Thermal lensing investigation on bulk ceramics and thin-film PLZT using visible and far-infrared laser beams

The real-time thermo-optical properties of thin-film relaxor ferroelectric (9/65/35) lead lanthanum zirconate titanate (PLZT) films (∼2 μm) were investigated and compared to identical composition of thick PLZT ceramics (∼1 mm). Since PLZT absorbs strongly in the far-infrared, a CO2 laser beam (λ = 10.6 μm) was used to create a Gaussian temperature distribution at the surface of the material, emulating a lens. Subsequently, a low power visible He-Ne laser, travelling along the same path as the CO2 laser, probed the optical properties of the induced PLZT thermal lens. It was found that identical composition thin-film and thick PLZT ceramics have opposite thermal lensing behaviors. An explanation of this phenomenon is provided from basic physical concepts.