In order to improve light-emission efficiency without degrading protection performance of a light-emitting layer structure a three p-type layer structure composed of first to third layers is provided in contact with a light-emitting layer structure. The sensor may have in integral heater. A method for sensing a focal spot, the method includes: receiving an x-ray beam into an opening of a focal spot sensing device; interpreting a position of the x-ray beam; and calculating or measuring a position of a focal spot. The mechanism further includes a rotatable element having a distal portion with helical threading.