Optical Coatings

PERCENT INTERNAL TRANSMITTANCE
99.997
99.995
99.993
99.991
99.990
99.97
99.95
99.93
99.91
99.90
99.7
99.5
99.3
99.1
99.0
97
95
93
WAVELENGTH IN NANOMETERS
200 400 600 800 1000 1200 1400
UVGSFS
BK7
OH bond
resonance
200 400 600 800 1000 1200 1400
WAVELENGTH IN NANOMETERS
Figure 4.2 Semilogarithmic comparison of internal
transmittances of UVGSFS and BK7
The internal transmittance of UV-grade synthetic fused silica
shows a pronounced dip at 950 nm, while the data for BK7 give
no hint of a corresponding feature. It should be understood that BK7
and UVGSFS are manufactured by very different processes. One
of the many differences in these materials is that UVGSFS has a
much higher content of OH chemical bonds (hydroxyl content)
than does BK7. The dip in UVGSFS transmittance corresponds to
the OH bond resonance.
1 Malitson, I.H. “Interspecimen Comparison of the Refractive Index
of Fused Silica,” Journal of the Optical Society of America 55, no. 10
(October 1965): 1205–1209.
SYNTHETIC FUSED-SILICA CONSTANTS
Abbé Constant: 67.880.5
Change of Refractive Index with Temperature (0º to 700ºC):
1.28 ! 10 45 /ºC
Homogeneity (maximum index variation over 10-cm aperture):
2 ! 10 45
Density (at 25ºC): 2.20 g/cc
Continuous Operating Temperature: Maximum 900ºC
Coefficient of Thermal Expansion: 5.5 ! 10 47 /ºC
Specific Heat (25ºC): 0.177 cal/gºC
Dispersion Formula 1 at 20ºC (l in mm):
2
2
0.6961663l
0.4079426l
2
n 4 1 =
+
2 2 2 2
l 4 (0.0684043) l 4 (0.1162414)
2
0.8974794l
+
. (4.7)
2 2
l 4 (9.896161)
Refractive Index of UV-Grade Synthetic Fused Silica*
Wavelength
(nm)
180.0
190.0
200.0
213.9
226.7
230.2
239.9
248.3
265.2
275.3
280.3
289.4
296.7
302.2
330.3
340.4
351.1
361.1
365.0
404.7
435.8
441.6
457.9
476.5
486.1
488.0
496.5
514.5
*Accuracy 83!10 45 .
Index of
Refraction
1.58529
1.56572
1.55051
1.53431
1.52275
1.52008
1.51337
1.50840
1.50003
1.49591
1.49404
1.49099
1.48873
1.48719
1.48054
1.47858
1.47671
1.47513
1.47454
1.46962
1.46669
1.46622
1.46498
1.46372
1.46313
1.46301
1.46252
1.46156
Wavelength
(nm)
532.0
546.1
587.6
589.3
632.8
643.8
656.3
694.3
706.5
786.0
820.0
830.0
852.1
904.0
1014.0
1064.0
1100.0
1200.0
1300.0
1400.0
1500.0
1550.0
1660.0
1700.0
1800.0
1900.0
2000.0
2100.0
Index of
Refraction
1.46071
1.46008
1.45846
1.45840
1.45702
1.45670
1.45637
1.45542
1.45515
1.45356
1.45298
1.45282
1.45247
1.45170
1.45024
1.44963
1.44920
1.44805
1.44692
1.44578
1.44462
1.44402
1.44267
1.44217
1.44087
1.43951
1.43809
1.43659
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