P. Urenski

Submicron ferroelectric domain structures tailored by high-voltage scanning probe microscopy

We have developed a high voltage atomic force microscope that allowed us to tailor submicrometer ferroelectric domains in bulk ferroelectrics. One- and two-dimensional domain configurations have been fabricated in LiNbO3, RbTiOPO4, and RbTiOAsO4 ferroelectric crystals. It is found that the application of superhigh electric fields (reaching 5×107 V/cm) by the atomic force microscope tip leads to a unique polarization reversal mechanism, and open the way to a technology for photonic and acoustic devices.

Single-frequency continuous-wave optical parametric oscillator system with an ultrawide tuning range of 550 to 2830 nm

We present a cw single-frequency laser source with what is to our knowledge the largest emission range ever demonstrated, from the green to the mid-IR range. It employs a cw optical parametric oscillator with subsequent resonant frequency doubling. Typical output powers are 30–500 mW, with 160 mW at 580 nm. Mode-hop-free oscillation, high absolute frequency stability, 20-kHz-signal linewidth, and up to 38-GHz continuous tuning are demonstrated. Both PPLN and PPKTP are used as nonlinear materials, and their performance is compared.

Mid-infrared difference–frequency generation in periodically poled KTiOAsO 4 and application to gas sensing

Tunable mid-infrared radiation (3.45-3.75 microm) with a power level of 0.14 microW is generated by quasi-phase-matched difference-frequency mixing of a Nd:YAG laser and a tunable-diode laser (near 1.5 microm) in multigrating periodically poled KTiOAsO(4) . The wavelength and temperature bandwidths are approximately 65 nm cm and approximately 62 degrees C, respectively. The temperature-tuning slope of the phase-matched idler wavelength, -0.94 nm/ degrees C, is almost twice that of periodically poled KTiOPO(4) . We use the measurements to derive a mid-infrared-corrected Sellmeier equation for the Z axis of KTiOAsO(4). The generated mid-infrared radiation is applied to sensitive high-resolution spectroscopy of the nu(3) band of methane.

Polarization reversal and domain grating in flux-grown KTiOPO4 crystals with variable potassium stoichiometry

A significant decrease is observed in the dielectric dispersion, conductivity, coercive and internal fields of KTiOPO4 crystals grown with relatively high potassium concentration in the flux. A periodic domain structure with a period of 24.7 μm was fabricated on a 10 mm long crystal by electric field poling. Whereas standard flux-grown KTiOPO4 crystals can be periodically poled only at low temperatures (near 170 K), the periodic poling in this case was successfully performed near room temperature at a much lower electric field. Quasiphase-matched frequency doubling of 1550 nm radiation was achieved with the poled crystal.

Dielectric relaxation in flux grown KTiOPO4 and isomorphic crystals

Dielectric spectroscopy and dc conductivity have been studied in KTiOPO4 and isomorphic crystals in a temperature range 150–400 K. The experimental data indicate two temperature regions related to different types of relaxation processes. Alternation of the activation energy, suppression of the dielectric dispersion, and decreasing dissipation factor by three orders of magnitude has shown that the superionic state in KTiOPO4 and its isomorphs transit gradually to the dielectric state with temperature lowering. The transition leads to variation of transport properties from ionic to electronic conductivity. It was found that the parameters of the relaxation process (activation energy in the superionic state, temperature range of transition from ionic to electron conductivity) are determined by the sort of mobile cations. The temperature dependence of conductivity relaxation time was obtained from the electric modulus plots.

Periodically poled KTiOAsO4 crystals for optical parametric oscillation

Polarization switching and dielectric spectroscopy of KTiOAsO4 (KTA) crystals have been studied. This has allowed, for the first time, the fabrication by low temperature poling of periodically-poled domain structures in KTA crystals (0.5 mm thick, 10 mm long) and also the observation of optical parametric oscillation in the mid-infrared region. The integrity of the periodic domain pattern and the structural perfection of the periodically poled crystal have been demonstrated using scanning electron microscopy (SEM) and high-resolution x-ray diffraction imaging.

Anisotropic domain structure of KTiOPO4 crystals

Highly anisotropic ferroelectric domain structure is observed in KTiOPO4 (KTP) crystals reversed by low electric field. The applied Miller–Weinreich model for sidewise motion of domain walls indicates that this anisotropy results from the peculiarities of KTP crystal lattice. The domain nuclei of dozen nanometer size, imaged by atomic force microscopy method, demonstrate regular hexagonal forms. The orientation of domain walls of the elementary nuclei coincides with the orientation of the facets of macroscopic KTP crystals. The observed strong domain elongation along one principal crystal axis allows us to improve tailoring of ferroelectric domain engineered structures for nonlinear optical converters.

Scanning probe microscopy of well-defined periodically poled ferroelectric domain structure

We analyze and determine the factors governing the contrast in contact mode atomic force microscopy of domain-structured ferroelectric crystals. The analysis is applied to measurements conducted on KTiOPO4 crystals with artificially created well-defined domain structure. It is found that the amplitude contrast is due to difference in the work functions of the antiparallel domains.

Pyroelectric effect in KTiOPO4 and family crystals with monodomain and domain patterned structures

The pyroelectric effect was studied in KTiOPO4 and isomorphic ferroelectric crystals in a wide temperature range including the transition region from a superionic state to a dielectric state. The developed method of pyroelectric current monitoring has allowed the fabrication of various periodic and quasi-periodic ferroelectric domain configurations of high quality in KTiOAsO4, KTiOPO4, RbTiOAsO4 and RbTiOPO4 crystals for diverse nonlinear optical converters.

Bulk ferroelectric domain nucleation in KTiOPO4 crystals

Ferroelectric domain inversion in KTiOPO4 crystals has been studied for two different states of these crystals: superionic (at room temperature), and dielectric (at low temperature, when the ion transport is frozen). The structure of the ferroelectric domain inverted at room temperature demonstrates a dramatic domain broadening due to a bulk domain nucleation. The observed effect is ascribed to highly mobile potassium ions that contribute to the minimization of the depolarizing field and the surface energy of domain walls of new domain nuclei.