Thermo-optically based interferometric determination of laser power

We describe here a new technique for measuring the power in a continuous-wave, principal-mode Gaussian beam. This new method is based on the thermal lensing of the beam by a sample of an absorptive liquid. Both this method and a previous method depend on self-phase modulation of the beam and determine the beam power by measuring some prominent feature of the Fraunhofer diffraction pattern. The power delivered by a continuous wave, principal-mode Gaussian laser beam may be determined from the diameter of the outermost ring in the Fraunhofer diffraction pattern arising from thermal lensing of the beam.