Search

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, absorption, scattering.

Threshold measurements for laser-induced breakdown of different organic tissue (cornea, brain, enamel) and inorganic matter (fused silica) have been extended to the sub-lOOfs time regime. A Ti:Sapphire laser system delivers 450 microjoules at repetition rates up to 1kHz. Single shot experiments are performed with pulse durations from 35fs to 240fs. To ensure a consistent determination of the threshold fluence, damage is detected by the alteration in amplitude of scattered light and/or by the occurrence of a plasma spark. In our single shot experiment with human enamel, no significant threshold dependence on pulse duration was observed. For soft tissue (cornea, brain), however, a slight decrease of threshold fluence is found when shortening the pulse duration. Fused silica is chosen as an additional target to compare the obtained data with those of recent experiments.

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.

The potential of all-in-one techniques in modern femtosecond solid state lasers is being discussed. For first experiments we designed an electrooptically switched Ti:Sapphire laser. Q-Switching and dumping was performed at half-wave voltages. The generation of ultrashort pulses with energies at the μJ-level in one single cavity seems to be within the realms of possibility.