Fig. 1. Instability of droplet. (a) Lateral instability; (b) vertical instability

Fig. 2. Droplet generator. (a) Typical DOD droplet generator; (b) continuous droplet flow generator

Fig. 3. Schematic of double pulse scheme

Fig. 4. Working sequence of EUV light source

Fig. 5. Schematic of laser scattering synchronization

Fig. 6. Sample photodiode signal^[17]

Fig. 7. Schematic of typical shadow imaging

Fig. 8. Intensity profiles of droplet images^[24]

Fig. 9. Droplet image captured by shadow imaging

Fig. 10. Schematic of droplet parameter sensing and feedback control

Fig. 11. CE of different target profile created by pre-pulse^[63]

Fig. 12. Side-on shadowgraphs of expanded microdroplets irradiated by laser of different intensities at 0.5 μs^[65]