Thomas R. O'Meara

Imaging threshold detector using a phase-conjugate resonator in BaTiO 3

We have demonstrated an imaging threshold detector using a phase-conjugate resonator to provide high spatial resolution and signal regeneration near threshold. The device is based on spatially resolved grating erasure in photorefractive BaTiO(3) and has the capability of high resolution and low cross talk.

Materials inspection and process control using compensated laser ultrasound evaluation (CLUE): demonstration of a low-cost laser ultrasonic sensor

We demonstrate the use of a nonsteady-state photo-induced-emf adaptive photodetector as a robust, low-cost laser ultrasonic sensor. This class of sensor enables high-fractional bandwidth ultrasound detection and, in addition, all-optical compensation of adverse in-factory noise, including vibration, speckle, relative platform motion, and optical fiber modal dispersion. Reference-beam and fiber-based time-delay interferometric configurations were demonstrated, as well as the use of a diode laser as a compact optical probe.

Characterization of the photo-EMF response for laser-based ultrasonic sensing under simulated industrial conditions

Summary form only given as follows. There is a desire in manufacturing environments to nondestructively evaluate components and control processes in real time. Laser-based ultrasound has the potential to be a robust diagnostic for many applications. A simple and inexpensive sensor based on the photoinduced-electromotive effect has been demonstrated to be functional under a variety of manufacturing conditions. To optimize the detector performance, a parametric study was undertaken in which we measured the bandwidth, linearity, and sensitivity of our device as a function of various sensor material properties and optical architectures, as well as under simulated (yet quantifiable) industrial conditions. To quantify the sensitivity of the detector, an interferometric apparatus was set up with a calibrated phase signal introduced by an electro-optic (EO) modulator in one of the legs. To simulate different amplitudes of ultrasonic surface displacements, the detector output was monitored as a function of the EO drive voltage, at a fixed-drive frequency. The data show a high degree of linearity in the displacement range of interest for many commercial applications.

Single-pixel demonstration of innovative adaptive optics by use of a charge-transfer membrane light modulator

We have constructed and demonstrated a single-pixel implementation of an all-optical membrane-based spatial light modulator as a compact optical wave-front error correction device. High rates of response of as much as 20 kHz in an open-loop configuration were obtained. The device was then used in an adaptive-optics servo to compensate successfully for a 1-kHz sinusoidal phase error with a peak-to-peak excursion of approximately pi/7 rad. A small-signal servo gain of the order of 10 was inferred from the closed-loop measurements.

Expanding the capability of photo induced-emf arrays [nondestructive testing]

Summary form only given. We present architectures and simulations of a new form of laser based ultrasonic receiver arrays which are suitable for non-contacting, in situ, nondestructive evaluation. These receiver arrays are capable of high spatial resolution by employing synthetic acoustic imaging lenses formed by opto-electronic techniques and signal post-processing. The arrays capitalize on the advantages inherent in photo induced-emf sensors, specifically the simplicity, robust operation and reduced fabrication cost. The arrays could be manufactured on monolithic semiconductor structures, which would include the detector, amplifiers and post processing modules. Furthermore the arrays could easily be mass produced at relatively low cost by capitalizing on the processing and packing techniques developed for the microelectronics industry.

Optical Phase Conjugation in Laser Resonators

The use of phase conjugating “mirrors” in oscillating optical structures has been a subject of recent interest, both experimentally and theoretically. One of the attractive features of a phase conjugate resonator, PCR, is its ability to provide an output wave whose wavefront depends only on the quality of the output coupler and is essentially independent of intracavity aberrations. Several concepts for PCR’s will be presented in which either degenerate four-wave mixing or stimulated Brillouin scattering is employed as the phase conjugate mirror; advantages and drawbacks of each will be discussed.