A laser beam diagnostic device is presented, which allows the determination of the intensity profiles of high-power carbon-dioxide 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 a use of a digital signal processor (DSP) and an especially adapted software, the device is capable of analyzing the temporal behavior and the stability of the intensity distribution on-line. 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. For the pulse-mode of a laser, its transient behavior, for example changes in the intensity distribution, can be determined with high time-resolution. This is achieved by the method of sequential equivalent time sampling. The calculation of further statistical functions by the DSP makes it possible to estimate the uniformity of the laser pulses on-line as well. Using a partially transmitting mirror in the beam delivery system, measurements can be performed during material processing.