Scaling of high average power, short-pulse CO2 lasers

The scaling rule of high average power, short-pulse CO2 lasers is described based on the physical fundamentals. Specifications are required for lasers applied to high-volume manufacturing extreme-ultraviolet light sources, simultaneously on the average power over 10 kW, the beam quality less than 2 for M-2, and the pulse width in the 10 ns range. The amplifier is operated by a cascade amplifier arrangement, and the ruling principle is approximately described by the Frantz-Nodvik equation, with effective small-signal gain g(0) and saturation fluence E-s depending on the amplifier medium and amplified pulse width. Thermal distortion is caused in the optical components, leading to beam propagation instability. The general rule of g(0)L < 3, where L is the optical gain length, is the requirement to isolate each amplifier by optical shutters. Multiline amplification is efficient to increase the extraction efficiency in the case of less-efficient rotational relaxation. It is concluded that a well-designed single-beam, short-pulse CO2 laser is operable at 20 kW average output power based on available components, by satisfying all requirements. (c) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.JMM.11.2.021113]