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Investigation of beam pointing stability, far-field divergence angle and power density distribution of a high-power CO2 laser

A high power carbon-dioxide laser beam, sampled by a diffraction grating, is monitored simultaneously by a Hartmann sensor to measure the wavefront and by a pyroelectric matrix camera to obtain the far field distribution. The maximum sampling frequency of the Hartmann sensor is 1 kHz with a resolution of 10 (mu) rad for the measurement of the beam direction. The data of the pyro- camera can be analyzed with a maximum frequency of 5 Hz and the beam direction in the far field can be measured with an angular resolution of 50 (mu) rad. Both methods reveal a periodic change of the beam direction with an amplitude of nearly 50 (mu) rad and a periodic change of the beam divergence with an amplitude of about 150 (mu) rad. Far field profiles measured with the matrix camera show that the angular stability is limited by fluctuations of the power density distribution. These changes of the transverse beam profile are closely connected to fluctuations of the laser gas pressure, which are due to the gas pressure regulation system.