Q-switched CO2-laser material machining system comprising acousto-optic modulators
A Q-switched CO2 laser material processing system with acousto-optic modulators (AOM) is employed, on the one hand, inside the resonator for Q-switching the CO2 laser and, on the other hand, externally for efficient suppression of the radiation feedback between a laser and workpiece. The frequency shift of the radiation diffracted at the AOM is taken into account which exactly corresponds to the excitation frequency of the acoustic wave in the AOM crystal under the aspect of the amplification of the radiation in the active medium. Since this frequency shift significantly reduces the amplification of the radiation, it has to be avoided in the Q-switching process, which is achieved, by means of a tandem of two AOMs with identical excitation frequencies but with the acoustic waves propagating in opposite directions in the crystal. The frequency shift advantageously suppresses radiation feedback between the laser and workpiece.
1. A Q-switched CO2 laser material processing system, comprising acousto-optic modulators (AOM) for beam shaping, wherein
a) for the Q-switch two AOMs arranged behind each other and preferably close to a resonator end mirror or a laser output coupler plate, said AOMs being characterized by identical excitation frequencies and opposite directions of propagation of the acoustic wave in the crystal, are arranged with the proviso that a beam incident on the first AOM is diffracted, a diffracted beam resulting therefrom is once again diffracted at the second AOM, and this beam resulting from the dual diffraction, after reflection at the resonator end mirror or the laser output coupler plate, is reflected back in itself and is fed back as a beam after another diffraction at the two AOMs into an active medium, and thus a laser function is realized, when a corresponding switching voltage is applied to the two AOMs, and when turning-off this voltage the laser function is interrupted, and
b) a thus produced laser beam coupled-out by means of an output coupling element prior to use, for material processing by laser, is sent through a third AOM arranged outside of the resonator and preferably immediately behind the output coupling element, wherein for the intended use the beam diffracted by means of a corresponding switching voltage at the third AOM is employed, and the excitation frequency of the acoustic wave in the crystal of this third AOM is at least in the order of the frequency full-width at half-maximum of the gain profile of the active medium, and between 40 and 100 MHz,
wherein the laser material processing system is decoupled from radiation reflected back from a workpiece placed into the laser material processing system.
2. The Q-switched CO2 laser material processing system according to claim 1 , wherein only the first or the second AOM is used for power modulation or Q-switching of the laser by corresponding variable control of the switching voltage, and the respectively other AOM operates with a constant switching voltage.
3. The Q-switched CO2laser material processing system according to claim 1 , wherein the first or the second AOM is used for Q-switching of the laser by variable control of the switching voltage, and the respectively other AOM is controlled such that freely selectably individual pulses or pulse groups are selected and/or the power of the Q-switched radiation is varied.
4. The Q-switched CO2 laser material processing system according to claim 1 , wherein the external third AOM is controlled such that the radiation pulses generated by the laser are adjusted in their power to the respective intended use, and in particular the power profile within the pulses, particularly the peak power of the Q-switching peak, is substantially freely selectable.
5. The Q-switched CO2 laser material processing system according to claim 1 , wherein between the third AOM and the workpiece, a combination of ATFR mirror and λ/4 phase shifter is arranged.
6. The Q-switched CO2 laser material processing system according to claim 1 , wherein between the third AOM and the workpiece in the beam shaping unit, optical elements, preferably cylindrical lenses, for compensation of the beam deformations caused by the AOM are arranged.
7. The Q-switched CO2 laser material processing system according to claim 1 , wherein the external third AOM is replaced by an AOM cascade of two or more AOMs, and the coupled-out laser beam is divided by beam splitters and deflection mirrors into two or more partial beams such that each AOM is loaded with one of the partial beams.