By the use of a 16 W femtosecond laser we demonstrate steep wall angles and small feature spacings for non-thermal melt-free laser drilling and contour cutting of 100 to 500 μm thick metals like Cu-alloy, stainless steel, titanium and tantalum as well as for ceramics and polymer (polycarbonate). Especially processing of thin materials is a challenge, because heat accumulation in thermal processing usually causes mechanical distortion or edge melting as well as material.
The combination of beam deflection in trepanning optics and sample motion allowed us to work in a special "laser milling mode" with rotating beam. Zero degree taper angle as well as positive or negative tapers can be achieved at micrometer scale.
In this paper the results of micromachining of polycarbonate polymer foils and SUS304 stainless steel thin sheets are reported, performed by an industrial femtosecond laser operated at 1030 nm and 515 nm (SHG) wavelength. For a typical Galvoscanner setup the ablation scribing was investigated at a spotsize of 20 μm which is typical for contemporary feature size used for medical stents. At this value a maximum peak intensity of 6.4*1013 W/cm² can be reached, which enables significant nonlinear absorption in the polymer.
Laser pulse overlap was varied to optimize overlap values for best edge quality and for best ablation rate.
From the results some guidelines for complete cutting of thin sheets were derived. For an acceptable edge quality a maximum ablation rate of 2.6 mm³/min was demonstrated for stainless steel thin sheets, whereas up to 9,4 mm³/min have been reached for polycarbonate.
For SUS304 the use of the SHG does not increase ablation rate or edge quality, whereas for polycarbonate the cutting quality is better, but at a smaller ablation rate.
In medical device manufacturing there is an increasing interest to enhance machining of biocompatible materials on a
micrometer scale. Obviously there is a trend to generate smaller device structures like cavities, slits or total size of the
device to address new applications. Another trend points to surface modification, which allows controlling selective
growth of defined biological cell types on medical implants.
In both cases it is interesting to establish machining methods with minimized thermal impact, because biocompatible
materials often show degradation of mechanical properties under thermal treatment. Typical examples for this effect is
embrittlement of stainless steel at the edge of a cutting slit, which is caused by oxidation and phase change. Also for
Nitinol (NiTi alloy) which is used as another stent material reduction of shape-memory behavior is known if cutting
temperature is too high. For newest biodegradable materials like Polylactic acid (PLA) based polymers, lowest thermal
impact is required due to PLA softening point (65°C) and melting temperature (~170 °C ).
Laser machining with ultra-short pulse lasers is a solution for this problem. In our work we demonstrate a clean laser cut
of NiTi and PLA based polymers with a high repetition-rate 1030 nm, 400-800 fs laser source at a pulse energy of up to
50 μJ and laser repetition rate of up to 500 kHz.
Continuous carbon fibre reinforced plastics (CFRP) are recognized as having a significant lightweight construction potential for a wide variety of industrial applications. However, a today‘s barrier for a comprehensive dissemination of CFRP structures is the lack of economic, quick and reliable manufacture processes, e.g. the cutting and drilling steps. In this paper, the capability of using pulsed disk lasers in CFRP machining is discussed. In CFRP processing with NIR lasers, carbon fibers show excellent optical absorption and heat dissipation, contrary to the plastics matrix. Therefore heat dissipation away from the laser focus into the material is driven by heat conduction of the fibres. The matrix is heated indirectly by heat transfer from the fibres. To cut CFRP, it is required to reach the melting temperature for thermoplastic matrix materials or the disintegration temperature for thermoset systems as well as the sublimation temperature of the reinforcing fibers simultaneously. One solution for this problem is to use short pulse nanosecond lasers. We have investigated CFRP cutting and drilling with such a laser (max. 7 mJ @ 10 kHz, 30 ns). This laser offers the opportunity of wide range parameter tuning for systematic process optimization. By applying drilling and cutting operations based on galvanometer scanning techniques in multi-cycle mode, excellent surface and edge characteristics in terms of delamination-free and intact fiber-matrix interface were achieved. The results indicate that nanosecond disk laser machining could consequently be a suitable tool for the automotive and aircraft industry for cutting and drilling steps.
If laser scanning microscopy with enhanced spatial or temporal resolution is performed on sensible biological samples it is essential to prevent damage or substantial alteration of the object due to intense laser illumination. Considering a simplified model for temperature rise and photochemical reactions conclusions concerning scanning and measuring conditions are drawn. A method for improving the spatial resolution of the laser scanning microscope by image processing is described. This method is based on a local deconvolution procedure and yields an improvement of the resolution of about 1. 7 in a discussed example. It is applied to images of chromosomes. For time-resolved fluorescence microscopy on the basis of time-correlated single photon counting methods for obtaining images of fluorescence decay parameters under the condition of weak fluorescence intensity are discussed. As an example intensity and relaxation time images of a tumour cell incubated with HpD are presented. 1.