High-damage-threshold fluoride UV mirrors made by ion-beam sputtering

Roughness and light scattering of ion-beam-sputtered fluoride coatings for 193 nm

“…As expected, the measurements show a gradual increase in roughness with increasing num- 4 This result can be expected on the basis of the mechanical and structural properties exhibited by IBS fluoride coatings ͑high packing density, low inhomogeneity, compressive stress͒. 2,5 The PSD functions sustain these observations and complement the information on the microstructure of the IBS coatings. Figure 6 displays a selection of PSD functions for QW stacks.…”

“…In contrast, the ion-beam-sputtering ͑IBS͒ technique does not require substrate heating and, moreover, the high energy of the sputtered atoms leads to the deposition of coatings with higher density and compressive stress. 5 It has also been shown that the coatings produced with these techniques are highly homogeneous, whereas the optical constants are close to the bulk values. 2,6 The major problem encountered with ion-beam-sputtered UV coatings is the difficulty of compensating for fluorine deficiencies in the films, which gives rise to optical losses.…”

“…The feasibility of such coatings with low absorption and a high laser-induced damage threshold has been demonstrated in previous papers. 5,7 Nevertheless, a systematic study of scattering losses at 193 nm and their relation to the film microstructure has not yet been carried out to our knowledge.…”

“…[1][2][3] The achievement of optimized coatings for these components constitutes one of the major challenges, as problems arise that are minor at larger wavelengths. 4,5 Absorption and scattering losses of the layers are critical obstacles that compromise coating performance. Key issues for minimizing these losses consist of a careful selection of the most appropriate coating materials and fine tuning of the deposition processes.…”

Procedure to characterize microroughness of optical thin films: application to ion-beam-sputtered vacuum-ultraviolet coatings

“…The investigation of these samples was driven by the technological challenges at short wavelengths: the selection of materials with low absorption and scattering in the VUV and the choice and optimization of the deposition processes. 14,15 It has been proven that for applications in the UV range fluorides are the preferred materials because of their larger energy gap. However, not every deposition technique is suitable to produce appropriate fluoride coatings: Conventional evaporation techniques tend to produce coatings with high tensile stress because substrate heating is required for improving the coating adhesion and because of the large differences in thermal expansion coefficient between substrates and coating materials.…”