This invention relates to a measurement device, for optically measuring a property of a measurement object, the measurement device comprising a main resonator having a first and a second reflecting end defining a cavity having an effective optical cavity length, an optical gain element for generating light travelling along an optical beam path between the first and second reflecting ends, and a dispersive focusing resonator element which is positioned along the optical beam path between the optical gain element and the second reflecting end, whereby the measurement object is arranged to be at least partly positioned within the optical beam path of the main resonator, and whereby the measurement device further comprises a detection means for detecting a characteristic of light emitted from the main resonator, the value of the detected characteristic being a measure of a property of the measurement object.