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2000
Conference Paper
Titel
UV beam sources for double pulse generation
Abstract
An even higher integration in semiconductor technology can be realized with a memory technology based on thin film ferroelectrical materials. Because these materials are usually transparent to light of the visible and infrared regions, optical processing with ultraviolet light is of significant interest due to the process versality compared to the traditional methods, including position resolved high speed processing. Depending on the pulse-length, the pulse energy and the repetition rate, the processing effect differs significantly. In conventional ultraviolet solid state laser-sources these parameters can only be varied in a certain range and obey physical relations. Depending on the laser crystal and pumping, average power TEM(00) lasers are designed rather to produce high energies at low repetition rates or low pulse energy at high repetition rates up to 100 kHz In any case the UV-pulsewidths stay short. The basic parameter to be varied is the pulse-length, which becomes longer at higher repetition rates. This is accomapgnied by a decrease of the pulse energy, which is not desired for the processing targeted. To overcome these problems, the concept of two laser sources has been developed, whose pulse generation signals and light paths are synchronized. This can be realized with an accuracy in the nanosecond range, so the two temporally shifted pulses act onto the material with a separation significantly shorter than the thermal dissipation time of several microseconds, hence appearing to the target as one pulse, but keeping the original pulse energies of the two given pulses. The acoustooptically Q-switched lasers consist of a double folded linear cavity, and are pumped from one side by a fiber-coupled diode laser module producing 20 W. The fundamental radiation is frequency doubled and tripled by two LBO crystals, producing a maximum of 1.4 W at 355 nm and 3.1 W at 532 nm operating at a repetition rate of 13 kHz. The central frequency of the two lasers at which the highest output power is produced has been chosen to be 8 kHz for one and 13 kHz for the second laser to broaden the average output power curve dependent on the repetition rate. To correct the acceptance angle difference in the frequency tripling process, a cylindrical focussing method has been applied.
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