Characteristics of power meters for high power CO2 lasers

Four different instruments used for measuring CO2 laser beam power in the kilowatt range were evaluated. The techniques used to determine the laser beam power included temperature increase from an absorber of known mass and specific heat, temperature increase from a steady flow of water used to cool the absorber, thermal gradient caused by edge-cooling a circular absorber, and diffuse scattering from a small portion of the water-cooled absorber surface. The parameters evaluated included response time, repeatability, sensitivity to position of the incident laser beam and beam mode, and linearity of response. The accuracies of the instruments were not determined as no NIST standard exists. Response times varied from 1 to 15 s. Each instrument had good reproducibility in indicated power values. Some meters exhibited sensitivity to beam mode, diameter, and position. All meters had very good to excellent linearity in response. Comparison of the indicated power values showed that each instrument tended to give slightly different values. For the range 400–6000 W the indicated power values from all meters differed by <15% from the mean value.