By Research Support Instruments (RSI)
Laser Ultrasonics (or Laser-based Ultrasound) is the generation and detection of ultrasonic waves with lasers. When a laser pulse strikes a material, the material converts the light energy into thermal energy causing the material to locally expand near the impact point. This expansion creates the ultrasonic wave. There are several ways to detect the wave once it has passed through the material. Typically these methods reflect a laser beam off of the surface of the material. The reflected light is gathered in an interferometer which then converts that to an electrical signal. These techniques have one major disadvantage, the system is inherently dependent on the optical qualities of the system. They function really well on mirror-like surfaces, and not-so-well on others. With GCLAD, the detection beam never touches the surface, so it works well on all types of materials. GCLAD also requires no electro-optic stabilization, or fine-tuning. A general setup is shown below. Fig1: A typical GCLAD setup used for sensing ultrasound in materials. The deflection shown is greatly exaggerated.
