Fabrication of Large Aperture PPRKTP with Short Period (3.43 µm) Using Coercive Field Engineering

Large aperture periodically poled Rb-doped KTiOPO 4 (PPRKTP) with good domain homogeneity over a 5 mm 2 aperture has been proven very useful for high-energy output optical parametric oscillators (OPO) [1] . So far, large aperture quasi-phase matched (QPM) devices have only been demonstrated for long periods, on the range of 30-40 µm. Typically, these periods satisfy parametric processes pumped at 1µm. Nevertheless, shrinking the period an order of magnitude would allow for high-energy applications pumped at shorter wavelengths. Furthermore, it would be of major interest for quantum optics, as for a given intensity of the pump laser, the spontaneous parametric down conversion process will scale linearly with increasing area of illumination of the pump laser. Moreover, if the grating period for large aperture crystals can be further reduced, it would be possible to achieve high-energy backward-wave parametric processes. However, fabricating thick PPRKTP is challenging due to the difficulty of propagating the domain grating throughout the whole crystal thickness with minimal domain broadening. This becomes even more problematic when the grating period is as small as 3.43 µm.