Beam power measurement with widening

The invention relates to a method and an apparatus for the direct and precise measurement of the power and/or energy of a laser beam, which make a measurement possible even in areas close to the focus of a laser beam, A device is proposed for this purpose that contains a radiation sensor, an expansion device, and a support mount. The radiation sensor has a receiving surface and is configured for the generation of an electrical signal, which is dependent on the power of the laser beam or the energy of the laser beam. The expansion device and the radiation sensor are positioned on the support mount at a distance from one another. The expansion device is configured in such a way as to increase the angle range of the laser beam. The laser beam propagates to the radiation sensor with an increased angle range. A diameter of the laser beam propagated on the receiving surface is greater than a diameter of the laser beam in the area of the expansion device. The receiving surface of the radiation sensor encloses at least 90% of the cross-section surface of the laser beam propagated.