Chromatic confocal displacement sensing at oblique incidence angles.

A commercial chromatic confocal displacement sensor, designed for probing a target at normal incidence, is adapted to probe reflective targets at an oblique incidence angle. The sensor is modified by positioning two low-cost optical elements-a collimating lens and a retro-reflector-in the reflection plane.

Expanding the realm of fiber optic confocal sensing for probing position, displacement, and velocity.

We describe a fiber optic confocal sensor (FOCOS) system that uses an optical fiber and a lens to accurately detect the position of an object at, or close to, the image plane of the fiber tip. The fiber characteristics (diameter and numerical aperture) and optics (lens F/# and magnification) define the span and precision of the sensor and may be chosen to fit a desired application of position and displacement sensing. Multiple measurement points (i.e., fiber-tip images) may be achieved by use of multiple wavelengths in the fiber, so that each wavelength images the fiber at a different plane due to the chromatic dispersion of the optics. Further multiplexing may be achieved by adding fibers on the optical axis. A FOCOS with multiplexed fibers and wavelengths may also be used for velocity measurements.

Time-resolved electric-field-induced second harmonic: simultaneous measurement of first and second molecular hyperpolarizabilities.

The standard electric-field-induced second-harmonic (EFISH) technique for measurement of the first hyperpolarizability (beta) of nonlinear optical molecules is limited by the fact that the second hyperpolarizability (gamma) also contributes to the second-harmonic signal from which beta is deduced. We present a modified time-resolved EFISH in which the first and the second hyperpolarizabilities can be determined separately and accurately in the same experiment. We studied para-nitro aniline dissolved in a highly viscous solvent, glycerol, under conditions whereby the electric field was applied faster than the characteristic time for molecular rotation. This technique enabled the gamma contribution to the signal to be resolved separately from the beta contribution. The results confirm that for this molecule gamma contributes only ~10% of the total EFISH hyperpolarizability.

Resonantly enhanced real hyperpolarizability.

We show theoretically and experimentally how the first hyperpolarizability of a three-level molecule at a two-photon resonance can obtain a real value with strong resonant enhancement. This phenomenon arises from destructive interference of the usually dominant imaginary parts of the resonant hyperpolarizability.

Creation of second-order nonlinearity in polymers by light-induced asymmetric charge injection.

A new method for creating and enhancing second-order optical nonlinearity in polymer-dye films by asymmetric photoinjection of electric charges is introduced. The samples are composed of two separate layers, an organic photoconductor that generates the electric charges and a hyperpolarizable organic film that traps them. The nonlinearity caused by asymmetric charge injection does not arise from dipolar alignment; consequently, it can be observed either in the absence of, or to enhance, the conventional dipolar alignment nonlinearity.

Two-dimensional poling of organic and polymer films for improved nonlinear-optical properties.

Nematic films doped with molecules of high nonlinear polarizability can exhibit two-dimensional asymmetry after electric-field poling along one direction only. Consequently, these films exhibit more nonzero components of the second-order susceptibility tensor than are obtained through usual poling techniques. These films can exhibit very high nonlinear optical coefficients (close to 10(-7) esu/cm(3)) and retain most of their nonlinearity one week after removal of the poling field.