We present a novel line confocal microscope for investigating biological samples that simultaneously acquires images
from three fluorescent channels. This instrument provides the majority of the benefits of confocal microscopes, such as
depth sectioning and improved contrast, while allowing more of the excitation illumination to reach the sample area,
resulting in reduced exposure times. One configuration of the line confocal fluorescent microscope is designed to work
with a four laser illuminator, and three discrete cameras, while an alternate configuration allows the instrument to act as
a multispectral microscope that captures the fluorescent emission over the visible and NIR wavelength range.
A diffusion approximation to the radiative transfer in a medium with varying refractive index has been proposed as a theoretical model for the ultrasonic tagging of fluorescence or FluoroSound, in a scattering medium. It has been found that the diffuse modulation is a defocusing effect. Defocusing is related to scatter - more the scatter, more the defocusing and there exists a component of the defocusing effect of scatter at the ultrasonic frequency. This is in contrast to the modulation for ballistic photons that originates in the focusing effect of the acoustic lens created by the ultrasonic wave. Simulations with circular phantoms of 1.5 and 2.0cm radius have shown that defocusing is minimum when the acoustic lens is midway between the source and the detector. These results are consistent with physics and demonstrate the capability of the model to function as a predictive tool for FluoroSound instrument design. Both ballistic and diffuse FluoroSound signatures can help in the simultaneous localization of the anomaly and determination of its optical properties. As an adjunct, optimally designed ultrasound beams can be also used to enhance diffuse photon modulation signal through acoustic guidance. Optical properties provide a way to discriminate between normal and diseased tissue. FluoroSound could therefore potentially achieve a fusion of anatomical and functional information non-invasively in a single measurement. The additional information made available by this method will improve the speed and accuracy of optical imaging as a tool in the identification and validation of targets.
In this paper we describe a laser ultrasonic system for real-time monitoring of the degree of cure of a graphite-epoxy composite part during manufacturing. The system is integrated with a Resin-Transfer Molding (RTM) machine, and contains (i) a fiberized laser ultrasonic source, and (ii) an embedded ultrasonic sensor based on an intrinsic fiber optic Sagnac interferometer. Bulk ultrasonic waves generated by the laser source are transmitted into the composite structure and are subsequently detected by the embedded ultrasonic sensor. The degree of cure can be obtained from measurements of ultrasonic velocity and attenuation in the composite part. The use of an optical switch in the fiber optic delivery system of the laser ultrasonic source allows ultrasonic generation at several locations of the composite part. In this paper we discuss the design of the laser ultrasonic source and the sensor optimized for cure monitoring applications, and their integration with the RTM mold. The results of ultrasonic measurements during manufacturing of a composite specimen are presented. Our results show that laser ultrasonics offer distinct advantages for manufacturing of modern composite structures including the ability to operate in a high temperature and high pressure environment and provide distributed sensing that can cover critical areas of a component.
A new design for a fiberized laser ultrasonic source for process monitoring and bio-medical applications is proposed. The laser ultrasonic source consists of a pulsed laser, a fiber-optic cable, and a generation head. The generation head is a miniature hermetically sealed chamber, which can be embedded into solid structures or immersed in liquid media. The face of the chamber acts as a target for the laser irradiation. Bulk ultrasonic waves generated inside of the target are transmitted into the surrounding liquid media or solid structure. It is shown that ultrasonic pulses of 1 microsecond(s) to 30 ns duration can be generated. Sources with different radiation patterns with respect to the optical axis of the fiber, such as normal, angular, and focused, have been devised. An example use of these sources combined with a fiber optic ultrasonic sensor for inspection of small tubes is presented.
A new laser ultrasonic approach, the Scanning Laser Source (SLS) technique, is presented for detection of small surface-breaking defects. In this approach we do not monitor the interaction of a generated ultrasonic wave with a flaw, as in the case of traditional pitch-catch or pulse-echo methods, but rather monitor the changes in the laser generated ultrasonic signal as the source is scanned over a defect. Changes in the amplitude and frequency content of the laser-generated ultrasound are observed resulting from the changed conditions under which the ultrasound is generated over areas without and with a surface- breaking crack. These changes are quite readily detectable using existing ultrasonic detectors. The SLS system includes a fiberized portable Q-switched YAG:Nd laser, which can be combined with either convention PZT transducers or laser interferometers. Results are presented for detection fo small EDM notches and fatigue cracks on flat and curved specimens and thin plates including real structures such as an aircraft turbine disk. It is shown that the SLS technique has several advantages over the conventional pitch-catch approach, including: (i) enhanced signal-to-noise performance, (ii) detection of defects with size smaller than the ultrasonic wavelength (at least 0.125 mm length and 0.06 mm depth), (iii) ability to detect defects of various orientations with respect to the scanning direction, (iv) inspection of surfaces with complex geometry such as bore holes and turbine disk slots.
In this paper, we report the development of an intrinsic fiber-optic Sagnac-type ultrasound sensor for cure monitoring. The Sagnac ultrasonic sensor consists of a Sagnac demodulation unit and a sensing segment which can be embedded in a composite structure. The Sagnac optical demodulator is common-path and hence self-stabilized and much simpler than the alternate Fabry-Perot or Michelson type sensors which require external stabilization. Any phase variations that the sampling beams experience due to ultrasound impinging on the sensing segment are demodulated by the Sagnac sensor to produce a signal proportional to ultrasonic signal. The sensing fiber segment of the Sagnac is placed within the composite at the time of manufacture. As the composite is cured, this sensor detects ultrasound that is generated by a laser source or a pzt-transducer. The wavespeed and attenuation of the ultrasound are measured as the cure process proceeds, and these provide information on the state of cure of the composite. We discuss the details of the above intrinsic Sagnac sensor, as well as report on its characteristics including frequency response, sensitivity, and directionality. Results of a cure monitoring are also presented.
Surface and plate acoustic waves are commonly used to nondestructively investigate the near-surface region of a solid component for cracks and other defects. An attractive method of generation and detection of ultrasonic signals is laser based ultrasonics (LBU). Because it is non-contact, LBU can be implemented for inspection of limited access components using optical fibers, requiring only a small cross-sectional area for access. The work presented here employs optical fibers to remotely generate and detect ultrasound with energy focused into a selected narrow frequency band. The generation system uses a binary diffraction grating to separate the single laser beam into 10 equal but spatially separated laser beams which are focused into 10 individual fibers, thereby maximizing optical throughput to the component surface. In addition, a low noise fiberized Sagnac interferometer for ultrasonic signal measurement is discussed. The main advantage of this interferometer is improved signal-to-noise ratio, which has been achieved using an optical frequency shifting technique for biasing to quadrature and for elimination of parasitic interference between sampling beams and other unwanted beams in the interferometer. The Sagnac interferometer is truly path-matched, and as such is insensitive to low frequency thermal fluctuations and vibration noise. An acousto-optic modulator is included in the Sagnac loop, and serves a two-fold purpose: frequency shifting and quadrature biasing. Experimental results are presented for both the fiber-optic ultrasound generating array and the Sagnac interferometer.