New Technologies for High-Power Eye-Safe Lasers pra-0107

Full Title New Technologies for High-Power Eye-Safe Lasers Tech Area / Field

• PHY-OPL: Physics / Optics and Lasers

• MAN-MCH: Manufacturing Technology / Machinery and Tools

Brief Description of Technology Presently, several non-traditional approaches for the design of eye-safe (2-3 mm) solid-state lasers are being developed at the ILP. They are based on the use of a quasi-two-level holmium-doped gain media with a high concentration of the dopant (up to 10²² cm^-3), direct pumping of the upper laser level by laser diodes and integral optics technology for the manufacture of "active mirrors". The use of high dopant concentrations provides full absorption of the pumping light within a 100 mm-thick layer of the gain medium and allows to achieve a gain of up to 100 cm^-1. The development of this approach will provide solutions to problems connected to the limited thermal damage threshold of gain elements in high-power lasers due to the transfer to very thin gain elements (0.1-0.2 mm) with diode pumping and conductive heat removal (so called "active mirror configuration") and particularly to provide steady-state operation of the laser. Using such "active mirrors" makes it possible to create large-size monoaperture laser amplifiers with a large field of view and high output power.

The direct pumping results in a significant decrease of the pumping power being converted into heat extraction in the gain medium (it can be less than 10% of the pumping power) and allows to transfer the problem of heat extraction to the pumping diodes, where requirements towards the quality of radiation are absent. The decrease of the thermal loading of the gain elements allows to increase specific laser-power extraction efficiency up to 2-3 kW/cm² and to reduce heat-induced aberrations of laser beams.

The application of integral optics technology in the production of "active mirrors" will allow to implement large-aperture gain elements of high optical quality, to shape their surface in a predetermined way and to form a special volumetric spatial structure providing anisotropy of the gain in different directions and damping of superluminescence. It will also allow to eliminate passive optical elements from the optical train of high-power laser radiation.

The proposed apporach has more advantages. For instance, the large field of view of the amplifiers based on active mirror geometry simplifies the problem of beam direction control. The steady-state behavior of phase distortions and their large-scale character simplifies the task of aberration correction. The high gain is favorable for the application of nonlinear optic techniques in aberration correction and beam wave front clean up.

Legal Aspects There are author certificates from the former Soviet Union concerning new laser media, laser design and beam direction control.

Special Facilities in Use and Their Specifications Standard laboratory equipment at the ILP should be used in this research, such as optical tables (with clean areas) equipped with a major part of optical components, and measurement technique. Other ILP facilities (mechanical, electronic and optical laboratories) will be used for the development and construction of some of the optical components, mounts, assemblies and electronic units.

Scientific Papers Nikitichev A.A., Serebryakov V.A. Average power limits of diode laser pumped Ho:YAG lasers. Laser Physics, Proc. SPIE, 1993, V.2095, pp.94-101.

Nikitichev A.A., Pismennyi V.A. 1W CW 2.12 mm lamp-pumped room temperature YAG:Yb-Ho laser. Advanced Solid-State Lasers, OSA Proceedings on Trends in Optics and Photonics, V.1, Washington, D.C., 1996, pp. 326-329.

Nikitichev A.A. Upconvertion coefficient measurements in Tm-Ho:YLF and YAG crystals. Advanced Solid-State Lasers, OSA Proceedings, V.24, Washington, D.C., 1995, pp.498-500.

A.F. Kornev, V.P. Pokrovskii, L.N. Soms, V.K. Stoupnikov. A scanning laser with an amplifier system - Izvestia AN USSR, Ser. Fiz., V55, #2, pp.298-302, 1991.

A.F. Kornev, A.A. Mak, V.P. Pokrovskiy, L.N. Soms, V.K.Stupnikov. Laser systems with internal scanning. Proc.SPIE, Solid State Lasers 4, V.1864, pp.17-30, 1993.

B.M. Antipenko, A.A. Nikitichev, CW 2 mcm laser action of (Y,Yb)₃Al₅O₁₂-Ho crystals when pumped by a lamp. Optika i Spektroskopiya, V.71 (1991) p.553.

B.M. Antipenko, A.A. Nikitichev. A repetitively pulsed YAG:Cr,Tm-Ho laser. Izvestiya Akademii Nauk SSSR, Ser. Fiz. V.55 (1991) p.267.

A.A. Nikitichev. Temperature dependence of the gain in Y₃Al₃O₁₂:Cr,Tm-Ho. Sov.J. Quantum Electron. V.18 (7) (1988) p.918.