Material Surface Treatment for Design of Composite Optical Elements
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ICAL ELECTRONICS
Material Surface Treatment for Design of Composite Optical Elements M. V. Zorinaa, I. I. Kuznetsovb, M. S. Mikhaylenkoa, O. V. Palashovb, A. E. Pestova,*, and N. I. Chkhaloa a Institute
for Physics of Microstructures, Russian Academy of Sciences, Nizhny Novgorod, 603950 Russia Russian Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, 603950 Russia *e-mail: [email protected]
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Received April 12, 2020; revised April 12, 2020; accepted April 12, 2020
Abstract—The quality of surface treatment of different laser materials has been studied aimed at designing composite elements. We have shown that flatness of samples should be no worse than λ/10 and roughness no more than 1.0 nm. Characteristics of ion-beam etching were found that cause no roughness degradation: Ar ions, Eion = 800 eV, and grazing angle θ = 5°. Ytterbium-doped yttrium aluminum garnet composite elements (Yb:YAG), along with a terbium gallium garnet (TGG) magnetoactive crystal with sapphire monocrystals, have been designed. DOI: 10.1134/S1063784220110286
INTRODUCTION Active composite elements present a challenge for development of modern laser systems, in particular, for simultaneous attainment of a high average power and high pulse energy. In most cases, the thermal diffusion bonding method is used for design of composites, which significantly limits the variety of appropriate materials to those with close thermal expansion coefficients [1]. The design of composite elements from optical materials exhibiting high thermal conductivity is of special interest, since such materials will serve for elimination of heat from an active medium (monocrystals of sapphire Al2O3, silicon carbide SiC, synthetic diamond, etc.) [2]. They can be used in powerful lasers both as active elements and magnetoactive Faraday isolators [3]. Currently, the most popular laser material is an Yb ion-doped yttrium aluminum garnet (Yb:YAG) and the most popular magnet-active material is a TGG crystal. Design of composites with a multilayer reflective or antireflective interface coating is of special interest. The presence of the reflective coating will make it possible to use opaque high heat-conductive materials, and the antireflective coating will make it possible to eliminate the radiation losses at interfaces of materials with different refraction indices. In this work, we describe the method of design of composite elements from dissimilar optical materials, in which treatment of contact surfaces by a highenergy Ar ion-beam is performed before joining elements together with an optical contact.
SURFACE ACTIVATION BY AN ION BEAM Surface activation is performed using an ion-beam etching facility [4]. To realize the method, the facility was slightly upgraded; in particular, a hinged sample holder was fabricated. The hinge consists of a pair of sapphire elements: the ball and base (washer) for the sample holding. Low friction in this hinge reduces elimination of mismatch in the angles of joint elements (no bite occurs as in the case of
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