12 Nov 2004
The pick of this week's patent applications including a fiber-laser based EUV lithography source.
• Title: Fiber laser based EUV-lithography
Applicant: The Regents of the University of Michigan, US
International application number: WO 2004/097520
Patent application WO 2004/097520 discusses a fiber laser based extreme ultraviolet (EUV) light source. The system uses a fiber laser and adaptive optics to focus the laser beam into a small diffraction-limited spot on to a plasma which then emits EUV light. The authors say one advantage of this setup is that large complex laser systems and high-energy power supplies are not required. They add that using adaptive optics minimizes the volume of the plasma target and reduces the amount of laser-produced debris.
• Title: Laser apparatus for material processing
Applicant: Southampton Photonics Limited, UK
International application number: WO 2004/098003
Southampton Photonics has applied to patent a laser system for material processing applications such as welding sheet metal. The system comprises a rare-earth doped-fiber laser which is pumped with a diode laser. The fiber laser output is then combined with that from a short-pulsed source, such as a Q-switched laser. This combination provides a train of pulses containing a pre-pulse and a main pulse. The average peak power of the pre-pulse is said to be greater than the peak power of the main pulse. "The apparatus provides savings in equipment costs as well as reduced infrastructure and utility costs," say the inventors.
• Title: Singlet telescopes with controllable ghosts for laser beam forming
Applicant: BAE Systems Information and Electronic Systems Integration Inc, US
International application number: WO 2004/097465
BAE Systems has designed a singlet telescope which it says minimizes ghost back-reflections when it is used as an intracavity component to reshape a laser beam. Such ghost reflections are known to arise when using multi-element telescopes and can damage other optical components in the cavity as well as the pump laser. "The number of lenses is reduced to one, such that there are only two reflective surfaces which contribute to retro-reflective ghosts," say the inventors. "For example, when utilizing the singlet lens for demagnification, each of the two surfaces is convex towards the pump beam. This means that back reflection is diverging and has less effect on the Q-switch used by the pump laser."