Chapter 24: Lasers and Light Devices

INTRODUCTION

Since 1960, when the first laser was invented by T.H. Maiman at the Hughes Research Laboratory, the research arm of the Hughes Aircraft Company in Malibu, CA, research into and development of lasers has blossomed into a multibillion dollar industry. People have been especially fascinated by the capabilities and possibilities of “laser light.” Beginning with the ruby laser, these instruments have quickly become an integral part of many medical specialties, including dermatology. Lasers and light devices are now used in almost every area of medicine and our daily lives, including DVD and CD players, grocery store scanners, holograms, and even traffic lights.

LASER BASICS

To realize their usefulness in medicine and aesthetic medicine in particular, it is important to understand the basics of laser terminology (Box 24-1). Understanding the interactions of light with the skin helps make clinical treatments more successful. The word “laser” is actually an acronym for light amplification by stimulated emission of radiation. A laser amplifies light by stimulating photons, storing them, and releasing them as a beam of light. In order to accomplish this, the laser must have a source of energy referred to as the “pump.” This energy gets absorbed by atoms in the form of photons. When the atom emits its photons, it releases its energy in the form of light. All of this occurs in the lasing medium. Many lasers are named based on the type of lasing medium that they contain. Lasing mediums can be liquid (dyes such as rhodamine), solid [e.g., ruby, alexandrite, Nd:YAG, diode (semiconductor)], or gas (e.g., helium-neon, argon, CO₂).

Several of the instruments in the cosmetic armamentarium that will be discussed here are not “true” lasers. This fact does not render them any less useful in treating patients, but it is an important distinction to make. The importance lies in the nature of the interaction between light and skin. In 1983, Anderson and Parish introduced the theory of selective photothermolysis.¹ This theory states that the selectivity of a laser for its target relies on the fact that different wavelengths of light will be absorbed by different chromophores in the skin (Box 24-2). This allows us to “selectively” destroy these targets without damaging the surrounding tissues. In order to accomplish this, the pulse width should be sufficiently long to heat the tissue to the level of destruction, but not long enough for that heat to transfer out of the target to the surrounding normal skin. The duration of active lasing is termed the “pulse width” or “pulse duration.” The ideal pulse duration for selective destruction of a target ...