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Development of the laboratory of the diagnostics of novel optical materials for advanced lasers in 2013 – 2015

Name
KENITI
Surname
UEDA
Scientific organization
University of Electro-Communications
Academic degree
Doctor of Science
Position
Professor Emeritus
Scientific discipline
Physics & Astronomy
Topic
Development of the laboratory of the diagnostics of novel optical materials for advanced lasers in 2013 – 2015
Abstract
The “Laboratory for Diagnostics of New Optical Materials for Advanced Lasers” to perform high-level world-class research and solve topical problems of creating lasers with high peak and average power aiming at improving their consumer properties was established.
The results of the carried out research were published in more than 34 papers in high-rate peer-reviewed journals, presented at about 100 different Russian and international conferences. 14 applications were submitted for recording the intellectual property rights.
Keywords
high power lasers, optical media properties, laser ceramics, cryogenic cooling.
Summary

 

Introduction.

In the last years a large number of promising laser media has appeared. It is connected with rapid developing the technology of producing the laser and optical ceramics, which allows to obtain active and optical elements faster, cheaper, larger, with a higher concentration and homogeneity of the active ion; to obtain the ceramics from a variety of materials, including the materials which are technologically impossible to grow in a single crystal form. The comprehensive investigation of media properties (laser, thermo-optic, nonlinear optical, spectral, etc.) is relevant for laser systems for efficiency improvement, new types of lasers creation and spread its use in scientific experiments as well as for practical purposes. The measurement of material constants and its dependences on temperature, wavelength, the concentration of the active ion etc. for new promising laser materials allows its properties optimizing and obtaining the unique characteristics of the optical elements for advanced lasers.

 

Goals and objectives of the scientific research project activities.

The principal goal of the project was establishing the “Laboratory for Diagnostics of New Optical Materials for Advanced Lasers”, that would allow performing high-level world-class research and solve topical problems of creating lasers with high peak and average power aiming at improving their consumer properties.

The main tasks of the project were production and diagnostics of new optical materials (ceramics, crystals, and glasses) and development on their basis of optical units (laser components) with unique characteristics. The diagnostics included development of measurement benches, measurement techniques, and software for measuring different characteristics (photoelastic, thermo-optical, laser, magneto-optical, spectral) of the new materials. At the stage of developing optical units (quantum amplifiers, optical isolators), with the aim to improve their characteristics it was intended to study the opportunities for reducing and compensating parasitic effects. It was also planned to improve the methods of creating new media (sintering of ceramics, crystal growth). The implementation of the project was supposed to advance a number of critical/concurrent technologies (creating composite elements, effective heat sinks, sources of constant magnetic fields, etc.).

Scientific research project activities.

In the course of project implementation, methods for measuring photoelastic, thermo-optical, nonlinear-optical, laser, magneto-optical and spectral characteristics in the 80…300К temperature range were developed for optical media diagnostics. 12 measurement benches with the corresponding software for processing experimental data were created.

  1. Photoelastic constant meter.

  2. Meter of Verdet constant and magneto-optical figure of merit in the 80…300 К temperature range.

  3. 2D-scanning Hartman sensor.

  4. Meter of nonlinear optical susceptibility.

  5. Meter of mechanical resistance of coatings, surface and bulk damage threshold.

  6. Meter of thermal resistance of solid body contacts.

  7. Meter of thermal conductivity of solids.

  8. Meter of laser media characteristics.

  9. Profilometer.

  10. Measurer of spectral characteristics.

  11. Measurer of thermo-optical characteristics.

  12. Gage of the temperature dependence of thermo-optical constants.

The developed techniques and measurement benches were used to conduct theoretical and experimental studies of the following characteristics of different optical media:

- optical (refractive index inhomogeneity, depolarization ratio, and others);

- thermo-optical (thermal conductance, thermal expansion coefficient, and others);

- magneto-optical (Verdet constant, magneto-optical figure of merit).

The impact of variations of these characteristics on optical beam propagation was investigated.

Methods of producing new laser media: ceramic (techniques of synthesizing nano-powders with characteristics demanded for laser ceramics, of compacting ceramics with high homogeneity, and of high-temperature sintering of TAG and YAG ceramics), and monocrystalline (development of an optimal method of growing garnet, terbium phianite and terbium vanadate crystals, quality studies of TSAG crystals of different compositions) were developed and upgraded.

Theoretical and experimental studies of weak signal gain (stored energy) and total gain (multipass, using a regenerative amplifier, and so on), cw generation modes, Q-switching, nonlinear optical conversion of radiation, reduction of parasitic thermal effects etc. were carried out for different laser components.

An important part of the work was creation of two technological benches:

- for thermodiffusion bonding of optical elements, and

- for producing sources of magnetic fields.

 

Results.

Based on the results of the research and the works performed on the 12 created measurement and 2 technological benches, the following devices were developed:

- cryogenic Yb:YAG disk laser (MOPA circuit; energy 54 mJ at a pulse repetition rate of 200 Hz and pump energy of 200 mJ; energy 30 mJ at a pulse repetition rate of 1 kHz and cw pumping);

- disk laser head (comprising high-efficiency AE water cooling system and optical multipass pump input scheme; weak signal gain of 1.25 at a stored energy of 400 mJ was attained);

- cryogenic disk laser head (AE aperture of 20 mm);

- polarization apodizing diaphragm (allows correcting e.m. radiation distribution in the optical range);

- Faraday isolator on a shortened element (30 dB at a power of 650 W);

- Faraday isolators on a new medium – TAG and Ce:TAG ceramics;

- Faraday isolators on TGG ceramics (with internal compensation: 30 dB up to 2.7 kW; with external compensation: 30 dB up to 2 kW; traditional scheme: 30 dB up to 1 kW; cryogenic: 30 dB over 2 kW);

- Faraday isolator with magnetic system having preset field inhomogeneity (7-fold reduction of depolarization level);

- Faraday isolator on a new medium – TSAG crystal;

- large-aperture Faraday isolator (on a TGG crystal having aperture of 30 mm (33.5 dB at 1.5 kW).

Also, the following crystal samples were manufactured: TSAG, Tb-containing phianite, terbium vanadate, and optical ceramics: TAG, YAG, MgAl2O4 doped by a Tm3+ ion.

 

Conclusion.

The developed material base (measurement and technological benches) and the professional skill of the team allow obtaining world level results. Based on the results of the carried out research we developed and manufactured prototypes of optical units with unique characteristics, including laser oscillators, amplifiers, Faraday isolators with water and cryogenic cooling having different configurations of active and magnetooptical elements and heat sinks. Using the developed technologies we manufactured samples of TSAG, Tb-containing phianite and terbium vanadate crystals and samples of optical ceramics: TAG, YAG, and Tm3+ ion activated MgAl2O4.

The results of the carried out research were published in more than 34 papers in high-rate peer-reviewed journals, presented at about 100 different Russian and international conferences. 14 applications were submitted for recording the intellectual property rights. These indicators confirm the high scientific and technical level of the research results that correspond to or excel the best world’s achievements in the field of optical media diagnostics, creation of composite optical elements, manufacturing magnetic systems with record values of magnetic field intensity, optical units and components with unique characteristics.