Detector Development

Figure 1. The structure of the EUV detector.

With the phosphor screen preceding the MCP intensifier, EUV photons become visible and are therefore able to penetrate the window of MCP intensifier. To verify the phosphor's response in the EUV band, the screen was tested at the Beijing Synchrotron Radiation Facility (BSRF). The phosphor screen was illuminated with EUV radiation and a photodiode was placed just behind the screen. The output current of the diode was measured as a function of incident radiation wavelength ranging from 6 nm to 27 nm (see Fig. 2).

Wavelength (Aiigtram)

Figure 2. Response test of the EUV-converting phosphor screen.

Wavelength (Aiigtram)

Figure 2. Response test of the EUV-converting phosphor screen.

Because the spectral intensity distribution over the tested EUV wave band was not calibrated, Fig. 2 does not exactly reflect the spectral response. The purpose of the experiment was to simply check if the phosphor is sensitive over the waveband concerned. Figure 3 shows the relationship of the photodiode's current generated by phosphor radiation and the current of the circulating electrons in the storage ring of the synchrotron radiation facility. Since the latter varies roughly linearly with respect to the intensity of the EUV radiation beam, Fig. 3 roughly reflects the linearity of the phosphor. The output of the diode did not increase after the current in the storage ring reached 90mA; this resulted from saturation of the phosphor.

The resolution of the MCP image intensifier is 57 Lp/mm. The gain is 8900 cd/m2/Lx, which leads to an equivalent background irradiance 0.16 ^Lx. The resolution of the optic taper is better than 102Lp/mm. Figure 4 shows the integrated detector. The left panel shows the inside structure and the right panel shows the exterior.

Figure 3. The relationship of the photodiode's current generated by phosphor radiation and the current of the circulating electrons in the storage ring.
Figure 4. The integrated EUV detector.

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