Lasers

BASIC LASER CONCEPTS

What does the acronym LASER stand for?

Light Amplification by Stimulated Emission of Radiation.

What are the three unique properties of laser light as opposed to natural light?

1. Coherent—laser light is coherent (all waves are spatially and temporally in phase).

2. Monochromatic—the delivered light is of a single spectral color and of a single precise bandwidth.

3. Intense—laser light delivers the greatest number of photons per unit area.

What is “thermal relaxation time”?

Time required for a tissue to absorb and diffuse the thermal energy to surrounding tissues.

What is “pulse energy”?

The energy of one pulse.

So why do these last two facts matter?

The pulse duration of a laser should be set for LESS time than the thermal relaxation time of the target tissue if you want the target tissue to be heated and destroyed. If the pulse duration is MORE than the thermal relaxation time, the tissue will absorb and diffuse the energy to surrounding tissues before it is destroyed.

What is the optimal pulse duration time?

A time that is LESS than the thermal relaxation time of the target tissue, usually half.

What is “energy”?

The capacity to do work in joules.

What is “power”?

The energy delivered divided by the time of application.

What is “power density” (irradiance)?

The rate of energy delivered per unit area measured in watts per square centimeter.

What is “fluence”?

Total laser energy delivered per unit area expressed as joules per square centimeter. The volume of tissue removed is a function of the amount of energy applied.

What is a continuous wave (CW) laser?

Lasers producing a constant flow of laser energy and thus resulting in significant thermal tissue damage. They can be “gated” using a physical shutter to interrupt the flow of energy.

What is a pulsed laser?

These lasers produce high-energy, short pulses without the use of a physical shutter.

What is a Q-switched laser?

Q-switching produces particularly high-energy, short-pulse-duration beams.

Lasers are selected based on their ability to be selectively absorbed by target tissues. These target tissues in the skin are known as?

Chromophores.

CLINICAL APPLICATIONS

What is the difference between ablative and nonablative lasers?

• Ablative lasers remove tissue in a controlled fashion from the outside in resulting in a wound that the body must heal.

• Nonablative lasers target specific chromophores in the skin leaving the epidermis intact.

What is selective photothermolysis?

Selective thermal damage of a pigmented target when sufficient fluence at a wavelength is delivered during a time (pulse duration) equal to or less than the thermal relaxation time of the target. More simply, energy is delivered to the target more quickly than the target can dissipate it.

When targeting chromophores with selective photothermolysis what is another way other than adjusting the pulse duration to decrease injury to the surrounding tissues?