Study of the Quality of Thermal Diffusion Welding of Crystals in a Disk Optical Element by the Optoacoustic Method

The possibility of evaluating the quality of thermal diffusion welding of two yttrium aluminum garnet crystals in a composite optical disk has been studied using the optoacoustic method. To obtain acoustic images of thermal diffusion welding, an optoacoustic transducer connected through an optical fiber with a pulsed laser (wavelength of 532 nm, pulse duration of 10 ns) were used for scanning over the disk surface. The ultrasonic pulses in the frequency range up to 80 MHz are recorded simultaneously with movement of the transducer over an area of 16×16 mm with a step of 0.1 mm. Two ultrasonic scanning modes were used: forward and backward. The 15-mm-diameter composite disks with different quality of thermal diffusion welding were tested. The possibility of quantifying the quality of the diffusion layer using an optoacoustic method for objective comparison of the disks is discussed. The obtained data are confirmed by the results of measurements using an optical projection method.