H. Hsiung

Detection of ferroelectric domain reversal in KTiOPO4 waveguides

Segmented optical waveguides in KTiOPO4 are fabricated by ion exchange of Rb/Ba for K using molten nitrate salts. The waveguides have been utilized to generate efficient second‐harmonic generation (SHG) of blue light. Four techniques are described which demonstrate that the ion exchange can produce domain reversal in these waveguides, and quasi‐phase matching is utilized to obtain blue light. The experiments involve surface SHG, electrostatic toning, selective etching, and piezoelectric measurements.

Loss of optical nonlinearity in proton‐exchanged LiNbO3 waveguides

The second‐order optical nonlinearity in a planar waveguide of proton‐exchanged LiNbO3 is directly probed by second‐harmonic generation from 532 to 266 nm in a reflection geometry. Compared to untreated LiNbO3, a 30‐fold reduction in the optical nonlinearity is observed. Contrary to previous reports, we find that the optical nonlinearity cannot be effectively restored by thermal annealing.

Curie temperatures and dielectric properties of doped and undoped KTiOPO/sub 4/ and isomorphs

The Curie temperatures and dielectric properties of KTiOPO/sub 4/ (KTP), RbTiOPO/sub 4/, KTiOAsO/sub 4/, RbTiOAsO/sub 4/, CsTiOAsO/sub 4/, Ba:KTP, and Ga:KTP were measured with small-signal relative dielectric permittivity ( kappa ) analysis, piezoelectric resonance analysis, and optical second harmonic generation. All the isomorphs and the doped KTP exhibit lower Curie temperatures than KTP, ranging from 637 degrees C for CsTiOAsO/sub 4/ to 955 degrees C for hydrothermally (HT) grown KTP. The Curie-Weiss law is obeyed in all samples. With the exception of CsTiOAsO/sub 4/, all doped and undoped crystals show large dielectric relaxation at frequencies below 100 KHz throughout the temperature range of 500 degrees C-800 degrees C. For the barium-doped KTP, it was found that the Curie temperature decreases with increasing Ba/sup ++/-doping concentration. Barium doping also significantly modifies dielectric and piezoelectric properties of KTP.<<ETX>>

Ferroelectric phase transition in KTiOPO4: An optical second‐harmonic generation study

The ferroelectric phase transition in a single‐domain KTiOPO4 (KTP) crystal is studied with optical second‐harmonic generation. The optical nonlinearity decreases continuously with increasing temperature and vanishes at the Curie point (TC=952 °C) and above. Over a broad temperature range in the ferroelectric phase, the nonlinear optical coefficient d33∝(TC−T)0.5. This behavior is in good agreement with the Landau theory for second‐order ferroelectric phase transitions.

Modification of nonlinear optical response in Langmuir–Blodgett films by ultraviolet laser‐induced bleaching

Permanent modifications of the second‐order nonlinear susceptibility χ(2)(−2ω;ω,ω) of certain Langmuir–Blodgett (LB) films can be induced photochemically by local irradiation with UV laser light, with the spatial resolution limited only by the laser spot size. In a LB film consisting of alternating monolayers of poly[N‐(p‐perfluorodecylsulfonylphenyl)‐L‐prolinol acrylate] and a ‘‘buffer’’ polymer, the kinetics of the laser bleaching process, as studied by optical second‐harmonic generation, is found to be first order. The generation of a ‘‘χ(2)‐grating’’ in the LB film is also demonstrated.