Laser light induced domain engineering of lithium niobate for photonic and phononic applications

This thesis presents novel domain engineering techniques in lithium niobate (LiNbO3) crystals by using focused laser light irradiation to path the way to sub-micron domain periods for applications in the field of photonics and phononics.

A new technique for tailoring of ferroelectric surface domains is introduced on the non-polar cuts of LiNbO3 by scanning a focused ultraviolet (UV) laser beam (λ = 244 nm) across the surface, using a scheme of writing and partially erasing the previously written domains. Domain periods down to 4 μm are realised, where the domain depth profile is 'half-crescent-shaped'. Reduction of laser induced surface damage is achieved by coating the LiNbO3 crystal surface with a Cr layer, thereby combining the direct laser writing technique with a diffusion process to accomplish domain inversion. Bulk domain patterns with a period of down to 3 μm are obtained in MgO-doped LiNbO3 crystals by combining laser induced poling inhibition with a sequence of electric field poling steps.

The uniformity of the bulk domains is confirmed by nonlinear optical conversion of laser light with a wavelength of 1550 nm into 775 nm . Sub-micron surface domain patterns are achieved by patterned Cr and visible laser light irradiation (λ = 532 nm). This allows for the generation of 2D poling patterns with periods down to 100 nm. Finally, direct laser written domain patterns are used to excite surface acoustic waves to drive flow and suspended microparticles within a fluid droplet. This demonstrates that the platform can be exploited for practical microfluidic manipulation.