Claims
- 1. A process for providing a second order nonlinear optical medium having a stabilized noncentrosymmetric orientation of polymer molecules, which process comprises:
- (a) heating a film of polymer incorporating active units capable of exhibiting second order nonlinear optical response to a temperature of about the glass transition temperature (Tg) of the film;
- (b) poling the polymer medium by applying an external electric field to induce noncentrosymmetry in the polymer medium by molecular orientation of said active units which exhibit second order nonlinear optical susceptibility;
- (c) cooling the noncentrosymmetric polymer medium to about room temperature; and
- (d) during said cooling step, heat-treating the polymer film at a temperature of at least above about 40.degree. C. while maintaining said externally applied electric field to stabilize the second-order nonlinear optical activity of the film from decay over time such that the nonlinear optical medium so produced exhibits higher stabilized second order nonlinear optical activity than a corresponding medium produced by quenching the corresponding medium from about Tg to about room temperature in about 30 minutes under the influence of an electric field.
- 2. The process according to claim 1, wherein said step of heat-treating the medium includes the application of an elevated pressure.
- 3. The process according to claim 2, wherein said elevated pressure is from about 100 to about 10,000 atmospheres.
- 4. The process according to claim 1, wherein the step of heat-treating the polymer includes maintaining the polymer between about 80 per cent of its glass transition temperature (degrees C) and about 40.degree. C. for a sufficient length of time to stabilize the polymer.
- 5. The process according to claim 4, wherein the step of heat-treating the polymer includes maintaining the polymer between about sixty percent of its glass transition temperature (degrees C) and about 40.degree. C. for a sufficient length of time to stabilize the polymer.
- 6. A process for producing an optical medium having a stabilized noncentrosymmetric orientation of polymer molecules, which process comprises (1) heating a film of a polymer incorporating active units capable of exhibiting second order nonlinear optical response to a temperature of about the glass transition temperature (Tg) of the polymer; (2) poling the polymer medium by applying an external electric field to induce noncentrosymmetry in the polymer medium by molecular orientation of said active units which exhibit second order nonlinear optical susceptibility and (3) cooling the noncentrosymmetric polymer medium to about room temperature, wherein said step of cooling the polymer includes slow cooling of up to about 1.degree. C. per minute following poling to a substantially constant annealing temperature below Tg and above room temperature which annealing temperature is maintained for a time period greater than 30 minutes, said external electric field being maintained during said steps of slow cooling and annealing whereby the nonlinear optical medium so produced exhibits higher stabilized second order nonlinear optical activity than a corresponding medium produced by quenching the corresponding medium from about Tg to about room temperature in about 30 minutes under the influence of an electric field.
- 7. In a process for providing an oriented nonlinear optical medium having a noncentrosymmetric orientation of polymer molecules which includes heating a film containing NLO active units to an elevated temperature of about the glass transition temperature of the film, poling the film by applying an external electric field to induce molecular orientation and cooling the medium to a temperature of below about Tg to freeze the oriented structure into place, a method of heat treating the polymer film during said step of cooling the polymer comprising maintaining said electric field while cooling said film wherein said cooling step includes maintaining said film below about Tg and above about 40.degree. C. for at least about thirty minutes and wherein for at least one thirty minute period during cooling the film is maintained substantially below about Tg and the rate of cooling during said period is between about 0.degree. C. per minute and about 0.5.degree. C. per minute whereby the induced noncentrosymmetric structure is stabilized over time against decay.
- 8. The process according to claim 7, wherein for at least one thirty minute period during cooling the film is maintained substantially below about Tg and the rate of cooling during said period is between about 0.degree. C. per minute and about 0.1.degree. C. per minute.
- 9. The process according to claim 7, wherein for at least one sixty minute period the film is maintained substantially below about Tg and the rate of cooling during said period is between about 0.degree. C. per minute and about 0.5.degree. C. per minute.
- 10. The process according to claim 7, wherein for at least one six hundred minute period during cooling, the rate of cooling is between about 0.degree. C. per minute and about 0.1.degree. C. per minute.
- 11. The process according to claim 7, wherein for at least one six hundred minute period during cooling the film is maintained substantially below about Tg and the rate of cooling is between about 0.degree. C. per minute and about 0.5.degree. C. per minute.
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of U.S. Ser. No. 07/540,403 now U.S. Pat. No. 5,053,168 of the same title, filed May 22, 1990 which in turn was a continuation of U.S. Ser. No. 07/181,751 filed Apr. 14, 1988 abandoned. The disclosure of the aforementioned application is hereby incorporated by reference.
US Referenced Citations (1)
Number |
Name |
Date |
Kind |
5053168 |
Man et al. |
Oct 1991 |
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Continuations (1)
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Number |
Date |
Country |
Parent |
181751 |
Apr 1988 |
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Continuation in Parts (1)
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Number |
Date |
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Parent |
540403 |
May 1990 |
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