Radiation-Induced Wavelength Shifts in Fiber Bragg Gratings Exposed to Gamma Rays and Neutrons in a Nuclear Reactor.

Fiber Bragg gratings (FBGs) inscribed by UV light and different femtosecond laser techniques (phase mask, point-by-point, and plane-by-plane) were exposed-in several irradiation cycles-to accumulated high doses of gamma rays (up to 124 MGy) and neutron fluence (8.7 × 10/cm) in a research-grade nuclear reactor. The FBG peak wavelengths were measured continuously in order to monitor radiation-induced shifts.

Classification of tissue biopsies by Raman spectroscopy guided by quantitative phase imaging and its application to bladder cancer.

We present a multimodal label-free optical measurement approach for analyzing sliced tissue biopsies by a unique combination of quantitative phase imaging and localized Raman spectroscopy. First, label-free quantitative phase imaging of the entire unstained tissue slice is performed using automated scanning. Then, pixel-wise segmentation of the tissue layers is performed by a kernelled structural support vector machine based on Haralick texture features, which are extracted from the quantitative phase profile, and used to find the best locations for performing the label-free localized Raman measurements.

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.

Heterodyne interrogation scheme for Pi-phase-shifted fiber Bragg grating sensors.

A new implementation of heterodyning to measure spectral shifts of fiber Bragg gratings is described. A pair of closely matched phase-shifted gratings is used, and the separation of their transmission peaks is measured as a heterodyne beat frequency when illuminated with spectrally filtered incoherent light. This method can potentially offer high (<1  pm) resolution, fast (μs) measurement, and strain-temperature discrimination.

Multimode optical fiber photonic doppler velocimetery.

A new optical fiber head for Photonic Doppler Velocimetry (PDV) made from a combination of fiber types [multimode (MM) and single-mode (SM)] and lenses is described. The input laser beam is delivered by a SM fiber and imaged onto the target by simple optics, including an imaging lens centered inside a larger lens, whose role is to collect and image the back reflected light into the MM collection fiber. The large core of the MM fiber enhances the collection efficiency and also reduces its dependence on the target angle.