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We use two perpendicular crystals of periodically-poled KTP to directly generate polarization-entangled photon pairs, the majority of which are emitted into a single Gaussian spatial mode. The signal and idler photons have wavelengths of 810 nm and 1550 nm, respectively, and the photon-pair generation rate is 1.2x107 sec-1 for a pump power of 62 mW. The apparatus is compact, flexible, and easily to use.

Ferroelectric domain wall injection has been demonstrated by engineering of the local electric field, using focused ion beam milled defects in thin single crystal lamellae of KTiOPO4 (KTP). The electric field distribution (top) displays localized field hot-spots, which correlate with nucleation events (bottom). Designed local field variations can also dictate subsequent domain wall mobility, demonstrating a new paradigm in ferroelectric domain wall control.

We use the inverse piezoelectric effect for high-resolution imaging of artificially produced ferroelectric domains in periodically poled potassium titanium phosphate, KTiOPO4, and lithium niobate, LiNbO3, crystals using a modified atomic force microscope (AFM). By monitoring the vertical as well as the lateral deflection of the AFM tip, details of the domains and the domain walls were obtained at 1 nm resolution. With this approach we determine the domain wall width to be 20–80 nm for KTiOPO4 and about 150 nm for LiNbO3. The above technique is of importance in tailoring ferroelectric crystals for frequency conversion of lasers and studies of domain walls in ferroelectric and its magnetic analogs.

One of the unique features of mirrorless optical parametric oscillators based on counterpropagating three-wave interactions is the narrow spectral width of the wave generated in the backward direction. In this work, we investigate experimentally and numerically the influence that a strong phase modulation in the pump has on the spectral bandwidths of the parametric waves and on the efficiency of the nonlinear interaction. The effects of group-velocity mismatch and group-velocity dispersion are elucidated. In particular, it is shown that the substantial increase in temporal coherence of the backward-generated wave can be obtained even for pumping with a temporally incoherent pump. A configuration of a mirrorless optical parametric oscillator is proposed where this gain in spectral coherence is maximized without a penalty in conversion efficiency by employing group-velocity matching of the pump and the forward-generated parametric wave.

A 5 mm thick periodically poled bulk Rb-doped KTiOPO 4 (KTP) crystal with a period of 38.86 µm was fabricated by electric field poling. Chemical etching and optical evaluation show a high quality of the periodic ferroelectric domain structure through the whole crystal aperture. The fabricated quasi-phase matching (QPM) device was used in an optical parametric oscillator pumped at 1064 nm with 12 ns pulses at 100 Hz repetition rate to generate 60 mJ parametric radiation with a conversion efficiency of 50%.

We present an all solid-state narrow linewidth laser source emitting 670 mW output power at 671 nm delivered in a diffraction-limited beam. The source is based on a frequency-doubled diode-endpumped ring laser operating on the 4 F 3/2 → 4 I 13/2 transition in Nd:YVO 4 . By using periodically-poled potassium titanyl phosphate (ppKTP) in an external buildup cavity, doubling efficiencies of up to 86% are obtained. Tunability of the source over 100 GHz is accomplished. We demonstrate the suitability of this robust frequency-stabilized light source for laser cooling of lithium atoms. Finally a simplified design based on intra-cavity doubling is described and first results are presented.

In this study, the Volta potential distribution over the surface of duplex stainless steels ͑DSSs͒ has been mapped for the first time with submicrometer resolution by scanning Kelvin probe force microscopy ͑SKPFM͒. The different magnetic properties of ferrite and austenite enable the utilization of magnetic force microscopy ͑MFM͒ for visualizing their surface distribution without the need of surface etching. The combined MFM and SKPFM mapping of the same area makes it possible to associate the variation in the Volta potential to the phase distribution and phase boundaries. The difference in potential between the two phases is measurable and significant. Generally, the ferrite phase was associated to regions of lower potential, and the austenite phase to regions of more noble potential. This can be regarded as direct evidence of galvanic interactions between the two phases. The phase boundary regions often exhibited a lower potential in the ferrite phase, indicating a higher tendency to corrosion. The high lateral resolution of SKPFM provides the possibility of comparing these results with those obtained from other localized techniques, a necessary step for a deeper understanding of the local corrosion processes in DSSs.Duplex stainless steels ͑DSSs͒ are designed to have a microstructure consisting of ferrite and austenite in approximately equal volume fractions. Modern DSSs offer both high mechanical strength and superior resistance to corrosion and stress corrosion cracking especially in chloride environments, and are increasingly used in marine environments, in chemical, petrochemical, pulp and paper, oil and gas industries. 1-3 Due to the partitioning of alloying elements ͑Cr, Mo, N, and Ni͒ in the two phases, there is an intrinsic heterogeneity in the phase composition, which may result in a difference in their corrosion behavior. 4,5 This heterogeneity in microstructure may lead to galvanic effects between the two phases and cause a preferential corrosion attack of the weakest phase. 6,7 Localized corrosion on DSSs most commonly occurs at the ferrite/austenite phase boundaries, which also provide initiation sites for fatigue cracks and stress corrosion cracks. 4 The composition and processing parameters are vital for the control of the microstructure and, thus, the final industrial application. Quantitative metallography and microhardness are the common methods for characterization of DSSs. Conventional electrochemical techniques such as potentiostatic and potentiodynamic polarization measurements and surface analysis are often used in corrosion studies of DSSs. [6][7][8][9][10][11] During recent years, in situ high-resolution microscopy has been applied for studies of localized corrosion behavior of DSSs. 12 In situ local studies of DSSs were reported by the present authors in earlier works [13][14][15] in which electrochemically controlled scanning tunneling microscopy ͑EC-STM͒ was used to investigate the dissolution behavior of three DSSs with different alloying composition. The EC-STM images revealed het...