Fig. 1. ENEA DPP source: (a) picture; (b) schematic.

Fig. 2. Simplified electrical scheme of the DPP pumping circuit.

Fig. 3. Temporal evolution of the glycol capacitor voltage , the main discharge current and the EUV signal (see text for details on the related diagnostics).

Fig. 4. EUV fluence versus distance from the source for different pressure values of residual xenon: experimental data (points) and best fit with the theoretical absorption curve (solid lines, see text).

Fig. 5. Schematic of the setup for recording the spatial evolution of the discharge (not in scale).

Fig. 6. An example of plasma image processing: (a) picture of the HV electrode within the alumina capillary tube, converted to red; (b) picture of the visible light emitted by the plasma column, converted to blue; (c) composition of the two images. The CCD position was kept fixed throughout all the measurements.

Fig. 7. Sequence of false colour images of the discharge during the pre-ionization phase. The exposure time is , on distinct shots. The indicated time on each image is the delay with respect to the current onset.

Fig. 8. False colour images of the visible light emission from the plasma during the main discharge. Gate time was 20 ns. The indicated time on each image refers to the acquisition delay from EUV rise (50% of maximum). The temporal position of each image with respect to the EUV power emission (blue curve) is also indicated by green circles in the graph. The red curve is the discharge current .

Fig. 9. Calibration curve of the Gafchromic HD-V2 dosimetric film in the 10–20 nm spectral range: experimental grey levels (acquired by a quadratic-sensitivity 16-bit scanner, Canon, CanoScan 8400F, red channel) versus EUV fluence (circles) and best fit with the photographic thick-film function (see text).

Fig. 10. Portion of a radiography of an Al filter. A LiF crystal, covered by a 0.8--thick Al membrane, has been exposed to 8000 shots at 10 cm from the DPP source and observed by using a fluorescence microscope at magnification. The filter irregularities are visible as luminescent patterns.

Fig. 11. EUV exposure of an innovative zirconia-loaded photoresist behind a 150-nm thick Zr filter: the Ni mesh supporting the filter is imaged on the resist. The grid period is . The exposure total fluence was released in 7000 shots, at 128 mm from the source. The wire edges are blurred due to a distance of approximately between the filter and the photoresist.