Hideaki Kusama

Laser-triggered low timing jitter coaxial Marx generator

A coaxial Marx generator triggered with a UV laser pulse propagating coaxially through multigap switches is constructed. The Marx generator is operated at maximum voltage of 200 kV with a rise time of less than 10 ns. To trigger multigap switches in the Marx generator, the laser pulse is passed through fine metal mesh fitted in the holes formed along the central axis in electrodes of gap switches. Photoelectrons generated from the mesh part of the cathode trigger the discharge and close the switches. Timing jitter of the high voltage pulse with respect to the laser pulse is 800 ps for the case of single gap switch and 1 ns for the Marx generator with two stage gap switches. Since the spark path is always formed from the solid surface of the cathode instead of the metal mesh, the mesh part of the cathode is never damaged for a large number of shots, promising long lifetime of the electrodes.

Beam Manipulation Techniques for KrF Excimer Laser

Because of the high gain and short gain duration, the beam quality of an excimer laser is not good for fine machining. Excimer lasers with improved beam quality or modified beam characteristics are attractive light sources for material surface processing. We have developed various beam modification techniques together with beam diagnostics methods for a discharge pumped KrF excimer laser. The beam shaping and manipulation are done for wave front cleaning by optical phase conjugation, wavelength conversion by stimulated Raman scattering in H 2 , soft X-ray generation from a laser plasma, laser pulse width modification by a grating pair, pulse compression and a stretcher, and beam pattern flattening by a segmented mirror.