Squeezed light has also been used to improve nonlinear microscopy. Nonlinear microscopes use intense laser illumination, close to the levels at which biological damage can occur. This damage is a key barrier to improving their performance, preventing the intensity from being increased and therefore putting a hard limit on SNR. By using squeezed light in such a microscope, researchers have shown that this limit can be broken - that SNR beyond that achievable beneath photo-damage limits of regular microscopy can be achieved.