Electro-optical modulation with immunity to optical damage by bipolar operation in potassium lithium tantalate niobate.

A method for suppressing the formation of optical damage in quadratic electrooptic devices operated at short wavelengths is presented. Formation of optical damage is attributed to the generation of a trapped space charge induced by photoionization of impurity ions by the propagating beam. It is shown that in potassium lithium tantalate niobate where the electrooptic effect is quadratic, operating the electrooptic device by a bipolar driving voltage prevents the space charge from accumulating, which inhibits the formation of the optical damage. A 6 hours continuous operation of electrooptic modulator for a 30 W/cm(2) at λ = 445 nm input beam is demonstrated.

Simultaneous quantification of the fluorescent responses of an ensemble of bacterial sensors.

Bacterial bioreporters are genetically engineered microbial strains capable of detecting specific chemicals, groups of chemicals or global biological effects such as toxicity or genotoxicity. A scheme for simultaneous selective detection of the fluorescent signals emitted by a bacterial biosensor array, able to detect four different types of toxicants, using a single photodetector (photomultiplier) is presented. The underlying principle of the scheme is to convert the spatially distributed signals from all the elements in the array to temporally distributed frequency multiplexed signals at the output of the photodetector. Experimental proof of this concept is demonstrated in a four-channel system, in which low power (a few tens of picowatts) fluorescent signals produced by the bacterial sensors are measured, while maintaining a wide dynamic range of detection (more than 3 orders of magnitude). Simultaneous monitoring of concentrations down to a few mg/l of different chemicals in a liquid sample is demonstrated.

A sub wavelength localization scheme in optical imaging using conical diffraction.

In this paper we present a scheme for the acquisition of high temporal resolution images of single particles with enhanced lateral localization accuracy. The scheme, which is implementable as a part of the illumination system of a standard confocal microscope, is based on the generation of a vector beam that is manipulated by polarimetry techniques to create a set of illumination PSFs with different spatial profiles. The combination of data collected in different illumination states enables the extraction of spatial information obscured by diffraction in the standard imaging system. An implementation of the scheme based on the utilization of the unique phenomenon of conical diffraction is presented, and the basic strategy it provides for enhanced localization in the diffraction limited region is demonstrated.

Design methodology of refractive index engineering by implantation of high-energy particles in electro-optic materials.

Slab waveguides were constructed in K(1-x)Li(x)Ta(1-y)Nb(y)O(3) crystals by the implantation of (12)C(+4) ions at 30 MeV and (16)O(+5) ions at 30 and 40 MeV. The waveguides were characterized by a prism coupler setup. A refractive index drop of 10.9% was observed in a layer formed by the implantation of (16)O(+5) ions at 30 MeV. The carbon-implanted waveguides were found to be thermally stable after annealing at 450 degrees C. A semiempirical formula for predicting the change in the refractive index given the parameters of the implantation process was developed. It is argued that the combination of the basic implantation process with the semiempirical formula can be developed to become a generic method for constructing complex electro-optic circuits with a wave-guided architecture.