**4. EUV source**

Figure 4 is an illustration and a photograph of the LPP-EUV source composed of a rotating cryogenic drum and Nd:YAG slab laser. The drum, detectors, and irradiating samples are installed in a vacuum chamber because EUV light cannot transmit through air. Driving laser pulses passing through the window are focused perpendicularly on the target by the lens so that Xe plasma is produced and EUV radiation is emitted. At a repetition rate of 320 Hz and average power of 110 W, the laser pulses irradiate the Xe solid target on the rotating drum with laser intensity of ~1010 W/cm2. The rotation speed is 130 rpm and the vertical speed 3

Fig. 3. Experimental setup and photograph of the PC-MOPA laser system.

Figure 4 is an illustration and a photograph of the LPP-EUV source composed of a rotating cryogenic drum and Nd:YAG slab laser. The drum, detectors, and irradiating samples are installed in a vacuum chamber because EUV light cannot transmit through air. Driving laser pulses passing through the window are focused perpendicularly on the target by the lens so that Xe plasma is produced and EUV radiation is emitted. At a repetition rate of 320 Hz and average power of 110 W, the laser pulses irradiate the Xe solid target on the rotating drum with laser intensity of ~1010 W/cm2. The rotation speed is 130 rpm and the vertical speed 3

**4. EUV source** 

mm/s. The Xe target gas is continuously supplied at a flow rate of 400 mL/min. Under these operation conditions, we obtain continuous EUV generation with average power of 1 W at 13.5 nm and 2% bandwidth.

The driving pulse energy was determined to be 0.3 J under the optimal condition that higher CE and lower debris are simultaneously achieved, as detailed below. At present, the maximum achieved CE is 0.9% at 13.5 nm with 2% bandwidth for the optimal condition. Under drum-rotating operation, we found the good characteristics of increased CE and less fast ions compared with the case with the drum at rest. We next detail the EUV and debris characteristics of the EUV source.

Fig. 4. Experimental setup and photograph of the laser plasma EUV source.
