Pattern classification of UV-visible synchronous fluorescence of petroleum oils is performed using a composite system developed by the authors. The system consists of three phases, namely, feature extraction, feature selection and pattern classification. Each of these phases are briefly reviewed, focusing particularly on the feature selection method. Without assuming any particular classification algorithm the method extracts as much information (features) from spectra as conveniently possible and then applies the proposed successive feature elimination process to remove the redundant features. From the remaining features a significantly smaller, yet optimal, feature subset is selected that enhances the recognition performance of the classifier. The successive feature elimination process and optimal feature selection method are formally described. These methods are successfully applied for the classification of UV-visible synchronous fluorescence spectra. The features selected by the algorithm are used to classify twenty different sets of petroleum oils (the design set). A proximity index classifier using the Mahalanobis distance as the proximity criterion is developed using the smaller feature subset. The system was trained on the design set. The recognition performance on the design set was 100%. The recognition performance on the testing set was over 93% by successfully identifying 28 out of 30 samples in six classes. This performance is very encouraging. In addition, the method is computationally inexpensive and is equally useful for large data set problems as it always partitions the problem into a set of two class problems. The method further reduces the need for a careful feature determination problem which a system designer usually encounters during the initial design phase of a pattern classifier.

A recently developed Argon laser based system, deploying an optical fiber array of 12 silica fiber sensors each 75 m in length, with a core diameter of 200 micrometers, capable of giving real time measurements of marine phytoplankton populations of 0.1 micrograms/l is reported. The laser light is amplitude modulated and a phase sensitive detection system is used. A series of sea trials in the North Sea were conducted on board the Royal Research Vessel 'Challenger' during May 1995, to demonstrate the reliability of the system under extreme weather conditions, and that the system was capable of giving realtime fluorescence measurements. Initial tests using Fluorescein dye for calibration purposes were carried out in the laboratory. Results from the laboratory and sea trials have shown that the system is relatively insensitive to down-welling light, has long term stability and does not suffer from fouling. Also the results obtained from the laser system are generally in good agreement with results obtained by conventional phytoplankton sampling methods, giving confidence in the validity of the realtime data from the laser system.

An optical oxygen sensor system based on the process of fluorescence quenching is reported. The device detects the fluorescence quenching of a ruthenium complex [Ru(dip- phen)3(ClO)4] also known as RUDPP by sensing minute variations of a fluorescent membrane emission intensity. A dual channel design consisting of a reference branch and a sensing branch is used. Both branches include modulated light from a bright blue LED acting as the excitation source coupled through an enclosed channel to a photo-diode. The sensing branch has the RUDPP fluorescence quenching membrane sandwiched between the blue LED and the photo-diode, while the reference branch is void of such membrane. To avoid membrane saturation in the sensing branch, the excitation source is modulated with a 350 Hz square wave. The output signals of the two channels are amplified separately and subtracted from each other using a difference amplifier. Adjusting the difference amplifier output to zero effectively ensures excitation source interference cancellation. The photodiode in the sensing branch detects the intensity variations as a function of fluorescent quenching by oxygen. It was possible to isolate the fluorescent signal completely, based solely on electronic components, without the use of optical filters. The output signal from the difference amplifier is further amplified (with an adjustable gain for calibration) and displayed. Sensor performance was tested and it exhibited both excellent sensitivity and response time, compared to the recent oxygen sensors reported by others. A decrease of less than 4 percent oxygen concentration was readily detectable. We conclude that this design establishes the feasibility of developing an optical oxygen sensor, relying solely on optoelectronic components for detection.

Under picosecond laser excitation the ASE spectra of DAMC dye in polar solvents show two peaks whereas their fluorescence spectra always display only one peak. This paper presents the results of an experimental study of the ASE spectra of this molecule and offers an explanation for the observed dual ASE.

We have examined the inherent fluorescence of pepper and cinnamon samples exposed to radiation from a ⁶⁰Co gamma source. We find that in the pepper the fluorescence intensity increases with radiation dose and the ratio of fluorescence intensity at two specific wavelengths, 566 and 674 nm, increases with radiation dose. In contrast, in the cinnamon the distinction between unirradiated and irradiated is not clear. Our preliminary work on gamma ray irradiated pepper indicates that laser-induced fluorescence may be utilized to detect the absorbed dose of irradiation of food samples.

A new confocal scanning beam laser microscope/macroscope is described that combines the rapid scan of a scanning beam laser microscope with the large specimen capability of a scanning stage microscope. This instrument combines an infinity-corrected confocal scanning laser microscope with a scanning laser macroscope that uses a telecentric f*(Theta) laser scan lens to produce a confocal imaging system with a resolution of 0.25 microns at a field of view of 25 microns and 5 microns at a field of view of 75,000 microns. The frame rate is 5 seconds per frame for a 512 by 512 pixel image, and 25 seconds for a 2048 by 2048 pixel image. Applications in fluorescence are discussed that focus on two important advantages of the instrument over a confocal scanning laser microscope: an extremely wide range of magnification, and the ability to image very large specimens. Examples are presented of fluorescence and reflected-light images of high quality printing, fluorescence images of latent fingerprints, packaging foam, and confocal autofluorescence images of a cricket.

In the intense radiation fields with power density from 10⁴W/cm² to 10⁹W/cm² the essential modification of electronic states of atoms occurs displaying, in particular, in modifications of resonant fluorescence (rf) spectra. We use 'Fermi golden rule' for calculations of relative intensities and frequencies for rf multiplet for real multilevel initially unexcited atoms in two monochromatic laser fields of arbitrary intensity resonant to adjacent transitions of (Xi) or (Lambda) types and magnetic field, giving the level splittings of different values from Zeeman to Paschen-Back effect. The dependence of quasienergies on parameters obtained with the help of a sorting program permits us to define the values of parameters for which the states of the system are mixed and so to receive the correct probability amplitudes for instantaneous or adiabatic regimes of switching the perturbation. The analysis of the quasienergies and form of rf spectra permits us to get relations between the form of the spectra and modifications of electronic structure of the atom due to radiation fields and external magnetic field.

A new improved fluorescence correlation spectroscopy method for determining motional states of particles, fluorescence correlation spectroscopy with traveling interference fringe excitation (FCSTFE), is presented. In this method the modulated fluorescence signal from particles excited by an interference fringe moving at constant velocity is detected, and cosine and sine Fourier coefficients at the frequency of the traveling fringe are recorded. Autocorrelation functions of Fourier coefficients and the square of amplitude were found to express the motion of the fluorescent particles and to correspond to that of laser light scattering experiment in homodyne mode. The apparatus utilizing a photon counting system was constructed and the performance of the system in measuring diffusion coefficients of fluorescent polystyrene spheres suspended in water and ethylene glycol mixed solvents was demonstrated. The FCSTFE experiments using biological membranes are expected to yield similar information to that obtained from ideal laser light scattering experiments which are difficult to perform because of the complexity in data analysis due to stray light and multiple scattered light from the samples. The new method is also superior in avoiding severe problems, such as the damage in samples caused by the intense bleaching light, which may occur during the fluorescence photobleaching recovery.

In order for holographic storage applications to become more competitive, advances in recording materials are needed. To this end, two separate approaches for improving material properties are described, both of which involve various spectroscopic techniques for determining the efficacy of the approaches. First, post-growth high-temperature processing treatments are examined. These treatments combine oxidation/reduction for improved photosensitivity with hydrogen loading for efficient thermal fixing. Second, new rare earth dopants are considered for use in resonant two-photon recording with nondestructive readout.

Laser induced fluorescence has been observed in off the shelf optical materials when pumped with a copper vapor laser at 510 nm and 578 nm as well as when pumped with a doubled Nd:YAG laser at 532 nm at average irradiance levels of 80 and 10 watts/cm² respectively. The fluorescence spectra was observed using an avalanche photodiode photon counter and ranges from the excitation wavelength to 1100 nm. Lifetimes ranging from less than a microsecond to a millisecond, depending on the type and grade of optical material. The fluorescence is attributed to both impurities as well as intrinsic defects in the material. Fluorescence is observed in every type of material tested including UV grade fused silica, although such materials fluoresce several orders of magnitude less than standard optical grade materials such as flints and crowns.

A new technique to determine the exciton bandwidths of the lowest exciton bands in aromatic molecular crystals has been developed. This technique is based on the fact that in microcrystallites k is not a good quantum number, allowing the optical transition in whole exciton band states. In anthracene microcrystallites, the exciton band width increases with microcrystallite diameter, reaching its maximum value of 340 cm^-1. For microcrystallites larger than 65 A in diameter, the observed bandwidth decreases asymptotically to 300 cm^-1, which is interpreted to be the bandwidth of bulk crystal. For the above figures 340 cm^-1 and 300^-1 strong exciton scattering at microcrystallite surfaces is suggested. The same technique is applied to pyrene microcrystallites. The exciton bandwidth for bulk crystal is estimated to be at most 330 cm^-1. With the present results, the excitonic state and exciton relaxation processes in pyrene crystals are understood quite successfully. A brief discussion on the exciton bandwidth of the lowest exciton band in coronene is also given.

Free or conjugated pyrene molecules exhibit concentration dependent excimer fluorescence property. In membrane biophysics, single chain pyrene labeled fluorophores have been extensively used to investigate various physical properties of membranes, e.g., fusion, lateral distribution, stability, polymorphic phase behavior and lipid/protein interactions. Recently, intramolecular excimer forming dual-chain labeled dipyrenyl lipids have been proposed to probe the local conformation and dynamics of membranes. By systematically varying the length of pyrenyl chains of the probes, new information pertaining to the transverse distributions of nanosecond-resolved molecular dynamics of conjugated pyrene molecules can be revealed with spatial resolution approaching 2 - 4 angstrom along the direction perpendicular to the lipid/water interface. In this study, a 3-state kinetic model and a novel nonlinear least squares global analysis method have been used to recover the intralipid free volume and rotational and translational diffusion constants of conjugated pyrenes from the monomer and excimer fluorescence decays and steady state fluorescence intensity data. The transverse distributions of those intramolecular dynamics parameters in membranes with and without local curvatures are presented.

Picosecond fluorescence depolarization measurements of electronic excitation transfer (EET) are used to probe the structures and dynamics of polymer blends. Fluorescent chromophores are covalently incorporated into one of the polymers in the blend, and the rate of fluorescence anisotropy decay is measured using time correlated single photon counting. Analysis of the fluorescence anisotropy decays yields the time-dependence of the EET. EET is a very sensitive probe of interchromophore distance; therefore it can be used to examine the single chain structure and the spatial distribution of chains in the blend. At temperatures above the phase separation temperature, macroscopic phase separation eventually occurs. However, prior to macroscopic phase separation, the structure and dynamics of the onset of phase separation is not understood. Using EET, we are able to observe the aggregation of as few as two polymer chains at the onset of phase separation. These small aggregates are referred to an nanodomains. By lowering the sample temperature below the blend's glass transition temperature, the nanodomains can be trapped in the solid material. The number of chains in the nanodomains and the growth of the nanodomains are determined by analyzing the EET data with a detailed theory that relates the spatial distribution of chromophores to the EET observables. Varying the rate of heating allows us to study the kinetics of formation of these nanoscopic heterogeneities, and to observe the phase separation process at the molecular level, from its onset through macroscopic phase separation.

Our previous studies indicated that sterols (including cholesterol and dehydroergosterol) can be regularly distributed into hexagonal superlattices in the plane of liquid-crystalline phosphatidylcholine bilayers. It was suggested that regular and irregular regions coexist in the membrane. In the present study, we report supporting evidence for our sterol regular distribution model. We have examined the fractional concentration dependencies of dehydroergosterol (a naturally occurring cholesterol analog) fluorescence intensity and lifetime in various phosphatidylcholine and sphingomyelin bilayers. Fluorescence intensity and lifetime dips have been observed at specific sterol mole fractions. At those mole fractions, the acrylamide quenching rate constant of dehydroergosterol fluorescence reaches a local maximum. Those mole fractions match with the critical sterol mole fractions at which sterol molecules are expected to be regularly distributed into hexagonal superlattices. The results support the idea that the sterols in the regular region are embedded in the bilayer less deep than those in the irregular regions. Furthermore, finding evidence for sterol regular distribution in both phosphatidylcholine and sphingomyelin membranes raises the possibility that sterol regular distribution may occur within phospholipid/cholesterol enriched domains of real biological membranes.

Lyotropic liquid crystals belong to a class of self-assembling nanomaterials. Packing defects among molecules play an important role in the physical properties and dynamics of lyotropic liquid crystals. Time-resolved fluorescence depolarization technique has been used to detect and characterize the onset of packing defects in lyotropic liquid crystals (lipid/water mixtures). Fully hydrated binary mixtures of phosphatidylethanolamine/phosphatidylcholine (PE/PC) exhibit mesoscopic packing defect state (D) as well as 1-dimensional lamellar liquid crystalline (L_(alpha )) and 2-dimensional inverted hexagonal (H_II) phases. Based on previous electron microscopic investigations, the presence of this D state is characterized by the presence of interlamellar attachments and precursors of H_II phase between the lipid layers. Using a rotational diffusion model for rod-shape fluorophore in a curved matrix, rotational dynamics parameters, 2nd and 4th rank order parameters, localized wobbling diffusion and curvature-dependent rotational diffusion constants of rod-shape dipyenylhexatriene (DPH) labeled PC (DPH-PC) in the host PE/PC matrix were calculated from the measured fluorescence depolarization decays of DPH fluorescence. At the onset of packing defects, abrupt increases in the rotational dynamics parameters were observed. Our results suggest that rotational dynamics parameters are very sensitive in detecting packing defects in lyotropic liquid crystals. In addition, the presence of D state can be characterized by enhanced wobbling diffusional motion and order packing of lipid molecules and the presence of localized curvatures in the lipid layers.

An overview of the current and anticipated applications of optical techniques to the detection of latent fingerprints is presented. The focus is on time-resolved approaches. Other criminalistic applications that involve optical technology are taken up briefly.

A number of techniques, including 5-methoxyninhydrin/ZnCl₂, DFO, DMAC, physical developer, colloidal gold, membrane transfer and vapor development, have been explored in an attempt to distinguish between fingerprints on counterfeit currency before and after the inking. Color copying and offset printing counterfeiting were considered. The printing ink proves to be too permeable to permit ready distinction between 'before' and 'after' fingerprints. There are subtle differences between before and after fingerprint fluorescence spectra (5-methoxyninhydrin/ZnCl₂). However, given that one has to contend with finger contamination, the spectroscopy is at present not practically useful, but it shows potential if the fingerprint fluorescence spectrum can be correlated quantitatively with the ink absorption spectrum. Time-resolved spectroscopy in concert with rare-earth-based fingerprint development strategies may be useful as well.

A method has been developed for detecting DNA separated by capillary gel electrophoresis using single molecule photon burst counting. A confocal fluorescence microscope was used to observe the fluorescence bursts from single molecules of DNA multiply labeled with a thiazole orange derivative as they passed through the approximately 2 micrometer diameter focused laser beam. Amplified photoelectron pulses from the photomultiplier are grouped into bins of from 360 - 450 microseconds in duration, and the resulting histogram stored in a computer for analysis. Solutions of M13 DNA were first flowed through the capillary at various concentrations, and the resulting data were used to optimize the parameters for digital filtering using a low-pass Fourier filter, selecting a discriminator level for peak detection, and applying a peak-calling algorithm. The optimized single molecule counting method was then used to detect a separation of pBR 322 DNA from pRL 277 DNA. Clusters of discrete fluorescence bursts were observed at the expected appearance time of each DNA band. These separations were easily detected when only 50 to 100 molecules of DNA per band traveled through the detection region. This new detection technology should lead to the routine analysis of DNA in capillary columns with an on-column sensitivity of approximately 100 DNA molecules per band or better.

The ²E-⁴A₂ electronic transition of ruby at 694 nanometers has a lifetime of approximately 3 milliseconds. The wavelength, decay time and bandwidth of this transition combine to make ruby a nearly ideal fiber optic sensor material for radiation dosimetry of medical linear accelerators. Time-delayed signal detection eliminates, from the ruby signal, extraneous prompt visible light which is generated in the irradiated fiber. The prompt light originating in the fiber is produced by fluorescent and Cerenkov processes during the x-ray pulses. In addition, phosphorescent fiber signals are minimized by isolating the ruby emission with a narrow bandpass interference filter. Data is presented comparing signals from a 1 mm diameter ruby sphere and an ion chamber for a 4 MV photon beam and a 12 MeV electron beam.

Quantification of fluorescently labeled DNA in a two dimensional array provides biologists with a powerful new tool and optical engineers with a new design challenge. An objective lens for a scanning macroscopic system for this application is critically dependent on field uniformity, color correction and collection efficiency. The design of a fluorescent macro scanning objective is compared with classic designs and optimization of a unique design is discussed and tested.

Time-resolved fluorescence measurements have been carried out on charge-transfer fluorescent molecules incorporated in polymeric lattices, consisting of polystyrene cores and polyglycidylmethacrylate shells, and in polymethylmethacrylate thin films. New approaches to the analysis of fluorescence lifetime data obtained for molecules in polymer matrices had to be applied, since conventional analysis methods appeared not suitable for such strongly heterogeneous systems. The polymer lattices could be characterized by application of phase- resolved fluorescence lifetime measurements followed by maximum-entropy methods for data analysis. The thin films were studied using time-correlated single photon counting fluorescence lifetime measurements and data analysis with a home-built program based on stretched exponential decays. Interactions of the fluorescent guest molecules could be established by combined fluorescence lifetime and depolarization measurements. Suggestions for further improvements in fluorescence lifetime methods for characterization of polymeric materials have been made.