Patent ID: 6855941

Claim:
A multiphoton excitation scanning laser microscope, comprising: (a) a station for placing a sample to be observed; (b) a laser beam source for emitting a pulse laser beam for exciting said sample to cause the sample to emit a fluorescent light by multiphoton excitation phenomenon; (c) a detector for detecting said fluorescent light; and (d) an optical system for forming an optical path of said pulse laser beam for guiding said pulse laser beam from said laser beam source to said sample, said optical system including: a pre-chirp compensator disposed on said optical path such that the pulse laser beam passes therethrough, and preset to provide said pulse laser beam with a certain amount of pre-chirp compensation, said pre-chirp compensator comprising optical elements which cause components of the pulse laser beam to be emitted in order of wavelength such that shorter wavelengths are emitted earlier than longer wavelengths; a plurality of objective lenses adapted to be selectively placed on said optical path for collecting the pulse laser beam on the sample, the objective lenses including objective lenses having different optical path lengths, a revolver for switching the objective lenses, and a correcting mechanism for correcting an optical path length of said optical path so as to be constant no matter which of said objective lenses is selectively placed on said optical path, wherein said correcting mechanism comprises at least one flat optical correcting element adapted to be selectively inserted in said optical path in accordance with which of said objective lenses is selectively placed on said optical path, so as to maintain the optical path length of the optical system without moving said optical elements of said pre-chirp compensator, and wherein said certain amount of pre-chirp compensation provided by said pre-chirp compensator is set to prevent a pulse width of said pulse laser beam from widening due to a wavelength range of a pulse of said pulse laser beam when said pulse laser beam passes through said optical path whose optical path length is kept constant.