The research, published in the journal Sleep, focused on eight women between the ages of 18 and 34 who were studied intensively for two weeks at Stockholm's Karolinska Institute. The brainwaves, body temperature and other attributes of the women were measured as they followed prescribed patterns of being awake and trying to sleep.

The women rested best when they tried to sleep at 9 a.m. after having been up for 18 hours, the researchers found. They slept most poorly in the late afternoon and when they hadn't been up very long before going back to bed.

Unlike older lasers, which burn skin cells, the new laser, called Tatulazr, penetrates the skin and shatters the pigment that makes up the tattoo. The tiny pieces of pigment are then collected by white blood cells and eliminated from the body, he explained.