Raman spectroscopy is a technology that can detect and distinguish materials based on the materials' Raman
scattering. However, the signal produced using this technology is usually too small to be useful. The Raman
spectrum signal can be enhanced by creating rough patches on the surface of the material. In this paper, a novel
method to produce nanometer-sized features on optical materials such as glass, fused silica, and quartz substrate is
presented. Using a femtosecond laser, the transparent materials are sputtered and deposited. When the materials
cool down, they produce structures with nano-features. These nano-features on optical materials can make
designing optical sensing systems much easier. Scanning electron microscope photos of nano-structures on quartz
substrate and optical fiber show that features less than 100 nm in size have been successfully fabricated. The 3D
micro- and nano-structures of the sensor were studied using a confocal Raman spectrum microscope and focused
ion-beam milling. Raman spectrum signals show that the strength of the signal generated by Raman scattering was
greatly enhanced compared to substrates without nano-features.
A tapered optical fiber sensor (TOFS) is a kind of optical fiber sensor that uses special geometries to measure properties
of surrounding environments or samples using evanescent waves. This paper presents a fast, highly sensitive, and
inexpensive tapered optical fiber biosensor that, using a miniature sensing structure, enables the label-free direct
detection of biomolecules. The sensor takes advantage of the interference effect between the fiber's first two modes
along the taper waist region. This effect causes some interference fringes in the transmission spectrum. Because of its
sharp spectrum fringe signals and its long biomolecule testing region, the sensor is fast and highly sensitive. To better
understand the influence of various biomolecules on the sensor, a computer simulation that varied such bio-layer
parameters as thickness and refractive index was performed. The result of 0.4 nm/nm showed that the spectrum fringe
shift of the sensor was large enough to be easily measured even when the bio-layer was nanometers thick. A tapered
optical fiber biosensor was then fabricated and evaluated with an immune globulin G (IgG) antibody-antigen pair, and
showed good performance.
A novel ultrasound generator consisting of a single mode optical fiber with a layer of gold nanoparticles on its tip has
been designed. The generator utilizes the optical and photo-acoustic properties of gold nanoparticles. When heated by
laser pulses, a thin absorption layer made up of these nanoparticles at the cleaved surface of a single mode fiber
generates a mechanical shock wave caused by thermal expansion. Mie's theory was applied in a MATLAB simulation to
determine the relationship between the absorption efficiency and the optical resonance wavelengths of a layer of gold
nanospheres. Results showed that the absorption efficiency and related resonance wavelengths of gold nanospheres
varied based on the size of the gold nanosphere particles. In order to obtain the bandwidths associated with ultrasound,
another MATLAB simulation was run to study the relationship between the power of the laser being used, the size of the
gold nanosphere, and the energy decay time. The results of this and the previous simulation showed that the energy
decay time is picoseconds in length.
A novel Fabry-Perot interferometer pressure/acoustic sensor has been designed, fabricated, and tested. The sensor
consists of an angle-polished fiber, a V-shaped groove on a silicon substrate, and a silicon nitride diaphragm on the side
wall of the groove. The design uses MEMS technology to ensure precise cavity length control and diaphragm design
flexibility. Two shock wave tests were performed on the sensors: one where a balloon was popped near the sensors, and
another that used a shock tube to simulate a blast event. Multi-sensor assemblies, where all the sensors were calibrated to
have similar center wavelengths, were also put together. The assemblies were tested simultaneously using a single laser
source. The results of all these tests showed that the performance of the Fabry-Perot sensors closely matched that of the
reference sensors used.
A novel ultrasound generator-receiver built on a single-mode optical fiber using a layer of gold nanoparticles has been
designed. The generator takes advantage of the optical and photo-acoustic properties of gold nanoparticles. Thermal and
pressure waves are generated in the nano-particle layer when it is exposed to high intensity, short duration laser
radiation. The laser radiation is applied in an intensity range that creates an instantaneous surface heating of the layer
material that, in turn, drives a pressure wave into the layer. The pressure wave interacts with the layer-substrate interface
to create stress distributions of varying strengths and qualities, depending on the intensity and duration of the initial laser
pulse. The radiation due to laser-induced heating on the nano-particles was investigated using FEA analyses. The
maximum principal stress distribution was investigated by the FEA. Results indicate that the ultrasound generation
elements have almost zero effect on the diaphragm.
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