scatter so you can penetrate multiple millimeters even multiple centimeters in biological tissue when light is absorbed it generates some heating we use very short laser pulses nanosecond right one nanosecond is a 1 1 billionth of a second right very very short laser pulses so this heating is very very rapid and we don't need a lot of heating milli degrees right so one one thousandth of a degree would be adequate that will give you a detectable signal already so if you generate hundred hundreds of milli henries of million agrees then you have