Laser Tissue Interaction

Laser use in the field of medicine is large and steadily growing. This growth is based on the versatility of laser light. The characteristics of laser light are defined by its wavelength, pulsed or continuous wave operation as well as its average power. The unique capabilities to tailor laser light to a particular application opens up a wide space for laser tissue interaction. These interactions can be classified into three main categories:

Photothermal Reactions:

Laser light absorbed by chromophores in the tissue is converted into heat. A typical application is photocoagulation, where the laser light is absorbed by hemoglobin to stop bleeding or to seal blood vessels. Another example is thermal ablation when laser light vaporizes tissue water for tissue cutting. This interaction requires laser solutions that have high average power and a wavelength that matches the absorption levels of target tissue.

Photochemical Reactions:

Photons absorbed by tissue molecules. Excited molecules can undergo chemical reactions. A prominent example is Photodynamic therapy (PDT) where a photosensitive drug is administered. Using specific wavelengths enables applications such as selective photo thermolysis. Tattoo removal is an example of this. This interaction requires laser solutions that have high average power and a wavelength defined by molecule absorption.

Photoablation:

Laser light is used to break the molecular bonds in the tissue. Key applications include ophthalmology where UV laser light is used for refractive surgery of the cornea, as well as in lithotripsy where high energy laser pulses are used to generate plasma and shock waves that can break up kidney stones. Typical laser solutions operate in pulsed mode for high peak power and, depending on the type of tissue, have UV to NIR wavelengths.