Methods and systems for evaluating a target using pulsed, energetic particle beams

1. A method for evaluating a target, the target having a surface, the method comprising:

pulsing a defined, energetic particle beam through the surface and into the target such that a particle energy deposition from the particle beam is concentrated in a subsurface target volume within a target medium of the target;

wherein the particle energy deposition induces a thermoelastic expansion of the target medium in the target volume that generates a corresponding acoustic wave; and

detecting the acoustic wave from the target medium;

wherein:

the particle beam is an electron beam, a proton beam, or an X-ray beam; and

the method includes focusing the particle beam with a focal point located in the target medium at a positive, nonzero depth from the surface to concentrate the particle energy deposition from the particle beam in the target medium in the target volume.

2. The method of claim 1 wherein the acoustic wave is an ultrasonic wave.

3. The method of claim 1 wherein the particle beam is an electron beam.

4. The method of claim 3 wherein focusing the electron beam includes focusing the electron beam at the focal point using a lens system.

5. The method of claim 4 wherein the lens system includes an electromagnetic lens.

6. The method of claim 5 wherein:

the electromagnetic lens is a defocusing/focusing lens; and

focusing the electron beam includes focusing a collimated electron beam at the focal point using the defocusing/focusing lens.

7. The method of claim 1 wherein the particle beam is a proton beam.

8. The method of claim 7 including selecting an energy of the proton beam such that a Bragg peak of the proton beam is located at a selected depth in the target volume.

9. The method of claim 1 wherein the particle beam is an X-ray beam.

10. The method of claim 9 wherein focusing the X-ray beam includes focusing the X-ray beam at the focal point using a lens system.

11. The method of claim 1 including:

scanning the particle beam across the target such that the particle energy deposition from the particle beam is sequentially concentrated in a series of subsurface target volumes within the target; and

pulsing the particle beam while scanning the particle beam across the target.

12. The method of claim 1 wherein detecting the acoustic wave from the target volume includes detecting the acoustic wave using a transducer that converts the acoustic wave to an electrical signal.

13. The method of claim 12 including processing the electrical signal to characterize the target medium.

14. The method of claim 13 wherein processing the electrical signal to characterize the target medium includes identifying a presence of a discontinuity in the target.

15. The method of claim 13 wherein processing the electrical signal to characterize the target medium includes characterizing a size of a defect in the target.

16. The method of claim 13 wherein processing the electrical signal to characterize the target medium includes characterizing a bond between multiple layers in the target.

17. The method of claim 12 wherein the transducer is in contact with the target.

18. The method of claim 12 wherein the transducer does not contact the target.

19. The method of claim 1 wherein:

the target includes an intervening object and a gap defined between the intervening object and the target medium; and

the particle beam passes through the intervening object and the gap prior to entering the target volume.

20. The method of claim 1 wherein:

the target medium includes a subsurface void defined therein; and

the particle beam passes through the void prior to entering the target volume.

21. A system for evaluating a target, the target having a surface, the system comprising:

an energetic particle beam generator configured to pulse a defined, energetic particle beam through the surface and into the target such that a particle energy deposition from the particle beam is concentrated in a subsurface target volume within a target medium of the target;

wherein the particle energy deposition induces a thermoelastic expansion of the target medium in the target volume that generates a corresponding acoustic wave; and

an ultrasonic sensor configured to detect the acoustic wave from the target medium;

wherein:

the particle beam is an electron beam, a proton beam, or an X-ray beam; and

the energetic particle beam generator is configured to focus the particle beam with a focal point located in the target medium at a positive, nonzero depth from the surface to concentrate the particle energy deposition from the particle beam in the target medium in the target volume.

22. The system of claim 21 wherein the acoustic wave is an ultrasonic wave.

23. The method of claim 1 wherein an energy density of the particle energy deposition at the target volume is at least 10 times an energy density of a particle energy deposition from the particle beam at the surface.

24. The system of claim 21 wherein the particle beam is an electron beam.

25. The system of claim 21 wherein the particle beam is a proton beam.

26. The system of claim 21 wherein the particle beam is an X-ray beam.

27. A method for evaluating a target, the target having a surface, the method comprising:

pulsing a defined proton beam through the surface and into the target such that a particle energy deposition from the proton beam is concentrated in a subsurface target volume within a target medium of the target;

wherein the particle energy deposition induces a thermoelastic expansion of the target medium in the target volume that generates a corresponding acoustic wave; and

detecting the acoustic wave from the target medium;

wherein:

the proton beam is a collimated proton beam; and

the method includes selecting an energy of the proton beam such that a Bragg peak of the proton beam is located in the target medium at a selected positive, nonzero depth from the surface to concentrate the particle energy deposition from the proton beam in the target medium in the target volume.