An all-reflective optical system uses a mirror with a hole to transmit a focused laser beam to an on-axis elliptical mirror. The reflected beam from the ellipse is predominately reflected off the mirror with a hole and focused to a distant adjustable focus. This focus spot can be positioned by X-Y scanning...http://www.google.com/patents/US6078420?utm_source=gb-gplus-sharePatent US6078420 - Hole-coupled laser scanning system
