We have discovered that if input grating coupler is used to excite SEW the generated wave is differed essentially from
SEW. This wave is conventionally named "pressed wave" by us. We examine the evolution of wave field with distance
from input grating coupler and compare that with analogous dependence for SEW. It is shown that unlike SEW the
intensity of pressed wave decreases not exponentially while it propagates along the surface. Also we have got that the
pressed wave field profile is modified as it propagates along the surface.
The formation of blind narrow channels in polymethylmethacrylate (PMMA) volume under the action of one pulse of TEA CO2 laser radiation hues been discovered and experimentally studied. An existence of three distinctive regimes of laser-polymer interaction in different power density ranges due to an influence of plasma formation at low threshold nearsurface optical breakdown was shown. The formation of spherical type micro damages in a near surface layer of polymer produced due to local volume boiling were observed.
To study the material mechanisms of laser-induced silicon microrelief formation the periodic space-modulated heating up to melting point was used. On the basis of measurements of dynamics of surface thermal radiation and of the relief height the conclusion about material mechanisms of relief formation had been made.
Experimental studies of the laser element's radiation strength show that optical damage of transparent dielectrics may be accompanied by the formation of surface periodic structures (SPS). SPS with ripples oriented normally to the strength vector of the incident electric field were found on the output surface of a dielectric plate (alkali- halide crystal) under focusing near or middle IR laser radiations of a microsecond duration. This relief was assumed to arise from heating caused by interference between the incident light and the wave scattered from the surface defects on the assumption that scattered wave represents a rapidly decreasing field of the Coulomb type. More correct SPS model developed by V. S. Makin proposes participation of surface electromagnetic waves (SEW). As known, optical damage is accompanied by the development of plasma flash. When emission of electronics from solid surface is strong, the plasma dielectric constant runs out to be negative with its modulus exceeding the dielectric constant of the transparent medium. This causes the generation conditions for SEW to be fulfield on the dielectric-plasma boundary, which results in interference between the incident light and SEW, thus leading to formation of SPS. The model explains reasonably well, why these SPS can be observed only on the output surface when developing plasma produces no screening effect on the surface. For CO2 laser irradiation, the necessary electronic concentration is high but reasonable value and amounts about 1019 cm-. However, SPS formed by the short-wavelengths radiation cannot find correct explanation in the framework of this model, since electronic concentration at the wavelengths (lambda) equals micrometers should be no less than 1021 cm-3 in this case.
Possible mechanisms of formation of interference surface periodical structures (SPS) in the case
of optical damage of transparent media are discussed. Such structures were discovered many years ago,
when the action ofpulsed laser radiation ofmedium infrared and near infrared on alkali-halide and
semiconductor crystals. The period of SPS, for normal incidence of the radiation on dielectrics is equal
approximately to light wavelength in the dielectric. In this case the structures are formed on exit surface
preferably and their ripples are orientated perpendicular to light field.
Limitations of known models of phenomenon are examined (for example, ideas based on either surface
quasi-stationary dipoles or surface polaritons on dielectric boundary) when surface-active medium is
either a gas damage plasma or an erosion plasma oftarget material.
In this work the author proposes a model for SPS formation based on laser generation of waveguide modes
in a subsurface layer of dielectric materials. Thermo-optical changes of refraction index due to subsurface
heating are considered as the main cause of the induced waveguide. The theoretical analysis takes
into account the difference between light field distributions near the entrance and exit surfaces of a
sample.
The regular structures formation on a silicon surface under the millisecond pulse of linear- polarized, circular-polarized and unpolarized Nd-laser light irradiation has been studied experimentally. The surface structures induced by the interference of incident wave and surface electromagnetic waves and also the double- and triple-period structures with periods d equals 2 - 3 microns were observed in the nonhomogeneous melting regime. The diffraction pattern separation at higher incident fluence and incident angles have been observed. The main peculiarities of the surface structures formation were explained by polaritonic mechanism.
The regular structure formation on a silicon surface under the millisecond pulse of linear-polarized Nd-laser light irradiation has been studied experimentally. The surface structures induced by the interference of incident wave and surface electromagnetic waves and also the double-period structures with periods d — 2-3 microns were observed in the nonhomogeneous melting regime. The double-period structures formation was explained by polaritonic mechanism and was due to a nonlinear absorptance changes in semiconductor-metal phase transition.
The basic concepts of surface electromagnetic waves (SEWs) in the optical band, the unique features of their excitation by light at the boundary of condensed media, and the participation of SEWs in the
formation of periodic structures and other photophysical processes that occur on surfaces due to the influence of high-intensity laser radiation are presented. The use of middle infrared SEW for measuring optical characteristics of materials is considered. A method, developed by the authors, for measuring the real part of the SEW wave vector to obtain metal plasma frequency directly, is presented.
Experimental investigation of ordered and disordered surface structure formation under the pulse laser radiation effect of titanium and zirconium metal surfaces primary in oxidizing environment are presented. A model for qualitative explanation of formed structures is proposed. The occurrence of dilate stress fluctuation will induce the vacancy concentration growth that consequently results in tensile stress growth.
Heterodyning surface electromagnetic wave (SEW) interferometer for measuring SEW phase velocity and the corresponding metal plasma frequency is described. Plasma frequency measurements for gold and copper are reported.
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