Curved X-ray reflector

1. A method for producing X-ray optics, comprising:

providing a wafer of crystalline material having front and rear surfaces and a lattice spacing suitable for reflecting incident X-rays of a given wavelength; and

depositing a thin film on the front surface of the wafer so as to generate compressive forces in the thin film sufficient to impart a concave curvature to the rear surface of the wafer with at least one radius of curvature selected for focusing the incident X-rays.

2. The method according to claim 1 , wherein providing the wafer comprises providing a silicon wafer, and wherein depositing the thin film comprises depositing a metal film on the wafer.

3. The method according to claim 2 , wherein the metal film comprises at least one of tungsten and titanium.

4. The method according to claim 1 , wherein depositing the thin film comprises forming stripes of the thin film on the front surface, the stripes having a thickness, width and spacing selected to create the at least one selected radius of curvature.

5. The method according to claim 4 , wherein the thickness, width and spacing of the stripes are chosen so as to impart to the wafer a first radius of curvature about a first curvature axis and a second radius of curvature, different from the first radius of curvature, about a second curvature axis.

6. The method according to claim 4 , wherein forming the stripes comprises sputtering the thin film onto the front surface and then etching the thin film.

7. The method according to claim 1 , and comprising thinning the rear surface of the wafer after depositing the thin film, so that the thinned wafer curves to the selected radius of curvature.

8. An X-ray optic, comprising:

a wafer of crystalline material having front and rear surfaces and a lattice spacing suitable for reflecting incident X-rays of a given wavelength; and

a thin film deposited on the front surface of the wafer, having compressive forces in the thin film sufficient to impart a concave curvature to the rear surface of the wafer with at least one radius of curvature selected for focusing the incident X-rays.

9. The optic according to claim 8 , wherein the wafer comprises silicon, and wherein the thin film comprises a metal.

10. The optic according to claim 9 , wherein the metal film comprises at least one of tungsten and titanium.

11. The optic according to claim 8 , wherein the thin film comprises stripes of the thin film, the stripes having a thickness, width and spacing selected to create the at least one selected radius of curvature.

12. The optic according to claim 11 , wherein the thickness, width and spacing of the stripes are chosen so as to impart to the wafer a first radius of curvature about a first curvature axis and a second radius of curvature, different from the first radius of curvature, about a second curvature axis.

13. The optic according to claim 11 , wherein the stripes are formed by sputtering the thin film onto the front surface and then etching the thin film.

14. The optic according to claim 8 , wherein the rear surface of the wafer is thinned after depositing the thin film, so that the thinned wafer curves to the selected radius of curvature.

15. An X-ray spectrometer, comprising:

an X-ray source, which is operative to emit a beam of X-rays of a given wavelength;

an X-ray optic, which is configured and positioned to focus the beam of X-rays onto a sample, and which comprises:

a wafer of crystalline material having front and rear surfaces and a lattice spacing suitable for reflecting the X-rays of the given wavelength; and

a thin film deposited on the front surface of the wafer, having compressive forces in the thin film sufficient to impart a concave curvature to the rear surface of the wafer with at least one radius of curvature selected for focusing the X-ray beam.