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A Michelson Objective based Full Field Optical Coherence Tomography system is combined with fluorescence imaging and deconvolved with the point spread function to enhance the image resolution of biological tissue, exceeding classical resolution limits.

Der Transport von Personen und Wirtschaftsgutern mit einer Art Rohrpostsystem steht mit der Entwicklung der Hyperloop-Technologie vor einer Renaissance, technisch innovativ, nachhaltig energieeffizient und wirtschaftlich realisierbar. Global werden Versuchsstrecken geplant und vorbereitet, um die Machbarkeit zu uberprufen. An dem von SpaceX seit 2016 jahrlich ausgeschriebenen internationalen studentischen Wettbewerb „Hyperloop Pod Competition“ in Hawthorne, Los Angeles, nahm das Hochschulteam der Hochschule Emden/Leer und der Universitat Oldenburg „HyperPodX“ bereits zweimal am Konstruktionswettbewerb mit nur noch 19 weiteren Teams teil.

Shock wave emission induced by intense laser pulses is investigated experimentally. The present work focuses on the conditions of shock wave emission in glycerine and distilled water during the first bubble collapse. Experimental investigations are carried out in liquids as a function of temperature and viscosity. Comparison is made with the theoretical work of Poritsky (Proc 1st US Natl Congress Appl Mech 813–821, 1952) and Brennen (Cavitation and bubble dynamics, Oxford University Press 1995). To the best knowledge of the authors, this is the first experimental verification of those theories.

Laser-induced spherical shocks generated in water close to a liquid–air boundary break through this boundary layer and spread out in air as an elliptical or a cylindrical shock wave. After breakthrough, the shock wave is accelerated and its velocity in air is different perpendicular and tangential to the water surface. Immediately after surface breakthrough both shock velocities are higher than the shock velocity in liquid. If the position of the breakdown is about 0.1 mm below the water surface a laser-induced relatively weak spherical shock spreads out into the water space and also breaks through the water–air boundary. The surface breakthrough of the initial spherical shock wave drives a non-spherical strong shock wave in the air space above of the water surface. After some microseconds both velocity components of the shock in air as well as the initial weak shock in liquid propagate with sound velocities, respectively. As a consequence, the dynamical process is very different above and below the liquid surface if the initial optical breakdown occurs still in liquid but very near to the water–air boundary. The initial spherical shock in liquid will not only be transmitted into air but also reflected from the surface layer. Those rarefaction waves decrease the pressure in the liquid and interfere with the initial spherical shock. A cavitation bubble arises in liquid subsequently to the spherical shock wave. In this investigation the propagation of shock waves below and above the boundary liquid–air after surface breakthrough are in focus. The test liquid is distilled water. The phenomena have been studied by observing the boundary layer simultaneously from below and above the water surface with two synchronized CCD cameras.

A novel experimental method for the measurement of cavitation bubble dynamics is presented. The method makes use of a collimated cw HeNe laser beam that is focused onto a photodiode. A cavitation bubble centered in the laser beam leads to refraction and thus changes the diode signal. With sufficient temporal resolution of the measurement, the evolution of the bubble dynamics, and in particular, the collapse, could be well resolved (limitation is only due to diode response and oscilloscope bandwidth). In the present work this is demonstrated with cavitation bubbles generated with high-power nanosecond and femtosecond laser pulses, respectively. Bubble evolution is studied in two different liquids (water and glycerine) and at different temperatures and pressures.

Levels of dissolved manganese in water samples down to 80 μg/l are measured using emission spectroscopy. Optical emission spectroscopic methods tend to be insensitive in liquids due to strong quenching processes. Laser induced breakdown spectroscopy (LIBS) within a cavitation bubble overcomes this restriction. The output of a double pulsed Q-switched Nd:YAG laser, operated at 532 nm, is coupled to an optical fibre. The fibre guides the laser pulses to a silicon target immersed in a water sample contaminated with manganese. The cavitation process is initiated with the first laser pulse. At maximum bubble expansion, the second laser pulse ignites the plasma in the vapour/gas-filled cavitation bubble. Emission is collected by an additional optical fibre located near the bubble. Characteristic spectral line intensities of manganese are recorded and correlated to an internal calibration standard. Spectral analysis and data acquisition are carried out using an image-intensified optical multi-channel analyser.

In this investigation our interest is focused on the conditions of emitting shocks in glycerine and distilled water during the first bubble collapse as a function of liquid temperature, viscosity, and the position distance between the laser breakdown spot and the boundary of liquid-air

(PPLN) crystal pumped by two single-frequency diode lasers. A maximum DFG power of 1.6 μW at 3.6 μm was generated with a pump power of 61.4 mW at 832 nm and a signal power of 41.5 mW at 1083 nm incident on a 19-mm-long PPLN crystal, which corresponds to a conversion efficiency of 335 μW W-2 cm-1.

Digital Micromirror Device based microscopy combines fast confocal 4D-microscopy along with conventional methods for light microscopy and new technological approaches to a versatile tool for the observation of in vivo processes in living biological cells and measurement of technical surfaces. Due to the use of variable size pinholes and adjustable scan patterns conditions for confocal measurement can easily be optimized to the prerequisites of the sample "on the fly".

Cavitation is a major source of erosion for instance of ship propellers, pumps and water turbines. In such systems low pressure regions (pockets) exist where the water pressure suddenly becomes very low, almost a vacuum. These growing pockets, i.e. the “cavitation bubbles” propagate to high pressure regions, where they collapse immediately.

Cryogenic procedures are fundamental tools in modern biology, e.g. for conservation or purification of biological materials. The processes occurring in biological cells and tissues during freezing and thawing are subject to ongoing research. Optimization of cell survival rates demands the development and evaluation of exactly defined temperature profiles. 4D-DMD-microscopy is capable of imaging these highly dynamic processes with high spatial and temporal resolution, utilizing well established staining procedures for differentiating structures of interest.

By two-photon time-resolved confocal 4D-microscopy it is possible to image fluorescent objects at a high spatial and temporal resolution. The usage of femtosecond-laser light creates a two photon effect and therefore reduces bleaching of the fluorophore. With this technique 4D-visualization of dynamic processes in living cells is possible.

One of the most frequently performed blood tests, measurement of total hemoglobin concentration, requires invasive blood sampling. We developed an optoacoustic technique for noninvasive monitoring of total hemoglobin concentration and other blood variables by probing the radial artery or other blood vessels. Recently, we designed and built a focused, wide-band, polymer-based optoacoustic transducer for blood vessel probing with high, submillimeter lateral resolution and incorporated it into a highly portable, laser diode-based optoacoustic system. The focused optoacoustic transducer combines a fiber-optic delivery system and a wide-band piezosensor. First, we experimentally measured transducer parameters (lateral resolution, sensitivity, focal length). To test the transducer capabilities in measurement of total hemoglobin concentration and other blood parameters from blood vessels, we prepared a tissue phantom simulating strongly-scattering tissues with blood vessels of different diameters, spacing, and depths. Optoacoustic signals were acquired from blood at different hemoglobin concentration and oxygenation during transducer scanning over the phantom. In vivo experiments were performed from radial arteries and peripheral veins of different size, depth, and spacing. Submillimeter lateral resolution was obtained in the in vitro and in vivo experiments. The high resolution combined with the wide-band detection of the optoacoustic waves can be used for monitoring of blood variables in blood vessels with high accuracy, sensitivity, and specificity.

Time resolved 3D-microscopy using DMD-arrays utilizes the principles of confocal microscopy. Application fitted patterns optimize optical imaging of reflective, transparent, and fluorescent objects. High spatial resolution is achieved simultaneously with high temporal resolution due to fast DMD control. This enables to visualize and track processes in vivo within living biocells.

Spectroscopic results with laser induced breakdown spectroscopy (LIBS) in liquids have shown a signal improvement using double pulse experiments compared to single pulse measurements. A setup of two Q-switched Nd:YAG lasers in an orthogonal arrangement have led to bright illuminated plasma inside cavitation bubbles. A Nd:YAG laser pulse focussed by a lens (6 ns@532 nm, 2.9*10 19 W/m 2 ) into the center of a water filled cuvette gives rise to a cavitation bubble. A second tightly focused Nd:YAG laser pulse (5 ns@1064 nm, 3.1*10 19 W/m 2 ) induces a plasma at approximately 70 μs delay within the cavitation bubble. These absolutely reliable processes allow to capture image sequences of plasma filled cavitation bubbles with an ultrafast camera. The optical emission is guided via a quartz fibre to a Czerny-Turner spectrograph and recorded by an intensified CCD camera. A delay time of more than 1.7 μs between plasma ignition and spectroscopic data taking is necessary to avoid inverse bremsstrahlung and residual lines arising from bright plasma emission. Characteristic spectral line intensities of manganese (Mn) and Palladium (Pd) are recorded and correlated with an internal calibration standard using strontium (Sr) and chromium (Cr) respectively. The LOD of manganese is 0.3 mg/L.

Time resolved 3D-microscopy using DMD-arrays utilizes the principles of confocal microscopy. Application fitted patterns optimize optical imaging of reflective, transparent, and fluorescent objects. Diffraction limited spatial resolution is achieved at simultaneously high temporal resolution due to fast DMD controlling. This enables to visualize and track processes in vivo within living biocells as well as fast structural volume and surface mapping.

We developed an optoacoustic technique for noninvasive, accurate, and continuous monitoring of total hemoglobin concentration and venous oxyhemoglobin saturation by probing specific blood vessels. In this work we report the development and tests of novel, focused optoacoustic transducers that provide blood vessel probing with sub-millimeter lateral resolution. The focused transducers were incorporated in our highly portable, laser diode-based optoacoustic monitoring system for pre-clinical and clinical tests. Our studies demonstrated that: 1) the focused transducer response is linearly dependent on blood total hemoglobin concentration with a high correlation coefficient; and 2) the sub-millimeter lateral resolution provided higher specificity of blood vessel probing, in particular, for smaller blood vessels such as the radial artery (diameter 2-3 mm).

Fast-beam collinear laser spectroscopy with resonance detection by counting of fluorescence photons provides a versatile tool for precise determinations of nuclear ground-state properties. The intrinsic high sensitivity of this method can be further increased by almost three orders of magnitude if measuring schemes based on ion or atom counting are introduced. The optical pumping from one atomic state to another at an appreciably different excitation energy is detected via state-selective collisional charge exchange processes and charge-state separated atom or ion counting. Applications of these techniques on alkaline earth, noble gas, mercury and thallium beams is examined.

An enukleierten Augen führten wir experimentelle Untersuchungen zur Ablation des Trabekelwerks (AT) durch. Eine Quarzfaser wurde durch die Vorderkammer bis zum gegenüberliegenden Trabekelwerk geführt und dieses mit einem Excimer Laser mit 248 und 308 nm bestrahlt. Es reichte eine Energie von 0,3-1,5 mJ, um eine offene Verbindung zwischen Vorderkammer und Schlemmschem Kanal herzustellen. Die histologische Untersuchung der Bulbi bestätigte die klinische Beobachtung einer offenen Verbindung zwischen Vorderkammer und Schlemmschem Kanal. Dabei wurde keine nennenswerte Hitzewirkung an den abladierten Geweben festgestellt. Auf die genannte Weise konnten wir auch Cyclodialysen und basale Iridektomien durchführen. Die Durchführung der Operation ist einfach und sehr treffsicher., In an experimental investigation we examined the possibility to create an open pathway between the anterior chamber and Schlemm 's canal by excimer laser ablation of the trabecular meshwork (AT) in enucleated eyes. A quartzfiber was directed through the anterior chamber to the opposite chamber angle. With an energy of 0.3-1.5 mJ and wavelenghts of 248 and 308 nm pores were easily made into the trabecular meshwork leading to a direct connection between the anterior chamber and Schlemm's canal. This result was confirmed by histologic examination of the globes. The trabecular meshwork has disappeared completely. The surrounding tissue reveals only minimal thermal effects due to the laser burns. With the same method cyclodialysis and basal iridectomy may be performed. The operation is simple and effects can be placed with great accuracy.

Our experiments on transmitting high-power excimer laser pulses through optical fibers and our investigations on excimer laser ablation of hard tissue show the feasibility of using the excimer laser as an additional instrument in general and accident surgery involving minimal invasive surgery. By combining XeCl-excimer lasers and tapered fused silica fibers we obtained output fluences up to 32 J/cm2 and ablation rates of 3 m/pulse of hard tissue. This enables us to cut bone and cartilage in a period of time which is suitable for clinical operations. Various experiments weOur experiments on transmitting high-power excimer laser pulses through optical fibers and our investigations on excimer laser ablation of hard tissue show the feasibility of using the excimer laser as an additional instrument in general and accident surgery involving minimal invasive surgery. By combining XeCl-excimer lasers and tapered fused silica fibers we obtained output fluences up to 32 J/cm2 and ablation rates of 3 μm/pulse of hard tissue. This enables us to cut bone and cartilage in a period of time which is suitable for clinical operations. Various experiments were carried out on cadavers in order to optimize the parameters of the excimer laser and fibers: e.g., wavelength, pulse duration, energy, repetition rate, fiber core diameter. The surfaces of the cut tissue are comparable to cuts with conventional instruments. No carbonisation was observed. The temperature increase is below 40°C in the tissue surrounding the laser spot. The healing rate of an excimer laser cut is not slower than mechanical treatments; the quality is comparable.re carried out on cadavers in order to optimize the parameters of the excimer laser and fibers: e.g., wavelength, pulse duration, energy, repetition rate, fiber core diameter. The surfaces of the cut tissue are comparable to cuts with conventional instruments. No carbonisation was observed. The temperature increase is below 40°C in the tissue surrounding the laser spot. The healing rate of an excimer laser cut is not slower than mechanical treatments; the quality is comparable.

Collinear fast-beam laser spectroscopy, with improved sensitivity for ions with hyperfine split transitions, is performed to measure the hyperfine structure and the isotope shift of the well deformed short-lived 99Sr. The new method consists in ground state depopulation by a two-step optical pumping sequence prior to state selective neutralization and fast-atom counting. A definitive nuclear spin value I = 3 2 , the change in mean square charge radius δ〈r2〉98,99 and the nuclear moments are derived. These results are compared to nuclear spectroscopy information and are interpreted in the frame of the particle plus deformed core model.

The authors present an extension to low-lying states of francium (10s, 11s, 8d, 9d) of a previously published high-resolution experiment performed on the ns and nd Rydberg levels. These four levels were investigated at CERN with the on-line mass separator ISOLDE using stepwise laser excitation in collinear geometry. Accurate energy measurements lead to a more reliable determination of the quantum defects of the whole ns and nd series, together with the ionization potential for 212Fr (nuclear spin I=5) which is found to be 32848.872 (9) cm-1. The measurement of the fine structure splittings for the nd 2D3/2, 5/2 doublets was completed at the same time. The main result of the study is the first observation and measurement of hyperfine structures in 2S and 2D states.

Nuclear spins, moments and mean square charge radii of78–100Sr have been obtained by fast ion-beam collinear laserspectroscopy. The experiments performed at ISOLDE have been extended to include99Sr, measured by a non-optical detection scheme with a two-step optical pumping sequence. The results for the strongly deformed isotopes are discussed in the frame of the particle-plus-deformed core model.

Hyperfine structures and isotope shifts of strontium isotopes with A=78 to A=98 and A=100 were measured by collinear fast beam laser spectroscopy. Nuclear spins, moments and changes in mean square charge radii are extracted from the data. The spins and moments of most of the odd isotopes are explained in the framework of the single particle model. The changes in mean square charge radii are compared with predictions of the droplet model and of Hartree-Fock-plus-BCS calculations. For the isotopes in the transitional regions below and above the N=50 shell closure, the inclusion of quadrupole zero point motion in the Droplet model describes part of the observed shell effect. An additional change in the surface region of the charge distribution at spherical shape is suggested by the microscopic model. Furthermore, we propose that the isotopes $^{78}\mathrm{Sr}$ and $^{80}\mathrm{Sr}$ may show an unusual shape-sharing structure, with different mean deformations in the ground and ${2}_{1}^{+}$ excited states.

Laser-induced breakdown spectroscopy (LIBS) in liquids using a double-pulse Q-switched Nd:YAG laser system has provided reliable results that give trace detection limits in water. Resonant laser excitation has been added to enhance detection sensitivity. A primary laser pulse (at 532 nm), transmitted via an optical fiber, induces a cavitation bubble and shockwave at a target immersed in a 10 mg l(-1)-100 mg l(-1) indium (In) water suspension. The low-pressure rear of the shockwave induces bubble expansion and a resulting reduction in cavity pressure as it extends away from the target. Shortly before the maximum diameter is expected, a secondary laser pulse (also at 532 nm) is fed into the bubble in order to reduce quenching processes. The plasma field generated is then resonantly excited by a fiber-guided dye laser beam to increase detection selectivity. The resulting resonance fluorescence emission is optically detected and processed by an intensified optical multichannel analyzer system.

Shock waves and cavitation bubbleswere investigated in regular and retrograde liquids. Interactions of the shock waves with the wall and another shockwaves were observed. Distilled water, isooctane, glycerine and water with additives were investigated to show an influence of liquid properties. Initial laser pulses were produced by Nd:YAG and Tm:YAG lasers. The picture recording was realized through a ultrafast CCD camera.

Environmental science is concerned about the content of dissolved heavy metals in coastal tidal waters. Fluorescence spectroscopy methods do offer a chance for the detection of dissolved chromium. Due to strong quenching processes in liquids, optical emission spectroscopy often lacks sensitivity. In this study we intended to use subsequent Nd:YAG Q-switched laser pulses to create a plasma directly in front of an optical fiber tip. The plasma emits light at characteristic chromium wavelengths. The emitted fluorescence was recorded using an optical multi-channel analyzer.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Temporal evolution of laser generated cavitation bubbles and shock waves were studied. Q-switched Nd-Yag laser pulses at 1064 nm are focused into the liquid. An Imager 3 CCD camera with multi exposure mode allows recording of 10 images with minimal exposure delay of 100 ns and minimal exposure time of 100 ns. Illumination is provided by xenon flash lamp for single exposure (shock wave recording) and by halogen lamp for multi exposure mode (bubble recording). Distilled water and a retrograde fluid, isooctane, have been under investigation to identify the differences in the cavitation process and shock wave propagation. The calculation of the shock wave velocities in water and isooctane are based on image recording at constant exposure time of 100 ns and using laser differential interferometry. Strong differences of bubble oscillation were observed in water and isooctane. Gilmore's model is used for numerical simulation of bubble dynamics.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Wild-type Chinese hamster cells CHO K1 and their radiosensitive mutant xrs5 were irradiated at 308 nm, using light pulses of a XeCl excimer laser with total energy fluences of 0.1 kJ/m 2 to 4.08 kJ/m 2 . Chromosome-type and chromatid-type chromosome aberrations have been observed at pulse irradiances of 2.5×10 7 W/m 2 and 1.7×10 8 W/m 2 , indicating that in mammalian cells DNA double-strand breaks occur already in this irradiance range. The results obtained with laser irradiation are compared with X-ray irradiation

Cavitation bubbles generated in water by Tm:YAG laser pulses were studied. Timer-resolved photography was applied to determine volume change with time and surface velocities of expanding and collapsing cavitation bubbles. A new method of determining vapor densities inside bubbles based on reflection changes of a fiber probe placed inside the cavitation bubble has been developed. Density distribution changes with time were measured spatially at 17 points within the bubble. Maximum bubble diameter was about 4.5 mm. Densities measured were compared to the growth of the bubble as shown by ultra fast imaging. Temporal and spatial pressure and temperature distribution will be computed from density distributions based on equilibrium values at maximum bubble extension.

The motivation for this work has been to detect and assess the role of certain gases that are important in biomedical systems.

A Tm:YAG laser system (wavelength 2.01 µm, pulse duration 400–1600 µs, fluence 350–530 J/cm2, repetition rate 1–3 Hz) has been used to ablate different types of biological tissue. The surrounding medium was either air or aqueous solution. Mechanical stress induced by cavitational effects and pressure transients are under investigations by ultrafast imaging techniques. Depending on the applications (contact or non-contact) as well as the chosen laser parameters characteristic damage of the distal fiber end has been observed. This has to be taken into consideration for a safe and reliable clinical laser treatment in order to avoid so-called fiber burning.

Applying Tm:YAG laser pulses to biological tissue results in rather high ablation rates with moderate thermal side effects, since its wavelength of 2.01 μm coincides with a strong absorption band of water. The pulse duration of the employed system in the free running mode has been measured to be 400–1600 μs. Optical fibers of 600 μm core diameter have been used to guide the laser radiation at typically 80% transmission rate. The energy was set to 0.5–1.5 J. The ablation process is accompanied by microplasma formation and intense fluorescence emission. This fluorescence is probed by a second fiber, detected by an intensified optical multichannel analyzer, and displayed and recorded on-line via a PC-based frame grabber system. First results on fluorescence spectra taken from different tissue samples are presented. Bone tissue spectra show, for example Calcium lines even if the samples are irradiated in aqueous solution. Long pulse measurements at 2.94 μm with an Er:YAG laser and investigations with Q-switched pulses from the Tm:YAG laser system are in preparation.

It is important to understand the ablation process in order to improve the medical use of excimer and other relevant lasers. For this reason we have developed a method to image the ablation plume two dimensional and time-resolved, secondly to draw conclusions on the calcium density distribution from these pictures.

The use of different ultraviolet lasers for fluorescence spectroscopic detection of water pollutants with fiber optical sensors has been studied. Especially detection of small aromatic hydrocarbons via laser induced fluorescence requires short wavelength excitation. Interaction of intense ultraviolet light with the commonly used fused silica fibers leads to a decrease of fiber transmission. Some transmission affecting laser parameters have been studied. A new concept for the use of fiber optic sensors with ultraviolet excitation has been developed. This method is based on transmission of visible laser radiation through the fiber and creation of ultraviolet radiation by optical harmonic generation at the distal end of the fiber. So the unfavorable fiber behavior at short wavelengths can be avoided. Simultaneous coupling of the beam from a single laser source into several optical fibers is interesting for distributed sensor applications. In order to minimize coupling losses for these purposes we developed a new coupling scheme based on a special optical lens array.

Simultaneous coupling of the beam from one laser source into many optical fibers or fiber bundles is of interest for many applications. We developed a coupling scheme based on lens arrays to reduce transmission losses. The laser beam is splitted into focused partial beams. Positioning of an optical fiber near each focus allows multiple fiber coupling with similar efficiency as obtained for a single fiber. A prototype designed for coupling of excimer laser radiation into fiber bundles is presented.

An elegant approach to guide surgical laser systems makes use of laser induced fluorescence (LIF) emission during the ablation process. The possibility of a controlled laser ablation by means of LIF spectra as feedback signal has been investigated. A XeCl excimer laser pulse (wavelength λ = 308 nm, pulse width Δτ = 30 ns), transmitted through an optical fiber, is used to perform an efficient ablation of different tissue types. The same laser delivery fiber also probes the fluorescence radiation, which is then recorded by an intensified optical multi-channel analyzer (OMA). Samples of bone, cartilage, meniscus, and soft tissues have been under investigation to evaluate fluorescence characteristics. In general the fluorescence light from the ablation plume is dominated by broad-band emission spectra, typical for complex organic molecules. The influence of surrounding media on the LIF spectra, e.g. air, blood or saline solution, has also been investigated.

Cutting and drilling of hard biological tissue, e.g. bone or cartilage, by means of conventionally employed mechanical instruments in trauma surgery is heavily traumaticising itself. The demands for a replacement by laser surgical tools will be given in brief.

Laser irradiation of biological tissue with short UV-pulses (pulse width Δτ = 30 ns, wavelength λ = 308 nm) generates acoustical transients, which propagate as well into the surrounding medium as through the tissue. A fiber guided XeCl excimer laser has been used to perform ablation of different tissue samples at fluences below and above ablation threshold. Tissue samples have been immersed in water or saline solution. The amplitude and profiles of the resulting acoustical and shock waves have been recorded as a function of laser fluence using a pressure transducer in combination with a digital storing oscilloscope (cf. Figure). Open image in new window

We have investigated systematically the dependence of ablation efficency on laser pulse duration, pulse energy, number of applied pulses, and fluence using freshly slaugthered rib bone samples immersed in water. The 308 nm radiation was guided by a tapered quartz fiber. The conically shaped front part reduces the laser fluence and avoids surface damage in the launching section of the optical fiber. Laser lesions were examined by scanning laser and scanning electron microscopy. No carbonisation was observed; the temperature increase of the tissue was below 40°C in the surroundings of the laser spot. Laser pulse duration was increased in steps of 30 ns up to 220 ns.The ablation rate increased linearly with applied pulse energy, but did not depend on the pulse duration.

The interaction of various pulsed lasers with meniscus and bone of freshly slaughtered bovines and pigs was examined. Our aim was to find lasers useful for accident surgical operations (e.g. bone or callus dystopy inside joints or nearby important vessels or nerves after fractures). Laser wavelengths of the UV- and infrared spectral range were investigated: XeCl- excimer lasers (wavelength 308 nm, pulse duration 28 ns, 60 ns, 300 ns) Nd:YAG (1.06 micrometers , 400 microsecond(s) ), Tm:YAG (2.01 micrometers , 400 microsecond(s) ), Ho:YAG (2.12 micrometers , 400 microsecond(s) ), CrEr:YSGG (2.79 micrometers , 400 microsecond(s) ), and Er:YAG (2.94 micrometers , 400 microsecond(s) ). The excimer laser radiation was guided by a tapered fused silica fiber, whereas for all other lasers the tissue samples were positioned in the focus of a lens with 100 mm focal length. Ablation rates were determined by perforating samples of defined thickness, and the effects of laser ablation on tissue were controlled macroscopically, by light microscopy and by scanning electron microscopy.

Power transmission of xenon chloride excimer lasers through optical fibers is necessary for medical applications where tissue removal is performed within the human body. The most important application at present is excimer laser coronary angioplasty. Typical levels of energy densities applied by optical fibers for this application cause color center generation in fused silica leading to transmission decrease called photodegradation. This effect depends essentially on the grade of the fused silica. Important parameters are fiber length, pulse duration, energy density, and the irradiated cross sectional area of the optical fiber endface. For a new grade of core material the influence of these parameters on the transmission performance is described. The obtained material improvement leads to a significant reduction of the observable transmission decrease as a function of the number of laser pulses applied. Thus continuous operation of the laser in the region of the typical transmission plateaus at considerably higher and constant energy levels at the distal fiber end becomes feasible. This offers a new option for more reliable dosimetry in medical applications.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.