Patent Number: 
Section: claims

1. A system, comprising:a charged particle source comprising a tip;a charged particle column;a detector configured to obtain an image of the tip of the charged particle source;a moveable optical reflective element having a first position in the charged particle column and a second position outside the charged particle column; anda positioning device configured to move the optical reflective element between its first and second positions, the positioning device being configured to move in a first plane and in a second plane perpendicular to the first plane,wherein:the tip is configured to emit light when heated;the tip is configured to emit charged particles during use of the system; andthe moveable optical reflective element is configured in the first position to reflect light from the charged particle source to the detector to obtain the image. 2. The system of claim 1, wherein in the second position, the optical reflective element cannot reflect light passing through the charged particle column to the detector. 3. The system of claim 1, further comprising:a first actuator configured to move the positioning device in the first plane; anda second actuator configured to move the positioning device in the second plane. 4. The system of claim 1, wherein the charged particle source is configured so that during use at least some of the charged particles generated by the charged particle source pass through the charged particle column and wherein the charged particle source is configured so that, when it emits light, the light goes into the column and can be reflected by the optical reflective element when it is in the first position. 5. The system of claim 1, wherein the charged particle column is an ion beam column. 6. A system, comprising:a charged particle source comprising a tip;a charged particle column having an axis;a detector configured to obtain an image of the tip of the charged particle source; andan optical reflective element positioned within the charged particle column and displaced off-axis with respect to the axis of the charged particle column, the optical reflective element being coupled to the charged particle column and configured to reflect light from the charged particle source to the detector,wherein the optical reflective element is fixed with respect to the charged particle column. 7. The system of claim 6, further comprising:a housing; anda mount fixedly mounting the optical reflective element to the housing,wherein the mount, the optical reflective element, the charged particle source and the charged particle column are housed within the housing. 8. The system of claim 6, wherein the charged particle source is configured so that during use at least some of the charged particles generated by the charged particle source pass through the charged particle column without interacting with the optical reflective element and wherein the charged particle source is configured so that, when it emits light, the light goes into the column and can be reflected by the optical reflective element. 9. The system of claim 6, wherein the charged particle column is an ion beam column. 10. A method, comprising:emitting light from a tip of a charged particle source so that the light enters a charged particle column;reflecting at least a portion of the light in the charged particle column to a detector;obtaining an image of the tip of the charged particle source based on detected light; andbased on the image of the tip, modifying a shape of the tip. 11. The method of claim 10, wherein modifying the shape of the tip comprises changing at least one parameter selected from the group consisting of a temperature of the tip of the charged particle source, a gas pressure of a chamber housing the charged particle source, and an intensity of light emitted by the charged particle source. 12. The method of claim 11, further comprising, based on the detected light, increasing at least one parameter selected from the group consisting of a charged particle source temperature and a gas pressure in a chamber housing the charged particle source. 13. The method of claim 10, wherein the charged particle source is a gas field ion source. 14. The method of claim 10, comprising making a tip of a charged particle source. 15. The method of claim 14, wherein the charged particle source is a gas field ion source. 16. The method of claim 10, further comprising, before reflecting at least the portion of the light in the charged particle column to the detector:mounting an optical reflective element on a positioning device;moving the positioning device in a first plane; andmoving the positioning device in a second plane which is perpendicular to the first plane.