(1) Laser and information technologies of submicron structure formation, and production
of new optoelectronic components and base elements for the information optical systems:
- The theory and technology have been worked out for generating submicron structures at
the surface of semiconductors, metals and dielectrics. To this end, an analytical theory
has been elaborated that gave birth to the maskless multibeam technology of generating the
submicron (0.23 m m) relief at semiconductor surface. This theory made possible the studies
of diffraction of the plane electromagnetic waves, the limited light beams, and the
ultrashort light pulses on the surface relief providing a superposition of a random number
of arbitrarily oriented discrete gratings. The theory is valid under resonance excitation
of the surface electromagnetic waves (SEW) both on metals and dielectrics; it is
nonlinear regarding the amplitude of surface relief modulation, and allows for strong
multiple rescatterings of different diffraction orders. The optimum conditions have
been found for the manifestation of Wood anomalies – the phenomena of specular
reflection total suppression, abnormally high (nearly 100%) absorption of light by a
surface, and a sharp (about 20-fold) buildup of the field amplitude near a surface.
- The theory of periodic surface relief generation (with the period of the order of the
incident radiation wave length) on metals, semiconductors, and dielectrics has been
elaborated. The periodic relief is formed by a single powerful
(>106-108W/cm2) laser beam
(a) under induced generation of the resonance SEW and the surface acoustic waves
in solids in pre-melting mode;
(b) under induced generation of the resonance SEW, the surface capillary and evaporation
waves in melts. The theory has been advanced to interpret the laser induced generation
of the periodic surface microrelief in pyrolytic etching and deposition of metals,
semiconductors, dielectrics, and in photochemical etching of semiconductors exposed
to a continuous-wave laser of the power of 1W or below.
- To develop the technology of laser deposition of the submicron and nanometer films,
the laser-induced luminescence method was used in the experimental determination of
the functions of velocity distribution of the atoms and ions in the plume resulting
from ablation of a solid target under nanosecond laser pulses. It has been shown that
far apart from the target (more than 40 mm) at ablating laser radiation energy density
F=1-2 J/cm2, from 1 to 3% of the total number of particles
are in the ionized state, and the function of velocity distribution of the atoms is
characterized by the bimodal structure, i.e. a portion of particles possesses the
relatively low velocities (2-3·105 cm/s), and the other portion has the higher
velocities (5-6·105 cm/s). The high-energy particles grow in number as F
increases, and at F=5 J/cm2 they can make 40% of their total number. With the plume
expanding in the buffer gas, the effect of ion acceleration process is decreased,
and at the buffer gas density of about 0.1 Torr the particle velocity distribution
function differs from the Maxwellian function by no more than 10%. The deposition of
films on the rotating disk permitted studying the distribution of the microparticles
by their velocities. It has been shown that in laser ablation with nanosecond pulses
the scattering velocities of the microparticles (droplets) are for any target an
order of magnitude lower than those of the atoms, or the ions. Both the form of
velocity distribution functions and the distribution of the microparticles in size
allow one to conclude that the mechanism of droplet formation is governed by the
target material. A mechanism of microparticle separation has been suggested, and
a device (separator) has been produced that makes possible the deposition of the
films which are free of microparticles.
- As a result of these studies, the technologies have been developed for laser
deposition of thin films from the following materials: HTSC films,
GaAs, InGaAs, PbTe, Bi, ZrO2, SrTiO3, ZnO, and diamond-like
films. The ultrathin PbTe films exhibited the influence of the dimensional
quantization on third-order nonlinear optical susceptibility; the dimensional
quantization of conductance and the quantum Hall effect were observed in the ultrathin
Bi films. The technologies of deposition of the HTSC and diamond-like films are now
used in producing HTSC SQUIDS (jointly with the M.V.Lomonosov MSU). The multipurpose
laser-based plants have been developed for deposition of both the films and the oxides.
These plants have passed the international tender, and two of them were supplied to
Slovakia, where they have been successfully exploited for 2 years.
- With the view of producing the frequency-selective elements of the optical
multiplexers/demultiplexers, the propagation of electromagnetic waves has been simulated
in the inhomogeneous, nearly periodic media with the phase shifts for various materials,
among these are semiconductors (reflectance from 1.8 to 3.5), glass (reflectance 1.53),
and polymers (reflectance from 1.47 to 1.56). The structures of this kind have good
frequency-selective properties and can be used in the manufacture of the passive
selective devices for fiber networks. The peculiarities of the picosecond light
pulses propagation in the periodic media with varying in space parameters have also
been theoretically studied. This work resulted in the development of a narrow-band
optical filter having the shape of the reflection/transmission band close to rectangular,
and in the production of the narrow-band reflection filters for the telecommunication
wave length range of 1.5 m m, which comprise a single-mode
side-polish quartz fiber and a periodic Bragg grating located in the area of fiber
propagation mode. The filters feature the reflectance R > 98% and the close-to-rectangular
shape of the reflection band 0.4 to 0.8 nm wide. The filters can be used in the optical
multiplexers/demultiplexers as the frequency-selective elements to combine and separate
the signals in the high-bit-rate multichannel fiber-optic communication lines.
The "Report on RAS activities in 2003" reflects the significant progress of ILIT RAS
in laser and information technologies.:
The thin-film distributed-feedback lasers have been developed. A first-order-grating
Bragg resonator using InP/OnGaAs and GaAs/GaAlAs heterostructures has been produced.
A single-frequency laser of 1.5 m m range has been assembled
and tested.
(2) Laser-information technologies for remote fabrication of 3D objects and biomodeling.
This goal implied the development of the physical, chemical and information foundations
of the laser stereolithography being the technology of operative manufacturing the real
copies of the computer-designed 3D models. The new materials, software and equipment
required for this technology implementation have been developed. A small-lot production
of the plants to realize the laser stereolithography, and of the expendables for these
plants has been organized. This method has been proved to perform well in modeling and
manufacture of the structural components for machine-building and aerospace, of the
accessories for various kinds of precision casting, dies and molds.
The laser-based micron-resolution computer stereolithography has yielded the priority
results. With this purpose, the experimental and theoretical investigations have been
undertaken on the polymerization of the acrylic monomers and olygomers, and the
composites based on them; the polymerization was initiated by the pulse and
continuous-wave laser radiation. This research enabled devising the efficient
methods to calculate the molecular-mass distributions when polarization is initiated
with an arbitrary train of laser pulses, and generating the corresponding program.
These methods allow the kinetic constants of radical polymerization to be determined
from the experimentally obtained distributions. The laser photo-initiated polymerization
was located in the volume of less than 10 m m3.
As the result, in the fabricated 3D structure the minimum linear dimension of the
element made up 2.5 m m.
The Institute is currently engaged in the development of the femtosecond
nanostereolithography technology which is expected to provide for fabricating
the 3D objects with a resolution of several tens of nanometers.
A plant has been built and a technology has been developed for direct growing of
3D objects from the working material (metal, ceramics, biocompatible compositions)
by the method of layer-by-layer sintering of powders.
(3) Adaptive correction of radiation in high-power industrial lasers and in lasers
used in fundamental research.
The developed bimorph-type wave front correctors, the Shack-Hartmann wave front sensor
and the original control software were used in the adaptive optical system permitting
correction of wave front aberrations to the 6th order. The basic parameters of the
adaptive systems are: the entrance aperture – to 100 mm;
the correction range – to 15 m m; the correction accuracy – 1/10;
the corrected aberration frequency – 12.5 Hz. The employment of such a system
in the Ti-sapphire laser ATLAS, Germany (the pulses of 1.5 J energy, 130 fs duration,
and 10 Hz repetition rate) made it possible to increase the Strehl factor of radiation
from 0.1 to 0.8 and to attain the intensity density of 4·1019 W/cm19 in
the parabolic mirror focus. The irradiation of the deuterium target increased the
neutron yield per pulse a thousand times.
(4) Local modification of nanoporous and polymer materials
The new approach relies on supercritical impregnation of the organic compounds
and on nonlinear UV photolysis of the impregnated compounds. A fiber-optic
densitometer has been developed and produced to exercise the phase control of
the multicomponent supercritical media phase behavior.
(5) Processes of spatial and temporal self-organization of nanoclusters,
nanodefects, and localized structures in the condensed media
The investigation has been pursued for the sake of devising the optimum methods of
process control in solids by means of external energy flows, including laser
radiation, as well as in a view to forecast the behavior of the materials used
under extreme conditions.
In the course of these investigations, the processes of nanodefects and nanoparticles
self-organization have been simulated, and the mechanisms and conditions of the
localized states (the solitons and a concentration switching wave) excitation in
the subsystems of point defects have been found.
The above research work resulted in revealing the physical mechanism of the
formation of the nanoscopic (nanometer) spatially periodic structures of nanodefects
in the irradiated solids and in the development of an analytical model for this
process which provides for an open dissipative system self-organization under the
conditions being far from thermodynamic equilibrium. It has been found that self-ordering
of defects is mainly due to the nonlinear dynamic interaction of nanodefects with point
defects and to their diffusive mobility.
