Optics and Lasers in Medicine

• Biomedical Optics
• Applications of Lasers in Medicine
• Lasers in Dentistry

Lasers are now available with output wavelengths ranging from the far ultraviolet to the mid-infrared. A growing number of these laser wavelengths are being applied in medicine. For a laser to have the desired effect, its energy must be absorbed in the targeted tissue. As such, lasers are selected for specific applications based on the absorption characteristics of their wavelength(s) in tissue and the means available to get the laser energy to the treatment site.

Effect of lasers on the tissue: When the laser energy is incident on tissue, three things happen. Some of the light will be reflected, some will be absorbed at the treatment site, and some will be transmitted into tissues beyond the treatment site.

For the laser to be effective the light must be absorbed by the targeted tissues. The degree to which each occurs is a function of the laser wavelength and how the laser energy interacts with the tissue being irradiated.

Effects of irradiance: Irradiance is the degree to which laser energy is concentrated on the targeted tissues. Irradiance on target is laser power divided by target area, and the unit of measurement is watts/cm². Since the vast majority of surgical laser output beams are round, and the area of a circle is defined as Br² , if the target spot radius is increased or decreased, the resultant change in irradiance will be increased or decreased as an inverse function of r². Therefore, a small change in spot size can have a dramatic effect on target irradiance and correspondingly the rate at which the laser will destroy tissue.