Patent Number: 
Section: claims

1. A device comprising:a luminescent material, the luminescent material being a parallelepiped having a first side and a second side that are squares and having a third side that is a rectangle or a square, the first side and the second side being perpendicular to the third side;a beam stop plate attached to the first side of the luminescent material; andan optical fiber having a first end and a second end, the first end of the optical fiber attached to the third side of the luminescent material. 2. The device of claim 1, wherein the luminescent material is selected from a group consisting of cerium-doped yttrium aluminum garnet, lead tungstate, cadmium tungstate, and diamond. 3. The device of claim 1, wherein first side and the second side of the luminescent material are about 250 microns to 1 millimeter by about 250 microns to 1 millimeter, and wherein the third side of the luminescent material is about 250 microns to 1 millimeter by about 250 microns to 1 millimeter. 4. The device of claim 1, wherein the luminescent material comprises three or four blocks of material, and wherein each block of material has dimensions of about 250 microns to 1 millimeter by about 250 microns to 1 millimeter by about 80 microns to 350 microns. 5. The device of claim 1, wherein the optical fiber comprises a multi-mode optical fiber. 6. The device of claim 1, wherein the optical fiber has a circular cross section having a diameter of about 350 microns to 450 microns. 7. The device of claim 1, wherein the optical fiber has a length of about 10 centimeters to 2 meters. 8. The device of claim 1, wherein the beam stop plate comprises a metal selected from a group consisting of silver, gold, tantalum, and tungsten. 9. The device of claim 1, wherein the beam stop plate has circular shape and a diameter of about 250 microns to 2 millimeters. 10. The device of claim 1, wherein the beam stop plate has an oval shape with an about 250 micron to 2 millimeter short axis and an about 300 micron to 3 millimeter long axis. 11. The device of claim 1, wherein the beam stop plate is about 100 microns to 1 millimeter thick. 12. The device of claim 1, further comprising:a hollow sleeve, wherein an end of the hollow sleeve is attached to the beam stop plate, and wherein the hollow sleeve includes a cutout to allow the optical fiber to contact the luminescent material. 13. The device of claim 12, wherein the hollow sleeve comprises a metal selected from a group consisting of silver, gold, tungsten, and tantalum. 14. The device of claim 12, wherein a wall of the hollow sleeve is about 100 microns to 300 microns thick. 15. The device of claim 12, wherein the beam stop plate has a circular shape, wherein the hollow sleeve is a hollow cylinder, and wherein an outer diameter of the hollow sleeve is the same as a diameter of the beam stop plate. 16. The device of claim 1, further comprising:a photodiode, wherein the photodiode is attached to the second end of the optical fiber. 17. The device of claim 1, wherein the optical fiber is one of a plurality of optical fibers that form a bundle of optical fibers. 18. The device of claim 17, wherein each optical fiber of the bundle of optical fibers has a circular cross section having a diameter of about 100 microns to 300 microns. 19. A device comprising:a luminescent material, the luminescent material being a parallelepiped having a first side and a second side that are squares and having a third side that is a rectangle or a square, the first side and the second side being perpendicular to the third side;a beam stop plate attached to the first side of the luminescent material; anda bundle of optical fibers having a first end and a second end, the first end of the bundle of optical fibers attached to the third side of the luminescent material. 20. A method comprising:(a) providing a luminescent material, the luminescent material being a parallelepiped having a first side and a second side that are squares and having a third side that is a rectangle or a square, the first side and the second side being perpendicular to the third side;(b) attaching a beam stop plate to the first side of the luminescent material; and(c) attaching a first end of an optical fiber to the third side of the luminescent material.