Two lasers can be the same power but each can have totally different fluences.
The difference mostly has to do with it being collimated, monochromatic or if it is coherent. These are the 3 distinguishing things that separate the fluence from one laser to another.
Collimation/Non-Divergence: A laser beam is collimated, meaning it consists of waves traveling parallel to each other in a single direction with very little divergence. This allows laser light to be focused to very high intensity. Other light waves spread and lose intensity quickly.
Monochromatic: Monochromatic refers to the single (wavelength) color of a laser beam. Ordinary white light is a mixture of colors, as you can demonstrate by shining sunlight through a prism. Because the wavelength of laser light determines its effect on tissue, the monochromatic property of laser light allows energy to be delivered to specific tissues in specific ways.
Coherence: Laser light is coherent, which means all the light waves move in phase together in both time and space. A laser has a very tight beam that is strong and concentrated. A flashlight, by comparison, releases light in many directions; the light is weak and diffuse.
The laser diode that has the most fluence will deliver the most joules of energy to an area at one time. A 60 watt laser at full power has a difference fluence than two 30 watt lasers aimed at the same place. A continuous wave laser will have double the fluence as a pulsed laser if they are the same wattage but since a pulsed delivers higher wattage in bursts while the continuous lasers often deliver a lower wattage (constant power). I always like a higher fluence laser when treating larger areas.
Update: I will not sell lasers that are not FDA cleared. Too many doctors have gotten sued since I started this site. I will let everyone know which lasers are now approved
I will never trash talk lasers that did not get approved or those that were never cleared with the FDA. See my requirements for lasers that are not FDA cleared.
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