All lasers/IPLs work by producing light of a very specific wavelength. If the wavelength of the laser is matched to a target colour (such as the red of blood in the vessel wall), the energy of the laser is absorbed specifically by the target but not by the surrounding tissues. The IPL produces a slightly wider range of wavelengths of light, but works in exactly the same way.
The IPL delivers a series of energy pulses generating heat for very short periods of time; this energy closes down the thread veins, without perforating them.
The damaged veins are gradually dissolved away and disappear over several weeks after treatment.
