What property is critical for dichroic mirrors when reflecting light in flow cytometry?

The property that is critical for dichroic mirrors when reflecting light in flow cytometry is the angle of incidence. Dichroic mirrors are designed to selectively reflect certain wavelengths of light while transmitting others, and this process is significantly influenced by the angle at which incoming light strikes the mirror's surface.

When light hits a dichroic mirror at a specific angle, the mirror can effectively direct the light that corresponds to its designed reflection characteristics. This selective reflection is essential for flow cytometry, where different colors of light (representing different fluorescent labels) need to be separated efficiently to analyze the various parameters of cells as they pass through the laser beams. Ensuring the proper angle of incidence optimizes the performance of the mirror, enhances the signal detection, and maintains the integrity of the fluorescence signals.

The other options do not capture this critical aspect of dichroic mirrors. While the intensity of incoming light, the color of reflected light, and the duration of exposure are relevant factors in fluorescence measurement, they do not pertain specifically to the essential geometric and optical properties needed for the effective functioning of dichroic mirrors in flow cytometry settings.