Laser cutting of human bone and tissue is one of the oldest and most widespread applications of biophotonics. Due to the unique absorption of different kinds of tissue, choosing an appropriate laser wavelength allows selective ablation of tissue. Consequently, a large variety of laser sources with different emission wavelengths have been successfully applied to an equally large variety of medical indications. However, only a limited set of successful tissue-interaction experiments have translated into standard minimally-invasive procedures. One of the main reasons for this discrepancy between medical research and clinical practice is the lack of a commercially viable, flexible, and easy-to-use fiber optic beam delivery systems for wavelengths longer than 2 μm. In this paper, we will show how OmniGuide fibers, a new type of photonic bandgap fibers, could solve this problem. Recent performance data will be presented for both straight and bent fibers, including losses and power capacity, for delivery of CO₂ lasers. We will also highlight medical procedures where these fibers could find first applications.

Endoscopic applications of the Erbium:YAG laser have been limited due to the lack of an optical fiber delivery system that is robust, flexible, and biocompatible. This study reports the assembly and testing of hybrid optical fibers consisting of 1-cm-length, 550-micron-core, silica fiber tips attached to either 350-micron or 425-micron germanium oxide “trunk” fibers. Er:YAG laser radiation with a wavelength of 2.94 microns, pulse lengths of 70 and 220 microseconds, repetition rates of 3-10 Hz, and laser output energies of up to 300 mJ was delivered through the fibers for testing. Maximum fiber output energies measured 180 ± 30 mJ and 82 ± 20 mJ (n=10) under straight and tight bending configurations, respectively, before fiber interface damage occurred. By comparison, the damage threshold for the germanium fibers without silica tips during contact soft tissue ablation was only 9 mJ (n=3). Studies using the hybrid fibers for lithotripsy also resulted in fiber damage thresholds (55-114 mJ) above the stone ablation threshold (15-23 mJ). Hybrid germanium / silica fibers represent a robust, flexible, and biocompatible method of delivering Er:YAG laser radiation during contact soft tissue ablation. Significant improvement in the hybrid fibers will be necessary before their use in Er:YAG laser lithotripsy.

The Erbium:YAG (λ = 2.94 μm) and Erbium: YSGG (λ = 2.79 μm) laser are currently being used for tissue ablation in several medical specialties, including dermatology, ophthalmology and dentistry. Some of these applications may benefit from the availability of an optical fiber capable of delivering sufficient short-pulse, Q-switched Erbium laser energy for precise and rapid ablation of hard and soft tissues. Fiber transmission studies were conducted using both free-running (300 μs) and Q-switched (500 ns) Er:YSGG laser pulses delivered at 3 Hz through 1-meter-long samples of 450-μm germanium oxide and 425-μm sapphire optical fibers. Fiber optic transmission of free-running Er:YSGG laser radiation averaged 76% and 88% for the germanium and sapphire fibers (n = 7), respectively. Transmission of Q-switched Er:YSGG laser radiation averaged 57% and 65% for the germanium and sapphire fibers (n = 7) , respectively. Fiber optic transmission of Q-switched pulse energies as high as 42 mJ was achieved through the fibers. However, damage at the input ends of the fibers began to occur at input / output pulse energies above 40 mJ / 25 mJ (n = 2), respectively. Both germanium oxide and sapphire optical fibers are capable of transmitting sufficient free-running and Q-switched Er:YSGG laser radiation for hard and soft tissue ablation.

Polycrystalline silver halide AgClBr fibers are highly transparent in the mid-IR. They are flexible, insoluble in water non-toxic and biocompatible. These fibers are potentially useful for many applications, such as laser surgery, fiberoptic thermometry and infrared spectroscopy. Typical core/clad fibers consist of Br rich core and Cl rich cladding, and they normally have relatively large cores (diameters larger than 350μm) and low transmission losses. There is a wide interest in the development of core/clad fibers with core diameters smaller than 200μm, yet with low transmission losses. Such small core fibers would be useful for all the applications mentioned above. We have developed core/clad fibers with core diameters 140μm and with transmission losses of about 1dB/m at a wavelength of 10.6 microns. The properties of the fibers and some of their applications will be discussed.

Tissue ablation with pulses in the femtosecond regime is generally more efficient and causes less collateral and thermal damage to the surrounding tissue compared to ablation with longer pulsewidths. A compact, flexible fiber delivery system that could transmit these pulses would be advantageous over free-space beam delivery, since it would allow ultrashort pulse tissue ablation in vivo. However, the extremely high intensities associated with ultrashort pulses have deleterious effects in conventional silica fibers such as nonlinearities and fiber damage. Hollow silica waveguides with a silver inner coating essentially guide the pulses in air, thereby avoiding many of these problems. The transmission characteristics of four hollow waveguides with bore diameters of 300, 500, 750 and 1000μm and lengths up to 1m were tested using pulses from a femtosecond regime Ti:Sapphire laser operating with input pulses <150fs duration and energy up to 700 microjoules at a repetition rate of 1kHz. Coupling was primarily to the HE₁₁ mode and straight and bending losses were measured. Beam profiles were also taken at the output of straight and bent waveguides. Autocorrelation measurements show minimal pulse broadening for straight waveguides and increasing pulsewidth with waveguide bend. Diffractive micro-optics were used to focus the output and ablation of fresh cadaveric porcine liver and heart tissues was accomplished using an x-y-z translational stage moving at 1 mm/second. Targeted tissues were then processed for light and electron microscopic examination. Light and scanning electron microscopy demonstrated near a-thermal ablation with depth correlating to energy application.

Many medical applications have need of 'broad' irradiation patterns, but benefit from small diameter fibers to provide minimal invasive surgery. These applications also benefit from using the low intrinsic loss character of silica based core material as well as the power capability of a silica/silica construction. Pure silica core, all silica optical fibers are now available with an NA of 0.30 ± 0.02. Variations include fibers with non-solarizing ultraviolet transmissions as well as fibers with transmission through the near infrared [IR] region of the electromagnetic spectrum. Additionally ultra high NA fibers with silica cores and silica/silica structures are now available for use in the visible and near IR regions with effective NAs higher than 0.6. Properties of these fibers are presented and the advantages over other fibers and potential medical applications are also discussed.

In contrast to Nd:YAG-lasers no amorphous material is existing which can be used as flexible solid optical fiber for far infrared wavelength as it is emitted by CO₂-lasers. This is resulting in some disadvantages regarding beam guiding and handling, e. g. reduced motion flexibility and accessibility, relative large and stiff devices for beam guiding. It is well known that beam guiding by hollow waveguide structures is possible in principle. Main problems in the development and realisation of such kind of beam guiding systems have been limitations in transfer efficiency, flexibility, length and diameter. A possible technical solution for the medium-power range is basing on flexible silica capillaries which are coated inside with a double layer system out of silver (metallic) and silverjodid (dielectric) using a chemical deposition process. These capillaries can actually be produced with inner diameter between 0,5 mm - 2 mm and a length up to 13 m, covered by a mechanical protection out of acrylic material. The optical principle of the hollow-core-waveguides (HCW) is presented as well as some first results regarding their influence on the transported beam. So investigations will be presented for instance showing the attenuation depending on different parameters of the waveguide system. In addition to that it will be shown that, because of the influence on the wave front and of the numberical aperture, the focussability of a laser beam is reduced but nevertheless the transmitted beam can be focused to small diameters. The principal usability as well as the limits of flexible HCW in the medium power range, which is typically used in medical applications, will be demonstrated by the presented results.

Hollow glass waveguides (HGWs) have been fabricated with CdS and PbS dielectric coatings deposited on Ag. HGWs were fabricated with both single layer CdS and PbS coatings on Ag and with multilayer CdS/PbS coatings on Ag. The straight and bending losses for the Ag/metal-sulfide HGWs have been measured at 10.6 μm. Single layer Ag/metal-sulfide HGWs have theoretical losses comparable to the traditional Ag/AgI fibers, but the transmission range can be extended to wavelengths as short as 500 nm for CdS films. The use of multiple metal-sulfide layers can reduce the losses substantially, with a theoretical 3-fold reduction in loss using a 3 layer CdS/PbS/CdS stack. The measured losses of metal/metal-sulfide HGWs are higher than predicted by theory. A single layer CdS HGW has a loss 3-4 times higher than Ag/AgI. A single layer Ag/PbS HGW has a loss 8 times higher than Ag/AgI. A 3-layer Ag/CdS/PbS/CdS have a loss 50% lower than single layer Ag/CdS

New step-index all-silica fibers with high-transparency in the whole spectral region from DUV (200nm) to IR (2200 nm) will be introduced. The light-guiding core-material consists of high-purity silica, especially with low-OH content of less than 10 ppm. In UV region, the losses are mainly influenced by Rayleigh scattering and electronic transitions leading to the Urbach-tail. On the other hand, the losses in the IR region are limited by traces of OH-groups (in the order of approx. 2 ppm) and fundamental vibration-bands. The fibers possess high resistance against UV radiation in spectral region of interest, which is comparable to high-OH all-silica fibers specially developed for UV-application below 250 nm. The properties of the new fiber in respect to basic attenuation and spectral damage in the UV-region will be discussed, in comparison to high-OH fibers, based on the same measurement-technique.

Shaped fiber tips are machined or sculpted fiber ends which are formed using the glass from the fiber with no additional glass material. The tips are fabricated through either mechanical or laser machining processes. The tips are very useful in medical and industrial applications which require high power laser delivery (material or tissue cutting), even light distribution over a broad area (tissue ablation or photodynamic therapy), modified beam divergence or spot size (materials processing and communications links), or optical power redirection from the axis of the fiber in areas with small space restrictions (tissue ablation or perforations inside the human body). Descriptions of various shaped tips are provided, with concentration on tapered tips. The tapered tip is the most commonly used. The primary objective of this study was to measure the optical loss of such tapers vs. taper length, input (launch) numerical aperture (NA), and fiber diameter. The tapers fabricated and analyzed were 2:1 tapers using 0.22 NA fibers with 200, 400, and 500 um cores. The optical loss at 633nm for fibers with a 0.22 NA was measured to be 5.9dB (25% transmission) for a fully filled input NA and 0.8 dB (83% transmission) for a 0.12 input NA. The taper loss was found to depend strongly on input NA, but be relatively independent of taper length and fiber diameter. An optical modeling ray trace program was used to analyze the taper performance and validate the actual measurements. The modeling analysis will be a useful tool in design of tapers as well as other shaped fiber tips.

Noninvasive diagnostic techniques have been explored in past for detecting tissue abnormalities. Near infrared and long wavelength visible light can penetrate deep into biological tissues with minimum absorption, however light traversing biological tissues undergoes multiple elastic scattering events. The objective of the photon migration studies is to reduce or eliminate the resulting turbidity, which obscures embedded lesions. A richer information can be achieved with time resolve/time gated spectroscopy, where light is pulsed and detected luminescence is time gated to collect only early arriving photons. Our experimental set-up enhances the current state of art techniques for time resolved spectroscopy and imaging by providing alternative source that can be modulated at desired frequencies and repetition rates. In this paper we explore use of an array of Vertical Cavity Surface Emitting Lasers (VCSELs) as emitter (excitation source) as an integral part of bio-optical imaging system. In this paper we describe the effect of Laser (excitation source) Jitter on the performance of time resolved/time gated spectroscopy and imaging system. In diffusion, trans-illumination and fluorescence tomographic techniques, the timing jitter of an excitation source itself seriously degrades the temporal resolution of the collected luminescence, which significantly effects the detection and localization of tumor or other desired regions of interest. The discussed technology promises high performance, better spatial resolution and signal to noise ratio without compromising sensitivity. The structure of excitation source also allows for on-wafer testing and easy integration with other photonic components and high channel capacity free space diffractive micro-optical elements.

Trans-endoscopic Infrared Imaging (IRI) relates the possibility to conduct IRI diagnosis of internal body surfaces under minimal invasiveness. It may also be utilized to control and to optimize the thermal interactions and the potential side effects during Minimally Invasive Surgeries (MIS). However, transferring the thermal images transendoscopically requires the usage of IR imaging bundles, which are neither yet mature nor commercially available. In our setup we have used two basic types of recently-developed imaging bundles: Ag/AgI-coated Hollow Glass Waveguide (HGW) bundles and Silver Halide (AgClBr) core-clad fiber bundles. The optical setup system was consisted of IR optics (e.g. ZnSe lenses, reflective objectives) and a thermal IR camera. We have succeeded to image objects through the bundles, such as various shapes of electrically heated wires, ex-vivo biological phantoms (samples of porcine stomach) and in-vivo phantom models (mice) irradiated by CO₂ laser. Measurements were conducted for both - static and dynamic object states.

Sealed hollow waveguides have been used to transmit nanosecond red light pulses for photodynamic therapy. With a 1-mm inner diameter, 1-m long, COP (cyclic olefin polymer)-coated silver hollow waveguide, available transmitted pulse energy exceeded 15 mJ, the corresponding peak power and intensity at the output window being 3 MW and 380 MW/cm² respectively. Because the diameter of the window was as small as 1.5 mm, the waveguide can be introduced to catheters.

The utilization of scintillation light as a measure of radiation dose has many attractive features for medical applications. When high doses of ionizing radiation are being administered to cancer patients, precise and accurate dosimetry in terms of absolute dose and its location are essential. Fiber Optic Dosimeters [FOD] are unique in this pplication, since compared to other medical radiation dosimeters, they are smaller, more reliable and most significantly, they are human tissue equivalent. The principal limitation of the FOD is its signal to noise ratio, a feature that we discuss in terms of materials science and physical optics. The aim of this study is to outline a theoretical approach to dosimeter design based on geometrical optics that has the potential to increase the signal and decrease the noise.

Monitoring of tissue vitality (oxygen supply/demand) in real time is very rare in clinical practice although its use as an early warning alarming system, for clinical care medicine, is very practical. In our previous communication (SPIE 2003) we described the Tissue Spectroscope - TiSpec02, by which tissue microcirculatory blood flow (TBF) and mitochondrial NADH fluorescence were measured using a single light source (390nm). In order to improve the measurement capabilities as well as to decrease dramatically the size and cost of this clinical device, we have changed the TiSpec02 into a multi-wavelength illumination system in the new TiSpec03. In order to measure microcirculatory blood flow by laser Doppler flowmetry we used a 785nm laser diode. For mitochondrial NADH fluorescence measurement we adopted the 370nm LED. For the determination of the oxygenation level of hemoglobin (HbO₂) we used the 2-wavelength reflectance technique. This new monitored parameter that was added to the TiSpec03 increases the accuracy of the diagnosis of tissue vitality. The bundle of optical fibers used to connect the tissue to the TiSpec03, was integrated into a special anchoring methodology depending on the monitored tissue or organ. In order to test the performance of the improved TiSpec we have used it in experimental animals brain models exposed to various pathophysiological conditions. Rats and gerbils were anesthetized and the fiber optic probe was located epidurally used dental acrylic cement. During anoxia and ischemia the lack of O₂ led to a clear decrease in TBF and HbO₂ while NADH shows a large elevation. When brain activation was induced by cortical spreading depression (SD), the elevated O₂ consumption was recorded as a large oxidation (decrease) of mitochondrial NADH while TBF increase dramatically. Blood HbO₂ was not affected significantly by the SD wave.

A visible-near IR (500-1,000nm) fiber optic sensor is under development that is intended to non-invasively assess muscle metabolism through the measurement of tissue pH and oxygen partial pressure. These parameters are calculated from the spectra of hemoglobin and myoglobin in muscle. The sensor consists of transmit (illumination) fibers and receive (detection) fibers that are coupled to a spectrometer. Light from the probe must penetrate below the surface of the skin and into a 5-10mm thick layer of muscle. A study was conducted to quantify the relationship between transmit and receive fiber separation and sensor penetration depth below the surface of the skin. A liquid phantom was created to replicate the absorption (μ_a) and reduced scatter coefficient (μ_s') profiles typically found in human blood and tissue. The phantom consisted of a solution of Intralipid and India ink in the appropriate concentrations to achieve desired reduced scatter coefficient and absorption profiles. The reduced scatter coefficient of the liquid phantom was achieved to an accuracy of +/-10% compared to previously published data. A fixed illumination fiber and translatable detector fiber were placed in the liquid phantom, and the fiber separation was varied from 3-40mm. Values of μ_a and μ_s' varied from 0.03-0.40 cm^-1 and 5.0-15.0 cm^-1 respectively. Results from the experiment demonstrate a strong correlation between penetration depth and fiber separation. Additionally, it was found that penetration depth was not substantially influenced by absorption and scatter concentration. As signal-to-noise is an important parameter in many non-invasive biomedical applications, the relative signal as a function of fiber separation was determined to follow an exponential relationship.

In order to realize an efficient absorption measurement based evanescent-wave sensor, a long interaction length and a strong penetration of the optical field into the sample space is required. For an optical fiber based device, with a solid silica core immersed into a liquid sample, the strength of the evanescent field increases with decreasing core radius. When the core diameter is comparable to the wavelength of the light, a large fraction of the light propagates in the evanescent field. We demonstrate evanescent-wave sensing on aqueous solutions of fluorophore labeled biomolecules positioned in the air holes of a hollow-core photonic crystal fiber (PCF). The aqueous solutions can be positioned in close proximity to light guided in small cores without removing the coating and cladding, thus ensuring a very robust device. In order to make selective DNA detection, we coated the inside of the hollow-core PCF with a sensing layer, which by hybridization selectively immobilize specific molecules. A fluorescence measurement method, where a line-shaped laser beam expose the fiber from the side and excites the fluorophore molecules, was realized. The emitted fluorescence tunnels via the evanescent field into the fiber core(s) and is analyzed by a spectrometer at the fiber end.

Based on a fiber-optic approach, we present a fundamental in vivo study of optical properties and light transmission characteristics of single and multiple tissue layers and blood in a Sprague Dawley rat model. In our experiments, we utilize either coherent laser sources with various energy and spectral characteristics or incoherent light sources in a broadband spectral range covering the visible and near-infrared (from 400 nm to 1200 nm). The measurement techniques are based on a simple minimally invasive fiber-optic light delivery system that provides an effective method for homogeneously and precisely controlling the light irradiation of the tissue medium as well as being a highly sensitive detector of the tissue's scattered light. The delivery-sensor probes are placed into different tissue layers (skin, sub-cutaneous connective and deep connective tissue, back muscle, bone and spinal cord) and blood, and broadband spectral transmission characteristics of these media are measured in vivo. The transmission spectra are analyzed in order to determine the specificity of interaction of different tissues with light. The main goal is to determine the most effective coherent or incoherent light sources and their optimal parameters that might be used for minimally invasive therapeutic and optical diagnostics techniques.

Fluorescence is a powerful tool for biosensing, but conventional fluorescence measurements are limited because solid tumors are highly scattering media. To obtain quantitative in vivo fluorescence information from tumors, we have developed a two-photon optical fiber fluorescence (TPOFF) probe where excitation light is delivered and the two-photon fluorescence (TPF) excited at the tip of the fiber is collected back through the same fiber. In order to determine whether this system can provide quantitative information, we measured the fluorescence from a variety of systems including mouse tumors (both ex vivo and in vivo) which were transfected with the gene to express varying amounts of green fluorescence protein (GFP), and tumors which were labeled with targeted dendrimer-based drug delivery agents. The TPOFF technique showed results quantitatively in agreement with those from flow cytometry and confocal microscopy. In order to improve the sensitivity of our fiber probe, we developed a dual-clad photonic-crystal fiber which allowed single-mode excitation and multimode (high numerical aperture) collection of TPF. These experiments indicate that the TPOFF technique is highly promising for real-time, in vivo, quantitative fluorescence measurements.

This paper describes a paradigm shift in the technology for sensing electro-physiological signals. In recent years, SRICO has been developing small lithium niobate photonic electrodes, otherwise called "Photrodes” for measuring EEG and ECG signals. These extrinsic fiber-optic sensing devices exploit the extremely high electrical input impedance of Mach-Zehnder Intensity (MZI) electro-optic modulators to detect microvolt and millivolt physiological signals. Voltage levels associated with electrocardiograms are typically on the order of several millivolts, and such signals can be detected by capacitive pickup through clothing, i.e., the Photrode may be used in a non-contact mode. Electroencephalogram signals, which typically have an amplitude of several microvolts, require direct contact with the skin. However, this contact may be dry, eliminating the need for conductive gels. The electrical bandwidth of this photonic electrode system stretches from below 0.1 Hz to many tens of kHz and is constrained mainly by the signal processing electronics, not by the Photrode itself. The paper will describe the design and performance of Photrode systems and the challenging aspects of this new technology.

We report improvements of an optical fiber-based humidity sensor to the problem of breathing diagnostics. The sensor is fabricated by molecularly self-assembling selected polymers and functionalized inorganic nanoclusters into multilayered optical thin films on the cleaved and polished flat end of a singlemode optical fiber. Recent work has studied the synthesis process and the fundamental mechanisms responsible for the change in optical reflection from such a multicomponent film that occurs as a function of humidity and various chemicals. We briefly review that prior work as a way to introduce more recent developments. The paper then discusses the application of these humidity sensors to the analysis of air flow associated with breathing [1]. We have designed the sensor thin film materials to enable the detection of relative humidity over a wide range, from approximately 5 to 95%, and for response times as short as several microseconds. This fast response time allows the near real-time analysis of air flow and water vapor transport during a single breath, with the advantage of very small size. The use of multiple sensors spaced a known distance apart allows the measurement of flow velocity, and recent work indicates a variation in sensor response versus coating thickness.

Transmission experiments of Er:YAG laser light under water were performed by a laser delivery system comprising a hollow fiber and an end sealing cap. The experiments were based on a high energy fluence which produces vapor bubbles in water. Transmission properties of Er:YAG laser light were evaluated with various laser energy and pulse-repetition rates. The results show that, at high laser fluence, the attenuation coefficient of water is very small because water on light axis is fully vaporized.

Optical microsphere resonators have been recently utilized in quantum optics, laser science, spectroscopy, and optoelectronics and attracted increasing interest due to their unique optical properties. Microspheres possess high quality factor (Q-factor) optical morphology dependent resonances, and have relatively small volumes. High-Q morphology dependent resonances are very sensitive to the refractive index change and microsphere uniformity. These tiny optical cavities, whose diameters may vary from a few to several hundred micrometers, have resonances with reported Q-factors as large as 3x109. Due to their sensitivity, morphology dependent resonances of microspheres are also considered for biosensor applications. Binding of a protein or other biomolecules can be monitored by observing the wavelength shift of morphology dependent resonances. A biosensor, based on this optical phenomenon, can even detect a single molecule, depending on the quality of the system design. In this work, elastic scattering spectra from the microspheres of different materials are experimentally obtained and morphology dependent resonances are observed. Preliminary results of unspecific binding of biomolecules onto the microspheres are presented. Furthermore, the morphology dependent resonances of the microspheres for biosensor applications are analyzed theoretically both for proteins such as bovine serum albumin.

In the deep ultra-violet (DUV) and the mid infra red (MIR) regions of the spectrum, the so-called Hollow Core Waveguide (HCW) is an alternative for light-delivery systems. In addition to efficient light transportation, the HCW can be used as an intrinsic sensor: due to the long path-length through the HCW the spectral absorption of the gas under test can easily be monitored. Based on preliminary studies, the UV-region from 170 nm up to 250 nm seemed to be a very attractive alternative for gas-analyses, in comparison to the IR-region with the well-known gas-absorption bands. Using improved and adjusted components, the existing system for UV-spectroscopy was optimized. The new system will be described in details. Especially, the time-response using an external gas-feeding system is an additional parameter of the studies. Within the spectral range of the new CCD-array spectrometer from 175 to 210 nm, highly structured spectra have been determined, with a spectral resolution of less than 50 pm. In nitrogen, selected gases with extremely low concentrations in the order of 1 ppm have been measured; the absorption spectra are compared to those from IR measurements, using the HCW approach, too.

When near infrared spectroscopy (NIRS) is applied noninvasively to the adult head for brain monitoring, extra-cerebral bone and surface tissue exert a substantial influence on the cerebral signal. Most attempts to subtract extra-cerebral contamination involve spatially resolved spectroscopy (SRS). However, inter-individual variability of anatomy restrict the reliability of SRS. We simulated the light propagation with Monte Carlo techniques on the basis of anatomical structures determined from 3D-magnetic resonance imaging (MRI) exhibiting a voxel resolution of 0.8 x 0.8 x 0.8 mm³ for three different pairs of T1/T2 values each. The MRI data were used to define the material light absorption and dispersion coefficient for each voxel. The resulting spatial matrix was applied in the Monte Carlo Simulation to determine the light propagation in the cerebral cortex and overlaying structures. The accuracy of the Monte Carlo Simulation was furthermore increased by using a constant optical path length for the photons which was less than the median optical path length of the different materials. Based on our simulations we found a differential pathlength factor (DPF) of 6.15 which is close to with the value of 5.9 found in the literature for a distance of 4.5cm between the external sensors. Furthermore, we weighted the spatial probability distribution of the photons within the different tissues with the probabilities of the relative blood volume within the tissue. The results show that 50% of the NIRS signal is determined by the grey matter of the cerebral cortex which allows us to conclude that NIRS can produce meaningful cerebral blood flow measurements providing that the necessary corrections for extracerebral contamination are included.

Short Er:YAG laser pulses were delivered by a cyclic olefin polymer coated silver hollow glass (COP/Ag) waveguide specially designed for a high power radiation. Er:YAG laser was Q-switched by an electro-optic shutter - LiNbO₃ Pockels cell with Brewster angle cut input/output faces. The maximum energy output obtained from this system was 29 mJ with the length of pulse 69 ns corresponding to 420 kW output peak power. The system was working with the repetition rate of 1.5 Hz. A delivery system composed of a lens (f = 40 mm), protector and waveguide with the 700/850 μm diameter and 50 cm or 1 m length. The measured maximum delivered intensity was 86 MW/cm² what corresponds to the transmission of 78.6 % for whole delivery system. Using of a sealed cap, this delivery system gives a possibility of the contact surgical treatment in many medicine branches, for example ophthalmology, urology or dentistry.

No abstract

Surface Plasmon Resonance (SPR) is an optical phenomenon which can be used for the sensitive detection of macromolecular interactions at a sensor surface by detecting small changes in refractive index resulting from adsorbed species. Previous work toward fiber-optic SPR sensors has employed metal films sputtered or evaporated onto waveguides. In this work, a novel nanofabrication approach using a combination of self-assembled monolayers (SAMs) and electrostatic layer-by-layer (LbL) self assembly was investigated toward precise deposition of metal nanomaterials onto fibers, which could enable excellent control over surface properties as well as provide an enhanced plasmon signal due to the roughened metal surfaces. Furthermore, nanoassembly allows production of nanocomposite materials that may possess attractive optical properties. To study this possibility, ultrathin films with architecture {Au/polymer}n (n=1-10) were deposited on flat silica substrates, then on optical fibers. Physical measurements of deposited mass were performed with quartz crystal microbalance (QCM). The influence of particle size, number of layers, and distance from surface on the magnitude of optical signals was investigated by measuring the absorption spectrum for each configuration. In addition, sequential and simultaneous bimetallic (Au/Ag) film layering and testing was also completed to assess the effect of nanocomposite metal films on SPR signals. Fluorescent anti-Immunoglobulin G (IgG) antibody was deposited on the outside surface, which was then exposed to IgG for observation of shifting resonance peak due to target binding. The results show that nanoassembly is a promising approach to precise yet cost-effective fabrication of optical biosensors.

We have developed a new technology for the non-invasive continuous monitoring of tear glucose using a daily use, disposable contact lens, embedded with sugar-sensing boronic acid containing fluorophores. Our findings show that our approach may be suitable for the continuous monitoring of tear glucose levels in the range 50 - 500 μM, which track blood glucose levels that are typically ≈ 5-10 fold higher. We initially tested the sensing concept with well-established, previously published, boronic acid probes and the results could conclude the used probes, with higher pK_a values, are almost insensitive toward glucose within the contact lens, attributed to the low pH and polarity inside the lens. Subsequently, we have developed a range of probes based on the quinolinium backbone, having considerably lower pK_a values, which enables them to be suitable to sense the physiological glucose in the acidic pH contact lens. Herein we describe the results based on our findings towards the development of glucose sensing contact lens and therefore an approach to non-invasive continuous monitoring of tear glucose using a contact lens.

Hollow glass fibers for delivery of mid-infrared lasers are drawn from a glass-tube preform to produce a long and flexible hollow fiber at low cost. A silver film is coated on the drawn glass tube with a wall thickness as small as 9.1 μm. A Pyrex-glass hollow fiber with an inner diameter of 340 μm and a length of 42 cm shows a loss of 3.0 dB for Er:YAG laser light.

Optimization of illumination-collection parameters may lead to an improvement in the efficacy of fluorescence spectroscopy devices for minimally invasive disease detection. While device-tissue interface geometry has been shown to have a strong influence on the origin of detected fluorescence, prior studies have tended to focus on systems which deliver and collect light at approximately normal incidence to the tissue surface. Optical fibers with beveled surfaces enable the delivery and/or collection of light at a range of angles. This feature may make it possible to interrogate subsurface tissue regions with a greater degree of spatial selectivity. In this study, simulations were performed using a Monte Carlo model of fluorescent light propagation in order to estimate the behavior and potential limitations of this approach. The effect of tissue optical properties, illumination angle, collection angle and illumination-collection fiber separation distance were investigated. Results indicated that beveled fiber probes may significantly improve the ability of fiberoptic probes to selectively interrogate specific tissue regions or layers, however, the advantage over flat fibers is reduced as tissue attenuation increases.

Speckle noise in OCT images originates in the high spatial coherence that allows interference between light backscattered from the tissue specimen. Speckle reduction techniques on which many investigators have reported all rely on averaging independent intensity images of the speckle field. Recently, we completed an experiment to test speckle reduction by averaging independent intensity images formed by incoherent spatial modes emitted from a broadband light source. Broadband light coupled into a multimode optical fiber produces a number of spatial modes that propagate along the waveguide at distinct velocities. When the spatial modes propagate length, modes become mutually incoherent. When the multimode fiber is placed in the source path of a Michelson interferometer, each spatial mode produces an intensity image of an independent speckle field. To illustrate speckle averaging using independent spatial modes, we recorded low-coherence interferograms of a scattering metallic surface using single mode and multimode source fiber. The interferogram recorded using a single mode source fiber is indicative of that observed by conventional OCT. Speckle noise in the interferogram recorded using the multimode source fiber is substantially reduced compared to the single mode case.