Flatness-insensitive pulsed electric current bonding of sapphire/Nd:YAG ceramics

Initial surface-flatness-insensitive bonding of sapphire and YAG ceramics for high-average-power laser materials was achieved via pulsed electric current bonding (PECB), a type of thermal diffusion bonding. Nd:YAG ceramics with surface flatness of λ/10, λ/5, and λ (λ = 632.8 nm) were bonded to sapphire (flatness < λ/10). All samples exhibited excellent optical performance irrespective of initial flatness. In-line transmittance approached theoretical limits, transmitted wavefront distortion was below 0.264λ, and polarization exceeded 35 dB. Minor unbonded regions appeared near edges for λ-flat samples, but overall performance remained unaffected. TEM analysis revealed interfacial microstructures, providing deeper insights. These findings demonstrate that PECB enables high-quality bonding with minimal dependence on initial flatness, making it advantageous for manufacturing large-aperture, high-average-power, and high-pulse-energy laser materials.