For the first time, we perform a theoretical investigation into the operation of a multilayer nanocomposite based optical fibre surface plasmon resonance hydrogen sensor. The sensor consists of Pd nanoparticles embedded in host material of Ta<sub>2</sub>O<sub>5</sub> over a thin continuous film of Ag, in place of a small unclad section of the fibre core. We compare the operation of this device to a sensor employing an individual multilayer based sensing stack (Ag/Ta<sub>2</sub>O<sub>5</sub>/Pd) by measuring the normalised output power through the fibre, and the sensor sensitivity. A much smaller modulation layer thickness is required in the NC structure in order to achieve the same spectral shift of the resonance location as compared to the IM based structure, thus indicating a faster response time. In both sensor types, sensitivity increased to a maximum with increasing modulation material thickness, beyond which it began to fall off. The NC based structure operated with overall higher sensitivity than the IM structure.
Hydrogen sensing technology by definition necessitates high accuracy, rapid response time, and durability. Thin film Pd has demonstrated excellent use in this field owing to large sensitivity and fast detection time. Interaction with hydrogen causes a crystallographic phase transition of the Pd lattice resulting in expansion. Subsequently repeated hydrogen loading cycles increases mechanical stress on the Pd lattice and thus leads to delamination of the hydrogen sensitive layer. By alloying Pd with Y, it is possible to mitigate the unwanted phase transition thereby significantly improving durability. We present the first optical fibre surface plasmon resonance (OFSPR) hydrogen sensor based on a multilayer Ag/SiO<sub>2</sub>/PdY deposited on the unclad core of a silica optical fibre. In this submission, we investigated the spectral influence of fibre numerical aperture in addition to Ag and SiO<sub>2</sub> thickness within the multilayer. Sensor sensitivity and figure of merit were found to reach a maximum when a fixed Ag thickness was paired with a set of corresponding SiO<sub>2</sub> thicknesses. We demonstrate that changing the thickness of one of these layers alters the optimal thickness of the other. We present a figure by which an array of optimal sensing structures can be determined. The largest sensor figure of merit in this study was found to be 0.062732, and was produced using Ag = 50nm, and SiO<sub>2</sub> = 70nm. This sensor operates with sensitivity of 17.57nm to 4% hydrogen, detection accuracy of 0.014282nm<sup>-1</sup>, and operated at a spectral centre of 524.09nm.
In this paper, we experimentally studied both the bright-field and fluorescence images of microspheres by conventional and confocal scanning polarization microscopes. A qualitative analysis have been given to show a physical picture on the imaging of the microspheres. Emission spectra from melamine formaldehyde microspheres stained with Ethidium Bromide or covered by thin shell of CdTe nanocrystals have been experimentally studied. We adopted analytical expressions describing the resonance spacing in order to determine the size of the microspheres.
We present a description of our work in recent years on imaging in
confocal microscopy in the context of biological applications. The
first system presented considers a Nipkow disc type arrangement where a detailed investigation of optimal aperture arrangements and spacings is performed. The effect of varying these parameters on the optical sectioning characteristics and on the light throughput is evaluated. Novel routes to achieving alternative multi-aperture configurations are presented. A programmable array microscope demonstrator is described using a ferroelectric liquid crystal SLM. A novel system is also proposed which uses variable focus microlenses in a confocal imaging system. We also discuss current trends in confocal microscopy in biology.
Images of the microspheres are studied in three-dimensions by using the confocal and conventional scanning polarization microscopes. It is found that the polarization of the detected signals is mainly parallel to the initial polarization which is due to the high extinction coefficient of the confocal system. Arc pairs are observed at the edge of the microspheres with the conventional polarization microscope with a crossed analyzer. Theoretical analysis are given by using the vector field theory and the image formations of the two systems.
The direct-view microscope is a confocal microscope which allows faster image acquisition rates than typical confocal scanning optical microscopes through the use of a pinhole array rather than the usual single pinhole. We present a theoretical investigation of the effects of source coherence on optical sectioning in direct-view microscopy. As a first step we present an equation which describes the optical sectioning strength of a coherent source brightfield DVM employing an infinite pinhole array. By simulation of both this and the finite array equation which show the existence of certain `principal' sidelobes which are likely to represent the most problematic artifact of coherent source imaging. By further analysis of the infinite array equation, we arrive at an expression which describes the defocus positions where the principal sidelobes occur. Finally, we move on to show how rectangular arrays are predicted, by the infinite array equation, to outperform square arrays and we show examples of this.
We present a programmable array microscope (PAM) which uses a pair of
ferroelectric liquid crystal spatial light modulators (FLC SLMs). The
system is similar to a confocal imaging system called a direct-view
microscope (DVM), in which scanned aperture arrays are used to obtain
real-time confocal images. The PAM, unlike the DVM, allows arrays to
be scanned electronically rather than mechanically. In our system,
one SLM is placed in the source plane of a conventional microscope
system; the other is placed in the detector plane. Confocal aperture arrays
are displayed and scanned synchronously on the SLMs and confocal
imaging results. The resolution is improved when compared to a
similar previously presented system which employed a single SLM. We
present axial resolution measurements for a variety of array
dimensions and investigate the use of aperture correlation techniques
to improve the light throughput in the devices.
We describe a Programmable Array Microscope (PAM) system which is implemented using a single Ferroelectric Liquid Crystal Spatial Light Modulator in a double pass configuration. The SLM array is placed such that it is in both the source and detector planes of a confocal microscope. The pixels of the SLM are arranged to form an aperture array similar to the type found in confocal direct- view microscopes (DVMs). Among the advantages of the PAM system over DVM systems are a lack of moving parts, and complete control over the aperture function. We present optical sectioning curves taken using scanned grids of square apertures of varying number and spacing, showing how these parameters affect the confocal behavior. In particular, we demonstrate the effect which the finite contrast ratio of the SLM pixels has on the optical sectioning curve and introduce a simple theory which explains this effect. Finally, we show confocal images captured from test samples using the PAM system.
Using a new device which contains an array of microlenses whose focal lengths can be electrically varied, we have been able to control the input from one microlens to a single mode fiber using an applied voltage. For such a microlens array many closely-spaced focal spots can be generated in parallel, and electrically switched to address, potentially, an array of receiver fibers. We show how the particular switching characteristics of the device, whereby the lenses switch from diverging to converging, serves in turn to disperse light and to focus it into the fiber.
Confocal fluorescence imaging is widely used, particularly for biological applications, and also notably in direct-view microscopes. Recent work has compared the use of coherent and incoherent illumination sources on the optical sectioning characteristics of fluorescence direct-view microscopes. However this detailed comparison has been done in theory. This paper addresses the experimental aspects of using coherent light sources in fluorescence imaging using a range of finite- sized, multiple-aperture arrays. The experimental difficulties of choosing a suitable uniform, flat, fluorescent plane with a high quantum efficiency are considered. Axial response curves obtained with a fluorescent laser dye sample are presented.