Chemical and physical processes driven by multiphoton absorption make possible the fabrication of complex, 3D structures with feature sizes as small as 100 nm. Since its inception less than a decade ago, the field of multiphoton fabrication has progressed rapidly, and multiphoton techniques are now being used to create functional microdevices. In this Review we discuss the techniques and materials used for multiphoton fabrication, the applications that have been demonstrated, as well as those being pursued. We also consider the outlook for this field, both in the laboratory and in industrial settings.

We demonstrate that highly efficient photoluminescence is generated from gold nanoparticles as small as a few nanometers in diameter upon irradiation with sub-100-fs pulses of 790-nm light. Strong emission is observed at excitation intensities comparable to or less than those typically used for multiphoton imaging of fluorescently labeled biological samples. The particles have polarized emission, can radiate more efficiently than single molecules, do not exhibit significant blinking, and are photostable under hours of continuous excitation. These observations suggest that metal nanoparticles are a viable alternative to fluorophores or semiconductor nanoparticles for biological labeling and imaging.

Optical Kerr effect spectroscopy has been employed to study the behavior of six symmetric-top liquids (acetonitrile, acetonitrile-d3, benzene, carbon disulfide, chloroform, and methyl iodide) over a broad range of temperatures. In all of the liquids, an exponential intermolecular response is observed on a time scale of a few hundreds of femtoseconds. Comparison of the temperature dependence of the time scale of this relaxation with the viscosity and single-molecule and collective orientational times in the liquids suggests that the exponential relaxation arises from motional narrowing.

The reorientational dynamics of liquids confined in nanoporous sol-gel glasses have been investigated in detail using femtosecond optical Kerr effect spectroscopy. We review the results of experiments performed on both weakly wetting and strongly wetting liquids in nanoconfinement. In all cases the liquid partitions into bulk-like and surface populations, each of which has unique dynamics. We demonstrate how optical Kerr effect spectroscopy can be used to probe the dynamics and structure of these populations in quantitative, molecular-level detail.

When a liquid is restricted to volumes on a molecular distance scale, its orientational and translational dynamics are perturbed strongly by the confinement. Nanoporous sol-gel glasses are an excellent model system for studying the effects of confinement on the behavior of liquids, and in this Account we review experiments in which ultrafast optical Kerr effect spectroscopy has been used to study the orientational dynamics of liquids confined in these media. We contrast the effects of confinement on the orientational dynamics of weakly wetting, strongly wetting, and networked liquids, and we discuss the influence of factors such as pore size, molecular shape, and surface chemistry.