Abstract: An apparatus for performing photochemical measurements on a liquid or liquid-containing sample includes a light generating system, an optical system configured for directing light from the light generating system towards the sample and a sensing system for measuring at least one optical property of the sample, wherein the light generating system is configured for generating light with intensity levels adjustable within a range, spanning at least three and preferably at least five orders of magnitude; and in that the optical system is configured for directing light from the light generating system towards the sample so as to generate a substantially uniform light intensity level, within a cylindrical region of the sample having a height larger than or equal to five time its radius.

Abstract: A method for detecting a reversibly photoswitchable chemical species in a sample, includes the steps of: a) illuminating the sample with light suitable to be absorbed by the chemical species triggering a reaction affecting an optical property of the chemical species, the first light being periodically-modulated at a fundamental modulation frequency; b) measuring the evolution of the optical property; c) extracting at least one of an in-phase component at a frequency which is an even multiple of the fundamental modulation frequency; and a quadrature component at a frequency which is an odd multiple of the fundamental modulation frequency of a signal representing the evolution; and d) using the extracted component or components for detecting the chemical species. An apparatus for carrying out the method is also provided.

Abstract: A method for detecting a photochemically active chemical species in a sample, comprising the steps of: a) illuminating the sample with light at a wavelength suitable to trigger a reaction affecting an optical property of the chemical species according to an illumination sequence, such that: in at least a first time window, the kinetics of the first reaction is limited by a photochemically-activated step of the reaction; and in at least a second time window, the kinetics of the first reaction is limited by a thermally-activated step; b) measuring the evolution of the optical property during the first and the second time windows; c) determining at least a first and a second time constant representing the kinetics of the first reaction in the first and the second time windows, respectively; and d) using the determined time constants for identifying the chemical species. An apparatus for carrying out such a method.