D. Milam, W. H. Lowdermilk, F. Rainer, J. E. Swain, C. K. Carniglia, and T. Tuttle Hart, "Influence of deposition parameters on laser-damage threshold of silica–tantala AR coatings," Appl. Opt. 21, 3689-3694 (1982)
A series of 4-layer silica–tantala antireflection coatings was deposited under 18 different combinations of substrate temperature (175, 250, and 325°C), oxygen pressure (0.5, 1.0, and 2.0 × 10−4 Torr), and rate of deposition (1.5 and 5 Å/sec). Measurements of laser-damage threshold for 1064-nm, 1-nsec pulses, average absorption, net stress, and reflectivity were then made on these coatings. Coatings deposited at the lowest temperature had the highest damage thresholds. Damage thresholds were found not to be directly related to average absorption or net stress. Coatings deposited on fused silica substrates which had been polished by a bowl-feed process had generally higher damage thresholds than coatings deposited on conventionally polished fused silica or on BK-7 glass polished by either conventional or bowl-feed processes. Baking coatings in air for 4 h at 400°C generally reduced average absorption and net stress, changed the net stress from compression to tension and, in some cases, increased the damage threshold.
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Samples are designated by a symbol which indicates the coating set (A or B), the particular coating run (1–18), and an additional designator (a or b) to distinguish two parts made in a single coating run.
Table II
Damage Thresholds (1 nsec, 1064 nm) of Ta2O5/SiO2 AR Coatings With λ/2 SiO2 Undercoats Deposited on 3 Types of Substrate at T = 175°C, Rate = 1.5 Å/sec, and O2 Pressure = 1.0 × 10−4 Torr; 18 Coatings Were Made in 3 Separate Runs
Samplea
Substrate material
Substrate polish
Damage threshold (J/cm2)
C1-a
fused silica
conventional
9.2 ± 0.9
C1-b
fused silica
conventional
6.8 ± 1.3
C1-c
BK-7
conventional
5.5 ± 0.9
C1-d
BK-7
conventional
8.5 ± 1.2
C1-e
BK-7
bowl-feed
6.3 ± 0.6
C1-f
BK-7
bowl-feed
9.0 ± 1.0
C2-a
fused silica
conventional
5.8 ± 1.0
C2-b
fused silica
conventional
3.7 ± 0.6
C2-c
BK-7
conventional
7.0 ± 0.8
C2-d
BK-7
conventional
5.8 ± 0.6
C2-e
BK-7
bowl-feed
10.2 ± 1.0
C2-f
BK-7
bowl-feed
13.1 ± 1.3
C3-a
fused silica
conventional
9.4 ± 1.0
C3-b
fused silica
conventional
11.4 ± 1.2
C3-c
BK-7
conventional
6.0 ± 0.8
C3-d
BK-7
conventional
7.7 ± 0.8
C3-e
BK-7
bowl-feed
7.7 ± 0.8
C3-f
BK-7
bowl-feed
11.3 ± 1.2
Sample designation indicates the coating run (C1, C2, or C3) and the particular substrate (a–f).
Table III
Summary of Damage Threshold Data (1 nsec, 1064 nm) for Ta2O5/SiO2 AR Coatings With λ/2 SiO2 Undercoats Deposited on 4 Types of Surface; (T = 175°C, Rate = 1.5 Å/sec, O2 Pressure = 1 × 10−4 Torr)
Material
Polish
Number of samples
Median threshold (J/cm2)
Range of observed thresholds (J/cm2)
Fused silica
bowl-feed
3
14.9
10.3–18.7
BK-7
bowl-feed
6
9.6
6.3–13.1
Fused silica
conventional
6
8.0
3.7–11.4
BK-7
conventional
6
6.5
5.5–8.5
Table IV
Damage Thresholds (1 nsec, 1064 nm), Net Stress, and Absorption for 14 Ta2O5/SiO2 AR Coatings Measured Before and After the Coatings Were Baked In Air for 4 h at 400°C
Samples are designated by a symbol which indicates the coating set (A or B), the particular coating run (1–18), and an additional designator (a or b) to distinguish two parts made in a single coating run.
Table II
Damage Thresholds (1 nsec, 1064 nm) of Ta2O5/SiO2 AR Coatings With λ/2 SiO2 Undercoats Deposited on 3 Types of Substrate at T = 175°C, Rate = 1.5 Å/sec, and O2 Pressure = 1.0 × 10−4 Torr; 18 Coatings Were Made in 3 Separate Runs
Samplea
Substrate material
Substrate polish
Damage threshold (J/cm2)
C1-a
fused silica
conventional
9.2 ± 0.9
C1-b
fused silica
conventional
6.8 ± 1.3
C1-c
BK-7
conventional
5.5 ± 0.9
C1-d
BK-7
conventional
8.5 ± 1.2
C1-e
BK-7
bowl-feed
6.3 ± 0.6
C1-f
BK-7
bowl-feed
9.0 ± 1.0
C2-a
fused silica
conventional
5.8 ± 1.0
C2-b
fused silica
conventional
3.7 ± 0.6
C2-c
BK-7
conventional
7.0 ± 0.8
C2-d
BK-7
conventional
5.8 ± 0.6
C2-e
BK-7
bowl-feed
10.2 ± 1.0
C2-f
BK-7
bowl-feed
13.1 ± 1.3
C3-a
fused silica
conventional
9.4 ± 1.0
C3-b
fused silica
conventional
11.4 ± 1.2
C3-c
BK-7
conventional
6.0 ± 0.8
C3-d
BK-7
conventional
7.7 ± 0.8
C3-e
BK-7
bowl-feed
7.7 ± 0.8
C3-f
BK-7
bowl-feed
11.3 ± 1.2
Sample designation indicates the coating run (C1, C2, or C3) and the particular substrate (a–f).
Table III
Summary of Damage Threshold Data (1 nsec, 1064 nm) for Ta2O5/SiO2 AR Coatings With λ/2 SiO2 Undercoats Deposited on 4 Types of Surface; (T = 175°C, Rate = 1.5 Å/sec, O2 Pressure = 1 × 10−4 Torr)
Material
Polish
Number of samples
Median threshold (J/cm2)
Range of observed thresholds (J/cm2)
Fused silica
bowl-feed
3
14.9
10.3–18.7
BK-7
bowl-feed
6
9.6
6.3–13.1
Fused silica
conventional
6
8.0
3.7–11.4
BK-7
conventional
6
6.5
5.5–8.5
Table IV
Damage Thresholds (1 nsec, 1064 nm), Net Stress, and Absorption for 14 Ta2O5/SiO2 AR Coatings Measured Before and After the Coatings Were Baked In Air for 4 h at 400°C