Hello there,
I've been working on fs laser processing on the surface of transparent materials, i.e. BK7, sodalime glass slide, polymers such as PMMA. I am trying to optimize laser process (given that pulse duration is 400fs and wavelength is 1030nm) so that after laser ablation (trenching, grooving, free form cavities) the surface roughness remains as small as possible (ideally still transparent).
I can achieve some 500nm Ra after laser machining myself. Anyone here doing better or knows how to do it better than that?
Cheers
For your second question about polymer smoothing, you can look into the direction of thermal post-treament. There are approaches for example to obtain a thermal reflow of PMMA layers, after 3D e-beam lithography. You can check out this paper for instance: Schleunitz, A., & Schift, H. (2010). Fabrication of 3D nanoimprint stamps with continuous reliefs using dose-modulated electron beam lithography and thermal reflow. Journal of Micromechanics and Microengineering, 20(9), 095002. A simple hot plate at ambient conditions and at a constant temperature is used for thermal reflowing of the polymer.
You can try a laser polish after ablation for glasses with longer pulses. There is some literature about this. The pulse duration depends on how much topology you would like to be flattened. Probably ns for flattening shallow topography, longer for higher. Be aware of strain induced by this.
Direct thermal reflow by a furnace heating never worked out for me. I guess the local surface geometries of laser processed and E-beam processed surfaces are quite different. And the laser one prevents reflow to happen. Otherwise it is some physico-chemical property different between the PMMA polymers.
On the other side, MIR lasers such as a CO2 laser do cause surface material melt and reflow, and hence an improved surface smoothness.