Light sheet fluorescence microscopy (LSFM) or Selective/Single plane illumination microscopy (SPIM) is a fluorescence microscopy technique with an intermediate optical resolution, but good sectioning capabilities. In contrast to Epi fluorescence microscopy only a thin slice (usually a few hundret nanometers to a few micrometers) of the sample is illuminated perpendicularyl to the direction of observation. For illumination a laser lightsheet is used, i.e. a laserbeam which is focused only in one direction (e.g. using a cylindrical lens). A second method uses a circular beam scanned in one direction to create the lightsheet. As only the actually observed section is illuminated, this method reduces the photodamage and stress induced on a living sample. Also the good sectioning capability reduces the background signal and thus creates images with higher contrast, comparable to confocal microscopy.
This method is used in cellular biology and for microscopy of whole living creatures, such as embryos. It is now often used for the longtime observation of embryonal development in different model organisms.
LSFM was developed during the first years of the 21. century and introduced an illumination scheme into fluorescence microscopy, which has already been used successfully for dark field microscopy under the name ultra microscopy.