A measurement method and apparatus rely upon the coherent optical interference between a reference beam and a diffractionless sensing beam having an optical path length that has been disturbed. The interference pattern can be analyzed to determine a measurement parameter of the disturbance. The diffractionless beam is particularly a Bessel beam. Exemplary optical interferometer types including Mach-Zehnder, Michelson, Sagnac and Fabry-Perot include a Bessel beam generator to generate a diffractionless beam as the sensing optical beam and in some aspects the reference optical beam of the interferometer. The sensing optical beam propagates along a sensing optical beam path in free-space. The reference optical beam path may be a free-space medium or a material medium such as an optical fiber. The sensing optical beam path is subject to a disturbance manifested by the optical interference pattern between the sensing optical beam and the reference optical beam. Parameters of the disturbance, such as motion, acoustics, environmental conditions and others can be determined by analysis of the interference pattern.