Fig. 1. Schematic of cooling laser system and error signals. (a) Schematic of cooling laser system; (b) error signal when reference cavity of ECDL-1 is locked; (c) error signal when SAS of DUV-1 is locked

Fig. 2. Schematic of OPLL between seed lasers

Fig. 3. Beat spectra of different lasers when OPLL is locked. (a) Two IR seed lasers at 1014.9 nm; (b) two VIS lasers at 507.4 nm;

Fig. 4. Beat spectral lines of two DUV lasers when DUV frequency is locked

Fig. 5. Relative frequency instabilities of two seed light lasers in free operation (square) and locked state (diamond) and relative frequency instability of locked ultraviolet light (cycle)

Fig. 6. Schematic of OPLL with feedforward control

Fig. 7. Dynamic performance of OPLL