Authors: AP Joglekar H Liu GJ Spooner E Meyhöfer G Mourou AJ Hunt
Publish Date: 2003/08/01
Volume: 77, Issue: 1, Pages: 25-30
Abstract
A remarkable feature of material damage induced by shortpulsed lasers is that the energy threshold becomes deterministic for subpicosecond pulses This effect coupled with the advent of kHz and higher repetition rate chirped pulse amplification systems has opened the field of femtosecond machining Yet the mechanism of optical breakdown remains unclear By examining the damage threshold as a function of polarization we find that contrary to established belief multiphoton ionization plays an insignificant role in optical breakdown The polarization independence combined with the observed precise and uniform dielectric breakdown threshold even for nanometerscale features leads us to conclude that the fundamental mechanism is ‘selfterminated’ Zenerimpact ionization and that the deterministic and uniform damage threshold throughout the sample threshold stems from the uniform valenceelectron density found in goodquality optical materials By systematically exploring optical breakdown near threshold we find that we can consistently machine features as small as 20 nm demonstrating great promise for applications ranging from Micro ElectroMechanical Systems MEMS construction and microelectronics to targeted disruption of cellular structures and genetic material
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