Lowdown on lasers

This week's column is devoted to the basic laser terms - and the technologies that those terms describe - that are critical to understanding, naming and operating any laser or light-based system. It is with these basic concepts that laser surgery has made such rapid advances in such a short period of time.

Laser commonalities

Laser devices are similar in that all have three main components:

Pulse also considered

In addition to being named by the type of lasing medium they use, many lasers are named by the type of pulse they emit.

The pulse of a laser can be continuous, quasicontinuous or pulsed.

With the introduction of the theory of selective photothermolysis (Anderson and Parrish, 1983), the pulsed laser systems gained popularity over the others. This theory explains how we can use lasers to selectively destroy a target without damaging the surrounding tissues. A pulse is essentially the duration of time of active emission of light. Tissues react differently to different-length pulses.

The pulse duration plays a very important part in the clinical outcome. Practitioners can get completely different clinical results using the same wavelength and same power, but different pulses.

The lasers that emit the shortest pulses are termed "q-switched" lasers, with pulses in the nanosecond range. Because all of the energy is emitted in such a short period of time, high peak powers are attained, with intense tissue destruction. These lasers are mostly used for removal of pigment - for instance, lentigos and tattoos.