Patent Number: 
Section: claims

1. A method of producing a localised concentration of energy comprising:creating at least one shockwave;propagating the at least one shockwave through a non-gaseous medium;allowing the at least one shockwave to be incident upon a pocket of gas suspended within the medium, wherein the pocket of gas is spaced from a concave surface; andreflecting said at least one shockwave from the concave surface onto said gas pocket. 2. The method as claimed in claim 1, wherein the concave surface comprises a plurality of discrete portions. 3. The method as claimed in claim 2, wherein the discrete portions are piecewise polynomial. 4. The method as claims in claim 1, wherein the concave surface focuses the reflected at least one shockwave onto the gas pocket. 5. The method as claimed in claim 4, wherein the concave surface focuses the reflected shockwave to a point. 6. The method as claimed in claim 1, wherein the gas pocket is placed no more than three times a maximum radius of curvature of the closest section of the concave surface away from the concave surface. 7. The method as claimed in claim 6, wherein the gas pocket's edge closest to the concave surface is spaced from it by a distance of less than five times the dimension of the gas pocket's widest part. 8. The method as claimed in claim 1, comprising using an external device to apply one or more shockwaves to a static volume of the non-gaseous medium to create the at least one shockwave propagating through the non-gaseous medium. 9. The method as claimed in claim 8, comprising using the external device to create the shockwave with a pressure of between 0.1 GPa and 50 GPa. 10. The method as claimed in claim 1, comprising using a lithotripsy device to create the shockwave with a pressure of between 100 MPa and 1 GPa. 11. The method as claimed in claim 1, wherein the gas pocket is formed with the use of a membrane that defines the boundary between the gas pocket and the non-gaseous medium, and wherein the membrane is frangible and breaks upon impact from the shockwave. 12. The method as claimed in claim 11, wherein the membrane includes a line or region of weakness that breaks upon impact from the shockwave. 13. An apparatus for producing a localised concentration of energy comprising:a non-gaseous medium having therein a pocket of gas, wherein the pocket of gas is spaced from a concave surface; andan external device for creating at least one shockwave propagating through said medium so as to be incident upon said pocket of gas,wherein said concave surface is shaped so as at least partially to reflect said shockwave in such a way as to direct it onto said gas pocket and wherein the gas pocket is placed no more than three times a maximum radius of curvature of the closest section of the concave surface away from the concave surface. 14. The apparatus as claimed in claim 13, wherein the non-gaseous medium comprises a static volume of non-gaseous medium and wherein the external device is arranged to apply one or more shockwaves to the static volume of non-gaseous medium to create the at least one shockwave propagating through the non-gaseous medium.