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Thin films of nickel have been irradiated using femtosecond laser pulses in vacuum. Subsequent emission of plasma ions is diagnosed using an ion probe. Angular distributions of the emitted ions are presented for a range of target film thicknesses. Data are compared to the Anisimov model of plasma expansion [S. I. Anisimov, D. Bauerle, and B. S. Luk’yanchuk, Phys. Rev. B 48, 12076 (1993)]. The tendency of the ions to be ejected at small angles to the normal of the target surface is explained in terms of the initial conditions of the plume. Results are explained in terms of the initial shape and adiabatic index of the plasma.

Percussion drilling of blind holes and vias in Kapton ® film was investigated using Q-switched solid state lasers operating at UV (355nm) and VUV (266nm) wavelengths. Holes were analyzed using different methods such as scanning electron microscopy (SEM) and surface profilometry. Ablation rates for the two wavelengths are compared. No abrupt thresholds were found and there was no evidence of an incubation effect within the first few pulses. Introducing pauses during the drilling increased the number of shots required for perforation of the film. The effects of fluence on diameter, depth and taper of the holes are presented. Smaller and neater holes are achieved more accurately with a lower fluence. An observed skin effect brought about by long exposure to low fluence VUV laser light is also discussed.

Abstract-Frequency doubling with a free-running long-pulse Nd:YAG laser and LBO or KTP nonlinear crystals yields conversion efficiency of up to 17.5% and 162 W peak power in the second harmonic. This efficiency is obtained for a TEM beam with rectangular temporal pulse shape of 50 to 400 s. To our knowledge, this is the highest second-harmonic generation (SHG) efficiency reported for the long-pulse free-running configuration. The efficiency is limited by optical damage with much lower threshold than in the Q-switch domain. The damage is preceded by a saturation effect of the SHG efficiency. Both wavelengths (fundamental and second-harmonic) are necessary for the creation of the catastrophic damage. We present first evidence for a mechanism that involves creation of transient absorption centers by the second-harmonic radiation due to multiphoton absorption. Absorption of the fundamental wave at these centers leads to local heating and ultimately catastrophic damage.

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