Laser Safety

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Abstract

After a short introduction on current applications of lasers at the beginning of this chapter, Sect. 25.1 gives some historical remarks on laser safety.

In Sect. 25.2, biological interactions and the effects of laser radiation on human tissue are described. Absorption, penetration, and transmission of optical radiation are dealt with in detail. The wavelength-dependent transmission through the eye from the cornea to the retina and the role of the pigment epithelium as a selectively absorbing layer are illustrated quantitatively. The optical gain as a result of the focusing capability of the eye is demonstrated, together with the increase of irradiance on the retina relative to the power density of the laser beam in front of the eye. State-of-the-art descriptions of photochemical, photothermal, and photoionizing effects on biological tissue in general are given, and the effects of laser radiation, especially on the various parts of the eye, are described. Retinal and nonretinal injuries of the eye are analyzed and illustrated. In addition, injuries to the skin are shown.

The topic of Sect. 25.3 is maximum permissible exposure. Its relevance to the prevention of short- and long-term effects is described, and some remarks on safety or reduction factors are made. The relationship between radiant exposure and irradiance is derived, and its general connection to maximum power values and exposure duration is demonstrated. For the eye, the influence of physiological factors such as eye movements is discussed in more detail for the case of continuous-wave exposure from a point source. In addition, the concept of an angular subtense to describe the irradiation from an extended optical source is analyzed. Furthermore, recent results are described which show that the strong belief in aversion responses and especially in the blink reflex as a reliable physiological reaction is no longer valid, since no more than about 20% of people perform a blink reflex and even less avert the head. In addition, indirect effects such as disturbance of visual functions as a result of temporary blinding due to intrabeam viewing are described for the first time.

International standards and regulations on laser safety worldwide are summarized in Sect. 25.4.

Laser classes are described in Sect. 25.5 according to the classification scheme of the international standard IEC 60825-1. The meanings of acceptable exposure limits and time base are explained. A comprehensive description of the various laser classes is given, and valuable hints about dealing with each laser class are also described. It is shown how the nominal ocular hazard distance might be calculated from given data.

In Sect. 25.6, protective measures are described. As is usually the case, technical and engineering measures rank more highly than administrative and personal protective measures. The protective measures are assigned to the respective laser classes. In addition, the role of a laser safety officer is described.

In Sect. 25.7, special recommendations for the most hazardous situations are given and common unsafe procedures are listed. Finally a special topic deals with laser pointers and gives a résumé on the most recent findings on temporary blinding as a consequence of direct laser beam viewing.