DEVICE FOR LASER APPLICATION IN FLUID ENVIRONMENT

Abstract: The invention includes the use of a beam homogenizer (scattering surface) at the input aperture of a tapered optical fiber to avoid hot spots (2) in the tapered section which would otherwise destroy the fiber (10).

Description: DEVICE FOR LASER APPLICATION IN FLUID ENVIRONMENT 1. Field of the Invention The invention is a method and a device that allows for h nh speed and high precision cutting of biological tissues in a liquid environment with minimal physiological damage to the surrounding tissue. 2. Background of the Invention Lasers have been shown to be effective and convenient surgical tools. Among the variety of possible surgical lasers the ArF excimer laser has been found to be the best choice for producing precise cuts during tissue removal in a gaseous environment without collateral damage to the surrounding tissue layers (C.A. Puliafito, R.F. Steinert, T.F. Deutch, , F. Hillencamp, E.F. Dehm, CM. Adler, Ophthal ol. 92, 741(1985) ; S.L. Jacques, D.J. McAulitte, I.H. Blank and J.A. Parrish, J. Inv. Derm. 88, 88(1987) ; J. Marshall, S. Trokel, S. Rothery and R. Krueger, British J. Ophthalmol. 70, 487(1986) . This considerable advantage of the ArF excimer laser is based on a photochemical, rather than thermal, mechanism of the tissue removal (R. Srinivasan, P.E. Dyer, B., Braven, Lasers Surg. Med. 6, 514(1987)) . The energy of the 193 nm photon is sufficient for breaking almost all chemical bonds in biological compounds. This fast photochemical reaction followed by fast tissue removal prevents heat deposition and other side effects caused by other lasers. Up to now all surgical applications of the ArF excimer laser were based on the treatment of tissue surface in an air environment. Excellent results were obtained, for example, in 1A refractive surgery (F.A.L'Esperance, J.W. Warner, William B. Telfair, P.R. Roger, C.A. Martin, Arch. RECTIRED SHEET (RULE 91) Ophtalmol., 107, 131(1989)) and skin treatment (S.L. Jacques, D.J. McAulitte, I.H. Blank and J.A. Parrish, J. Inv. Derm. 88, 88(1987)) . During the last few years new methods based on fiber optic delivery systems have been developed for laser angioplasty (T.G. van Leeuwen, L. van Erven, J.H. Meertence, M. Motamedi, M.J. Post, C. Burst, J.Am. Coll. Cardiol . , 19, 1610(1992) ; T. Tomary, H.J. Geschwind, G. Boussignac, F. Lange, S.J. Tank, Am. Hear J. , 123, 8861992) ) , bone and cartilage cutting and drilling (M. Dressel, R. Jahn, W. New and K. H. Jungbluth Lasers Surg. Med. , 11, 569(1991)), and other surgical applications. These methods are simple, convenient and allow the delivery of a lε er beam to the required position in a liquid environment. The laser wavelength ranges being transmitted through these fibers were mainly associated with the spectral range of the fiber's transmittance, which is the mid IR, visible and near UV and thus, these wavelengths were used for tissue cutting even though such wavelengths are not the optimum for tissue removal. In all such tissue removal applications with these laser wavelengths different measures of thermal injury or shock waves caused side effects in the surroundings of the lesion. The best results were obtained with the 308 nm excimer laser (T.G. van Leeuwen, L. van Erven, J.H. Meertence, M. Motamedi, J.J. Post, C. Burst, J.Am. Coll. Cardiol., 19, 1610(1992) ; T. Tomary, H.J. Geschwind, G. Eoussignac, F. Lange, S.J. Tank, Am. Heart J. , 123 8861992)) . But even in this case the mechanism of laser/tissue interaction was shown to be thermal. All attempts to effectively deliver the ArF excimer laser beam through quartz fibers failed because of both the non-linear absorption at high intensities and induced color centers formation at this wavelength. As a result, at high radiation intensities and for multiple pulses quartz fibers were shown to become almost nontransparent (M. Dressel, R. Jahn, W. Neu and K.-H. Jungbluth Lasers Surg. Med., 11, 569(1991)). Until recently only one method of the ArF laser delivery into a liquid environment was developed (A. Lewis and D. Palanker U.S. Patent No. 5,288,288). The laser beam was guided through a hollow glass tapered micropipette, in which a gas was introduced at a pressure equal to the capillary force of the liquid at the pipette exit. The micropipette served at the same time as a beam guide, a concentrator and an aperture. This method allowed the drilling of precise and reproducible holes in the zona pellucida of oocytes for enhancement of sperm penetration (D. Palanker, S. Ohad, A. Lewis, A., Simon. J. Shenkar, S. Penchas and N. Layfer, Lasers Surg. Med., 11, 580(1991)). For this application the diameter of the tapered tip was about 8 microns and a low energy fluence was applied. For larger tips and a high energy fluence the method of static gas pressure is not effective for maintenance of an air/liquid boundary at the exit of the tip. The instrument we have devised overcomes all of the problems of ArF laser delivery to a tissue in a highly absorbing liquid environment and allows the cutting of materials with high speed and high precision without observable heat injury. 3. State of Prior Art The ArF excimer laser was applied in medicine until recently for refractive surgery (J. Marshall, S. Trokel, S. Rothery and R. Krueger, British J. Ophthalmol., 70, 487(1986) ; F.A. L'Esperance J.W. Warner, William B. Telfair, P.R. Roger, C.A. Martin, Arch. Ophthalmol., 107, 131 - 139 (1989) , skin treatment (S.L. Jacques, D.J. McAulitte, I.H. Blank and J.A. Parrish, J. Inv. Derm. 88, 88(1987)) , and in-vitro fertilization (D. Palanker, S. Ohad, A. Lewis, A. Simon, J. Shenkar, S. Penchas and N. Layfer, Lasers Surg. Med., 11, 580(1991)) . The first two techniques are applicable only to dry surface treatments and are not suitable for surgery of internal organs and tissues covered by biological liquids. The last approach is not suitable for tissue microsurgery because it is based on the use of glass air-filled micropipettes . These pipettes are not applicable if the tip diameters exceed 20 microns, since it is difficult to maintain positive air pressure in the micropipette to prevent liquid from entering. The pipettes also cannot withstand high energy fluences and are rather brittle. Thus, with the ArF excimer, microsurgical operations of internal organs and tissues covered by biological liquids were not performed. 4. Summary of Invention A device and a method that allows for flexible delivery, concentration and aperturing of the ArF excimer laser beam and enables soft tissues microsurgery in liquid or gaseous environments. The device consists of three main elements: - a concentrator of energy; - a beam homogenizer, and - a flexible delivery system. In addition, this device is able to deliver a variety of other laser beams permitting parallel operations to be performed. 5. Brief Description of Drawings The various objects, features and advantages of the present invention will be apparent to those of skill in the art from the following detailed description of a preferred embodiment, taken with the accompanying drawings, in which: Figs. 1A illustrates a scheme of light propagation in a conical structure; Fig. IB is a schematic representation of the energy distribution in a conical structure; Fig. 2A is a schematic diagram of the beam energy fluence distribution inside and outside a conical tip having a polished entrance surface; Fig. 2B is a schematic diagram if the beam energy fluence distribution inside and outside a conical tip having a scattering entrance surface (arrows indicate propagation direction) ; Fig. 3 is a micrograph of light exiting from a tapered fiber tip at the plane corresponding to the position of the circular peak (one or two) of Fig. 2A (arrow indicates excimer laser caused damage) ; Fig. 4A is a 3-dimensional plot of the energy fluence distribution of an excimer laser beam exiting from a tapered tip with a polished entrance surface; Fig. 4B is a 3-dimensional plot of the energy fluence distribution of an excimer laser 6 beam exiting from a tapered tip with a ground entrance surface; and Fig. 5 is a graph illustrating the calculated dependence of an idealized quartz fiber transmission at 193 nm on the energy fluence for various fiber lengths. 6. Description of the Invention All the fibers available until now for the deep ultraviolet close to the vacuum ultraviolet are made from UV grade fused silica. The very high nonlinear absorption coefficient of this material at 193 nm (R.K. Brimacombe, R.S. Tailor and K.E. Leopold, J. Appl. Phys. , 66 4035(1989)) limits the energy output. Even for intravitreal surgery when the minimal length of a fiber can be about 4.5 cm, it is impossible to obtain enough energy fluence at the tip of such a fiber. Fiberguide G fibers, for example, allow the delivery through this length of only a 160 mJ/cm 2 /pulse when the energy fluence at the entrance approaches the damage threshold of fused silica ( <F thresh (193 nm) > = 1500 mJ/cm 2 /pulse) . Such an energy fluence is not enough for effective tissue cutting even for such soft tissues as the retina and epiretinal membranes (A. Lewis, D. Palanker, I. Hemo, J. Pe'er and H. Zauberman, Invest. Ophthalmol. Vis. Sci., 33, 2377(1992)). In order to overcome this problem, we developed a method and a device to convert the best fused silica fibers into a conical concentrator with a specially tapered tip at an entrance surface that enables an increase in the output energy fluence up to the level required for effective tissue cutting. 6.1. Beam Concentrator Calculations were completed of the energy fluence distribution inside conical structures for a constant reflection coefficient (i.e.,. metal walls) in H. Schmidt-Kloiber and H. Schoeffman, Appl. Optics, 25, 252(1986), for a durable reflection coefficients - sapphire tip in a water environment in R. M. Verdaasdonk and C. Borst Appl. Optics., 30, 2172(1991) and for an air- filled glass pipette in D. Palanker and A. Lewis, unpublished. A scheme of light propagation through a cone 10 is shown in Figure 1A, wherein the light will exit from the cone after different numbers of reflections (or modes 0,1...) depending on the distance of the incoming light from the optical axis (zones 0,1...). For simplicity in the drawing, only modes up to No. 3 are shown. Fig. IB is a schematic representation of the energy distribution within cone 10. The energy fluence distribution of the beam inside and outside of the conical tip is shown qualitatively in Figure 2A, which is a schematic diagram of a conical tip with a polished entrance surface. Fig. 2B is a schematic diagram of the beam energy fluence distribution with a scattering entrance surface. Energy fluence at the pipette entrance plane is assumed to be constant. The maximal peak intensity inside the core corresponds to the damage threshold of the fiber. The mean energy concentration coefficient for each mode of propagated light is proportional to the relationship of the enter/exit surface areas and to the appropriate reflection coefficients. An important feature of laser beam concentration in a conical structure is that the energy fluence 8 distribution is highly non uniform, as illustrated in Figure 2A. The energy fluence in the focusing area is inversely proportional to the distance from the optical axes and to the beam divergence. A central peak appears inside the cone when the first reflected rays reach an optical axis, and ends when the last reflected rays (mode 1) leave this axis, with its height inversely proportional to the beam divergence. In practice, at least three additional factors can influence the energy distribution and may even sharpen the energy peaks. They are: (1) non-coaxiality of the beam with the fiber axes, (2) gradual increase of the cone angle at the beginning of the cone, and (3) interference of the reflected rays inside the material. The cone remains transmitting unless the peak of energy fluence exceeds the damage threshold of the cone material. Since these peaks for a low divergence beam are rather sharp, the maximal average energy fluence transmitted through the fiber cannot be substantially increased by its tapering, or else the cone will be destroyed at its very beginning. For example, in the case of tips made from fused silica Fiberguide G fibers the destruction of the cone material in the bulk was found for the tip diameters of about 0.7 of the entrance diameter when the average output fluence was as low as 30 mJ/cm 2 /pulse. In this case the destruction is caused by a circular energy peak, illustrated in Figures 2A and 2B and Figure 3 at peak 2 , even before the central peak formation. Figure 3 is a micrograph, at a magnification of 200, of light exiting from the tapered fiber tip 10 at the plane which corresponds to the position of the circular peak 2 shown in Figure 2A. The arrow indicates the excimer laser-caused damage, which is located at the same place as the peak of the energy fluence distribution. The exit diameter of the tapered fiber tip is 0.7 of the fiber diameter. For smaller exit diameters the tip will be destroyed at even lower mean energy fluence. Such a level of the energy fluence is not sufficient for an effective ablation of soft tissue, where an energy fluence of about 250 to 350 mJ/cm 2 /pulse is required. In order to maximize the average energy delivered through the cone the distribution peaks inside should be broadened. 6.2 Beam Homogenizer In order to broaden these peaks the entering beam divergence should be increased. This may be accomplished by scattering the beam through rough optical surface before entering the tip (see Figure 2B) . This may be carried out by an entering surface of the tip or by a surface of an additional plate placed before the tip. The angle distribution of the scattered beam depends on the roughness of that surface. Insertion of a scattering surface allows the use of fused silica fibers at rather high energy fluence without their destruction by hot spots of the energy inside the fiber as the result of either non ideal fiber orientation, inhomogeneity of the laser beam, or beam interference inside the fiber. A three- dimensional plot of the energy fluence distributions of the excimer laser beam exiting from the tapered tip are shown in Figures 4A and 4B for both a polished (4A) and a ground (4B) entrance surface. Grinding of the entrance 10 surface was accomplished with the use of a grinding paper having a particle size of less than 20 microns. As can be seen in these Figures, such scattering lowers the intensity and broadens the peaks of the energy distribution, and this enables an increase of the entering energy. As a result, the total energy transmitted through the conical tip can be increased without damaging it. On the other hand, the increasing beam divergence reduces the energy exiting from the conical tip since the reflection coefficient of the walls decreases as the angle of incidence increases beyond the angle of total internal reflection. This means that there is some optimal level of roughness of the scattering surface that enables delivery of a maximal energy throughput from the tip. This level is determined by the material's damage threshold, the cone's angle x, and a relation of the exit / entrance cone diameters. We found that for tips made from Fiberguide G fibers with the angle x ~ 0.2 and an exit diameter of about 0.3 of the entrance diameter, the surface should be roughened by grinding paper with a maximal particle dimension of 20 microns. In this case insertion of the scattering surface decreases the energy output by only 33% but enables an increase of the entering and average transmitted energy by at least 10 times, as a result of broadening the peaks of the energy distribution. Thus, the addition of this optimal scattering surface enables the tips to deliver about 500 mJ/cm 2 /pulse and this is enough for effective soft tissue cutting. It should be mentioned tha 4 - an additional concentric tube around a tapered tip 11 through which a liquid is suctioned out could be used to mechanically protect the device, to lift the irradiated tissue by suction and to evacuate the gas bubbles and tissue debris that result from laser/tissue interactions. 6.3 Parameters for an All Fiber Flexible Delivery System. In order to flexibly deliver the laser beam into a surgical field the special articulated arm described in Patent No. 5,288,288 may be used. The large excimer laser beam is focused inside the articulated arm in order to obtain the required energy fluence on the exit of the arm and in order to use the beam in a more efficient way. A few requirements for the focusing system should be fulfilled. The beam dimensions at the exit of the arm should exceed the fiber diameter in order to compensate for beam shifts induced by the arm movements. The entering beam has to be rather parallel in order to be effectively concentrated in the fiber tip. These requirements could be fulfilled by either a long focal length lens inside the articulated arm, or a telescope that can be fixed at the arm's exit. In the present system a long-focal length (500 mm) lens was placed inside the arm in order to concentrate the radiation on the entering surface of the tapered fiber to the required level (about 150 to 250 mJ/cm 2 /pulse) . The dimensions of the beam at the fiber entrance plane were 3 x 1.5 mm. Thus, in the case of a 1 mm core diameter, about 20% of the laser energy entered the fiber and was utilized for microsurgery. Such an articulated arm could be used together with the herein-described new tip for 12 flexible delivery of the ArF excimer laser for microsurgery in liquid environments. Nonetheless, it is apparent that efficiency of the energy transfer from the articulated arm to the fiber cannot be high, because of the above mentioned unavoidable beam movements. In order to minimize energy losses, one can consider the parameters for an all-fiber delivery system containing the cone on the exit and the energy homogenizer on the entrance. This system will allow for microsurgery in deeper lying tissues and internal organs, which is difficult or even impossible to accomplish with the articulated arm. We are able now to determine the parameters of such a fiber-based system and its limitations on the basis of the known properties of the fused silica fibers. It is well known that color center formation occurs in fused silica fibers that have been subjected to repeated exposure of high power UV laser radiation. Color center formation results in a decrease of transmission with an increase of the number of laser pulses, and eventually transmission reaches some saturation level. This saturation effect is believed to be due to a finite number of defect sites which can result in color center formation. At an energy fluence 0.5 J/cm 2 , fiber transmission decreased tenfold during the first 30 pulses up to a -== 0.1 cm- 1 and then the decrease became slower (R.K. Brimaco be, R.S. Tailor and K. A E. Leopold J. Appl. Phys. , 66, 4035(1989) ) . It was found also that at 193 nm the fiber transmission begins to drop for single pulses with intensities as low as 1 MW/cm 2 . The nonlinear absorption coefficient a was found to be 13 approximately 2x10- 3 cm/MW (R.K. Brimacombe, R.S. Tailor and K.E. Leopold, J. Appl. Phys., 66, 4035(1989)). This coefficient was independent within experimental error for different fiber types and thus, it was concluded that the coefficient is solely the property of the bulk material, which was fused silica. It is possible to evaluate the transmission of an ideal fiber when single photon absorption and color center formation are absent. In this case the change in fluence as a function of fiber length is given by (R.K. Brimacombe, R.S. Tailor and K.E. Leopold J., Appl. Phys., 66, 4035 (1989)): - l/FxdF/dx=Fxa, (Eq. 1) where F is an energy fluence, x is the length of a fiber, and a is a non-linear absorption coefficient. Integration of this differential equation results in the following dependence of the exiting energy fluence F on the entering fluence F 0 and a fiber length L: F=l/γaL + 1/F 0 (Eq. 2) This function is presented in Figure 5 for three different lengths: 5, 50 and 100 cm. It is evident that the exiting energy fluence reaches some saturation level that depends on the fiber length. It is impossible, for example, to obtain more than 0.2 J/cm 2 at the exit of a 50 cm fiber. This observation shows that even through ideal quartz fiber it is impossible to obtain enough energy fluence for the ArF laser for microsurgical applications. One way to increase the efficiency of radiation delivery through such a fiber is to lower the energy fluence by increasing the core diameter. 14 For microsurgical applications however, only fibers that are not thicker than 1 mm can be used since thicker fibers are too rigid. At this diameter through an ideal fiber of 1 m in length and an entrance fluence of 0.4 J/cm 2 /pulse it is possible to obtain an exit energy fluence of 80 mJ/cm 2 /pulse. By tapering the end of the fiber as it is described in paragraph 6.1 it is possible to concentrate the energy. Thus, a tip with a 0.3 mm diameter exit and with a cone angle that does not exceed 0.2 the exiting radiation will be concentrated to 700 mJ/cm 2 /pulse. This fluence is even higher than is required for effective cutting of soft tissues in a liquid environment. Thus, in spite of the strong multiphoton absorption of fused silica with nanosecond 193 nm excimer laser pulses, it is possible to use such fibers as a flexible delivery system if the amount of defect sites that result in color center formation are sufficiently decreased. The proper choice of parameters (such as entering energy fluence, fiber diameter and tip diameter) makes a fiber-based delivery system more convenient and effective for microsurgical applications of this laser than an articulated arm. 6.4 Applications of the Device. Numerous applications of the present device are possible in the field of soft tissue microsurgery. One of the most promising of them is vitreoretinal membrane removal, because the accepted mechanical peeling and cutting of such membranes is often associated with retinal damage. Furthermore the present device can be used in all microsurgical procedures, including microsurgery of the internal organs. In addition, the 15 technique can be used in cell microsurgery, such as drilling of the zona pellucida of oocytes for in vitro fertilization. 7. Experiments. Several experiments were completed in order to demonstrate the efficiency of the device in vitreoretinal surgery in vivo and in vi tro. We used 4.5 cm long pieces of Fiberguide G fibers with a core diameter of 0.8 mm coupled to the articulated arm. They each had a 2 mm tapered tip at the end with a 0.2 to 0.3 mm aperture. The entrance plane of these fibers tips was ground with grinding paper (particle size less than 20 micron) . The energy fluence output from the tip was in the range 150 to 500 mJ/cm 2 /pulse. It was shown that it is possible to cut retinal tissue and vitreoretinal membranes at a rate of 1 to 2 mm/s with a pulse repetition rate of 20 Hz. Characteristic width of these cuts was 100 to 200 microns. The cut depth was shown to be controlled by the energy fluence and by the number of pulses. It was also found that the cutting occurred only when the tip was in contact with the tissue. The absence of observable damage when the retina was irradiated without contact demonstrates that vitreal membranes can be safely removed from the retina when they are separated by even a thin layer of liquid. These experiments are the first step in demonstrating a variety of delicate surgical procedures that will evolve as a result of the application of this new device and method.

Claims: 16 Claims 1. A device consisting of a beam homogenizer at the large end of a piece of tapered fiber acting as an energy concentrator so that light with damaging effects on the fiber can be concentrated by it in a manner that keeps the intensity of the light within the fiber below the threshold of fiber damage while light concentration is occurring, resulti g in sufficient flux at the exit aperture of tb tapered fiber, which can even be in the size don. ^ xn of microns, to permit the ablation of materials in highly absorbing liquid and gaseous environments by such laser light. 2. A device as recited in claim 1 that allows for concentration, aperturing, and delivery of a laser beam such as an ArF excimer laser beam to a tissue surface in order to perform soft tissues microsurgery in highly absorbing liquid or gaseous environments. 3. A device as recited in claim 1 which is connected to an exit of an articulated arm - based delivery system that allows for flexible delivery of the laser beam in order to perform material removal in highly absorbing liquid or gaseous environments. 4. A device as recited in claim 2 which is connected to an exit of an articulated arm - based delivery system th. :. allows for flexible delivery of the laser beam in order to perform soft tissue microsurgery in highly absorbing liquid or gaseous environments. 17 5. A device as recited in claim 1 which is connected to a flexible fiber delivery system that allows for the flexible delivery of the ArF excimer laser beam in order to perform material removal in highly absorbing liquid or gaseous environments. 6. A device as recited in claim 1 in which the fiber is long enough to be flexible. 7. A device as recited in claim 5, that allows for soft tissue microsurgery in highly absorbing liquid or gaseous environments, including the microsurgery of deep lying tissues and internal organs. 8. A device as recited in claim 2, that permits microsurgical applications in the eye such as the removal of vitreoretinal membranes. 9. A device as recited in claim 2, that permits the generation of full and partial-depth holes and openings in the zona pellucida of oocytes for in vitro fertilization applications. 10. A device as recited in claim 1 with an additional concentric tube around a tapered tip which allows for the mechanical protection of the tapered fiber tip and permits lifting the irradiated tissue, and the evacuation of gas bubbles and tissue debris that result from the laser/tissue interactions. 11. A method for delivering a high enough flux of laser light at a wavelength that is normally 18 damaging to optical fibers consisting of a beam homogenizer at the large end of a piece of a tapered fiber which acts as the energy concentrator so that such light with damaging effects on the fiber can be concentrated by it in a manner that keeps the intensity of the light within the fiber below the threshold of fiber damage while light concentration is occurring and resulting in sufficient flux at the exit aperture of the tapered fiber, which can be in the size domain of microns, to permit the ablation of materials in highly absorbing liquid and gaseous environments by such laser light. 12. A method as recited in claim 11 permitting soft tissues microsurgery in highly absorbing liquid or gaseous environments. 13. A method as recited in claim 11 further including an articulated arm - based delivery system that allows for flexible delivery of the laser beam in order to perform material removal in highly absorbing liquid or gaseous environments. 14. A method as recited in claim 13 permitting the flexible delivery of the laser beam in order to perform soft tissue microsurgery in highly absorbing liquid or gaseous environments. 15. A method as recited in claim 11 further including a flexible fiber delivery system that allows for the flexible delivery of the ArF excimer laser beam in order to perform material removal in highly absorbing liquid or gaseous environments. 19 16. A method as recited in claim 11 in which the fiber is long enough to be flexible. 17. A method as recited in claim 16, that allows for soft tissue microsurgery in liquid or gaseous environments, including the microsurgery of deep lying tissues and internal organs. 18. A method as recited in claim 12, that permits microsurgical applications in the eye, such as the removal of vitreo-retinal membranes. 19. A method as recited in claim 12, that permits the generation of full and partial-depth holes and openings in the zona pellucida of oocytes for in vitro fertilization applications. 20. A method as recited in claim 11 further including a concentric tube around a tapered tip which allows for the mechanical protection of the tapered fiber tip and permits lifting the irradiated tissue, and the evacuation of gas bubbles and tissue debris that result from the laser/tissue interactions. 21. A method consisting of the insertion of a scattering surface on the front face of a fiber or grinding the entrance surface of the fiber so that high energy fluences can be concentrated in the fiber without damaging the tapered fiber and its tip by hot spots of energy inside the fiber as a result of either non-ideal fiber orientation or as a result of inhomogeneity of the laser beam, or as a result of beam interference inside the fiber. 20 22. A method consisting of the insertion of a scattering surface on the front face of a fiber or grinding the entrance surface of the fiber so that high energy fluences can be introduced into the fiber without damaging it by hot spots of energy inside the fiber as a result of either non-ideal fiber orientation or as a result of inhomogeneity of the laser beam, or as a result of beam interference inside the fiber.

Inventors: LEWIS AARON, PALANKER DANIEL, TUROVETS IGOR, LEWIS, AARON, PALANKER, DANIEL, TUROVETS, IGOR
Applicants: AARON LEWIS, PALANKER DANIEL, TUROVETS IGOR, LEWIS, AARON, PALANKER, DANIEL, TUROVETS, IGOR
Application year: 1995
Main classification: A61N5
IPC codes: A61B18