Ultraviolet laser induced domain inversion on chromium coated lithium niobate crystals

Direct UV laser writing on chromium coated lithium niobate (LiNbO3) crystals is found to produce spontaneous domain inversion associated with the exposed UV laser tracks. Experimental evidence suggests that this effect is attributed to local out-diffusion of oxygen, reducing the LiNbO3 crystal surface due to the presence of chromium. The thin chromium film becomes hot and reactive after absorbing the UV laser radiation thus acting as an oxygen getter. This very efficient process enables the inversion of domains at lower intensities as compared to other direct laser based poling methods practically eliminating the deleterious surface damage induced by the direct absorption of the UV laser radiation by the crystal. Furthermore, the versatility of this domain fabrication method, is demonstrated by the production of inverted domain structures on Z-, Y- and 128°YX-cut substrates.