# A Versatile 100 Hz Laser System with Few-Cycle and TeraWatt Pulses for Applications
## 6 Applications
### Femtosecond Cutting  
One of the advantages of cutting with ultrashort laser pulses is that the thermal load on the material during the process is negligible [28; 29]; therefore, the edge of the trimmed surface is clean without droplets and barbs. This is especially important in case of porous solid materials, where any thermal effect would result in large, melted droplets.  
Figure 13: The spatial stability measurement of the liquid sheet target. Insert: the schematics of the setup.  
The secondary target, the neutron converter, for the laser-generated neutron experiments [26] is made of granulated C\({}_{2}\)D\({}_{4}\). The powder is put into a round, stainless steel form, and pressed down with a 10 t device, resulting in a round tablet with a thickness between 0.5 mm and 1.2 mm. The accelerated deuterons hit this C\({}_{2}\)D\({}_{4}\) tablet and generate neutrons through DD fusion reaction. To monitor and control deuteron acceleration from the liquid jet described above, the deuteron beam needs to be monitored and let through the tablet upon the irradiation. Hence, a sufficiently small hole, with a diameter of 0.5 mm, must be cut into the tablet. Mechanical boring and water jet cutting made this porous tablet crack into several pieces, while traditional laser cutting melted and pulverized the surroundings of the hole. Hence, we explored cutting with laser pulses from the FE. Since the diameter of the hole is relatively large, direct laser boring is out of question. Instead, an optical assembly was designed and implemented, when the hole is cut (instead of bored) with tightly focused femtosecond pulses.  
The setup consisted of an optical shutter, a motorized rotation stage mounted on a three-axis translation stage system, and a focusing element. The former enabled the regulation of the number of pulses reaching the surface during the cutting process. Focusing was performed with a 1\" bi-convex lens with a focal length of 25.4 mm (Figure 14a), providing a focal spot of 15.1 \(\upmu\)m 1/e\({}^{2}\) on the sample. For the positioning of the sample, the rotation stage was put onto a manual three-axis stage. The horizontal positioning of the rotation axis of the sample relative to the optical axis of the lens allowed us to set the diameter of the hole. The smallest focal spot on the surface was adjusted by shifting the sample vertically, and was monitored and controlled regularly upon the cutting process. The precise, uniform, and constant-speed rotation was ensured by a DC servo motor-driven rotation stage. The optimal rotation speed and repetition rate were determined empirically.  
For cutting the tablets, we used the \(-\)450 \(\upmu\)J laser pulses from the FE, compressed in bulk and with chirped mirrors. We explored the cutting conditions for various hole diameters and tablet thicknesses. As for the extremes, it took around 5 min to cut a hole with a diameter of 0.5 mm into a 0.5 mm thick sample, while the preparation of a hole with a diameter twice this size in a 1 mm thick sample took almost 30 min. As can be seen, the hole was a regular circle with a very clean edge (Figure 14b).  
Figure 14: The cutting assembly (**a**), and the hole precision-cut onto a pressed C\({}_{2}\)D\({}_{4}\) tablet (**b**).