Method of forming thin optical membranes

• US 4,536,240 A
• Filed: 02/22/1983
• Issued: 08/20/1985
• Est. Priority Date: 12/02/1981
• Status: Expired due to Term

• Current Assignee: Advanced Semiconductor Products Incorporated
• Original Assignee: Advanced Semiconductor Products Incorporated
• Inventors: Winn, Ray
• Primary Examiner(s): Lowe, James
• Application Number:
  US06/468,468
• Time in Patent Office: 910 Days
• Field of Search: 264/2.1, 264/310, 264/311, 264/1.7, 156/74, 156/230, 156/241, 156/246
• US Class Current: 156/74
• CPC Class Codes: B29D 11/00634 Production of filters

Abstract

Edge-supported and fully supported membranes having substantially uniform thickness, and substantially parallel surfaces, and having the capacity to transmit at least about 90% of incident light with very little diffraction, dispersion or absorption of incident light are made by forming a polymer/solvent mixture, spin-coating a film of the polymer from the mixture onto a rotatable surface, which may have a release agent thereon, and, where a release agent is present, joining a frame or other support to the membrane and removing the membrane with its attached support from the surface. Apparatus for making such membranes includes a dispenser for dispensing a polymer/solvent mixture onto a rotatable support; a device for spinning the rotatable support at gradually increasing speeds from a first to a second speed; and a device for maintaining the speed of rotation of the support at the second speed until the membrane forms.

Claims

1. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined thickness in the range of about 0.5 about 10 micrometers, with a precision of plus or minus about 2%, edge-to-edge variations in said thickness of less than about 2% over a distance of at least about 2.5 centimeters, and a capacity to transmit an average of at least about 91% of incident light with less than about 2% combined absorption and diffraction losses of said incident light over a span of wavelengths of incident light in the range of about 260 to about 1,000 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

29. The method of claim 1 or claim 2 or claim 3 or claim 4 or claim 5 or claim 6 or claim 7 or claim 8 or claim 9 or claim 10 or claim 11 or claim 12 or claim 13 or claim 14 or claim 15 or claim 16 or claim 17 or claim 18 further comprising removing said membrane from said rotatable supporting surface, and attaching said membrane to means for providing edge support to said membrane.

30. The method of claim 1 or claim 2 or claim 3 or claim 4 or claim 5 or claim 6 or claim 7 or claim 8 or claim 9 or claim 10 or claim 11 or claim 12 or claim 13 or claim 14 or claim 15 or claim 16 or claim 17 or claim 18 further comprising attaching said membrane to means for providing edge support only to said membrane and removing said membrane from said rotatable supporting surface.

31. The method of claim 1 or claim 2 or claim 3 or claim 4 or claim 5 or claim 6 or claim 7 or claim 8 or claim 9 or claim 10 or claim 11 or claim 12 or claim 13 or claim 14 or claim 15 or claim 16 or claim 17 or claim 18 or claim 19 or claim 20 or claim 21 or claim 22 or claim 23 or claim 24 or claim 25 or claim 26 or claim 27 or claim 28 further comprising attaching said membrane to means for providing edge support to said membrane, and thereafter removing said membrane from said rotatable supporting surface.

32. The method of claim 1 or claim 2 or claim 3 or claim 4 or claim 5 or claim 6 or claim 7 or claim 8 or claim 9 or claim 10 or claim 11 or claim 12 or claim 13 or claim 14 or claim 15 or claim 16 or claim 17 or claim 18 or claim 19 or claim 20 or claim 21 or claim 22 or claim 23 or claim 24 or claim 25 or claim 26 or claim 27 or claim 28 wherein said membrane is a pellicle, further comprising removing said pellicle from said rotatable supporting surface, and thereafter attaching said pellicle to means for providing edge support to said pellicle.

33. The method of claim 1 or claim 2 or claim 3 or claim 4 or claim 5 or claim 6 or claim 7 or claim 8 or claim 9 or claim 10 or claim 11 or claim 12 or claim 13 or claim 14 or claim 15 or claim 16 or claim 17 or claim 18 or claim 19 or claim 20 or claim 21 or claim 22 or claim 23 or claim 24 or claim 25 or claim 26 or claim 27 or claim 28 wherein said membrane is a pellicle, further comprising attaching said pellicle to means for providing edge support to said pellicle, and thereafter removing said pellicle from said rotatable supporting surface.

2. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a precise, predetermined thickness in the range of about 0.5 to about 10 micrometers, the precision being plus or minus about 2%, edge-to-edge variations in said thickness of less than about 2% over a distance of at least about 2.5 centimeters, and a capacity to transmit an average of at least about 91% of incident light over a span of wavelengths of incident light where the span of wavelengths of said incident light is in the range of about 260 to 1,000 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

3. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a precise, predetermined thickness in the range of about 0.5 to about 10 micrometers, the precision being plus or minus about 2%, and a capacity to transmit an average of at least about 91% of incident light with less than about 3% combined absorption, diffraction and dispersion losses of said incident light where the wavelength span for the average transmission of incident light is in the range of about 260 to about 1,000 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

4. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined, precise thickness in the range of about 0.5 to about 10 micrometers, the precision being plus or minus about 2%, and the capacity to transmit an average of at least about 91% of incident light where the wavelengths of incident light range from about 260 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

5. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined, precise thickness in the range of about 0.5 to about 10 micrometers, the precision being plus or minus about 2%, edge-to-edge variations in said thickness of less than about 2% over a distance of at least 2.5 centimeters, and the capacity to transmit about 99% of incident light at at least one predetermined wavelength of incident light in the range of about 260 to about 1,000 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

6. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a precise, predetermined thickness in the range of about 0.5 to about 10 micrometers with a precision of plus or minus about 2%, edge-to-edge variations in said thickness of less than about 2% over a distance of at least 2.5 centimeters, and the capacity to transmit about 99% of incident light at at least one predetermined wavelength of incident light in the range of about 260 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

7. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined, precise thickness in the range of about 0.5 to about 10 micrometers, the precision being plus or minus about 2%, edge-to-edge variations in said thickness of less than about 2% over a distance of at least about 2.5 centimeters, said membrane being a pellicle with a capacity to transmit an average of at least about 91% of incident light where the incident light wavelengths range from about 260 nanometers to about 450 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

8. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined thickness in the range of about 0.5 to about 10 micrometers, with a precision of plus or minus about 2%, and a capacity to transmit an average of at least about 91% of incident light over a span of wavelengths of incident light in the range of about 260 to about 1,000 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

9. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed and having a precise, predetermined thickness in the range of about 0.5 to about 10 micrometers, the precision being plus or minus about 5%, and a capacity to transmit an average of at least about 91% of incident light over a span of wavelengths of said incident light in the range of about 260 to about 1,000 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

10. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined, precise thickness in the range of about 0.5 to about 10 micrometers, and the capacity to transmit an average of at least about 91% of incident light where the wavelengths of incident light range from about 300 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation on said surface; and

removing said optical membrane, after formation, from said rotatable surface.

11. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined, precise thickness in the range of about 0.5 to about 10 micrometers, the precision being plus or minus about 2%, and the capacity to transmit about 99% of incident light at at least one predetermined wavelength of incident light in the range of about 260 to about 1,000 nanometers, said method being comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotatational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

12. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a precise, predetermined thickness in the range of about 0.5 to about 10 micrometers with a precision of plus or minus about 2%, and the capacity to transmit about 99% of incident light at at least one predetermined wavelength of incident light in the range of about 260 to about 546 nanometers, said method comprising dispening a polymer/solvent mixture onto a rotatable supporting surface, and spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following:

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

13. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined, precise thickness in the range of about 0.5 to about 10 micrometers, the precision being plus or minus about 2%, said membrane being a pellicle with a capacity to transmit an average of at least about 91% of incident light where the incident light wavelengths range from about 300 nanometers to about 450 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

14. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined thickness in the range of about 0.5 to about 10 micrometers, with a precision of plus or minus about 2%, and a capacity to transmit an average of at least about 91% of incident light with less than about 2% combined absorption and diffraction losses of said incident light in the range of about 350 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

15. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a precise, predetermined thickness in the range of about 0.5 to about 10 micrometers, the precision being plus or minus about 5%, and a capacity to transmit an average of at least about 91% of incident light over a span of wavelengths of said incident light is in the range of about 350 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

16. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a precise, predetermined thickness in the range of about 0.5 to about 10 micrometers, the precision being plus or minus about 2%, and a capacity to transmit an average of at least about 91% of incident light with less than about 3% combined absorption, diffraction and dispersion losses of said incident light where the wavelength span for the average transmission of incident light is in the range of about 350 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

17. A method for reliably and reproducibly making an optial membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a precise, predetermined thickness in the range of about 0.5 to about 10 micrometers, and the capacity to transmit about 99% of incident light at at least one predetermined wavelength of incident light in the range of about 260 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

18. A method for reliably and reproducibly making an optical membrane capable of being edge-supported, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a precise, predetermined thickness in the range of about 0.5 to about 10 micrometers, edge-to-edge variations in said thickness of less than about 2% over a distance of at least about 2.5 centimers, and a capacity to transmit an average of at least about 91% of incident light over a span of wavelengths of incident light where the span of wavelengths of said incident light is in the range of about 350 nanometers to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation of said surface; and

removing said optical membrane, after formation, from said rotatable surface.

19. A method for reliably and reproducibly making an optical membrane capable of being supported at its periphery, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined thickness in the range of about 0.5 about 10 micrometers, and the capacity to transmit an average of at least about 91% of incident light where the wavelengths of incident light range from about 330 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation on said surface; and

removing said optical membrane, after formation, from said rotatable surface.

20. A method for reliably and reproducibly making an optical membrane capable of being supported at its periphery, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined thickness in the range of about 0.5 about 10 micrometers, edge-to-edge variations in said thickness in the range of plus or minus about 5% over a distance of at least 2.5 centimeters, and the capacity to transmit an average of at least about 91% of incident light where the wavelengths of incident light range from about 330 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation on said surface; and

removing said optical membrane, after formation, from said rotatable surface.

21. A method for reliably and reproducibly making an optical membrane capable of being supported at its periphery, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined thickness in the range of about 0.5 about 10 micrometers, edge-to-edge variations in said thickness in the range of plus or minus about 4% over a distance of at least 2.5 centimeters, and the capacity to transmit an average of at least about 91% of incident light where the wavelengths of incident light range from about 330 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation on said surface; and

removing said optical membrane, after formation, from said rotatable surface.

22. A method for reliably and reproducibly making an optical membrane capable of being supported at its periphery, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined thickness in the range of about 0.5 about 10 micrometers, edge-to-edge variations in said thickness in the range of plus or minus about 3% over a distance of at least 2.5 centimeters, and the capacity to transmit an average of at least about 91% of incident light where the wavelengths of incident light range from about 330 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said members from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation on said surface; and

removing said optical membrane, after formation, from said rotatable surface.

23. A method for reliably and reproducibly making an optical membrane capable of being supported at its periphery, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined thickness in the range of about 0.5 about 10 micrometers, edge-to-edge variations in said thickness in the range of plus or minus about 2% over a distance of at least 2.5 centimeters, and the capacity to transmit an average of at least about 91% of incident light where the wavelengths of incident light range from about 330 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation on said surface; and

removing said optical membrane, after formation, from said rotatable surface.

24. A method for reliably and reproducibly making an optical membrane capable of being supported at its periphery, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined thickness in the range of about 0.5 about 10 micrometers, and the capacity to transmit an average of at least about 91% of incident light where the wavelengths of incident light range from about 250 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation on said surface; and

removing said optical membrane, after formation, from said rotatable surface.

25. A method for reliably and reproducibly making an optical membrane capable of being supported at its periphery, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined thickness in the range of about 0.5 about 10 micrometers, edge-to-edge variations in said thickness in the range of plus or minus about 5% over a distance of at least 2.5 centimeters, and the capacity to transmit an average of at least about 91% of incident light where the wavelengths of incident light range from about 250 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation on said surface; and

removing said optical membrane, after formation, from said rotatable surface.

26. A method for reliably and reproducibly making an optical membrane capable of being supported at its periphery, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined thickness in the range of about 0.5 about 10 micrometers, edge-to-edge variations in said thickness in the range of plus or minus about 4% over a distance of at least 2.5 centimeters, and the capacity to transmit an average of at least about 91% of incident light where the wavelengths of incident light range from about 250 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation on said surface; and

removing said optical membrane, after formation, from said rotatable surface.

27. A method for reliably and reproducibly making an optical membrane capable of being supported at its periphery, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined thickness in the range of about 0.5 about 10 micrometers, edge-to-edge variations in said thickness in the range of plus or minus about 3% over a distance of at least 2.5 centimeters, and the capacity to transmit an average of at least about 91% of incident light where the wavelengths of incident light range from about 250 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation on said surface; and

removing said optical membrane, after formation, from said rotatable surface.

28. A method for reliably and reproducibly making an optical membrane capable of being supported at its periphery, and capable of being removed, substantially intact, from the rotatable surface on which said membrane is formed, and having a predetermined thickness in the range of about 0.5 about 10 micrometers, edge-to-edge variations in said thickness in the range of plus or minus about 2% over a distance of at least 2.5 centimeters, and the capacity to transmit an average of at least about 91% of incident light where the wavelengths of incident light range from about 250 to about 546 nanometers, said method comprising dispensing a polymer/solvent mixture onto a rotatable supporting surface;

spinning said rotatable surface under conditions sufficient to form said membrane from said polymer, said conditions being selected from the following;

the viscosity of said polymer/solvent mixture, the rate of rotational acceleration of said rotatable supporting surface, and the final speed of rotation on said surface; and

removing said optical membrane, after formation, from said rotatable surface.