The paper presents applications of newly developed room-temperature mercury based photo-detectors (single-element and array type) in the measurement of infrared CO2 laser radiation during material processing. A specially designed measuring device to determine the intensity profile of high-power CO2 lasers in two perpendicular cross-sections with a time-resolution up to 10 kllz for a whole line-scan is presented. The data-acquisition and analyzing equipment based on a digital-signal-processor (DSP) enables to calculate parameters which characterize the temporal stability of the laser mode on-line.Experimental results illustrate the possibilities of the device. Moreover, the time-resolved measurement of laser beam parameters during material processing serves as a tool to investigate the influence of the laser beam on the dynamic process behavior. Optical signals obtained from the-laser beam welding process are correlated with laser beam power variations to determine the grade of interaction.Keywords: mercury based photo-detectors, digital-signal-processor, CO2 laser beam measurement, beam power, intensity profile, laser beam welding, process diagnostics.

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I.u laser beam welding a variety of complex physical interactions take place, leading to a fluctuating process behaviour. Most of the available 1nprocess control facilities measure signals emitted from the interaction zone like the lightemission in different spectral regions or acoustic waves. The obtained signals contain statistic as weli as periodic components, from which information about the temporal progress of the process has to be derived by well adapted signal analysing methods. The paper is presenting a 'hardware'tool for process diagnostics in laser beam welding that has been developed.By several examples the application of different signal analysing techniques is explained considering the signal level, signal statistics and frequency analysis. Finally, advantages and disadvantages are discussed in context to industrial use.

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The temporal beam power fluctuations of a highpower CO2 laser are analysed according to their frequency spectrum and its time dependent variation. Simultaneously to the laser beam diagnostic, signals obtained from the light emission during the cutting and welding process have been detected. By comparison of corresponding spectra the interaction between beam oscillations and process dynamics is studied. The influence on the surface structure of the processed material is discussed especially in the case of laser beam cutting. For this the spatial surface morphology is also analysed by means of local fast Fourier transformation. The overall result is that the spectra are not constant, but show time-dependent behavior. Thus a more detailed correlation analysis is necessary for full description of dynamical beam processinteractions.