Laser-generated ultrasound with liquid crystal on silicon (LCoS) technology in the thermoelastic regime

Composite materials like carbon fiber reinforced plastics (CFRP) are used more and more in commercial applications and offer several attractive ways for tailored solutions. However, for many safety issues these materials require adequate nondestructive testing. The extension of the ultrasound technique for nondestructive purpose with laser technology brings new possibilities into the production processes for example manufacturing of small complex components with the capability of an inline observation. One problem with laser based ultrasound is the conventional Gaussian beam shape and an inappropriate thermal penetration when using for example a YAG-laser, which is usually destructive for the properties of the material under test. We describe the successful implementation of laser-based ultrasound using a Liquid Crystal on Silicon (LCoS) spatial light modulator for beam shaping. A LCoS display optimized as phase-only modulator with 8-bit phase level addressing is used to adapt the intensity dispersal of the laser to a predetermined spatial light distribution for nondestructive optoacoustic interaction with CFRP materials in the thermoelastic regime.

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