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Since the first report on laser radiation by Maiman (1960), many potential fields for its application have been investigated. Among these, medical laser surgery certainly belongs to the most significant advances of our present century. Actually, various kinds of lasers have already become irreplaceable tools of modern medicine. Although clinical applications were first limited to ophthalmology — the most spectacular and today well-established laser surgery being argon ion laser coagulations in the case of retinal detachment — the fields of medical laser treatment have meanwhile considerably widened. Due to the variety of existing laser systems, the diversity of their physical parameters, and last but not least the enthusiasm of several research groups almost every branch of surgical medicine has been involved. This should not be interpreted as criticism, although much damage has been done in some cases — especially in the field of biostimulation — when researchers have lost orientation due to striving for new publications and success, and industries have praised laser systems that later turned out to be completely useless. In general, though, many really useful laser techniques have been developed and clinically established with the help of all kinds of scientists. These methods of treatment have been reconfirmed by other researchers and properly documented in a variety of well-accepted scientific journals. And, even with early laser applications primarily aimed at therapeutic results, several interesting diagnostic techniques have recently been added.

In this and the following chapter, we will discuss basic phenomena occurring when matter is exposed to light. While here we will be concerned with various actions of matter on light, the opposite effect will be discussed in Chap. 3. Matter can act on electromagnetic radiation in manifold ways. In Fig. 2.1, a typical situation is shown, where a light beam is incident on a slice of matter. In principle, three effects exist which may interfere with its undisturbed propagation: Reflection and refraction are strongly related to each other by . Therefore, these two effects will be addressed in the same section. In Fig. 2.1, refraction is accounted for by a displacement of the transmitted beam. In medical laser applications, however, refraction plays a significant role only when irradiating transparent media like corneal tissue. In opaque media, usually, the effect of refraction is difficult to measure due to absorption and scattering.

The variety of interaction mechanisms that may occur when applying laser light to biological tissue is manifold. Specific tissue characteristics as well as laser parameters contribute to this diversity. Most important among optical tissue properties are the coefficients of reflection, absorption, and scattering which were discussed in detail in the preceding chapter. Together, they determine the total transmission of the tissue at a certain wavelength. Thermal tissue properties — such as heat conduction and heat capacity — will be added in this chapter. On the other hand, the following parameters are given by the laser radiation itself: wavelength, exposure time, applied energy, focal spot size, energy density, and power density. Among these, the exposure time is a very crucial parameter when selecting a certain type of interaction, as we will find later on.

In this chapter, we will discuss principal applications of lasers in modern medicine. Due to the present boom in developing new laser techniques and due to the limitations given by the dimensions of this book, not all disciplines and procedures can be taken into account. The main intention is thus to focus on the most significant applications and to evoke a basic feeling for using certain techniques. The examples are chosen to emphasize substantial ideas and to assist the reader in grasping some technical solutions. Potential difficulties and complications arising from either method are addressed, as well. However, we should always keep in mind that any kind of laser therapy will not be indicated if alternative methods are available which offer a better rate of success, are less dangerous to the patient, and/or easier to perform.

Most parts of this chapter are adapted from the booklet “Laser Safety Guide” (Editor: D.H. Sliney, 9th edition, 1993) published by the . The permission obtained for reproduction is gratefully acknowledged.