We report on adhesive-free bonded (AFB"R") CVD diamond surfaces of 2 to 3 nm rms roughness to sapphire, YAG and optically coated YAG surfaces to form robust and stress free composite components. Considering the high thermal conductivity of CVD diamond with respect to YAG or sapphire, AFB"R" diamond/sapphire and diamond /YAG composites can be ideal components for thermal management of high power solid-state laser systems of certain design configurations.
We ascribe the attractive bonding forces at the interface between diamond and sapphire and other single crystals such as YAG and spinel largely to Van der Waals forces. Contrary to chemical bonds, Van der Waals forces consist of non-localized dipole-dipole interactions that manifest their long range effects by allowing relative movement between two bonded surfaces of different coefficients of thermal expansion, thus avoiding local stress during thermal cycling.
CVD diamond surfaces result in a much wider compatibility range for forming stress-free or low-stress composites compared to alumina compound single crystal counterparts. Feasibility of forming AFB"R" stress- free interfaces between diamond and optically coated oxide surfaces marks an important step in widening the range of AFB"R" for solid state laser and electronic applications.
Adhesive-free bonded (AFB®) composite crystals have proven to be useful components in diode-pumped solid-state lasers (DPSSL). The combination of a lasing medium of higher index of refraction with laser-inactive cladding layers of lower index results in light- or wave-guided slab architectures. The cladding layers also serve to provide mechanical support, thermal uniformity and a heat sink during laser operation. Therefore, the optical and mechanical properties of these components are of interest for the design of DPSSL, especially at high laser fluencies and output power. We report on process parameters and material attributes that result in stress-free AFB® composites that are resistant to thermally induced failure.
Formation of stress-free and durable bonds between two dissimilar materials requires heat-treatment of composites to a temperature high enough to ensure durable bonds and low enough to prevent forming of permanent chemical bonds. The onset temperature for forming permanent bonds at the interface sets the upper limit for heat treatment. This limiting temperature is dependent on the chemical composition, crystallographic orientation, and surface characteristics.
We have determined the upper temperature limits for forming stress-free bonds between YAG and sapphire, YAG and GGG, YAG and spinel, spinel and sapphire, spinel and GGG, and sapphire and GGG composites. We also deduce the relative magnitude of thermal expansion coefficients amongst the respective single crystals as αGGG > αsapp_c > αspinel > αYAG > αsapp_a from interferometric analysis.
The thermally induced stress of the order of 200 MPa and strain of the order of 2 x 10-4 in adhesive free bonded (AFB) YAG/sapphire single crystal composites have been determined as functions of crystallographic orientation by stress birefringence measurements using a polariscope and by surface figure measurements using a phase shift Fizeau interferometer, respectively. The deformation of YAG or sapphire end faces of the composite samples into anticlastic surfaces is likely due to thermally induced relative biaxial strain between the YAG and sapphire components during heat-treatment.
We have found that the YAG/sapphire composites stay stress- and strain-free when they are heat-treated below a critical temperature. The thermally induced stress and strain increase exponentially with respect to the heat-treat temperature that is above a critical temperature.
The magnitudes of thermally induced stress and strain in the heat-treated composite samples allow an estimate of the thermal stress resistance of YAG/sapphire composites.
Wright-Patterson Air Force Research Laboratory has supported this work under Phase II Contract F33615-03-C-5442.
Gadolinium Gallium Garnet single crystals doped with cobalt ions are used for suppression of parasitic as edge cladding layers in Nd:Gd3Ga5O12 (Nd:GGG) crystal amplifier plates for heat capacity and other high power solid-state laser applications. Co:GGG absorbs at the lasing wavelength of 1062 nm. Nd:GGG amplifier plates with edge cladding of Co:GGG of adjusted absorption coefficient at 1062 nm will be used as adhesive-free bonded (AFB) composite crystal components in a heat capacity laser system at Lawrence Livermore National Laboratory. Composite formation of Nd:GGG and Co:GGG involves heat treatment. The absorption coefficient of the as-grown Co:GGG single crystal changes as function of heat treatment. We report on a method of reversibly adjusting the absorption coefficient of Co:GGG in a certain range, e.g. for a specific Co ion concentration of 0.0046% between 0.45/cm and 0.95/cm.
The interpretation of the reversible adjustment of absorption coefficients based on absorption spectra, site symmetry and cobalt ion valency will be presented
We report on a technique for obtaining adhesive-free optical bonds between optical fibers and a wide range of optical elements, including other optical fibers. This technique overcomes problems associated with epoxies or inorganic adhesives at the bond interface. It consists of optically contacting a precision polished flat fiber-ferrule assembly against a precision polished mating surface. The optical fibers and ferrule both are of the same or similar material, e.g. fused silica, and the optical fiber inside the ferrule has been stripped of its organic polymer coating. The optical bond is then heat treated to produce a strong permanent bond with negligible loss at the interface. Applications include the attachment of a fused silica optical fiber/ferrule assembly to an optical element of fused silica with negligible Fresnel reflection loss. This type of connection is capable of transmitting high-power laser radiation to a site for materials processing without laser damage at the interface. Another important area of use for optically bonded interfaces is the delivery of high-power diode laser pump radiation to a clad laser fiber.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.