Pinpoint of light. Cuvette with dye showing the pinpoint of light effect produced by a laser. It has implications for laser use in microscopy, microsurgery and optical memory devices. The cuvette contains safranin dye which normally needs green light to make it fluoresce. The light beam (at upper centre) is caused by green laser light. The spot (lower centre) is caused by an infrared beam of a mode-locked pulsed laser which has been focused by a lens. Photons in this beam can be absorbed at the same time by the same molecule and so add their energies together. This 2-photon absorption only occurs at high intensities at the beam's focal point, leading to a precise pinpoint.