Patent ID: 11794277

Abstract:
A mechanism for detecting the inside of a workpiece includes a wavelength delaying unit for outputting each pulse of a pulsed laser beam emitted from a laser oscillator with time differences imparted to respective wavelengths, and a ring generating unit for generating a ring-shaped pulsed laser beam from the pulsed laser beam with the time differences imparted to the respective wavelengths and diffracting the ring-shaped pulsed laser beam into ring-shaped laser beams ranging from small to large at the respective wavelengths. When the ring-shaped laser beams with the time differences imparted to the respective wavelengths are applied to the workpiece, they produce an interference wave of ultrasonic waves in the workpiece, and vibrations are produced at a position where the interference wave of the ultrasonic waves is converged. A laser beam is applied to an upper surface of the workpiece at a position aligned with the center of the vibrations.