For delivery of ArF and KrF excimer laser light, a hollow fiber composed of a glass capillary tube and an aluminum thin film on the inside was proposed. A thin aluminum film is deposited by metal-organic chemical vapor deposition employing dimethylethylamine alane as the source material. Measured loss spectra in vacuum-UV and UV regions and measured losses for ArF-excimer laser light show the low loss property of the aluminum-coated fiber at both of the ArF and KrF excimer laser light. The straight loss of 1-m long, 1-mm bore fiber was 1.0 dB for ArF and 0.4 dB for KrF excimer lasers.

Linearly tapered hollow-glass waveguides (HGW) were fabricated using tapered silica glass tubing and wet chemistry techniques. Attenuation constants for these tapered HGWs were found to be higher than for similarly sized non-tapered HGWs, but the tapered guides showed reduced loss on bending. HGWs with rectangular and square cross-sections were also fabricated from non-circular bore silica glass tubing using wet chemistry techniques. These guides were able to maintain linear polarization of CO₂ laser light better than circular bore HGWs fabricated by the same methods, with as high as 97% of the input polarization preserved for a 227 μm X 1253 μm bore guide. The non-circular bore HGWs had higher attenuation constants than similarly sized circular bore HGWs and sacrificed some spatial purity of the output beam.

The study of output laser beam shape as a function of losses, internal diameter, off-center coupling and scattering is presented in this paper. The conditions where the beam shape has good correlation with the source beam shape were found (low losses, center alignment coupling and low scattering). A theoretical model of the mechanism of propagation of the radiation through the hollow waveguides was developed and the conditions under which the shape of beam is changed was calculated. Good agreement between the theoretical and experimental results was found.

By using a cyclic olefin polymer (COP) as a coating material inside a silver hollow glass tube, we have fabricated various fibers with special characteristic features. By changing the thickness of COP film, the red or green pilot beam has been transmitted with relatively small losses for fibers that transmit Er:YAG or CO₂ laser light simultaneously or independently with small losses. Sealing of input or output end of hollow fiber by the polymer COP has been conducted to make a special output device. The process of fabrication is simply made by using dipping and curing process. Power capability and output pattern of the sealed hollow fibers have been discussed experimentally.

Two types of flexible hollow waveguides -- cyclic olefin polymer-coated silver (COP/Ag) hollow glass waveguides and fluorocarbon polymer-coated silver (FCP/Ag) hollow glass waveguides -- specially prepared for the delivery of high power 1.06 micrometer radiation were investigated by using an oscillator-amplifier Nd:YAG laser system emitting a single pulse or a train of pulses. The length of an individual pulse was equal to 50 ps and the laser repetition rate was 2.5 Hz. The output single mode beam with a full divergence angle of 0.12 mrad was focused into the COP/Ag or FCP/Ag hollow glass waveguide and the radiation was transmitted through it under various conditions. Transmission/attenuation as a function of the input laser energy was measured together with the input/output time radiation characteristics and the spatial distribution of the output beam. The transmission losses for a straight waveguide were found to be 0.24 dB/m for COP/Ag and 0.38 dB/m for FCP/Ag hollow waveguides with the inner diameter of 1 mm. The maximum energy transmitted was 150 mJ for the train of pulses and 40 mJ for a single pulse from which follows the delivered power of 100 GW/cm². The characteristics obtained make these waveguides very promising for the delivery of high-power laser pulses in medical and other applications.

Coiled hollow glass waveguides (HGWs) were studied for use as gas sensors in the near and mid-IR regions of the spectrum. An analytic expression was obtained for the loss as a function of the number of turns, N, in the coil. The expected linear dependence of loss on N holds for radii greater than 13 cm, but deviates for smaller radii. The loss of HGWs is also shown to depend on silvering time and surface roughness.

The cyclic-olefin-polymer (COP)-coated silver hollow waveguide has been applied to transmit the 1064-nm, Q-switched Nd:YAG laser beam. The Nd:YAG laser pulses with 14 - 18 ns pulse widths (FWHM) were coupled to the 1-mm inner diameter, 1-m long waveguides. A single-shot laser energy of 142 mJ/pulse (9.8 MW) was transmitted with a transmission efficiency of 95.5% under the straight waveguide condition. The corresponding laser fluence and peak intensity at the waveguide output end reached as high as 18.1 J/cm² and 1.25 GW/cm² respectively. It was found that the waveguide bending and the increase in the pulse repetition rate caused decrease in the available maximum transmitted energy. But stable transmission of 50 mJ/pulse (6.5 J/cm²) was obtained at a pulse repetition rate of 10 Hz even under the 90-degree-bent waveguide condition (R equals 50 cm). We conclude that the hollow waveguide has the capability of transmitting high-peak-power (greater than 1 MW) laser pulses for use in some medical applications including tissue- ablation-based treatments.

The design of a handheld hollow waveguide-based probe is presented to deliver the unique output of the Vanderbilt Free Electron Laser (FEL) for medical applications. The neurosurgical hand piece incorporates a hollow waveguide, a focusing microlens, an optical fiber to deliver an aiming beam ((lambda) equals 632 nm) and a channel for purging the probe with nitrogen. The hollow waveguide is preferentially used to transmit a wavelength of lambda equals 6.45 micrometer (vibration mode of the amide-II band) and is able to tolerate the high peak intensity (greater than 10¹⁴ W/m²) of the picosecond micropulses of the FEL. The calcium fluoride lens focuses the beam to a spot diameter of 400 micrometer at a working distance of 20 mm. To maximize the transmission of the probe, the hollow waveguide is purged with nitrogen to prevent atmospheric absorption at 6.45 micrometer. Temporal broadening of the micro pulses that propagate in the hollow wave guide was studied using intensity autocorrelation measurements and beam profile measurements with a pyroelectric camera. Design consequences and application of the probe for FEL neurosurgery are discussed.

Amorphous Materials (AMI) has been engaged for several years in developing a process suitable for forming coherent imaging bundles from small diameter chalcogenide glass fibers. Currently, in a SBIR II program funded by the Navy Air Warfare Center at Patuxent River, Md., efforts are directed towards forming a bundle 10 meters in length from arsenic trisulfide glass fibers using the stacked ribbon method. A drum 10 meters in circumference was constructed on which to wind the ribbons. The fiber core diameter goal is 50 micrometer. The bundle will be 7 mm square with an active fiber area greater than 50% and an overall transmission goal of 50%. Anti-reflection coatings on both ends are provided using the AMI coating facility. A unique method of forming imaging bundles will be discussed. Images formed during evaluation will be shown.

A simple thermal imaging system based on silver halide fibers or glass hollow waveguides was constructed. The proximal end of each type of waveguide was fixed and attached to an infrared detector. The distal end of each waveguide was scanning in two directions. Such a device was used to construct a simple imaging system. The thermal image of a warm object may be formed at the focal plane of an infrared lens. The distal end of each waveguide scanned the image. The infrared radiation was transmitted through the waveguide to the detector. The signals from the detector were coupled into a suitable monitor that produced a representation of the thermal image. In preliminary experiments we used an unclad silver halide fiber of diameter 0.7 mm, and a hollow glass waveguide of diameter of 0.5 mm. A permanent magnet was attached to the end tip of each waveguide, and it was displaced by a varying electro magnetic field. The detector used was a room temperature pyroelectric detector. A MTF of about 0.2 at a spatial frequency of 1.25 cycles/mm, and a MRTD of 0.5⁰ Celsius deg at 0.1 cycles/mm were obtained with this simple imaging system.

IR glass optical fibers have been developed in order to optimize their response when they are used as evanescent wave chemical sensors. The diameter of the sensitive part of the fiber can be reduced by tapering the fiber during the drawing process or by chemical polishing. In using an FTIR spectrometer associated with a MCT detector, it was possible to evaluate the influence of the fiber diameter on the polymer coating IR signature as well as the sensitivity of a such sensor. The high flexibility of thin fibers allows the achievement of a detection probe which has been introduced in a microwave oven in order to follow a chemical reaction. It is verified that the chalcogen-based fiber is not sensitive to microwave radiation and gives excellent on line IR fingerprints to check kinetics and reaction mechanisms.

All-silica fibers with an undoped core are preferred for UV- applications. There are three different types of synthetic silica for core material, differing mainly in OH-content. Up to now, only high-OH fibers seem to be suitable for UV- applications, because fibers with low-OH core material suffer from pre-existing UV-absorbing color centers due to fiber drawing and generation of these defects during UV-irradiation. With the same loading technique used for commercially available high-OH fibers the amount of initial absorption sites and the generation of color centers, especially the E'- centers, has been reduced in low-OH fibers as well. We studied the influence of this processing on the UV-performance of low- OH all-silica fibers. Besides the E'-centers at 214 and 229 nm, the concentrations of further defects at 245 nm, 265 nm and 330 nm became smaller, too. In addition, a further step of reduction takes place during additional UV-irradiation. After these two steps of improvements, the UV-transmission is in the same range compared to high-OH fiber. This UV-VIS-NIR-fiber shows a broadband transmission from 250 nm to 1.7 micrometer wavelengths, using optimized parameters during the whole multiple-step manufacturing process.

A new type of optical fiber has been developed. It is made with all pure silica in both the core and cladding. This is possible because the cladding is a micro porous silica produced by a modified sol-gel technology. The formation and characteristics of this new optical fiber type are described. In particular the optical and mechanical properties are illustrated and described. The strength and fatigue of these optical fibers are very good, even without additional protective jackets. Unjacketed fibers have mean Weibull strengths in bending of 6.5 to 7.6 GPa with Weibull slopes in the 40 to 60 range. Fatigue results for fibers tested in ambient air, ambient water and boiling water are presented. The dynamic and static fatigue parameters are around 20. The micro porous structure of the sol-gel cladding provides sites for attaching different moieties which could activate biochemical reactions or be useful as sensing sites. Based on preliminary experiments, some possibilities are presented. In general this new structure can provide opportunities for as yet unidentified applications where chemicals and or light must be brought in close contact with body tissue to effect beneficial reactions there.

Since several years, UVI-fibers having higher solarization- resistance are well known stimulating new fiber-optic applications in the UV-region below 250 nm. Besides the description of the improved transmission properties of UV- light from different UV-sources, the mechanisms of improvement have been discussed in detail. The UV-defects, mainly the E'- center with the UV-absorption band around 215 nm, were passivated by using hydrogen-doping. Besides DUV-light, ionizing radiation like Gamma-radiation or X-rays can create similar defects in the UV-region. In the past, the radiation- damage in the UV-region was studied on silica bulk samples: again, E'-centers were generated. Up to now, no UV- transmission through a 1 m long fiber during or after Gamma- radiation had been observed. However, the hydrogen in the UVI- fibers behaves the same for Gamma-irradiation, leading to a passivation of the radiation-induced defects and an improved transmission in the UV-C region below 250 nm. On this report, the influence of total dose and fiber diameter on the UV- damage after irradiation will be described and discussed. In addition, we will include annealing studies, with and without UV-light. Based on our results, the standard process of Gamma- sterilization with a total dose of approx. 2 Mrad can be used for UVI-fibers resulting in a good UV-transmission below 320 nm. Excimer-laser light at 308 nm (XeCl) and 248 nm (KrF) and deuterium-lamp light with the full spectrum starting at 200 nm can also be transmitted.

Optical fibers and fiber bundles have been developed for UV applications in general but have specific benefits for UV applications within medicine such as excimer angioplasty and UV perforation of the heart wall in heart bypass operations. Optical fibers have been tested for transmission changes at 193 nm, 214 nm, 253 nm and 365 nm. Whereas standard synthetic silica optical fibers developed color centers within 10,000 pulses of 193 nm energy, the new CeramOptec fibers were observed to experience only minimal changes in attenuation after 100,000 pulses. Similarly under constant irradiation by a high power deuterium lamp only minor changes in the attenuation at both 214 nm and 253 nm were observed for the 'non-solarizing' UV fibers after 121 hours, whereas standard UV fibers lost up to 50% after only 24 hours of exposure. Fiber bundles have been produced which can stand up to the elevated temperatures experienced at the source end when strong UV sources are needed for specific applications. Test results and information on the testing as well as some information on the fibers tested is given below.

New applications for the Fiberoptic Evanescent Wave Fourier Transform Infrared (FEW-FTIR) method have been developed for the diagnostics of skin surfaces. Our technique allows for the detection of functional groups in the molecular structure of skin tissue noninvasively and in vivo. The FEW-FTIR spectroscopic method is direct, nondestructive, and fast. Our optical fibers for the middle infrared (MIR) range are nontoxic, nonhygroscopic, flexible, and characterized by extremely low losses. This combination of traditional FTIR spectroscopy and advanced fiber technology has enabled us to noninvasively investigate normal and cancerous skin tissue in vivo in the range of 900 to 4000 cm^-1. We have developed a special software package of programs with database for the treatment of spectral data that utilizes wavelet analysis, principle component analysis (PCA), image processing, artificial neural fuzzy logic, and data fusion. These programs provide us with the ability to make base line corrections, normalize spectra, and determine peak positions from second order derivative spectra. In this study, we investigated normal, precancerous, and cancerous skin tissue in the range 1480 to 1800 cm^-1 using these programs. The results of our surface analysis of skin tissue are discussed in terms of spectral parameters, DNA band assignments, and molecular structural similarities and differences.

A new powerful and highly sensitive technique for non-invasive biomedical diagnostics in vivo has been developed using Infrared Fiberoptic Evanescent Wave Fourier Transform Spectroscopy (FEW-FTIR). This compact and portable method allows to detect functional chemical groups and bonds via vibrational spectroscopy directly from surfaces including living tissue. Such differences and similarities in molecular structure of tissue and materials can be evaluated online. Operating in the attenuated total reflection (ATR) regime in the middle-infrared (MIR) range, the FEW-FTIR technique provides direct contact between the fiber probe and tissue for non-destructive, non-invasive, fast and remote (few meters) diagnostics and quality control of materials. This method utilizes highly flexible and extremely low loss unclad fibers, for example silver halide fibers. Applications of this method include investigations of normal skin, precancerous and cancerous conditions, monitoring of the process of aging, allergic reactions and radiation damage to the skin. This setup is suitable as well for the detection of the influence of environmental factors (sun, water, pollution, and weather) on skin surfaces. The FEW-FTIR technique is very promising also for fast histological examinations in vitro. In this review, we present recent investigations of skin, breast, lung, stomach, kidney tissues in vivo and ex vivo (during surgery) to define the areas of tumor localization. The main advantages of the FEW-FTIR technique for biomedical, clinical, and environmental applications are discussed.

The availability of low loss and high strength chalcogenide fibers is enabling many applications, including biomedical. We report the fabrication and use of chalcogenide fibers for biomedical spectroscopy, scanning near field IR microscopy (SNIM) and laser power delivery. For example, lateral resolution of 20 nm and optical resolution of about 100 nm have been demonstrated for SNIM. The preliminary results are very encouraging and more work is being performed in lowering the losses and improving the performance of the fibers in the appropriate applications.

This report describes an approach determining blood pressure noninvasively without cuff. Regarding an elastic, fluid-filled tube as a model of an arterial segment, the solution of the Navier Stokes differential equations delivers a relation between the pressure and velocity pulse. There, simulations prove a minimal sensitivity of blood pressure concerning blood density, blood viscosity and damping. Hence, these parameters can be regarded interindividually as constants. Blood pressure is essentially sensitive on the pulse wave velocity, the velocity pulse, the arterial diameter and the reflection coefficient. To perform measurements, a system was built up comprising at least one laser Doppler blood flow sensor, a high performance DSP hardware and a PC. After individual initial Riva Rocci calibration, arterial diameter and reflection coefficient can be determined. Flow and pulse wave velocity and thus blood pressure can be calculated measuring continuously at least one velocity pulse with the laser Doppler flow sensor at a superficial artery like the a. radialis and simultaneously another cardiovascular signal like an ECG or another flow pulse at a different site of the artery. As a first result, high linear correlations between systolic blood pressure and pulse transit time were obtained.

Aim of the project is the development of an in vivo endoscopic method to differentiate between cancerous from healthy tissue. The method is based on IR spectra in which each diseased state of the tissue has its own characteristic pattern as already shown in previous experiments. Two regions (1245 - 1195) cm^-1 and (1045 - 995) cm^-1 within the fingerprint (less than 1500 cm^-1) region were selected for analysis. This paper will present the technical design of the laboratory set up and outcome of the development as well as the experiments. Two lead-salt diode lasers were used as excitation sources. The IR-radiation was transmitted via silverhalide fibers to the tissue to be investigated. On the detection side another IR fiber was used to transmit the signal to an MCT-detector (Mercury-Cadmium-Telluride). Measurement modes are Attenuated Total Reflectance (ATR) and diffuse Reflection/Remission. Spatial resolution was 100 X 100 micrometer². The tissue used for these experiments was human colon carcinoma under humidity conditions. Samples were mapped using a stepper motor powered x/y/z-translation stage with a resolution of 1 micrometer. Results were compared with measurements carried out using a FTIR-interferometer and an FTIR-microscope in the region from 4000 - 900 cm^-1. Soft- and Hardware control of the experiment is done using Labwindows/CVI (National Instruments, USA).

We are developing a photoacoustic/photothermal optical fiber sensor for the minimally invasive, non-destructive detection of cancers and other tissue pathologies. It will make use of the optical, thermal, acoustic and spatial tissue properties to help make an immediate in vivo diagnosis. The sensor has the advantage that it can measure the photoacoustic and photothermal tissue responses simultaneously. Furthermore, the directions of optical excitation and of photoacoustic and photothermal detection are coaxial, thereby simplifying the measurements and their interpretation. The sensor is based on a thin transparent polymer film acting as a low-finesse Fabry- Perot interferometer that is mounted at the distal end of a multimode optical fiber and illuminated by a low power tunable diode laser. Laser pulses below the tissue damage threshold are launched into the fiber, transmitted through the polymer film and absorbed in the target, where both an ultrasonic thermoelastic wave and a low frequency thermal wave are produced. The changes in optical thickness of the film due to the acoustically and thermally induced stresses are detected interferometrically. We demonstrate the ability of the sensor to make photothermal measurements from which differences in the optical properties of phantom tissues (μ_a equals 0.05 mm^-1, μ_s' equals 0 - 2.5 mm^-1) can be detected. An absorption coefficient of 0.05 mm^-1 was found to be the lowest detectable absorption in the absence of scattering. A Finite Element model of heat diffusion is being employed to interpret the photothermal measurements made using the optical fiber sensor.

Infrared spectral analysis of human blood serum was carried out using FTIR-FEWS (Fourier Transform Infrared Fiberoptic Evanescent Wave Spectroscopy). The fiberoptic sensor elements were short (10.5 cm) lengths of unclad AgClBr fibers of diameter 0.9 mm. In order to protect the fibers from interaction with the blood serum we developed a dip coating technique, which made it possible to control the coating thickness. Three polymer materials were tested: polysulfone, polystyrene and room temperature vulcanized silicone elastomer. It was found that layers of thickness 2 - 3 micrometer provide chemical protection, while making it possible to carry out FEWS measurements. The measured spectra were analyzed by neural network analysis, to predict the concentrations of urea, uric acid, cholesterol, total protein and cretonne. The predicted concentrations were compared with the results obtained using standard chemical analysis of the blood (SMAC) and good correlation was observed, with errors of only few percent.

Deep UV application of optical fibers has been restricted due to the strong photodegradation in silica fibers transmitting deep UV light. We have developed an improved all silica preform for the production of multimode fibers with drastically improved resistance to UV-light. Two key experiments have been performed in order to characterize the solarization behavior of such fibers: (1) ArF-excimer laser and deuterium lamp photodegradation spectroscopy enables the in situ observation of defect center creation. (2) Long time photodegradation excimer laser experiments (ArF and KrF) are a good tool to predict the fiber's lifetime for applications with such lasers. Compared to standard high OH all silica fibers the optimized fibers show an exceptionally low creation of E'-centers (215 nm). Hydrogen doping of such fibers further increases the UV-resistance: Even after prolonged excimer laser irradiation (ArF: 20 X 10⁶ pulses, 5 mJ/cm², 400 Hz; KrF: 20 X 10⁶ pulses, 50 mJ/cm², 500 Hz) these fibers maintained their very high initial transmission, neither E'-center nor NBOH-center (265 nm) absorption could be observed.

The objective of this study was to examine if the diffusion process of topically applied drugs can reliably be monitored using FEWS in respect to timely distribution of the drug and chemical alterations of the drug during the diffusion process. In order to do this, recently excised human and pig skin was cut into slices of different thickness while also taking into account the different layers skin is composed of (e.g. Dermis, Stratum Corneum). These layers were first characterized spectroscopically and optically using a microscope before the drug itself was applied topically. The diffusion process was monitored by placing the sample on an ATR (attenuated total reflection) element. Time series from 1 - 4 hours were taken and the characteristic absorption bands of the drug were analyzed in the mid-infrared. By using a first order approach on Fick's diffusion equations (skin assumed to be homogeneous) we were able to fit these experimental values and to obtain diffusion constants, e.g. for water at 3376 cm^-1 in the order of 10^-5 cm²/s, which compare well with previously published values. The results indicate that this technique can be applied to the prediction of transdermal drug delivery.

Integratred optical Mach-Zehnder interferometric bio-sensors have been implemented in planar glass, by using ion-exchange waveguides. To simplify the fabrication of the sensors, periodically segmented waveguide has been used as the sensing arm, thus avoiding the need to open a sensing window over this arm. To evaluate the device performance, we performed two types of measurements. First, we measured the glucose concentration in a solution. The resulting sensitivity was less than 1 g/l, corresponding to less than 10^-4 in the cover index, for a sensor with a 1 cm long sensing arm, having a segmentation duty-cycle of (eta) equals 0.5. Second, we measured the thickness sensitivity, with respect to the adsorption of avidin molecules onto the glass substrate. The resulting thickness resolution was about 1 Angstrom. Considering that the avidin concentration in the buffer solution was 2.5 (mu) g/mL, that the full thickness of the avidin layer was 2.5 nm, and that the layer buildup time was 7 min., the corresponding sensitivity for the avidin sensor is about 0.25 nM/hr.