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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During the last years a variety of devices for beam diagnostics of high-power CO2 lasers have been developed enabling to measure different parameters like the beam power, the spatial intensity distribution, the state of polarization or different geometrical values such as beam diameter and beam divergence. This paper gives a short overview of the state-of-the-art in CO2 laser beam diagnostics, points out future perspectives and presents two new measuring systems. In search of facilities for a cost-efficient measurement of the beam position and beam diameter in industrial laser beam delivery systems a flexible device for this task has been developed. The apparatus operates with moving thermocouples and is small and rigid. Under aspects of mirror-allgnement and the control of significant beam parameters during processing the system has a modular design with the ability to connect several measuring devices with one central control unit. The investigation of dynamic interactions between the laser beam and the process in case of laser beam welding and cutting reveals the necessity of measuring the intensity profile with a time resolution up to several kHz. Due to the lack of time resolution of available diagnostic systems the development of a high-speed laser beam intensity-profiler based on a room-temperature MCT detector-array and real-time data analysis will be described. By the use of a partially transmitting mirror in the beam delivery system it is possible to perform beam diagnostics during materials processing. Measurements of the intensity profile can be obtained with repetition rates up to 10 kHz and will be analyzed on-line to characterize the temporal stabifity of the laser beam. Fig. 1 gives a review of facilities and techniques for CO2 laser beam diagnostics that are commercially available or known as in the state oflaboratory operation. Each of them has its capabilities and restrictions, hence, in any case, the best choice depends on the major requirements of the user. When designing a diagnostic device for CO2 lasers the most important point is to separate a small portion of the high-power laser beam to fit the sensitivity and thermal resistivity of the sensor. Attenuation of the laser beam can be achieved by different principles using either spatial scanning methods, e.g. rotating slits, needles, pinholes, or optical beam splitters like partially transmitting mirrors, holographic plates etc. The crucial disadvantage of the former scanning techniques is that the record of a total intensity profile usually takes a few seconds. A time dependent variation of laser beam parameters like the mode structure or the laser beam power occurring during this time leads to an inaccurate measuring result that has to be interpreted properly. Usually, depending on the temporal stability of the laser beam source, only an averaging of several measurements gives reliable results. In the scope of investigating dynamical interactions of the laser beam with the material processing an increasing knowledge about the temporal be...

Due to the increasing range of high-speed and high-accuracy applications in material processing, especially in laser beam welding and cutting, the temporal stability of the laser beam parameters becomes more and more important. In this paper a laser beam diagnostic device is presented, that allows the determination of the intensity-profiles of high-power Co2 lasers with high time-resolution. The detector of this device consists of two linear arrays of room-temperature HgCdTe-detectors, arranged perpendicularly to each other across the center of the beam. The data of the 70 detector elements is acquired simultaneously at rates up to 15 kS/sec for single shot events and several 100 kS/sec for repetitive laser pulses. Due to the use of a digital signal processor (DSP) and an especially adapted software, it is possible to analyze the fluctuations of the intensity distribution on-line. By help of a partially transmitting mirror in the beam delivery system, measurements can be performed during material processing. Therefore, the interaction of the laser beam source itself with the material processing due to beam reflection as well as influences of the industrial environment to the laser can be detected. The calculation of the local variance and mean values enables the dependence of the laser's short-and long-term stability to be investigated due to changes in the resonator alignment, the stability of the power supply, the gas composition etc. as well as to the influence of the processing. For the pulse-mode of a laser, its transient behavior like changes of the intensity distribution can be determined with high time-resolution. For the improvement of drilling processes, the calculation of further statistical functions by the DSP makes it possible to estimate the uniformity of the laser pulses online as well.