Laser energy absorption coefficient and in-situ temperature measurement of laser-melted tungsten

The energy absorption coefficient of tungsten surface (W) for 1064 nm Nd:YAG laser was measured as a function of the induced energy. Result was confirmed by the reference spectral emissivity up to the melting point. Then, two non-contact surface temperature measurement diagnostics, a pyrometer measurement and a two-dimensional (2D) temperature measurement, were constructed for the laser-melted W spot. The 2D temperature profile was obtained by analyzing two-color images from a high-speed camera with an image splitter and a long-distance microscope. An OpenCV based program was developed for corrections on the tilted angle view and wavelength dependence of the captured intensities. W surface bubbling at the surface temperature near 5000 K was indicated by high-speed camera images, unstable temperature developments, asymmetric temperature profiles, and the postmortem surface observations.