For medical application various types of lasers have come into use, and new types have been investigated for new applications. This paper gives a survey of the various types of laser tissue interactions, and the established and proposed technical solutions. Special emphasis will be given to the various problems within a practical system starting with the laser source itself, the beam delivery system, optical front-ends up to the accessories needed. In addition the product related market potential will be discussed.

If one regards the medical applications of lasers durign the last few years one observes in many fields a passionate development. Many different laser types are used for a big variety of applications.

Design considerations, constructional features and perfomance characteristics of a laser system enabling surgeons to use sequentially Nd-YAG or carbon dioxide laser energy.

The Nd:YAG laser has become a coagulation instrument, which has found acceptance in interdisciplinary surgery. Due to the low absorption and high scattering in tissue, the radiation of the Nd:YAG laser leads to a deep and homogeneous coagulation effect. The contactless treatment and the fact that blood and lymph vessels are coagulated and sealed have led to successful applications especially with regard to tumor surgery.

Within a very short time and an amazing period of research and development optical fibers changed the area of communications completely. While transmission of information through optical fibers has been considered first in 1966, 1970 Corning announced a breakthrough in fiber losses as low as 20 dB/km. Today's technology provides fibers commercially with losses of about 0.2 dB/km at 1.55 μm wavelength (i.e. transmitting over 15 km, 50 % of light power is still available).

Today many applications of high power lasers for medical purposes are known. In some applications it is advantageous, in others necessary to use laser-beam transmission via light guides. An assembly which transports laser light from the source to a target via a fiber is called a fiber optic beam delivery system or BDS. Most of these systems consist of the following parts (Fig. 1): - laser, - coupling optics, - fiber, and - focussing optics. Some systems contain even more components e.g. in ophtalmology for reflecting the beam into a microscope. Any practical system uses connectors to separate the individual parts. The fiber will be confectionated into a cable with connectors with or without optical systems integrated. Because the systematic development of BDS is only at the beginning, we will give some brief considerations how to achieve an optimized BDS. We will only consider continuous wave multimode laser beams. For a given problem one will have to - define the desired performance, - choose the appropriate components, and finally - adapt these components to each other.

The paper presents a new design of ophthalmic slit lamp which has been especially constructed for use in laser photocoagulators. A solution to various problems arising in existing systems, the optical possibilities for precisely controlling the spot diameter and an easier method of operating the manipulator will to discussed. This slit lamp offers all manufacturers of argon, crypt on and dye photocoaqulators a unique optical interface.

A major problem in using pulsed Neodym-YAG-Laser-Systems for ophthalmic break-down surgery is to supply a sufficient aiming beam which gives the operator a precise indication of the point of interaction, independent of multiple reflections within the anterior segments of the eye. In addition to that, to minimize side-effects, an optical solution to achieve a high cone-angle will be presented. These results will be shown as performed in a recently introduced system.

If the pupil of the eye is illuminated by a collimated laser beam the light returning from the eye exhibits Newton's interference fringes. This phenomenon can be used (1) to measure fundus tissue pulsations and (2) to measure the optical length of the eye. A first series of clinical measurements of patients with angiological problems has shown a clear correlation of the interferometrically measured fundus pulsations with circulation conditions. First measurements of the optical length of human eyes indicate a very high potential precision of this new technique.

The temperature dependence of fluorescence decay time of suitable materials is the basis of a sensor, which transforms the temperature to be measured into the modulation frequency of the exciting light. Different schemes of signal processing are treated mathematically and the optimum operating conditions are deduced and verified experimentally.

New surfaces with minimum specular reflection and low absorption have been developed for laser surgery instruments. Measurements of the scattered light distribution and the thermal response are presented.

A device is under development allowing the measurement of light intensity and temperature distributions in tissue. Measurement of these parameters in three dimensions can be achieved in real-time with the use of an especially designed multiplexing system. Preliminary results are reported for the light intensity distribution in liver and a computer analysis gives a value for "∂" the total absorption coefficient.

One of the most interesting fields of application of optical fibre technology is the medicine. Among other medical disciplines the field of ophthalmology is very interesting for these applications because of optical character of the organ of vision. After some remarks of a general nature, and concerning the needs of modern ophthalmology, we will review here our trials to apply optical fibre devices for the optical surgery, therapy and diagnosis in the ophthalmology. The devices include: optical fibre illuminators for the applications with operational probes (crioprobes, termal probes, a vitrotom etc.) and some of the diagnostic equipment (like Goldman lens etc.), optical fibre gradient microoptics for delivering of a laser beam to the appropriate internal structures of the eyeglobe, optical fibre lacrimaloscope for the screening of the lacrimal ducts and another one for the orbit. A general conception of the multitask fibre optic microprobe fcr ophthalmological applications - operations and diagnosis/1/ - concludes the work.

The increases in temperature of the tissues at different depths produced by a laser irra diation are the main effects used as a therapeutic agent. On the other hand the usual powers of the medical lasers (about 10 W) could expose the patients to risks (in the skin). That is why, it is necessary to estimate previously the increases in temperature which the treatment will produce. Due to the high temperature gradients the experimental measurements are not easy to take. Thus, we have considered it very interesting to present a relatively simple and quick method to determine the temperature distributions. In it, we have taken into account the cha racteristics of both the laser beam and the geometry of the irradiation area.

In Argon-Laser treatment of the retina the problem occurs that in case of large- area irradiation, for instance when coagulating neovascular areas, the laser energy is not applied uniformly over the coagulation area due to the Gaussian beam intensity distribution. This may cause heavy damages to the tissue and jeopardize or even prevent its regeneration. Furthermore the anterior eye segments, particularly the cornea may be damaged by the high beam energy and the flat cone angle which is needed to obtain a large coagulation spot.

Considerable controversy exists concerning the efficacy of so-called soft lasers for the treatment of various dermatological ailments. Based on a model of functioning of the human body as living matter a triple-blind method was developed to clear up the effects of low power cw ion lasers in comparison with thermal light sources, one of which was named the π-laser, and to find out whether their action on the living matter is an equilibrium or nonequilibrium phenomenon.