TeX glass fibers with a core-cladding structure are prepared by one of three methods: modified crucible method, preform method, or double crucible method. The raw elements are purified in order to eliminate some oxide impurities. They are then all distilled. The Te-Se-As- I system was chosen for the core and cladding glasses because of its stability against crystallization. The numerical aperture (N.A.) of the fiber is typically between 0.15 and 0.4. The diameter ratio of the core and cladding can be varied in the range of 0.15 - 0.9. These fibers are covered with a thermal plastic, to improve their mechanical properties. The optical losses of the fibers are measured between 2 and 13 micrometers by the cut-back method. The modified crucible method was the best to reduce the loss due to structural imperfections at the interface of the core and cladding. The lowest loss of 0.5 dB/m was achieved in the 7 - 9 micrometer region. Many applications of TeX glass fibers are actually tested in our laboratory such as thermal imaging, laser power delivery and remote spectroscopy. This last technology allows in-situ detection and quantification of several chemical compounds which have their characteristic absorptions in the 3 - 13 micrometer region.

The results of attempts to fabricate coherent imaging IR glass fiber bundles have been described previously. The stacked ribbon method was used. The need to use smaller diameter fibers, more evenly packed was pointed out. Better methods to evaluate the optical performance of the bundle need to be developed. Results of continued efforts to improve are described.

We have developed core/clad polycrystalline silver halide optical fibers with a loss of roughly 0.3 dB/m at 10.6 micrometers. Such fibers, with core diameters 0.3 - 0.6 mm and lengths of 1 to 2 meters are capable of continuously delivering output power densities as high as 14 KW/cm². The fibers were repetitively bent in the plastic and elastic regimes and the optical transmission monitored during bending. The mechanical properties of the core/clad fibers and of the core only fibers are similar. It was also demonstrated that the 'bending' properties of the core/clad fibers are determined by the cladding material. Our investigations suggest that proper design of the core/clad structure may give significant improvement in mechanical properties such as more cycles to optical failure. This will be very important especially for endoscopic laser surgery and other medical applications.

Sapphire fibers grown using the Saphikon EFG_TM technique have proven to be effective delivery systems for Erbium:YAG and Erbium:YSGG laser energy. Improvements to the growth process have decreased average fiber attenuation to 1.5 dB/meter with 0.2 dB/meter demonstrated. Diameter control has also improved considerably. Current growth capabilities include diameters ranging from 150 microns to 1500 microns, multiple strands grown simultaneously, and increased length of grown fibers. Laser damage threshold levels of 1250 J/cm² and power handling capacity of over 11 watts have been demonstrated, as have pulse lifetimes of 150,000 pulses at 275 mJ/pulse output energy. Use of sapphire fibers for high power applications such as dentistry along with other, non-medical applications is discussed.

Sapphire optical fibers have been grown using the laser-heated pedestal-growth method with losses as low as 0.3 dB/m at 2.94 micrometers and lengths as long as 5 m. With the incorporation of a computer-controlled feedback system we have been able to grow fibers with less than plus or minus 0.5% diameter variation, or plus or minus 1.5 micrometers for a 300 micrometer fiber. We have been able to decrease the loss in these fibers through a post-growth anneal at 1000 degrees Celsius in air; from 5.4 dB/m to 1.5 dB/m at 543 nm and from 0.4 dB/m to 0.3 dB/m at 2.94 micrometer. These fibers delivered 4.7 W at 10 Hz of Er:YAG laser power.

Polyimide-coated silver hollow glass waveguides with small losses have been fabricated for transmission of Er:YAG laser light. The total loss is around 0.7 dB for the straight waveguide with an inner diameter of 700 micrometers and the length of 2.3 m including a coupling loss from a laser. Even when the waveguide is bent to 180 degrees with a bending radius of 18 cm, the total loss is around 1 dB for the input energy of 500 mJ.

Hollow glass waveguides have been fabricated for the delivery of infrared radiation by chemical vapor deposition methods. A molybdenum film is first deposited inside 700- micrometer and 530-micrometer bore silica tubing by the hydrogen reduction of molybdenum chloride. Then, Al₂O₃, or TiO₂ film is deposited onto the molybdenum layer. These dielectric films enhance the reflectivity, and we observe a reduction in loss for the thin- film combination compared with the molybdenum film alone. The thickness uniformity of the dielectric films is estimated to be less than 5% of the desired thickness in a length of 50 cm. A loss spectrum of the Al₂O₃/Mo-coated waveguides shows that the losses for the Al₂O₃ guide in the 3 - 6 micrometer wavelength region are lower than the loss for the AgI-coated guide fabricated by liquid-phase deposition technique. The chemical vapor deposition techniques can be extended to the fabrication of hollow waveguides with multiple dielectric layers that have much lower losses than current single-layer designs.

Scattering of visible and mid-IR radiation transmitted through hollow flexible waveguides was measured employing two methods: total integrated scattered (TIS) and back scattered (BS) radiation. The root mean square ((sigma) ) of roughness was evaluated employing these two methods. This has also enabled evaluation not only of the (sigma) but also the location of important centers of scattering of the metal and dielectric deposited layers on the internal wall of waveguide tubes. Measurements of beam profile were performed using perspex cubes, in which the formed crater image has given information of the mode propagation into the waveguides as a function of distance from: (a) the coupling to the laser, (b) radius of bending, (c) ID of hollow tubes, and (d) coupled energy of laser in waveguide. It was shown that for given radii of bending whisper gallery mode of propagation appears.

The radiation of Er-YAG laser ((lambda) equals 2.94 micrometer) gives selective interaction with tissues. The extinction in soft tissues is only a few micrometers and in hard tissues is of the order of hundreds of micrometers. This makes this type of laser very suitable for treatments in dentistry, orthopedy, or ophthalmology. Because the usual silica fibers are not transmitting the radiation at lambda equals 2.94 micrometer of this laser, many applications cannot be presently performed. Fused silica hollow fibers for Er-YAG radiation were developed in our laboratory and several possible applications in dentistry, orthopedy and ophthalmology were indicated. Hole opening and implantation preparation of teeth were experimented, using Er-YAG laser and hollow plastic waveguide delivery systems. Hole drilling in cow bones was demonstrated for applications in orthopedy. A new procedure of delivering Er-YAG radiation on fibrotic membranes of inner eggshell as a model of the membranes in eyes was developed employing silica hollow waveguides of 0.5 and 0.7 mm ID or a plastic waveguide of 1.0 mm ID. For this purpose waveguides with sealed distal tip were employed to enable us to approach the delivery system through liquid media near to the membrane. This experiment demonstrates the possibility of surgical applications in vitectomy in ophthalmology using Er-YAG laser and silica hollow waveguides.

The free electron laser (FEL) is a unique laser which is tunable over a wide segment of the spectrum. Its tunability can open a wide range of applications in medicine -- both surgical and diagnostic. A delivery device such as a waveguide or a fiber, flexible enough, which will be coupled to its outlet, will enable maneuvering the beam conveniently at the operating site. The greatest obstacle for such a fiber or waveguide is the high peak power of several MWatts that characterize the beam and the wide range of wavelengths. Flexible hollow waveguides made of either a fused silica or a Teflon tubing, internally coated with reflecting/refracting layers, were used in experiments at 3 FEL centers in the U.S. A segment of the mid IR spectrum (between 6 and 7 micrometers). Results of the beam shape (both temporal and spatial) and transmission measurements have proven the potential of this waveguide for transmission of FEL radiation.

The minimum spot size from our current production of the Fiberlase is 0.8 mm at the waveguide tip and is suitable for many laser material applications. For some advanced medical and industrial applications, a very small spot size and high power density is required. A smaller laser spot size can be achieved by reducing the waveguide ID, however a tremendous amount of laser power will be lost as the guide diameter is reduced. In addition, it is increasingly difficult to couple a carbon-dioxide laser beam into ever smaller diameter waveguide. In order to concentrate carbon-dioxide laser light down to 0.3 mm or less, our first design approach is reimaging the laser spot from the waveguide with a single or double lens system. The other approach is by using a nonimaging conical waveguide taper to concentrate the carbon-dioxide laser light. The performance of these approaches is discussed in terms of the spot size, beam quality and power transmission.

Nd:YAG laser systems, coupled to silica fibers, have shown great benefits as surgical tools. Using the laser system with a bare silica fiber, laser surgeons can photocoagulate tissue to depths of 4 to 5 mm in a non-contact mode. In a contact mode, incision and cauterization of the nearby tissue can be achieved. Although these two capabilities provide powerful tools for hemostatic procedures, research performed at Iowa State University has shown that the silica fiber tips undergo extensive damage when in contact with tissue. Chemical and thermal degradation of the silica glass surface plays a key role. Damaged fibers do not transmit a significant fraction of the laser light launched down them. Instead, essentially all of the laser energy is converted to heat at the contact point. The tip can then be used only to incise tissue. We report here on the development and characterization of a new optical fiber that offers improved chemical resistance and also high temperature resistance. The new fibers were pulled from glass rods with a composition of 92.5 wt.% SiO₂ and 7.5 wt.% TiO₂ and then cladded with a fluorinated hard polymer. The new fibers effectively deliver energy even after the fiber comes into contact with tissue while the silica fiber tips undergo catastrophic damage. Also, preliminary clinical testing of the new fibers has demonstrated the stability of the fibers in contact with tissue during gynecological surgical procedures.

Excimer lasers are used for many medical applications, e.g. angioplasty and ophthalmology. In the medical field fiber delivery systems are predominantly used with XeCl-lasers (308 nm) up to now. The best suited core-material for the moment is undoped synthetic fused silica with high OH-content. At 193 nm transmission of these fibers is limited by high nonlinear absorption and color-center generation leading to increased absorption. For ArF-lasers at 193 nm wavelength new results of the nonlinear transmission properties of improved fused silica fibers are presented and discussed, taking the following parameters for medical laser-fiber- systems into account: fiber length, fiber diameter, fluence, and repetition rate. Finally the results are discussed regarding the difference in the generation of color centers.

We investigate the thermal loading of a bare silver-silver halide hollow waveguide with 1 mm core diameter and 1 m length when used to guide carbon-dioxide laser radiation with a power of about 100 W. It is shown that the heating of the waveguide results from two factors: losses at the input face of the fiber caused by beam 'clipping;' and distributed beam attenuation inside the waveguide. Both effects produce a temperature highest at the input face and decreasing along the fiber. The effects were studied theoretically and by experiment. It is found that the 'clipping' effect contributes more thermal loading than the beam attenuation, and also the greater part of the temperature gradient is caused by the 'clipping.' The thermal response to transverse misalignment at the launching is also investigated; it is found that the temperature increase at the front end of the waveguide is much more sensitive to misalignment than is the power transmission. The performance of butt-jointed fiber also is investigated. It is shown that while the transmission is sensitive to transverse alignment of the joint, it is relatively insensitive to the longitudinal misalignment (gap between the fibers); the second fiber normally has higher transmission than the first one due to the absence of the launch coupling loss. There is also no obvious temperature penalty at the joint. Therefore it is possible to use the standard connectors developed for silica fiber to extend the hollow waveguide length with little penalty.

In order to eliminate the mesh pattern due to pixels of the imagefiber, we have developed and studied the new image processing method. As a result, it has been found that the quality of the processed image is improved in brightness and contrast without blurring.

With the development of infrared transmitting fibers, medical applications such as minimally invasive surgery are becoming feasible. In particular we investigate liquid core waveguides with an Er:YAG laser at 2.94 micrometer. Because of their advantages like variability in diameter, high flexibility, and mechanical stability, liquid core waveguides appear to be an alternative to conventional IR waveguides. In this work we present two types of liquid CCl₄ filled lightguides that have been developed with plastic tube and quartz capillary as cladding. The former with an inner diameter of 1.6 mm showed an attenuation of 2.6 dB/m at 2.94 micrometer. For the quartz glass capillary with an inner diameter of 550 micrometers an attenuation of approximately 4.8 dB/m was determined in first experimental results. Due to the great flexibility and the high mechanical stability of both lightguides, bending radii below 10 mm are possible. Transmission losses depending on bending radii are discussed. A comparison between measurements with an IR-spectrometer and an Er:YAG laser shows that a minimum transmission loss of 2 dB/m can be achieved.

Advancements in minimally invasive surgery, in areas such as otology, require that the surgeon operates through a small opening, often with indirect access to the surgical field. Conventional carbon-dioxide laser delivery systems, such as the micromanipulator and the semi-flexible waveguide limit the surgeon's ability to perform such procedures. The ablation properties of a small, flexible, hollow carbon-dioxide laser waveguide (Medical Optics, Carlsbad, CA) were compared to a conventional surgical carbon-dioxide laser micromanipulator on chinchilla calvarium bone. This waveguide has a small diameter (O.D./I.D. equals 500/300 micrometer) and is therefore potentially useful for minimally invasive middle ear surgical procedures, such as carbon-dioxide laser stapedotomy. The beam diameter and the half angle divergence of the waveguide were estimated using a standard knife-edge measurement technique. Lesions were created at clinically relevant power settings with each delivery system on fresh harvested chinchilla bone. The crater size and the thermal damage width were then measured under a light microscope. The size of the lesions were found to be comparable between the two delivery systems. This preliminary study demonstrates that the two delivery systems have comparable effects on bone. However, further work is necessary to compare their effects on healing before the waveguide can be used clinically for surgical procedures such as carbon-dioxide laser stapedotomy.

We use a ray tracing technique in order to analyze the optical throughput and the side wall energy deposition for the glass fiber probes used in the near-field scanning optical microscopy (NSOM). It is shown that the significant part of the light can be dissipated tens or even hundreds of microns away from the probe apex due to absorption by metal coating. The results also indicate that a substantial part of the light coupled into the fiber probe is reflected back. The analysis elucidates the 'far-field' causes for a low throughput of NSOM probes and their overheating. The ways of further probe geometry and structure improvement are outlined.