An apparatus for irradiating a specimen: that includes an optical transmitter for transmitting light from a laser source an optical probe configured to receive the light from the optical transmitter and to apply the light upon emission from an optical exit to the specimen a position detector adapted to detect a position of the optical probe in a longitudinal direction and to output a signal indicative of the position or of a change in the position relative to a surface forward of the optical probe a drive coupled to the optical probe and adapted to controllably adjust a position of the optical probe in the longitudinal direction and a feedback controller adapted to receive the signal from the position detector and to control the drive to control the position to keep the optical probe at substantially a constant position relative to the surface forward of the optical probe.
