Processing of optical glasses by single, 34 fs pulses in the strong field ionization domain: ablation characteristics and crater morphology

摘要

The material response of Borofloat, BK7, and B270 glass targets to 34 fs pulses of 800 nm central wavelength is analyzed in the 1-30 J/cm~2 fluence domain. The contours of the craters change with the fluence very much the same for all three glasses up to approximately 20 J/cm~2, above which the Borofloat and BK7 continue behaving similarly, while bump formation sets on for the B270 glass. Analyzing the contours single-shot ablation thresholds are determined by applying both the conventional diameter regression technique and a multiphoton absorption-based fit to depth data. The ablation threshold values are equal within the 6.1 ±0.55 J/cm~2 domain for the three glasses as well as the three-photon absorption coefficients, which lie in the same magnitude (10~(-25) cm~3/W~2). Above the ablation threshold, the diameter values follow logarithmic dependence in the fluence range investigated, reaching similar values around 45 μm at 30 J/cm~2 with 51 ± 1 μm 1/e~2 beam diameter on the target surface as derived from the diameter regression technique. The onset of plasma formation derived from the changes in the energy reflected from the processed surface is also found to be similar for the three glasses (9.5, 10, and 8.0 J/cm~2) in good correlation with the ablation threshold values.