Stefan Jakobs,
Angela Duparré,
and Horst Truckenbrodt
S. Jakobs and A. Duparré are with the Fraunhofer Institute for Applied Optics and Precision Engineering Jena, Schillerstrasse 1, D-07745 Jena, Germany.
H. Truckenbrodt is with the University of Technology Ilmenau, PF 10 05 65, D-98684 Ilmenau, Germany.
Stefan Jakobs, Angela Duparré, and Horst Truckenbrodt, "Interfacial roughness and related scatter in ultraviolet optical coatings: a systematic experimental approach," Appl. Opt. 37, 1180-1193 (1998)
For a variety of UV optical coatings, surface roughness was
measured by use of an atomic-force microscope (AFM) to study its
dependence on the film material and thickness, coating design, and
deposition process. After analyzing the corresponding power
spectral density functions, we propose a simple classification model
for coatings according to the contributions of substrate roughness and
intrinsic film roughness to the scattering. Results of scattering
measurements on different types of coatings are presented and are found
to be in good agreement with predictions based on the AFM
data. Consequences for a scatter reduction strategy are
discussed.
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EBD, electron-beam deposition.
IAD, ion-assisted deposition, in which
Ei is the ion energy.
2H, 2L, half-wave layer of the high- and
low-index materials, respectively.
H, L, quarter-wave layer of the high- and
low-index materials, respectively.
Table 2
Rms Roughness Values of an SQ1 Substrate and of
Al2O3 and LaF3 Single Layers of
Different Thicknesses Deposited onto SQ1
Sample
Rms roughness [nm]
AFM image size
1 μm × μm
10 μm × 10 μm
50 μm × 50 μm
SQ1
0.35
0.54
0.60
Al2O3
37 nm
0.63
0.72
0.69
290 nm
1.25
1.00
0.84
965 nm
1.68
1.54
1.47
LaF3
37 nm
1.08
0.85
0.61
149 nm
4.8
5.1
3.4
380 nm
9.5
9.2
6.0
Table 3
Rms Roughness Values of Superpolished SP and RG 1000 and
of the 49-Layer Oxide System Deposited onto These Substrates
Sample
Rms roughness [nm]
AFM image size
1 × 1 μm2
10 × 10 μm2
Superpolished SP
0.11
0.06
SP/(HL)24H
1.53
1.52
RG 1000
0.56
0.67
RG 1000/(HL)24H
1.55
1.59
Table 4
Classification of the Investigated Single Layers and Layer
Systems According to the Contribution of the Substrate Roughness and
Intrinsic Film Roughness to the PSD of the Top Surface Within the
Scattering Bandwidth at λ = 325 nm
PSD Type
Samples
Total substrate replication
Al2O3 single layer of thickness 37 nm deposited by EBD on SQ1
Al2O3 single layer of thickness 350 nm deposited by IAD at 150 eV on SQ1, oxide layer system with as much as 3 quarter-wave layers on RG 1000
LaF3 single layer of thickness 37 nm on SQ1, fluoride layer systems with as much as 3 half-wave layers on RG 1000
Partial substrate replication
Al2O3 single layers of thickness 290 and 965 nm deposited by EBD on SQ1, oxide multilayer systems with 17 and 49 layers on RG 1000
LaF3 single layer of thickness 112 nm on SQ1
Thin-film dominance
Oxide multilayer system with 49 layers on superpolished SP
LaF3 single layer of thickness 380 nm on SQ1, fluoride layer systems on Si wafer, fluoride layer system with 16 half-wave layers on QZ
Table 5
Comparison of Measured and Predicted Total Backscattering
(λ = 325 nm) of the Oxide HR Coating on RG 1000 and
Superpolished SP
EBD, electron-beam deposition.
IAD, ion-assisted deposition, in which
Ei is the ion energy.
2H, 2L, half-wave layer of the high- and
low-index materials, respectively.
H, L, quarter-wave layer of the high- and
low-index materials, respectively.
Table 2
Rms Roughness Values of an SQ1 Substrate and of
Al2O3 and LaF3 Single Layers of
Different Thicknesses Deposited onto SQ1
Sample
Rms roughness [nm]
AFM image size
1 μm × μm
10 μm × 10 μm
50 μm × 50 μm
SQ1
0.35
0.54
0.60
Al2O3
37 nm
0.63
0.72
0.69
290 nm
1.25
1.00
0.84
965 nm
1.68
1.54
1.47
LaF3
37 nm
1.08
0.85
0.61
149 nm
4.8
5.1
3.4
380 nm
9.5
9.2
6.0
Table 3
Rms Roughness Values of Superpolished SP and RG 1000 and
of the 49-Layer Oxide System Deposited onto These Substrates
Sample
Rms roughness [nm]
AFM image size
1 × 1 μm2
10 × 10 μm2
Superpolished SP
0.11
0.06
SP/(HL)24H
1.53
1.52
RG 1000
0.56
0.67
RG 1000/(HL)24H
1.55
1.59
Table 4
Classification of the Investigated Single Layers and Layer
Systems According to the Contribution of the Substrate Roughness and
Intrinsic Film Roughness to the PSD of the Top Surface Within the
Scattering Bandwidth at λ = 325 nm
PSD Type
Samples
Total substrate replication
Al2O3 single layer of thickness 37 nm deposited by EBD on SQ1
Al2O3 single layer of thickness 350 nm deposited by IAD at 150 eV on SQ1, oxide layer system with as much as 3 quarter-wave layers on RG 1000
LaF3 single layer of thickness 37 nm on SQ1, fluoride layer systems with as much as 3 half-wave layers on RG 1000
Partial substrate replication
Al2O3 single layers of thickness 290 and 965 nm deposited by EBD on SQ1, oxide multilayer systems with 17 and 49 layers on RG 1000
LaF3 single layer of thickness 112 nm on SQ1
Thin-film dominance
Oxide multilayer system with 49 layers on superpolished SP
LaF3 single layer of thickness 380 nm on SQ1, fluoride layer systems on Si wafer, fluoride layer system with 16 half-wave layers on QZ
Table 5
Comparison of Measured and Predicted Total Backscattering
(λ = 325 nm) of the Oxide HR Coating on RG 1000 and
Superpolished SP
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