Output characteristics of a discharge-pumped F2 laser (157 nm) with an injection-seeded unstable resonator

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Abstract
To improve beam quality, an injection‐seeded unstable resonator was applied to a discharge‐pumped F2 laser, which is normally dominated by amplified spontaneous emission with a large beam divergence when using a normal stable cavity, due to the laser’s extremely high gain (a small‐signal gain‐length product ∼29). The time‐dependent injection‐seeding efficiency was obtained for various injection timings by measuring a ratio of the output laser intensity with the same polarization as the seed laser. Correlation of the injection‐seeding efficiency with the temporal evolution of the laser‐beam divergence was also studied. Both the time‐dependent beam divergence and the injection‐seeding efficiency showed degradation at a later part of the laser pulse.