A 
laser scanning 
microscope produces molecular excitation in a target material by simultaneous absorption of three or more photons to thereby provide intrinsic three-dimensional resolution. Fluorophores having 
single photon absorption in the short (
ultraviolet or visible) 
wavelength range are excited by a beam of strongly focused subpicosecond pulses of 
laser light of relatively long (red or 
infrared) 
wavelength range. The fluorophores absorb at about one third, one fourth or even smaller fraction of the 
laser wavelength to produce fluorescent images of living cells and other microscopic objects. The fluorescent emission from the fluorophores increases cubicly, quarticly or even 
higher power law with the excitation intensity so that by focusing the 
laser light, 
fluorescence as well as 
photobleaching are confined to the vicinity of the focal plane. This feature provides 
depth of field resolution comparable to that produced by 
confocal laser scanning microscopes, and in addition reduces 
photobleaching and 
phototoxicity. Scanning of the laser beam by a 
laser scanning microscope, allows construction of images by collecting multi-
photon excited 
fluorescence from each point in the scanned object while still satisfying the requirement for very high excitation intensity obtained by focusing the laser beam and by 
pulse time compressing the beam. The focused pulses also provide three-dimensional 
spatially resolved photochemistry which is particularly useful in photolytic release of caged 
effector molecules, marking a recording medium or in 
laser ablation or 
microsurgery. This invention refers explicitly to extensions of two-
photon excitation where more than two photons are absorbed per excitation in this nonlinear 
microscopy.