Provided is a nonlinear optical device capable of alleviating, without the need for a complicated compensation mechanism, temporal broadening and the waveform distortion resulting from a group-velocity dispersion slope, to thereby irradiate an object with short optical pulses having high peak power. The nonlinear optical device includes a short optical pulse source (10) for generating short optical pulses and a short optical pulse delivery system (20) for delivering the short optical pulses generated from the short optical pulse source to an object, in which there is generated substantially no nonlinear optical effect and there is substantially no amount of group-velocity dispersion, the short optical pulse source generates short optical pulses, and the short optical pulses have a spectral width (full width at half maximum) λ_FWHM satisfying λ_1<λ_FWHM<λ₂.

There is provided an optical analysis technique using the optical system of a confocal microscope or a multiphoton microscope for optical analysis techniques, such as the scanning molecule counting method, FCS, FIDA and PCH, in which it is enabled to judge whether or not a predetermined condition in the optical system is realized before performing a light intensity measurement. In the inventive optical analysis technique of measuring light intensity from a light detection region placed in a sample solution and analyzing the light intensity, there is performed a process of judging if a light detection region is placed in the sample solution and a measurement of the light intensity from the light detection region can be performed, and/or, the position or its area of the light detection region relative to the sample container in which a light intensity measurement can be performed based on the magnitude of signal intensity outputted by a photodetector during moving the position of the light detection region relative to the sample container.