The effects of degraded spatial coherence on ultrafast-laser channel etching.
When laser-etching channels through solid targets, the etch-rate is known to decrease with increasing depth, partly because of absorption at the sides of the channel. For ultrafast-laser pulses at repetition rates >100 MHz, we show that the etch-rate is also affected by optical properties of the beam: the channel acts as a waveguide, and so the pulses will decompose into dispersive normal modes. Additionally, plasma on the inner surface of the channel will cause scattering of the beam. These effects will cause a loss of spatial coherence in the pulse, which will affect the propagated intensity distribution and ultimately the etch-rate. We have characterized this effect for various foil thicknesses to determine the evolution of the beam while drilling through metal.
Dean
Jesse
J
Dept of Physics and Institute for Optical Sciences, University of Toronto, 60 St George St, Toronto ON M5S 1A7, Canada. jdean@physics.utoronto.ca
Bercx
Martin
M
Frank
Felix
F
Evans
Rodger
R
Camacho-López
Santiago
S
Nantel
Marc
M
Marjoribanks
Robin
R
D003198:Computer Simulation; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007834:Lasers; D008420:Manufactured Materials; D008962:Models, Theoretical