Observation of pitting due to field enhanced surface absorption during laser assisted cleaning of translucent particulates off metal surfaces

The field enhanced surface absorption that occurs as a result of focusing of the incident radiation through transparent/semi-transparent contaminant particulates, in addition to their removal, can also leave its signature on the surface in the form of pitting. This has been experimentally verified in case of removal of CsNO3 particulates off stainless steel surface with sub-nanosecond to nanosecond pulses of 1064 nm, 532 nm, and 355 nm wavelengths for which the particulates are semi-transparent. The threshold fluence for such pit formation has been studied as a function of both wavelength and pulse duration of the coherent radiation and was always found to be much higher than the cleaning threshold. Qualitative explanations have been offered to the observed experimental results.