a constant laser spot size of 10 mu m, and their widths varied linearly with the applied laser power. A decrease of about 15 decades in the resistivity due to the resultant tracings was observed, making the conductivity close to that of the pure metal. Auger spectroscopy analysis of the tracings has shown that the hydrocarbon component was completely eliminated from them. Furthermore, the thermal stability of the material allowed its realization in ambient conditions.

Laser Induced Phase Transformations in Thin Insb Films

ABSTRACTThin In46Sb54 films have been prepared on glass substrates by flash evaporation. Films of 1000 Å were deposited at room temperature. After 7 mins' thermal annealing at 450ºC, an average grain size increased from 20 nm to 200 nm. Under exposure to a Fraunhofer diffracted pulsed Nd-YAG laser beam, the films showed different microstructures for different applied laser power. In general, five regions are identified: ablation region, regions with grain sizes less than 20 nm, grain sizes ranging from 400 to 1000 nm, grain sizes ranging from 200 to 400 nm and unchanged region. The previous five regions are counted from the center of the exposed area outward. The pulse duration is 16 ns. In this paper, an atomic migration mechanism is proposed to explain the power dependent microstructures changes. Transmission electron microscopy was mainly used to characterize the films. The application of this type of phase transformations in the phase change optical storage is also discussed.

Photodeposition sputtering of titanium and TiN thin films

The interaction of any energy-carrying beam with solids leads to the degration of the solid crystals. The bombarded surface is sputtered and many effects on the atomic, microscopic and macroscopic scales can be observed. Very few experiments have been performed on the photodeposition sputtering of thin films, and the results obtained have been attributed to a variety of processes. In this work the results of the sputtering of and the morphological changes in titanium and TiN thin films induced by a point-focused neodymium-doped yttrium aluminium garnet laser beam are presented. The morphological changes, the shape and the size of the damaged area as functions of the laser beam density and the film thickness were investigated by scanning electron microscopy and profilometry studies. The results of the laser-induced damage have shown that the applied laser power density (in the range from 2 × 10 7 to 9 × 10 9W m −2) and the film thickness (from 22 to 2200 nm) were two very important parameters which strongly influenced the growth of the damage (exfoliation, hydrodynamic and thermal effects). The sputtering yield is a function of the laser beam power density. Its value increases with increasing power density and after reaching a maximum begins to fall owing to the plasma screening effect of the target.

Photostability studies of phycobiliprotein fluorescent labels

Photostability studies of four fluorescent phycobiliproteins were conducted to identify stable chromophores for biological labeling applications. Phycobiliprotein photodestruction was linear with the applied laser power and depended on the total number of photons absorbed per molecule. Photodestruction quantum yields φ of 1.1 × 10 −5 for R-phycoerythrin, 6.6 × 10 −6 for B-phycoerythrin, 4.5 × 10 −6 for allophycocyanin, and 2.5 × 10 −6 for C-phycocyanin were measured. C-Phycocyanin is a factor of 10.8 more photostable than fluorescein. The photostability of R-phycoerythrin was improved by a factor of 1.7 by adding n-propyl gallate. The addition of superoxide dismutase, catalase, sodium dithionite, ascorbate, dithiothreitol, EDTA, or deoxygenation with argon bubbling had no effect on the photostability of R-phycoerythrin.

Fabrication of channel optical waveguides in glass by cw laser heating

By focusing the 488-nm line of an argon-ion cw laser beam with the aid of a microscopic objective on the surface of a moving piece of highly absorbing glass, low-loss channel optical waveguides at longer wavelengths are produced. At the laser beam focal point, glass is evaporated, producing grooves 2–8 μm wide. Strong confinement of light was observed beneath the grooves. An explanation for the occurrence of waveguiding is given together with experimental data on waveguide width as a function of applied laser power and sample speed. This method allows us to fabricate channel waveguides possessing periodic structure for frequency-selective guiding.