Development and evaluation of optical-use MgO : LiNbO_3 single crystals by line-focus-beam acoustic microscopy

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Line-focus-beam (LFB) acoustic microscopy, with perfect directionality, is a very useful and unique method of quantitative material characterization by measuring the velocity of leaky surface acoustic waves (LSAWs), excited on the boundary between the specimen and the water coupling, through V (z) curve analysis. The system has been applied to material problems in the scientific and industrial fields of MgO deped LiNbO_3 crystals for estabishment of the crystal growh conditions and for evaluation of the device fabrication processes.1.The reliable LFB system with high accuracy in LSAW velocity of better than 0.01% over an entire scanning area of 100 mm X 100 mm has been established.2.Six MgO-doped LiNbO_3 crystals, specially grown with different MgO dopant concentrations ranging from 0 to 13 mol%, have been employed for velocity measurements. It has been shown for the first time that the velocities on the three basic crystal surfaces of X-, Y-, and Z-cut planes increase for all the surf … More aces and all the propagation directions monotonically as the dopant concentration increases, and the corresponding density decrease monotonically.3.The measured LSAW velocities have been compared with the measured chemical and physical properties, viz., chemical composition, density, lattice constant, refractive index, and Curie temperature. It has been shown that the LFB system has a much greater sensitivity and resolution in the determination of these properties than any other analytical methods.4.Measurements of LSAW velocity distribution have been carried out for substrates obtained from a MgO (5 mol%) : LiNbO_3 single crystal with 3-inch diameter and 80 mm long. LSAW velocity distributions with the largest difference of about 3m/s have been obtained successfully, which might reflect the changes of crystal growth conditions, such as the chemical composition of the melt and the rotating and pulling speeds, and the temperature distributions in the crucible and furnace.5.The system has been applied to characterization of a proton-exchnged layr fabricated on Z-cut MgO (5mol%) : LiNbO_3 substrate with a layr thickness of 0.5 mum. It has been demonstrated that the system has the capability to resolve the change of diffusion depth of 2 nm and the change of extraordinary refractive index of 5x10^<-4>. It has been suggested that this method should be adapted as a new analytical technique for development and evaluation of waveguide-type optical device fabrication processes and systems for the future mass production. Less