Optical microscope and imaging method

An optical microscope for imaging an image for tissue observation or pathological diagnosis, comprising:

• at least one laser light source configured to generate laser light with a laser wavelength for illuminating a sample containing a light absorbing material;
• a lens configured to focus the laser light to be focused on the sample;
• scanning means for changing a focusing position of the laser light on the sample;
• and
• a light detector configured to detect laser light transmitted through the sample as signal light with the laser wavelength, wherein
• a laser light intensity is changed to obtain a nonlinear region in which the laser light intensity and a signal light intensity have a nonlinear relation due to occurrence of saturation of absorption in the light absorbing material when the laser light intensity is maximized, and
• an image is generated based on a nonlinear component of the signal light based on the saturation of absorption in the light absorbing material,
• wherein
• the light absorbing material is a dye,
• the sample contains a tissue, a cell, or a bacterium stained with the dye,
• the laser wavelength is selected so that a value of a product CL is included in a range in which an inclination of a modulation harmonic component of a modulation frequency f included in a transmission signal is positive with respect to the product CL,
• the laser light is intensity modulated with the modulation frequency f,
• C indicates a concentration of the dye, and
• L indicates a thickness of the sample.