A scanning microscope includes a light source for generating a light beam having a wavelength, λ, and beam-forming optics configured for receiving the light beam and generating a quasi-Bessel excitation beam that is directed into a sample. The quasi-Bessel beam has a lateral FWHM and an axial FWHM that is greater than ten times the lateral FWHM, and the beam-forming optics include an excitation objective having an axis oriented in a first direction. The microscope includes beam scanning optics configured for scanning the quasi-Bessel beam in one or more directions that are substantially perpendicular to the first direction, and a detector configured for detecting signal light received from positions within the sample that are illuminated by the quasi-Bessel beam. The signal light is generated in response to an interaction of the excitation beam with the sample, and the signal light is imaged, at least in part, by the excitation objective, onto the detector.