Читать книгу Patty's Industrial Hygiene, Physical and Biological Agents - Группа авторов - Страница 90

All industrial and medical laser systems require a beam delivery system that is responsible for directing the power output of the laser to its target site of action. The application requirements and design of a laser's delivery system will, to a great extent, determine its hazards. It is quite apparent that a fixed delivery system that is incorporated into another instrument or machine will be safer than delivery systems that can be freely moved in space. A CO₂ laser beam directed downward by a focusing lens is fixed in space and even if directed by a joystick or similar control generally allows very limited movement of the beam. In many material‐processing systems, the laser beam is fixed (or with very limited movement) and is directed downward, and the work‐piece is moved under it. Fixed delivery systems are also typically found in many medical lasers (e.g. in ophthalmology) and may be connected to a microscope that permits the surgeon to both view the operative site and deliver the laser energy to the desired treatment site. Examples of more hazardous systems are hand‐held laser rangefinders, high‐power Class 3B laser pointers, and hand‐held surgical lasers which employ a freely moveable handpiece.

Delivery systems that are available to carry the laser beam's output from the laser cavity to the point of application may use either fiber optics or a conventional optical path, which is either fixed or articulated. The fiber optic delivery system is generally favored because of ease of use and its great flexibility for directing the beam to the worksite.

There are very real and practical limits to the use of fiber optics. Suitable fiber optic materials capable of transmitting the laser beam are not available for all wavelengths. For example, the 10.6 μm output wavelength of the CO₂ laser does not pass through conventional quartz or glass fiber optics. Because of this, CO₂ lasers, which are in widespread use in surgical and industrial laser systems, are limited to situations for which an articulated arm can be used. There have been frequent efforts to extend the applications of the CO₂ laser by developing fiber optic materials that transmit its output. These efforts have been only partly successful.

An articulated arm contains a series of mirrors that are mounted on pivots to allow the laser beam to be guided from its source in the laser cavity to its point of application. Typical delivery systems available today for the carbon‐dioxide laser employ hollow tubes to form an articulated arm. The laser energy may be transmitted through a fixed optical system as is commonly done in laboratory instruments or in excimer laser material processing equipment.