How it works
Selective photothermolysis is the whole idea, described by Anderson and Parrish in 1983. Melanin in the shaft and follicle drinks 808nm light; the epidermis above absorbs less. Push energy in faster than the follicle sheds heat and the germinal cells give up.
Cooling sets your real ceiling. A sapphire window rides a closed water loop, chilled before, during and after each pulse, and our manuals want 5 to 8 minutes of warm-up at 18°C before the first client. Three coupled dials do the rest: pulse width 5 to 200ms, frequency 1 to 10Hz, power from 33 percent upward. Widths of 5 to 20ms take the full 10Hz; 25 to 40ms drops you to 1-5Hz; 45 to 100ms to 1-2Hz; past 100ms, one pulse a second. That ceiling is thermal, and firmware enforces it. Schedule around it, because a stacked back at long widths is a slower room than legs at 10Hz.
Two honest styles fall out of that. In motion means short pulse, modest fluence, 10Hz, tip gliding fast while passes accumulate; our house start is 20ms at 10Hz, power at 33 percent. Stacking is the opposite: long pulse, big single-shot energy, tip held still, which coarse dense hair rewards. Feels sharp fast? Move quicker.
Phototype moves the numbers, not the method. Our parameter sheet starts types I-II near 8 to 10 J/cm² on lip, underarm, arms and legs, trims III-IV slightly, then drops type V to roughly 4 to 5 with shorter durations. For type VI it publishes nothing. Read how to read Fitzpatrick skin types, then patch test. You want small papules around the follicles, redness, warmth. Blistering is a mistake, not an endpoint.