molecule in the location that's fixed you can only focus light to that position so what we do here is to focus ultrasound to a given point and that ultrasound is going to attack light passing through the outside of tissue we detect attacked photons and time reverse the tagged photons back and it will come back to the outer assumed focal point so this technology is called time reversed ultrasound coded or true optical focusing in other technologies to use photo quistis as a guy star right so this this is called optical speckle