Article and coating having improved reflectance suppression

• US 4,735,488 A
• Filed: 03/03/1986
• Issued: 04/05/1988
• Est. Priority Date: 11/16/1983
• Status: Expired due to Term

• Current Assignee: JDS Uniphase Corporation (Lumentum Holdings Inc.)
• Original Assignee: Optical Coating Laboratory, Inc. (Lumentum Holdings Inc.)
• Inventors: Rancourt, James, Sanchez, Joseph, Beauchamp, William
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/835,375
• Time in Patent Office: 764 Days
• Field of Search: 350/166, 350/163, 350/164, 350/165, 136/256
• US Class Current: 359/586
• CPC Class Codes: G02B 1/115 Multilayers

Abstract

A structure that provides suppression of reflectance of radiation and thus enhanced emissivity is fabricated with a substrate that supports alternating absorber and spacer layers with interleaved antireflectance coatings formed of thin films of different materials having different indices of refraction. Alternate antireflectance coatings are mirror images of the prior deposited antireflectance coatings.

Claims

1. A structure for providing suppression of reflectance of radiation and for enhancing emissivity comprising:

a substrate formed of a material having a reststrahlen band;

at least one grouping of materials deposited over said substrate including a first antireflection coating deposited over said substrate;

a relatively thick first spacer layer deposited over said first antireflectance coating;

a second antireflection coating deposited over said spacer layer; and

a relatively thick first absorber layer deposited over said second antireflection coating and having intrinsic absorption in the reststrahlen band exhibited by the substrate, said first and second antireflection coatings, said spacer layer and said absorber layer being formed of materials having indices of refraction which in combination act in concert to substantially suppress the reststrahlen band of the substrate, said antireflection coatings permitting the use of materials in the spacer layer having a higher index of refraction than the index of refraction of the material of the absorber layer.

2. A structure as in claim 1, including a magnesium fluoride overcoat layer deposited over said at least one grouping for providing suppression of reflectance of radiation and for improving transmission of visible radiation.

3. A structure as in claim 2, wherein said magnesium fluoride overcoat layer has a thickness substantially the same as said antireflectance coatings.

4. A structure as in claim 1, wherein said first antireflectance coating is formed with first and second thin film layers of first and second materials respectively having different indices of refraction, and said second coating is formed with two thin film layers, the first deposited layer of said two layers having said second material and the second deposited layer of said two layers having said first material, thereby substantially forming a mirror image of said first antireflectance coating.

7. A structure as in claim 4, wherein said thin film layers of said first material have a thickness approximately one-half of the thickness of the thin film layers formed of said second material.

8. A structure as in claim 4, wherein said first material is selected from the group including calcium fluoride, barium fluoride, strontium fluoride, and rare earth fluorides.

9. A structure as in claim 1, wherein said substrate is formed of fused silica or alumina.

11. A structure as in claim 1, wherein said antireflectance coatings have a total thickness less than 0.1 micrometers.

12. A structure as in claim 1, wherein said antireflectance coatings are formed from a single material of gas-reacted silicon monoxide.

13. A structure as in claim 1, wherein said antireflectance coatings are formed from a multiplicity of thin film layers of different materials having different indices of refraction, the resultant index of refraction of each antireflectance coating being about 1.50.

5. A structure for providing suppression of reflectance of radiation and for enhancing emissivity comprising a substrate formed of a material having a reststrahlen band;

at least one grouping of materials deposited over said substrate including a first antireflection coating deposited over said substrate;

a relatively thick first spacer layer deposited over said first antireflectance coating;

a second antireflection coating deposited over said spacer layer; and

a relatively thick first absorber layer deposited over said second antireflection coating, said first antireflection coating being formed with first and second thin film layers of first and second materials respectively having different indices of refraction, and said second coating being formed with two thin film layers, the first deposited layer of said two layers having said second material and the second deposited laver of said two layers having said first material, thereby substantially forming a mirror image of said first antireflection coating, said first and second antireflection coatings, said spacer layer and said absorber layer being formed of materials having indices of refraction which in combination act in concert to substantially sup- press the reststrahlen band of the substrate, said antireflection coatings permitting the use of materials in the spacer layer having a higher index of refraction than the index of refraction of the material of the absorber layer, said first material being lanthanum fluoride and said second material being silicon dioxide.

6. A structure for providing suppression of reflectance of radiation and for enhancing emissivity comprising a substrate formed of a material having a reststrahlen band;

at least one grouping of materials deposited over said substrate including a first antireflection coating deposited over said substrate;

a relatively thick first spacer layer deposited over said first antireflectance coating;

a second antireflection coating deposited over said spacer layer; and

relatively thick first absorber layer deposited over said second antireflection coating, said first antireflection coating being formed with first and second thin film layers of first and second materials respectively having different indices of refraction, and said second coating being formed with two thin film layers, the first deposited layer of said two layers having said second material and the second deposited layer of said two layers having said first material, thereby substantially forming a mirror image of said first antireflection coating, said first and second antireflection coatings, said spacer layer and said absorber layer being formed of materials having indices of refraction which in combination act in concert to substantially suppress the reststrahlen band of the substrate, said antireflection coatings permitting the use materials in the spacer layer having a higher index of refraction than the index of refraction of the material of the absorber layer, said first material being transparent in the infrared and visible portions of the spectrum.

10. A structure for providing suppression of reflectance of radiation and for enhancing emissivity comprising a substrate formed of a material having a reststrahlen band;

at least one grouping of materials deposited over said substrate including a first antireflection coating deposited over said substrate;

a relatively thick first spacer layer deposited over said first antireflectance coating;

a second antireflection coating deposited over said spacer layer; and

a relatively thick first absorber layer deposited over said second antireflection coating, said first and second antireflection coatings, said spacer layer and said absorber layer being formed of materials having indices of refraction which in combination act in concert to substantially suppress the reststrahlen band of the substrate, said antireflection coatings permitting the use of materials in the spacer layer having a higher index of refraction than the index of refraction of the material of the absorber layer, said substrate being formed of fused silica or alumina, the reststrahlen reflectance of said fused silica substrate being suppressed over the wavelength range of 2 to 20 microns.