Line narrowing and injection locking of F2 lasers

To realize an ultranarrow-linewidth and high-output-power F-2 laser for next-generation lithography, line narrowing in a F2 laser injection locking system (ILS) that consists of a line-narrowed oscillator and an amplifier with a resonator was investigated. We found out that the time-resolved instantaneous spectrum of the oscillator laser pulse narrows from a start time of discharge and scarcely depends on laser pulse shape. Furthermore, the spectral shape of the ILS is locked to the instantaneous spectral shape of the line-narrowed injection laser when the amplifier discharge starts. We first realized a F2 laser with a linewidth (FWHM) below 0.2 pm and a pulse energy of more than 5 mJ (25 W at 5 kHz repetition rate).