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Absorption |
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Fused silica and fused quartz are dielectric materials. They are transparent in the ultraviolet, visible, and near infrared. The absorption boundary on the ultraviolet side is strongly affected by the presence of impurities. Synthetic fused silica, which is manufactured from extremely pure precursor, offers the highest transparency in the UV of any glasses, including fused quartz.
On the infrared side, the source of intrinsic absorption is molecular vibrations. The stretching vibration Si-O creates has a very strong absorption peak near 8.9 mm. Such strong absorption is associated with optical attenuation at the overtone frequency (4.5 micron).
Additional absorption bands are present in the near infrared. These are caused by impurities. For example water vapor creates absorption around 1.4, 2.1, and 2.8 mm. Synthetic fused silica is particularly likely to display water vapor absorption in the near infrared.
Shown below is typical transmission for 10-mm thick synthetic fused silica sample (uncorrected for surface reflection losses)...
And shown below is the typical transmission for 10-mm thick IR-grade fused quartz sample (uncorrected for surface reflection losses)...
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Temperature Dependence of Refractive Index |
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The refractive indices of the glasses are not only dependent on wavelength, but also upon
temperature.
The dn/dT for fused silica is 1.1x10-5/șC at 1064nm, near room temperature.
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Refractive Index |
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Wavelength (nm)
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Index of Refraction
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Wavelength (nm)
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Index of Refraction
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Wavelength (nm)
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Index of Refraction
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180.0
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1.58529
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404.7
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1.46962
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820.0
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1.45298
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190.0
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1.56572
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435.8
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1.46669
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830.0
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1.45282
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200.0
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1.55051
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441.6
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1.46622
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852.1
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1.45247
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213.9
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1.53431
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457.9
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1.46498
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904.0
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1.45170
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226.7
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1.52275
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476.5
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1.46372
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1014.0
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1.45024
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230.2
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1.52008
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486.1
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1.46313
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1064.0
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1.44963
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239.9
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1.51337
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488.0
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1.46301
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1100.0
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1.44920
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248.3
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1.50840
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496.5
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1.46252
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1200.0
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1.44805
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265.2
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1.50003
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514.5
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1.46156
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1300.0
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1.44692
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275.3
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1.49591
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532.0
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1.46071
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1400.0
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1.44578
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280.3
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1.49404
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546.1
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1.46008
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1500.0
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1.44462
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289.4
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1.49099
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587.6
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1.45846
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1550.0
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1.44402
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296.7
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1.48873
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589.3
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1.45840
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1660.0
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1.44267
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302.2
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1.48719
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632.8
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1.45702
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1700.0
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1.44217
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330.3
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1.48054
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643.8
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1.45670
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1800.0
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1.44087
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340.4
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1.47858
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656.3
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1.45637
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1900.0
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1.43951
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351.1
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1.47671
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694.3
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1.45542
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2000.0
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1.43809
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361.1
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1.47513
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706.5
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1.45515
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2100.0
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1.43659
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365.0
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1.47454
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786.0
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1.45356
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(Source: www.mellesgriot.com)
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