Research has shown in recent years that acute and cumulative exposure to excessive ultraviolet radiation (UVR) can cause a range of degenerative ocular conditions such as pterygium, photokeratitis and pinguecula. The increase in natural solar UVR as a result of the depletion of the ozone layer has led to a greater awareness of the adverse effects of UVR on the anterior ocular surface tissues. The relevance of this lies in the fact that these tissues are not immune to photodamage and that there is selective absorption of UVR by conjunctival and corneal tissue in the anterior ocular surface. Therefore, there is a demand for more precise quantification and localisation of UVR incidence at the anterior ocular surface. A novel solar blind photodiode sensor array has been designed, constructed and tested for this purpose. The emphasis of the measurements made by this sensor system is the acquisition of real time, field based surveys of the ocular UVR light field in a broad range of insolation environments. These data will then provide a thorough database of UVR irradiances that can be related to induced damage of anterior ocular tissue. Results to date show the first measured, in-vivo, absolute UVR levels on the eye, the corresponding relative field across the eye and the presence of nasal-temporal biases that exist.
The majority of soft contact lenses are manufactured using a process of ultraviolet (UV) radiation initiated photopolymerisation. The main source of UV radiation in this manufacturing process is from UV fluorescent lamps. However, there are a number of disadvantages to these lamps, namely, their intensity varies over time and has to be constantly monitored. This paper presents a comparison between light emitting diodes (LEDs), which emit in the UV, and fluorescent lamps used in the contact lens manufacturing industry. The spectral and temporal stability of both UV sources is presented. The ability of both sources to photopolymerise 2-Hydroxyethyl Methacrylate (HEMA), the main component of soft contact lenses, was measured using FTIR and Raman spectroscopy. The percentage polymerisation of HEMA, using both sources, was calculated for several UV sensitive photoinitiators and is presented here. The potential of these UV-LEDs in replacing fluorescent lamps in contact lens manufacturing is discussed.
The sensing of hydrocarbons, such as the BTEX compounds in water, is described. These hydrocarbons, which are constituents of petroleum can find their way into groundwater due to leaks in underground tanks and in associated piping, are known to be carcinogenic and threaten flora and fauna. An infrared fiber optic sensor based on the evanescent wave generated around the bare core fiber is utilised to perform qualitative and quantitative measurements on these analytes. A silver halide fiber is used for its low spectral attenuation between 4-16mm, for within this wavelength range the analytes have characteristic absorption peaks, which allow their concentrations in water to be determined using the Beer Lambert Law. Using narrow bandpass filters centred on a characteristic peak, the sensor can be selectively tuned to a single analyte. Coating the bare core with a hydrophobic plasticised PVC film increases analyte concentration within the active region of the sensor and minimizes water interference, which is considerable at these wavelengths.
Fungal infection of food causes billions of dollars of lost revenue per annum as well as health problems, to animals and humans, if consumed in sufficient quantities. Modern food sorting techniques rely on colour or other physical characteristics to filter diseased or otherwise unsuitable foodstuffs from healthy foodstuffs. Their speeds are such that up to 40,000 objects per second can be moved at 4 metres per second, through 1 m wide chutes that offer a wide view for colour and shape sorting. Grain type foods such as coffee or peanuts are often vulnerable to toxic infection from invading fungi. If this happens, then their texture, taste and colour can change. Up to now, only visible wavelengths and colour identification have been used to bulk-sort food, but there has been little research in the ultra violet regions of the spectrum to help identify fungus or toxin infection. This research specifically concentrated on the ultra violet (UV) spectral characteristics of food in an attempt to identify possible spectral changes that occur when healthy food items like peanuts become infected with toxin-producing fungi. Ultimately, the goal is to design, build and construct an optical detection system that can use these 'spectral fingerprints' to more quickly and efficiently detect toxically infected food items.
Current trends in optical design engineering are leading to the development of new systems which can analyze atmospheric pollutants in a fast and easy way, allowing remote-sensing and miniaturization at a low cost. A small portable fiber-optic based system is presented for the spectroscopic analysis of a common gas pollutant, NO2. The novel optical set-up described consists of a small telescope that collects ultraviolet-visible light from a xenon lamp located 600 m away. The light is coupled into a portable diode array spectrometer through a fiber-optic cable and the system is controlled by a lap-top computer where the spectra are recorded. Using the spectrum of the lamp as a reference, the absorption spectrum of the open path between the lamp and the telescope is calculated. Known absorption features in the NO2 spectrum are used to calculate the concentration of the pollutant using the principles of Differential Optical Absorption Spectroscopy (DOAS). Calibration is carried by using sample gas bags of known concentration of the pollutant. The results obtained demonstrate that it is possible to detect and determine NO2 concentrations directly from the atmosphere at typical environment levels by using an inexpensive field based fiber-optic spectrometer system.
Ultraviolet radiation is potentially damaging to ocular tissues. Incorporation of UV-blocking monomers into contact lens materials provides attenuation of this radiation, leading to a reduction in UV incidence at the corneal surface. The extent and spectral characteristics of this attenuation varies according to lens type and parameters. Spectrometry has traditionally been used to measure UV attenuation of a contact lens. A novel contact lens holder was designed and constructed to facilitate the mounting of the lens in an intact and hydrated state during measurement. The UV transmission characteristics of two commercially available hydrogel contact lenses were investigated using the Perkin Elmer Lambda900 UV/VIS/NIR dual beam spectrometer.
KEYWORDS: Statistical analysis, Fiber optics, Signal attenuation, Spectrometers, Control systems, Spectral resolution, Absorbance, Biological research, In vivo imaging, Absorption
We report the development of a microspectrophotometer system for use on micro samples of mitochondrial respiratory pigments. A novel optical fiber set-up uses visible spectrophotometry to monitor the reduction of mitochondrial electron carriers. Data is presented for the reduction of cytochrome-c and for the effect of temperature on the levels of complex II/III activity from the mitochondria of rat liver. This in-vivo simulation of the reduction of cytochrome-c can be observed using a fiber optic probe which requires less than twenty (mu) l of sample for analysis. The key features of the system are: front end adaptability, high sensitivity and fast multispectral acquisition which are essential for the biological reactions which are observed.
The continuing demand for non-invasive tools for use in clinical diagnosis has created the need for flexible and innovative optical systems which satisfy current requirements. We report the development of a microspectrophotometer system for use on mitochondrial respiratory pigments. This novel optical fiber set-up uses visible spectrophotometry to monitor the reduction of mitochondrial electron carriers. Preliminary data is presented for the reduction of cytochrome-c by two methods. In the first, cytochrome-c was reduced in isolation using sodium dithionite. The second was an in-vivo simulation of the reduction of cytochrome-c using the mitochondrial extract from rat liver. The key features of the system are; front end adaptability, high sensitivity and fast scanning capabilities which are essential for the rapid biological reactions which are observed.
The development of a novel Teflon-coated optical fiber sensor for chlorinated organic determination and a PVC- coated sensor for pesticide determination is described. Current analytical techniques for these compounds in water are not suited to in-situ or on-site measurements. As a result, straight-forward techniques that feature a short analysis time, sufficient selectivity and adequate sensitivity are in high demand. An infrared fiber optic sensor which operates in the 4 to 16 micrometer wavelength region has been developed for the in-situ monitoring of chlorinated hydrocarbons and pesticides in water. The sensing element consists of a silver halide (AgClxBr1- x) optical fiber, coated with Teflon or poly (vinyl chloride) (PVC) which enriches the analyte in the evanescent wave region of the fiber. Enrichment of the analytes occurs in the minute range and is reversible. Using trichloroethylene (TCE) and alachlor as representative pollutants, evanescent wave spectrometry in the mid-infrared (MIR) region is shown to provide good performance down to single ppm levels. Absorbance data were recorded at 938 cm-1 and 1104 cm-1 for TCE and alachlor respectively. Furthermore, it is shown that the technique can be applied to multi-analyte samples.
An infrared fiber optic sensor has been developed for the in situ detection of chlorinated hydrocarbons and other pollutant species in water. The sensing element consists of a silver halide fiber, coated with an appropriate polymer. The polymer both enriches the chemical species to be measured in the evanescent wave region of the fiber and serves to exclude water from the measurement region. Evanescent wave spectrometry is then used to accurately quantify chemical species such as chlorinated hydrocarbons which have their strongest absorption bands above 10 micrometers . In order to increase the evanescent absorbance signal, and therefore the sensitivity of the sensor, a number of novel launch designs and fiber configurations has been examined. Results from a range of such configurations are presented and conclusions are drawn regarding optimum sensor design.
Spectral reflectance measurements have been made over sugar beet crops from a helicopter during 1991, 1992, and 1993 using a portable multichannel spectrometer system. In 1994 the studies were extended to demonstrate the potential for the measurement of stress in other crops. The observations are made from an altitude of about 150 m over the spectral range 420 nm to 810 nm, with a bandwidth of 5 nm. Downwelling solar irradiance and upwelling reflected irradiance are monitored by the multichannel spectrometer simultaneously. Both the absolute values of the reflectance at each wavelength and the variance of these reflectance values across each plot are shown to be related to the state of the crop. Concurrent agricultural ground truth consisting of fresh leaf weight and dry matter accumulation, is used in defining the crop yield models. The study aims to determine the appropriate radiometrically derived parameters which could be used as alternative model inputs. Although significant spectral differences exist and can be extracted by conventional band ratio or singular value decomposition techniques, the variance in the samples of ground truth data constrain the ability to define meaningful radiometric parameters. Improved experimental procedures are proposed.
A preliminary investigation into the use of multiwavelength fiber drop analyzer (FDA) for the measurement of viscosity, spectral absorbance, and refractive index is made with a view to obtaining conservative estimates of the instrumental capability of the FDA for these measurands. Some important new insights into drop vibrations are made from studies on the fiber drop traces (FDTs) of mechanically excited damped vibrations in drops with a set volume. A brief description of the feasibility measurements on the first application of the FDA in the diagnosis of disease in synovial fluid is given. Strong experimental evidence is reported for the existence of the surface-guided wave (SGW) peak of the fiber drop trace and some new insights into the nature of the FDT are suggested based on a comparative study of the FDTs from a multiple-wavelength and a single-wavelength FDA. The earlier reported drop period dependence on applied electric field is critically reexamined, a new interpretation of this effect is suggested, and an experimental study of clarification is given. Finally, a brief review of the projected capabilities of the FDA based on the work reported here is provided.
A preliminary study has been made into the temporal and spectral characteristics of internally illuminated liquid drops using the Fiber Drop Analyzer (FDA) with the objective of using this instrument for the diagnosis of disease in synovial fluid based on measurements of viscosity, absorbance and other parameters. Two approaches to the measurement of viscosity are identified and described. This study describes for the first time the operation of a multiwavelength FDA. Spectral absorbance of liquids containing 10 ppb rhodamine-b are made and the sensitivity of the FDA compared with standard spectra-photometric techniques. The variation in returned signal as a function of drop growth phase obtained from three water based solutions are qualitatively investigated and the understanding of the measurement potential of the instrument system is discussed.
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