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Multiconnected Waveguides for Laser Radiation Focusing

#0759


Development and Application of Multiconnected Waveguides in the Problems of Laser Radiation Focusing onto the Areas of Subwavelength Dimensions

Tech Area / Field

  • INF-SIG/Sensors and Signal Processing/Information and Communications

Status
3 Approved without Funding

Registration date
01.10.1996

Leading Institute
Institute of General Physics named after A.M. Prokhorov RAS, Russia, Moscow

Supporting institutes

  • VNIIEF, Russia, N. Novgorod reg., Sarov

Project summary

The proposed project is directed to experimental investigation of the possibility of application of multiconnected waveguides in solution of the problems of focusing laser radiation onto the areas of subwavelength dimensions. The principle difference between multiconnected waveguides and uniconnected waveguides is following. Waveguide with conductive walls and uniconnected form of cross - section channels radiation with a wavelengths, which are not more than 2pa, where ‘a’ is the transverse dimension of the waveguide. For multiconnected waveguides this restriction on wavelength can be violated, with generation of so - called fundamental wave excited in the waveguide, which exists in this waveguide together with wavelength, which are similar to those ones in the uniconnected waveguide. Electric fields’ distribution over transverse cross - section of waveguide is corresponding to a flat electrostatic field between capacitors plates, which have different potentials. Waveguides with multiconnected transverse cross - section with dimension significantly smaller than the wavelength is well known in the microwave engineering. The application of these waveguides in the optical range is also possible. The discussed class of waveguides may be used as electromagnetic radiation concentrator on the areas with sub wavelengths dimensions.

In this project it is proposed to use the biconical trumpet as multiconnected waveguide. In this trumpet, composed of conductive surfaces, which cross - section by a spherical surface with a center of curvature in the common vertex of cones forms the doubly connected region, transverse spherical wave can propagate. The waves phase velocity is independent on the frequency and is equal to the velocity of light in free space, the group velocity equals to the phase velocity, the waveguide dispersion is absent. The characteristics of metal cones in skin - layer restricts the pulse duration, which is channeled without distortion. The spherical absorbing surface must be placed in the common point of the cones for eliminating electromagnetic wave reflection from this region.

The oscillating circuit made from lumped capacitance and inductance with wave resistance, equal to the wave resistance of biconical trumpet, may be proposed for use as nonreflecting load. Objects, whose behavior is assumed to be studied under high intensities of the optical fields, can be placed at the convergence point of the cones, which the biconical trumpet with absorbing sphere made of, or at capacitance and inductance, if the trumpet is connected with quasistatical network in the form of oscillating circuit.

The trumpet will fail with high power of supplied optical radiation. Nevertheless, formed plasma will possess necessary high conductivity and the trumpet will channel optical radiation, as long as expanded plasma overlaps the cross - section of waveguide. The short pulses have time to spread through trumpet. With the subsequent increasing power of radiation, plasma fly away will be kept by pressure of electromagnetic field.

As this biconical trumpet has cross - section in the base region with dimension, approximately equal to the wavelength and in vertex region ever much less one, the trumped must be fabricated by means of microtechnology.

In this way, proposed projects works will be fulfilled in the following directions:


- Theoretical analysis of the distribution of electromagnetic waves field in biconical trumpet, search of necessary bicones geometry, materials, skin layers thickness.
- Theoretical research of conditions of bicoaxials walls destruction, parameters of formed plasma and its influence on radiation channeling.
- Design and fabricating of biconical trumpet by means of microtechnology.
- Developing of facilities for input/output of optical radiation from bicone (absorbing loading, oscillating circuit, adapters with wave resistance, equal wave resistance of bicone).
- Diagnostics of focused optical radiation.

Technical approach and methodology

The reality of the project realization is based on following methods, developed in VNIIEF and IOFRAN:


1. The experimental apparatus for laser plasma diagnostics is developed, which allows to make measurements in the wide range of plasma parameters.
2. The matching facilities for optical radiation propagation in optical channel and its output from optical system is developed.
3. The reliable method set for optical radiation parameters diagnostics is developed.
4. The high technological levels of manufacturing, control and metrology of submicrometer structures and devices are reached.
5. The set of methods for high-resolution microscopy is developed.
6. The works will be done by scientists, who have large experience of theoretical and experimental investigation in the fields of waveguides theory, laser physics, plasma physics, radiation/matter interaction, microelectronic technology, optical and electron microscopy.

The theoretical analysis of the biconical trumpet radiation characteristics will be done on the basis of solutions of the Maxwell equations with corresponding boundary conditions on perfect conductors surface for the area between two cones with common point of the vertex.

The selection of trumpet material and geometry, as well as radiation characteristics (pulse duration at first) will be done on the basis of previous item computation results.

The theoretical investigations of trumpet destruction process under high radiation density will be done on the basis of laser plasma generation models and its interaction with radiation.

The project realization and biconical trumpet fabrication technological route development will be done on the basis of author’s experience in microelectronic device fabrication. Standard microelectronic technological equipment will be used for trumpet fabrication.

The optical radiation input to trumpet and its propagation through nonreflecting load will be done on the basis of well-developed methods.

The focused optical radiation diagnostics will be done on the basis of project authors developed reliable methods.

The large experience of laser equipment exploitation provides laser setup reliable work with stabilized parameters of laser radiation.

Expected results

Authors are planning to obtain as result of conducted investigations:


1. Radiation characteristics on biconical trumpet output, trumpet parameters (materials, geometry), pulse duration restriction from the point of view skin-layer thickness in comparison with bicone wall thickness.
2. Theoretical and experimental estimation of plasma generation characteristics in bicone destruction and plasma/radiation interaction characteristics.
3. To develop the technological route (set of technological documents) for manufacturing the conical surfaces with variable cross - section and submicrometer dimensions.
4. Modified setup for evaporation of metals (Ta, Ni, Ti, Cr) and dielectrics (SiO2, Si3N4) thin layers with varying thickness (0.1-0.5 mm) and arbitrary space orientation.
5. To develop the technological route (set of technological documents) for making varying thickness (1 - 10 mm) silicon membranes as biconical trumpet base.
6. To develop technological route for production of nanoobjects for focusing effects diagnosis with using of microlithography and electrochemical deposition (set of technological documents and samples of nanoobjects).
7. To develop, design and fabricate the system for precision alignment bicone and diagnostics objects on basis microcoordinate table with piezodrives.
8. The developed units for optical radiation input/output from bicone (absorbing load, oscillating circuit, adapters with wave resistance, equal to bicone wave resistance).
9. The results of diagnostics of optical radiation parameters at the bicone output. The results of two series of experiments for investigation of possibility for localizing and concentrating radiation onto small areas and application of this effect for a) optical microscopy, b) high intensity optical fields.

In future the results of the Project can be used for:


- creation of a point sources of radiation with increased luminosity;
- creation of high intensity optical fields;
- development of methods of a selective photostimulated deposition of films;
- development of microlithographic image generators with submicron element sizes;
- increase of record density on optical data storage media;
- essential increase of record duration on compact discs;
- development of a new class of photoelectric near-field scanning microscopes with increased resolution on the basis of bicone trumpet.

Participants of Project are open to collaboration with Western and Japanese organizations.


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