A small internal volume cell having fluid entry, and exit ports wherein at least one bubble trap is present in a fluid pathway which is continuous with the fluid exit port. There further being present an input/output aperture, for entering and exiting electromagnetic radiation, positioned to allow causing an input beam of electromagnetic radiation to impinge on a sample substrate at a location thereon at which, during use, fluid contacts; and a mirror for directing electromagnetic radiation which reflects from said sample substrate, toward and out of said input/output aperture; as well as methodology of its use.