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Light-Induced Electromagnetic Responses of Doped Polar Crystals

#A-695


Light-Induced Electromagnetic Responses of Doped Polar Crystals: New Methods and Tools for Diagnostics of Radiation and Media

Tech Area / Field

  • PHY-OPL/Optics and Lasers/Physics
  • PHY-SSP/Solid State Physics/Physics

Status
3 Approved without Funding

Registration date
12.03.2001

Leading Institute
Institute for Physical Research, Armenia, Ashtarak-2

Supporting institutes

  • Institute of Applied Problems of Physics, Armenia, Yerevan

Collaborators

  • Magnon, Inc, USA, MD, Reisterstown\nUniversidad Autonoma de Madrid / Facultad de Ciencias, Spain, Madrid\nUniversitat Paderborn , Germany, Paderborn\nLucent Technologies/Bell Labs Innovations/Optical Networking Group, USA, New Jersey\nBIOLASE Technology,Inc/ Dental, Aesthetic and Surgical Lasers, USA, CA, San Clemente

Project summary

The goal of the project is development of new methods and physical principles of operation of devices for determination of parameters of doped ferroelectric crystals and characteristics of radiation, based on research of mechanisms of the origin of electromagnetic responses in such materials upon optical excitations, resonant to absorption bands of impurity ions.

1. Introduction and overwiev
The electromagnetic responses of doped ferroelectric (polar) crystals to optical excitations, resonant to absorption bands of impurity ions, arise because of light-induced change of a macroscopic spontaneous polarization of the material, caused by the following main mechanisms:
1. Non-radiative relaxation of a part of absorbed energy of optical excitation in the phonon reservoir of a matrix (pyroelectric mechanism).
2. Change of electronic dipole moment of impurity ion upon transitions between different energy levels of impurity center (impurity mechanism)
3. Displacements of equilibrium positions of ligands and impurity ion itself under electronic – vibrational transition of impurity center (deformation mechanism).
Pioneering works of A.M. Glass and co-authors, devoted to the research of light-induced electromagnetic responses (LIEMR) in LiNbO3 and LiTaO3 crystals doped by Cr3+ and Cu2+ ions, have already demonstrated great potential for the application of such technique. So, for example, ultrashort (picosecond) and powerful (several amperes) electric pulses were obtained in an impurity subsystem of these crystals by "optical rectification". The quantum yields of radiation from different energy levels, the change of electrical dipole moments of the impurity centers at optical transition, and the lifetimes of the impurity levels were determined. However, as the investigated impurities belonged to the iron group transition metal ions with the electronic configuration 3dn, only the total contribution of mechanisms 2 and 3 has been estimated in these works because of a strong interaction of an optical electron of the impurity with the crystalline field.
The LIEMR of ferroelectric crystals of lithium niobate (LN), doped with the rare-earth (RE3+) and iron group transition metal ions, has been studied by the authors of the presented project. A number of new results is obtained, permitting separate research of the above mechanisms.
A new effect, a “light-induced piezoelectric effect”, in doped polar crystals has been predicted and theoretically investigated. It is shown that an optical excitation of impurities produces a deformation of crystal lattice, which results in a contribution to the macroscopic polarization of polar crystals owing to the direct piezoelectric effect. The deformation tensor and corresponding contributions to the macroscopic polarization of some polar crystals upon optical excitation of impurities have been calculated.
Within the framework of approximation of the point charge crystal field theory, the theoretical approach was developed for calculations of electrical dipole moments of RE3+ ions in different states.
An experimental setup was assembled and tested for such investigations, and a technique of contactless measurements was realized. The studies of kinetic and spectral dependencies of LIEMR of LN crystals, doped with the RE3+ (Nd3+, Er3+) and iron group transition metal (Cr3+, Ni2+) ions have revealed the value of such an approach, not only for obtaining main spectroscopic characteristics of the materials. They have also enabled experimental determination for values of such important parameters as polarizability of the impurity ion, its distribution in crystals, relaxation times of charge carriers in a conduction band of the crystal, period and domain sizes of periodic domain structures, etc.
Effect of the proposed project on progress in the given area:
Project work is directed towards filling gaps in the comprehension of the physical nature of electromagnetic fields, arising upon resonance excitations of impurity ion energy levels in non-linear crystals of polar classes.
Revealing the regularities and relations between experimentally observable responses and physical processes responsible for their generation will allow the development of alternative research techniques for the doped polar media and fundamentals of operation of an essentially new type of apparatus, for definition of parameters of the medium (spectroscopic characteristics, thermal, pyro - and piezo-electric constants, polarizability of impurity ions, impurity distribution in crystals, parameters of periodic domain structures, etc.), and characteristics of the exciting radiation (wavelength, intensity, duration, etc.).
The proposed research will promote the creation of quantum electronics and integral optics apparatus on the basis of bulk or wave-guide structures with a higher scale of integration of different devices “all in one crystal” (active medium, frequency doubler, detector, etc.). They will find applications in systems of optical communication and remote sensing, devices for recording and storage of information, for effective converters of optical pulses to electrical signals, etc.

The competence of the project participants:
Qualification of the main performers of the project is high; they have worked many years in laser physics and nonlinear optics, optical (including laser) spectroscopy, and they have wide experience of work with various sources of laser radiation. The qualification of the participants is partially reflected in the detailed publications.
The successful performance of the project is stipulated by the experience and a number of new results, obtained by staff involved in the field of the proposed project.

Expected Results and their Application:
· Revealing the role and contributions of different mechanisms of physical processes resulting in LIEMR, on the basis of detailed theoretical and experimental research.
· Development of the physical principles of operation of the apparatus for definition of parameters of doped ferroelectric crystals (spectroscopic characteristics, thermal, pyro- and piezo-electric constants, polarizability of impurity ions, impurity distribution in crystals, parameters of periodic domain structures, etc.).
· Development of the physical principles of operation of the apparatus for measurement of the characteristics of incident radiation (wavelength, intensity, polarization, duration, etc.).
· Revealing advantages and enlargement of possible fields of application of the contactless technique of measurements by use of the LIEMR.
The results expected during the course of the project will be both unique and significant. They will have not only relevant scientific value, but will also represent definite economic, commercial and industrial concern, by way of their usage for creation of new methods of spectroscopic measurements and high technologies, for development of scientific equipment for simultaneous diagnostics of the medium and radiation parameters.

Meeting ISTC Goals and Objectives

The project meets the purposes of the ISTC, and its execution will allow:


· The redirection of special equipment and highly qualified scientists towards the solution of peaceful problems;
· The consolidation of both fundamental and applied research and technological developments for civil purposes;
· Integration of scientists and engineers with knowledge and skills related to weapons into the international scientific community;
· A contribution to the solution of national and international technical problems;
The above-mentioned will be exhibited in production and application of scientific and technological novelties of IPR of NAS of Armenia, both in Armenia and neighboring countries, which will help in the solution of social and economic problems of Armenia and these countries.

Scope of Activities
The project is planned for 24 months and includes:
1. Growth and manufacturing of samples of LiNbO3 crystals doped with impurities of both rare-earth (Nd3+, Er3+, Yb3+ and Tm3+) and iron group transition metal ions (V, Cr, Ni, Cu), and with periodic domain structures.
2. Investigation of spectroscopic characteristics and research of spectral, kinetic, polarization, concentration and temperature dependencies of LIEMR of doped LiNbO3 crystals.
3. Experimental study of the light-induced piezoelectric effect and its possible applications.
4. Development of the quantitative theory of LIEMR arising under resonant optical excitation of impurity ions in polar crystals.
5. Development of a new technique and operation principles of devices for definition of parameters of doped ferroelectrics and for measurement of the characteristics of incident radiation.
6. Revealing advantages and enlargement of possible fields of application of the contactless magneto-optical technique of measurements.
7. Elaboration of recommendations for subsequent applications of the obtained results in various branches of integral optics, photonics and optical communication systems.

Role of Foreign Collaborators:
Cooperation with collaborators implies:
information exchange during project realization,
presentation of comments to ISTC technical reports,
meetings at conferences and seminars, direct visits and discussions.

Technical Approach and Methodology:
The following will be utilized for implementation of the project aims and for revealing the mechanisms of physical processes:
· Methods of theoretical spectroscopy (quantum theory of angular momentum, theory of groups, the genealogical scheme of Racah), theory of ligands field and other methods of theoretical physics.
· Different pulse- and continuous sources of radiation, including laser sources.
· Modified Chynoweth method with the technique of charge integration from polar faces of the crystals under study.
· Conventional experimental methods and those designed by authors of the project for investigations of absorption, excitation and luminescence spectra of the doped polar materials.
· A method, developed by the project authors for registration of low magnetic fields, based on the magneto-optical response of diluted alkaline vapor exposed to single-frequency tunable diode laser radiation.


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