This invention relates to a method for joining crystal segments to form a multiform crystal suitable for laser applications.
Large single crystals have advantages compared to small crystals in diverse applications, such as solid state laser and semiconductor applications. For example, large sized laser crystals are useful for generating high intensity laser beams in solid state laser applications, because these crystals provide an elongated resonance pathway for the light propagating through the crystal. In semiconductor applications, large silicon crystals are segmented into single crystal silicon wafers that are useful for efficiently processing large numbers of integrated circuit chips.
Current crystal growing methods, such as the Czochralski technique, can grow single crystals having limited sizes. Furthermore, it is difficult to grow large sized crystals whose quality level is sufficiently high for the crystal to be useful for applications that require high purity crystals, such as solid state lasers. As the cross-sectional area of the crystal increases, there is a greater tendency to form defects through the cross-section. Thus, there is a need for an efficient process for forming large sized single crystals with few crystalline defects.
Furthermore, in the crystal growing process, contaminants, such as halide and metal-containing species, form in the crystal. The halide contaminants typically comprise chlorine and fluorine, and the metal contaminants typically comprise iridium. These contaminants along with the lattice defects in the crystal adversely affect the light amplification properties of the crystal. Thus, there is also a need for a process for removing contaminants and crystalline defects from crystals, including single crystals.
Instead of growing large single crystals, large crystals can be formed by bonding or joining smaller crystal segments to one another. Diverse methods have been developed for joining small single crystal segments to form multi-segment crystals. For example, metallic single crystals useful for turbine engines can be bonded by diffusion bonding methods as disclosed in U.S. Pat. No. 4,033,792 to Giamei et al; and U.S. Pat. No. 4,475, 980 to Rhemer et al. Crystals can also be bonded with a bonding agent, such as epoxy or glass frit, in the joint between the crystal segments for adhering the single crystal segments to one another.
However, these crystal joining techniques have limited uses for forming large size crystals for applications requiring a high quality, high purity crystal, where the bond between the crystal segments must be substantially optically transparent or defect free. In solid state laser and opto-electronic applications, defects in the joint between the crystal segments cause attenuation and refraction of the light traversing the crystal. Traditional bonding methods do not provide a high degree of optical transparency in the interface between the joined single crystal segments. For example, when bonding agents are used to join the crystal segments, the resultant non-homogeneous bond between the crystal segments has a refractive index which does not match that of the adjoining crystal segments. The variation in refractive index through the joint causes refraction of the light propagating through the laser crystal. Diffusion bonding methods for joining metallic single crystals are designed to provide a high strength bond, and may not provide an optically transparent bond.
Thus, there is a need for a method for joining single crystal segments to form large multiform crystals having a substantially optically transparent bond. It is also desirable for the bond between the crystal segments be substantially free of defects and imperfections so that the light propagating through the crystal is not. refracted or reflected. There is also a need for a process for removing contaminants and lattice defects from single crystals.
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