John A. Coy

Enhanced responsivity of non-steady-state photoinduced electromotive force sensors using asymmetric interdigitated contacts.

The responsivity at a constant detection area of non-steady-state photoinduced electromotive force (photo-emf) detectors is improved by a factor equal to the number of contact pairs contained in asymmetric interdigitated surface contacts. The polar nature of photo-emf current generation requires contact asymmetry in which one increases the total signal by blocking the illumination between alternate contact pairs, in distinct contrast to the behavior of conventional interdigitated contacts fabricated upon isotropic photoconductors.

Enhanced responsivity of photo-induced-emf laser ultrasound sensors using asymmetric interdigitated contacts

An ongoing challenge for laser-based ultrasound sensors is to improve the sensitivity of adaptive photodetectors. This class of sensor is compact, robust, and simple to implement. Moreover, it can optically detect the desired ultrasound information and compensate for background industrial noise in real-time, including static and dynamic optical phase distortions, arising from relative platform motion, workpiece wobble and speckle, multimode fiber dispersion, and in-factory turbulence. A vision of this sensor is to approach the sensitivity of a shot-noise limited ideal interferometer, as well as to form large numbers of these compact detectors into small monolithic arrays, for single-shot ultrasonic image detection in opaque materials, with enhanced buried feature extraction capability. One class of adaptive photodetector is the photo-emf sensor, which combines the desired ultrasound detection and real-time noise compensation into a single semiconductor crystal. This sensor does not require any computation...

Exciton electroabsorption moments and sum rules

Abstract Excitonic electroabsorption spectra in semiconductor epilayers and heterostructures have spectral structure that contributes to modulator performance in broad-band applications such as femtosecond pulse manipulation. We define several electro-optic sum rules and electroabsorption moments combined into figures-of-merit that describe field sensitivities, bandwidths and signal-bandwidth products for semi-insulating GaAs heterostructures and AlGaAs/GaAs multiple quantum wells. The quantum-confined Stark effect and Franz–Keldysh field ionization are treated on an equal basis in the analysis. Franz–Keldysh field broadening produces larger electroabsorption than the quantum-confined Stark effect in quantum wells for electric fields smaller than 40 kV/cm.

Enhanced responsivity of photo-induced-EMF adaptive photodetectors using asymmetric interdigitated contacts: scaling limits and application to laser ultrasound sensing

We demonstrate enhanced responsivity in GaAs photo-EMF adaptive photodetectors using a novel asymmetric interdigitated electrode configuration with fine spacing. We observe enhancements even when only a fraction of an optical fringe is collected between the contacts.

High-responsivity photo-EMF receivers for laser ultrasonics

We describe the development of photo-EMF detectors that retain the adaptive advantages of conventional EMF receivers, while significantly improving responsivity. These EMF detectors use asymmetric interdigitated contacts (AIDC) to reduce the carrier transit time to increase the photoconductive gain.

Scaling limit in high multiplicity photo-EMF adaptive photoreceivers

Summary form only given.Photo-induced EMF provides an attractive means to perform adaptive interferometry that is insensitive to speckle or vibrations. One particular application is for laser-based ultrasound detection if the sensitivity of the technique can be improved. The responsivity of conventional photo-EMF receivers has suffered from small photoconductive gain, which have prevented their widespread use. We showed previously that the photo-EMF signal can be enhanced, at constant intensity, by using asymmetric interdigitated contacts to collect the EMF current. In the present work we studied the scaling of this enhancement up to 128 pairs of collecting contacts.