Experimental researches on acousto-optic Q-switched CO2 laser
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摘要: 为满足13.5 nm极紫外光刻(EUVL)等领域的应用需求,研制了高重复频率、高稳定性的声光调Q CO2激光器。首先,对声光Q开关的工作原理进行了分析,并实验研究了调制信号电压与衍射效率的关系。接着,研究了调制信号占空比对脉冲波形的影响,通过选择适当的占空比消去了脉冲拖尾。然后,对不同重复频率下的脉冲宽度、功率和脉冲幅值稳定性进行了测量和分析。最后,对激光器的光束指向稳定性进行了测量。实验结果表明:该激光器实现了重复频率1~100 kHz连续可调的脉冲输出,在重复频率1 kHz时,获得最小脉冲宽度252 ns和最大峰值功率7 579 W的激光脉冲输出。通过设计以殷钢管为主体的支撑架,使得激光器的脉冲幅值不稳定性小于3%,光束指向稳定性为46.6 rad。该声光调Q CO2激光器可作为高性能种子源在EUVL等领域中得到应用。Abstract: In order to meet the demand of 13.5-nm extreme ultraviolet lithography (EUVL), an acousto-optically Q-switched CO2 laser was developed, which has high repetition rate and high stability. First, the operating principle of the acousto-optic Q-switch was analyzed and the relationship between the voltage of modulated signal and diffraction efficiency was researched experimentally. And then, by studying the influence of modulated signal duty cycle on pulse waveform, the appropriate duty cycle was chosen to eliminate the pulse tail. Under the conditions of different repetition rates, pulse duration, power and the pulse amplitude stability were measured and analyzed. Finally, the beam pointing stability of the laser was measured. Experimental results indicate that the range of pulse repetition rate can be adjusted from 1 kHz to 100 kHz. When the repetition rate is 1 kHz, the minimum pulse duration is 252 ns and the maximum peak power reaches 7 579 W. By designing the support frames mainly made of invar steel, the unstablity of pulse amplitude is less than 3% and the beam pointing stability is only 46.6 rad. This acousto-optic Q-switched CO2 laser is suitable for a seed source used in EUVL.
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Key words:
- CO2 laser /
- acousto-optic Q-switch /
- repetition rate /
- stablity
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