Multiline oscillation of Q-switched cavity-dumped CO2 laser with intracavity diffraction grating

Extreme-ultraviolet (EUV) lithography employs a high-power short-pulse carbon dioxide (CO₂) laser based on master oscillator power amplifier architecture to produce Sn plasma generating the EUV light. We demonstrate multiline oscillation of a CO₂ laser with 20 ns of pulse duration for the master oscillator. An intracavity diffraction grating enables the 5-line oscillation (10.55, 10.57, 10.59, 10.61, and 10.63 μm) by separating the different 5 lines spatially in a gasdischarge gain medium. The multiline CO₂ laser employs a cavity length of 3000 mm and an electro-optically Q-switched cavity dumping to generate 20-ns laser pulses. The maximum output power is 10.6 W at 100-kHz repetition rate and the output stability is ±1.2% at 3σ over 30 minutes. The grating combines the separated 5 optical axes into one optical axis inside the cavity, which realizes the nearly single-mode (TEM00) oscillation with ~1.1 of M².