Introduction to Lasers and Light

Victor Ross, MD

“To understand laser tissue interactions and heat transfer is to understand laser medicine.” It’s important that Dermatologists understand how lasers work and how they interact with the skin. Electromagnetic radiation is energy. To best understand lasers, one should be familiar with the definitions that are associated with their use, i.e., fluence, pulse width, spot size and incident light. LASER is defined as Light Amplification by the Stimulated Emission of Radiation. It is a means to direct light in a focal, monochromatic way.  Why do we need to know how and why lasers work? This way, if something goes wrong, you have a basic troubleshooting guide. Non-familiarity with the device is probably the number one reason that complications occur.

Clinical Pearls

• Check beam profile
• Don’t forget that parts on the laser can break (mirrors, lamps, etc)
• Lots of different technologies exist
• Lots of different scanners available to enhance lasers
• Understand aesthetic laser wavelengths
• Understand pulse width
• The majority of laser interactions are thermal
• Cool the epidermis before the laser pulse comes down
• Pulse duration is very important You can’t use long pulses with tattoos
• We have a lot of cooling devices now available
• Use short pulses to resurface

There are three basic targets for skin and lasers:

• Water
• Blood
• Melanin

Three important considerations

• Photon migration in tissue
• Temperature increase as a response of chromophore absorption
• Response of chromophore to temperature-time combination (generally speaking, the higher the temperature, the less time to heat the target)

What is selective photothermolysis?

Site-specific, thermally mediated injury to pigmented targets; Only gets hot with the right wavelength and the right pulsewidth.

Physical Characteristics We can Exploit (e.g. scar)

• Hyperemia
• Hyper-pigmentation
• Exophytic nature
• Hyper-metabolism
• Inflammation

Photomodulation- Can we rejuvenate without heat?

Maybe some day we will see this, it’s not quite ready at this point.