Polariton wave imaging

• US 6,356,349 B1
• Filed: 07/09/1999
• Issued: 03/12/2002
• Est. Priority Date: 07/10/1998
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Adachi, Satoru, Koehl, Richard A., Nelson, Keith A.
• Primary Examiner(s): Evans, F L.
• Assistant Examiner(s): Smith, Zandra V.
• Application Number:
  US09/350,972
• Time in Patent Office: 977 Days
• Field of Search: 356/432, 356/432.T, 359/239, 359/237
• US Class Current: 356/432
• CPC Class Codes: G01N 2021/1725 Modulation of properties by light, e.g. photoreflectance
• CPC Class Codes: G01N 21/1717 with a modulation of one or more physical properties of the sample during the optical investigation, e.g. electro-reflectance
• CPC Class Codes: G01N 21/21 Polarisation-affecting properties G01N21/19 takes precedence
• CPC Class Codes: G01N 21/41 Refractivity; Phase-affecting properties, e.g. optical path length G01N21/21 takes precedence

Abstract

A method for characterizing a polariton wave within a material includes: generating the polariton wave; and imaging the polariton wave with optical radiation to produce a spatially-resolved image of portions of the optical radiation affected by the polariton wave. The method can be used to identify inhomogeneities in the material, detect electrical signals within the material, or characterize a polariton wave propagating within a waveguide, e.g., a waveguide formed within a photonic crystal. The optical imaging can be based on diffraction, polarization rotation, or spectral filtering of optical probe radiation transmitted through, or reflected by, the material.

Claims

1. A method for characterizing polariton propagation within a material, the method comprising:

generating a polariton wave at a first spatial location in the material;

waiting for a time interval sufficient to allow the polariton wave to propagate to additional spatial locations in the material; and

optically imaging the polariton wave at the additional spatial locations.

2. The method of claim 1, wherein optically imaging comprises:

directing optical radiation to the additional spatial locations; and

generating a spatially-resolved image of portions of the optical radiation affected by the polariton.

3. The method of claim 1, further comprising:

repeating the waiting and imaging steps for additional time intervals; and

generating a spatially-resolved image of the polariton wave for each of the time intervals based on each of the imaging steps.

4. The method of claim 3, further comprising:

identifying inhomogeneities in the material based on the images.

5. The method of claim 3, further comprising:

detecting electrical signals within the material based on the images.

6. The method claim 1, wherein the polariton wave is generated by converting fast electrical signals adjacent the first spatial location into the polariton.

7. The method of claim 1, wherein the polariton wave is generated optically.

8. The method of claim 7, wherein the polariton wave is generated with an optical pulse having a duration shorter than 1 ps.

9. The method of claim 7, wherein the polariton wave is generating by crossing a pair of optical excitation beams on the material to form an optical excitation grating pattern at the first spatial location.

10. The method of claim 1, wherein the optical imaging is based on diffraction.

11. The method of claim 1, wherein the optical imaging is based on polarization rotation.

12. The method of claim 1, wherein the optical imaging is based on spectral filtering.

13. The method of claim 1, wherein the optical imaging is based on reflection.

14. The method of claim 2, wherein the optical radiation directed to the additional spatial locations is substantially larger than the first spatial location.

15. The method of claim 2, wherein the optical radiation directed to the additional spatial locations has a size greater than or equal to about 1 mm.

16. The method of claim 2, wherein the optical radiation directed to the additional spatial locations has a size that overlaps the first spatial location.

17. The method of claim 1, wherein the polariton wave has an electromagnetic frequency within the range of about 300 GHz to 20 THz.

18. The method of claim 1, wherein the material is a semiconductor or a ferroelectric.

21. The method of claim 18, wherein the waveguide is formed within a photonic crystal.

19. A method for characterizing a polariton wave propagating within a waveguide, the method comprising:

introducing the polariton wave into a first location of the waveguide;

waiting for a time interval sufficient to allow the polariton wave to propagate to additional locations within the waveguide; and

optically imaging the polariton wave at the additional spatial locations.

20. The method of claim 19, further comprising:

repeating the waiting and imaging steps for additional time intervals; and

generating a spatially-resolved image of the polariton wave for each of the time intervals based on each of the imaging steps.

22. A method for characterizing a polariton wave within a material, the method comprising:

generating the polariton wave; and

imaging the polariton wave with optical radiation to produce a spatially-resolved image of portions of the optical radiation affected by the polariton wave.

23. The method of claim 22, wherein the optical radiation is has a central wavelength in the range of about 300 nm to 2.5 microns.