In 1963 Leon Goldman, a dermatologist at the University of Cincinnati, used a laser for the first time on human skin. He used a ruby laser, which emits laser energy at 694 nm, in the red part of the visible light spectrum. This laser was a "normal mode" ruby laser that produced pulses of laser energy about one thousandth of a second in length. (This was very early in the laser era. The first laser ever built, in 1960, was also a ruby laser.) Dr. Goldman's laser produced only a low power beam. He and his colleagues were curious about the effect the laser might have on human skin. There was little effect on the skin at this low power level except for singeing of hairs and a mild burn effect.
The following year Dr. Goldman and his colleagues used a "Q-switched" ruby laser on a man with a dark blue tattoo. (The
Q-switch is a device in the laser cavity that includes a polarizing filter to block the passage of photons. The material in the laser cavity is kept in a highly excited state and then an electrical signal changes the polarity for an extremely short time, allowing the passage of light through the filter. The Q-switch is many thousands of times faster than any mechanical switch and produces a very high energy laser pulse of extremely short duration.) These researchers observed an immediate whitening of the treated tattoo and correctly surmised that this effect was something other than simple heating of the skin. There was only mild pain and no adverse effect on the skin. Although they did not know it at the time, their treatment of this tattoo was the first ever example of selective photo-thermolysis.
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