Abstract
This paper reports for the first time on the direct creating microcavities in sub-surface of stainless steel using a single Nd:YAG laser pulse. The low peak power density is used in the process, which is in the order of 1 MW/cm(2). The formation of the microcavities in the sub-surface of stainless steel is an evidence of volume expulsion during laser-metal interaction. Direct patterning in the sub-surface of stainless steel is demonstrated by realizing a series of microcavities to form a pre-designed pattern. Potential applications of sub-surface patterning in metal, such as security marking, micro-heater, micro-insulator and micro-sensor, are discussed.
Highlights
Based on the experimental observations, we suggest that the microcavity at sub-surface of metal could be generated by an extremely special drilling process
The subsurface microcavities created by a series of single laser pulse were examined by scanning electron microscopy (SEM), optical microscopy, non-destructive computed tomography (CT) scan and x-ray imaging
The flexible changes in electrical resistivity [21], acoustic [22] and electromagnetic wave propagation and reflection properties [23] in a porous patterned metal may be designed to fabricate micro-devices, such as microheater, micro-insulator and sensors, etc. It is demonstrated for the first time on direct creating of microcavities in the sub-surface of stainless steel using a Nd:YAG laser pulse
Summary
Direct laser writing and patterning inside transparent materials is a well known technology. Optical engraving of three dimensional figures is one of the typical applications [1] In this technique, laser power density is controlled to be greater than the material damage threshold to induce microcracks [2], which results in an opaque portion and forms desired marks inside the transparent material. The change in refractive index is the result of permanent structural change through densification [4] or formation of defects [5] caused by the high peak power of fs laser This finding has led to wide investigations on direct laser writing waveguides and optical devices inside transparent materials [5,6]. The concealment of the patterns can be applied as security marking in automotive, aerospace and military industries
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