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INTRODUCTION

The field of laser-, light-, and energy-based technology has grown tremendously since the introduction of the first medical laser. These technologies continue to benefit from ongoing research and technical advancements, and the practicing surgeon must continuously learn and adapt to new and changing devices. The purpose of this book is to provide the laser surgeon with an updated comprehensive clinical guide to laser-, light-, and energy-based devices used in dermatology and dermatologic surgery. While a detailed overview of the physics of laser- and energy-based devices is beyond the scope of this book, a brief summary of the fundamentals of lasers and related technologies is included for general review. These concepts should help guide practitioners as they learn and modify techniques in response to new and changing technology.

OVERVIEW

The term laser stands for light amplification by stimulated emission of radiation. While differing laser designs exist, the basic components are similar. Energy or light passes through a gain medium where an amplified beam of light is generated through stimulated emission. The gain medium may consist of a gas, liquid, plasma, or solid, and the medium’s electrons absorb external energy (often from a light source or electrical field) and enter an excited quantum state. The electrons’ eventual transition back to a relaxed state from the excited state results in a predictable emission of radiation. Various design techniques exist to create a stimulated emission of radiation at a desired wavelength. Differing designs and gain mediums have enabled the production of lasers at many different desired wavelengths.

Emitted laser light is classically characterized as exhibiting temporal and spatial coherence. Temporal coherence implies polarized light waves of a single frequency moving in phase, troughs aligned with troughs and peaks aligned with peaks. Spatial coherence, on the other hand, describes a narrow beam of light with minimal diffraction or divergence. These characteristics of laser emissions distinguish them from other high-energy emissions of light. Laser emissions can be precisely measured, and several terms are commonly used to describe the energy output of a laser device. Fluence is the term used to describe the quantity of laser energy delivered to a given area (fluence = Joules/[centimeter]2). Pulse energy describes the quantity of energy delivered with each individual pulse of laser light. Power is a term used to describe the rate at which energy is transferred, and it is expressed in watts (1 W = 1 J/s).

Laser devices can deliver energy continuously over time (continuous mode) or in short pulses separated by intervals of time (pulsed mode). Most medical lasers used in dermatology operate in pulsed mode, and, conceptually, devices can be divided into categories based on wavelength and pulse duration. Wavelengths utilized in medical lasers include those in the ultraviolet, visible, and infrared spectra (see Table 1-1). Extremely short pulse durations, in the nanosecond and picosecond range, can ...

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