A system for measuring radiation at a peak wavelength that is radiated from a probe tip of a near-field scanning optical microscope (NSOM) probe used for laser machining, including: a laser source; the NSOM probe; a coupling substrate that is substantially transmissive to the peak wavelength; an NSOM mount to controllably hold the probe and the coupling substrate; an NSOM probe monitor coupled to the mount; an NSOM controller; and a photodetector optically coupled to the substrate. Light is coupled into the probe. The mount includes a Z motion stage. The probe monitor determines the distance between the probe tip and the coupling substrate. The controller is coupled to the probe monitor and the motion stage. It controls the distance between the probe tip and the coupling substrate such that radiation is coupled from the probe tip into the coupling substrate. The photodetector measures the power of this radiation.