Optical notch filter utilizing electric dipole resonance absorption

• US 4,099,854 A
• Filed: 10/12/1976
• Issued: 07/11/1978
• Est. Priority Date: 10/12/1976
• Status: Expired due to Term

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: The United States of America As Represented By The Secretary of Agriculture
• Inventors: Decker, Donald L., Tolles, William M.
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Lee, John D.
• Application Number:
  US05/731,285
• Time in Patent Office: 637 Days
• Field of Search: 350/147, 350/149, 350/154, 350/160 R, 350/160 LC, 350/267, 350/311, 350/312, 350/1
• US Class Current: 359/278
• CPC Class Codes: G02B 5/24 Liquid filters G02B5/23 takes precedence
• CPC Class Codes: G02F 1/172 based on a suspension of orientable dipolar particles, e.g. suspended particles displays

Abstract

An optical notch filter having a suspension of small absorbing particles which blocks a narrow band of frequencies. The small absorbent particles are suspended as a colloidal system which can have either a solid, liquid or gas as host material. The absorbing particles can be incorporated in a solid matrix as a transmission filter or used on the surface of a mirror as a reflection filter. The filter can be tuned by an externally applied electric field or by applying hydrostatic pressure.

Claims

1. An optical notch filter comprising:

a suspending material wherein said suspending material comprises a material selected from the group consisting of air, KBr, NaF, CaF₂, BaF₂, LiF, KCl, NaCl, KRS-5 and ZnSe; and

a plurality of absorbing particles within said suspending material to form a colloidal system, said particles having a dielectric constant such that a resonant absorption condition exists for a given wavelength of incident radiation, and being small in size relative to said wavelength.

2. An optical notch filter as recited in claim 1 further comprising a means for reflecting said incident radiation situated such that said colloidal system is between said reflecting means and said incident radiation.

3. An optical notch filter comprising:

a suspending material; and

a plurality of absorbing particles within said suspending material to form a colloidal system, said particles having a dielectric constant such that a resonant absorption condition exists for a given wavelength of incident radiation, and being small in size relative to said wavelength.

wherein said absorbing particles comprise a material selected from the group consisting of MgO, BeO, α

Al₂ O₃, BN, Ag_1-x Cd_x alloy system, Ag_1-x Zn_x alloy system and Ag.

4. An optical notch filter as recited in claim 3 wherein said Ag_1-x Cd_x and Ag_1-x Zn_x alloy systems comprise Ag alloyed with Cd and Zn, respectively, to at least 30% atomic concentration.

5. An optical notch filter as recited in claim 3 further comprising a means for reflecting said incident radiation, situated such that said colloidal system is between said reflecting means and said incident radiation.

6. An optical notch filter as recited in claim 3 wherein said suspending material comprises a material transparent to said incident radiation.

7. An optical notch filter as recited in claim 3 wherein said suspending material comprises a solid.

8. An optical notch filter as recited in claim 3 wherein said suspending material comprises a fluid.

9. An optical notch filter as recited in claim 8 wherein said fluid is a gas.

10. An optical notch filter as recited in claim 8 wherein said fluid is a liquid.

11. An optical notch filter as recited in claim 10 wherein said liquid is a miscible lyophilic liquid.

12. An optical notch filter comprising

a suspending material;

a plurality of absoring particles within said suspending material to form a colloidal system, said particles having a dielectric constant such that a resonant absorption condition exists for a given wavelength of incident radiation, and being small in size relative to said wavelength; and

means for tuning said filter.

13. An optical notch filter as recited in claim 12 wherein said tuning means comprises a means for applying an external electric field to said filter to vary said dielectric constant.

14. An optical notch filter as recited in claim 13 wherein said absorbing particles are non-spherical in shape so that the resonant absorption condition is dependent upon the geometric shape and orientation of said particles.

15. An optical notch filter as recited in claim 13 wherein said tuning means comprises a means for applying hydrostatic pressure to said filter.

16. An optical notch filter as set forth in claim 12 wherein said filter'"'"'s absorption wavelength is shifted by predetermined changes in the composition of said suspending material.

17. An optical notch filter as set forth in claim 12 wherein said filter'"'"'s absorption wavelength is shifted by predetermined changes in the composition of said absorbing particles.

18. A method for producing an optical notch filter comprising the steps of:

mulling a plurality of absorbing particles having a dielectric constant such that a resonant absorption condition exists for a given wavelength of incident radiation, and being small in size relative to said wavelength, together with a finely ground powder of a suspending material without changing the character of said absorbing particles; and

pressing said mulled powder mixture in a vacuum to form a solid matrix.

19. A method for producing an optical notch filter as recited in claim 18 further comprising the step of heating said mulled powder mixture to a temperature of about 150°

to 350°

C while pressing said powder mixture.

20. A method for producing an optical notch filter as recited in claim 19 wherein the step of pressing comprises pressing with a pressure of 100,000 lb/in² or less.

21. An optical notch filter comprising;

a suspending material selected from the group consisting of air, KBr, NaF, CaF₂, BaF₂, LiF, KCl, NaCl, KRS-5 and ZnSe; and

a plurality of absorbing particles within said suspending material to form a colloidal system said particles having a dielectric constant such that a resonant absorption condition exists for a given wavelength of incident radiation, and being small in size relative to said wavelength, wherein said absorbing particles are selected from the group consisting of MgO, BeO, α

Al₂ O₃, BN, Ag_1-x Cd_x alloy system, Ag_1-x Zn_x alloy system and Ag.

22. An optical notch filter as recited in claim 21 further comprising a means for reflecting said incident radiation such that said colloidal system is between said reflecting means and said incident radiation.