Luminescent markers play a key role in imaging techniques for life science since they provide a contrast mechanism between signal and background. We describe a new type of marker using second harmonic generation (SHG) from noncentrosymmetric BaTiO_3 nanocrystals. These nanoparticles are attractive due to their stable, non-saturating and coherent signal with a femtosecond-scale response time and broad flexibility in the choice of excitation wavelength. We obtained monodispersed BaTiO_3 nanoparticles in colloidal suspensions by coating the particle surface with amine groups. We characterized the SHG efficiency of 90-nm BaTiO_3 particles experimentally and theoretically. Moreover, we use the coherent SHG signal from BaTiO_3 nanoparticles for three-dimensional (3D) imaging without scanning. We built a harmonic holographic (H^2) microscope which records digital holograms at the second harmonic frequency. For the first time, high-resolution 3D distributions of these SHG markers in mammalian cells are successfully captured and interpreted by the H^2 microscope.

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Three-dimensional harmonic holographic microcopy using nanoparticles as probes for cell imaging

The first book on the topic, and written by the founder of the technique, this comprehensive resource provides a detailed overview of sum-frequency spectroscopy, its fundamental principles, and the wide range of applications for surfaces, interfaces, and bulk. Beginning with an overview of the historical context, and introductions to the basic theory of nonlinear optics and surface sum-frequency generation, topics covered include discussion of different experimental arrangements adopted by researchers, notes on proper data analysis, an up-to-date survey commenting on the wide range of successful applications of the tool, and a valuable insight into current unsolved problems and potential areas to be explored in the future. With the addition of chapter appendices that offer the opportunity for more in-depth theoretical discussion, this is an essential resource that integrates all aspects of the subject and is ideal for anyone using, or interested in using, sum-frequency spectroscopy.

Fundamentals of Sum-Frequency Spectroscopy

Classical crystal optics has recently undergone a renaissance as developments in optical microscopy and polarimetry, enabled in part by sensitive imaging CCD cameras and personal computers, now permit the analytical separation of various optical effects that are otherwise convolved in polarized light micrographs. In this tutorial review, we review recent developments in the measurement of the principal crystallo-optical quantities including linear birefringence, linear dichroism, circular birefringence, and circular dichroism, as well as new effects in crystal optics encountered in unusual mixed crystals. The new microscopies and polarimetries are applied to problems of crystallographic twinning, phase transformations, stress birefringence, symmetry reduction, and the design of new crystalline materials.

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Polarimetric imaging of crystals

A bibliography is given containing 2067 references published during 2002 and 2003 on piezoelectric and pyroelectric properties of materials and their applications. It contains listings of journal articles with complete bibliographic citations. This bibliography is the continuation of a series published semi-annually.

Guide to the Literature of Piezoelectricity and Pyroelectricity. 23

A three-step procedure is proposed to investigate growth-induced polarity arising in centrosymmetric crystals of dipolar molecules. It is based on (i) calculation of molecular interaction energies by force field methods, (ii) determination of the morphology, and (iii) use of the energies in a Markov-type growth mechanism on faces (hkl). Applied to trans-4-chloro-4‘-nitrostilbene (CNS), the procedure showed that CNS crystals, although globally centric, are composed of sectors exhibiting different polar properties. The sectors related to the +b and −b directions show opposite polarity and are mainly responsible for observed second-harmonic generation and pyroelectric effects. Influence of the calculation method on the results was investigated by comparing different force fields or charges.

Prediction of growth-induced polarity in centrosymmetric molecular crystals using force field methods

Phase-sensitive second-harmonic microscopy is applied to reveal grow-in polarity in topologically centrosymmetric crystals of 4-chloro-4′-nitrostilben. As predicted by the Markow model of layer-by-layer polarity formation, growth along + and −b-direction in P21/c is producing optical nonlinearity in both sectors associated with the b axis. Present experiments show that formation of a pyroelectric symmetry class is a stochastic property of molecular crystals grown from dipolar compounds and near to thermodynamic equilibrium.

Phase-sensitive second-harmonic microscopy reveals polarity of topologically centrosymmetric molecular crystals

Solid solution formation is a safe way to polarity formation in organic crystals. Molecular recognition at surfaces brings in orientational disorder, which can lead to grow-in polarity. Basic features of as-grown solid solutions are revealed by a new technique called phase sensitive second harmonic microscopy. Crystals are twinned and grow into a bi-polar structure.

S. Kluge

Papers

Phase-sensitive second-harmonic microscopy reveals polarity of topologically centrosymmetric molecular crystals

Polarity formation in solid solutions: (4,4′-dinitrostilbene)1 − x(4-chloro-4′-nitrostilbene)x, 1 > x > 0