Formation and characterisation of copper oxide coating for absolute radiant laser power measurement absorbing cavity

Abstract

The aim of this work is to optimise the different parameters for realisation of an absorbing cavity to measure the incident absolute laser energy. Electrochemical oxidation is the background process that allowed the copper blackening. A study of the blackened surface quality was undertaken using atomic force microscopy (AFM) analysis and ultraviolet-visible-infrared spectrophotometry using a Shimadzu spectrophotometer. A two-dimensional and three-dimensional microscopy of the formed oxide coating made by AFM shows that the copper surfaces became porous after electrochemical etching with different roughnesses. This aspect becomes more and more important with decreasing current density anodisation. In a 2 mol.L−1 NaOH solution at a temperature of 90°C and using a 16 mA/cm² constant density current, copper oxide formed has a reflectivity of around 5% in the spectral range between 300 nm and 1800 nm. Using 'mirage effect' technique, the obtained Cu2O diffusivity and thermal conductivity are, respectively, equal to (11.5 ± 0.5) 10−7 m2s−1 and (350 ± 20) Wm−1K−1. This allows us to consider that our Cu2O coating is a good thermal conductor. The results of optical and thermal study dictate the choice of the cavity design. The absorbing cavity is a hollow cylinder machined to its base at an angle of 30°. If the included angle of the plan is 30° and the interior surface gives specular reflection, an incoming ray parallel to the axis will undergo six reflections before exiting the device. So, the absorption of the surface becomes closely near 0.999999.