**Acknowledgements**

determines the size of the wire. As demand for microwire increases across the manufacturing sectors, large scale machines are currently used to produce wire of microlevel, but it is not economical in an industry. Micromachining with ultrafast laser, which made the hole size small, has been reported. Smooth surfaces, also, are generally preferred for precision machin‐ ing. **Figure 14** shows the SEM view of the bearing surface of drilled hole in dies. The compar‐ ison with fs and ns laser drilling results shows the advantage of fs laser drilling. **Figure 14(a)** shows a ripple for which spacing is generally <200 nm. The orientations of the ripple structures are parallel to each other. Similar ripple structure has been observed in various materials for fs laser drilling. Uneven and rough structures are shown in **Figure 14(b)**. It is clear that the material removal during the dies-hole drilling is accomplished by the formation of melt. Compared with two methods, micromachining with ultrafast laser creates much cleaner and

Ultrafast laser micromachining is an emerging technology for high-precision and cold-ablation material processing. For its advantages and potential uses, suitable ultrafast laser and laser operating parameters such as wavelength, repetition rate, average power, pulse duration, spot size, beam quality, and sample moving speed must be selected to achieve desired high-quality micromachining. In the near future, ultrafast laser micromachining will be used in various sectors including sub-micron material processing, surface structuring, photonics devices,

In conclusion, a room-temperature, diode-pumped, dual-crystal Yb:KGW laser operating as a Q-switched oscillator or regenerative amplifier has been developed where the gain bandwidth was extended by using Ng-cut + Np-cut or Ng-cut + Ng-cut configuration. It was shown that fine-tuning the mode sizes in the crystals in the resonator with high pump power is important to obtain the maximal output power since thermal effects change the operation point in the stability zone and mode matching conditions. It was demonstrated simply by shifting the position of the end mirror along optical axis in the resonator. Optimization of the laser resonator increased the output power from 18 to 24 W in case of Q-switched oscillator and from 17 to 21 W in case of regenerative amplifier. Such optimization of laser resonator improves not only output power but also stability of laser operation, especially for Ng-cut + Ng-cut crystal

The use of this regenerative amplifier enabled to create compact, high average power, high brightness, diode-pumped femtosecond Yb:KGW laser system. This laser, which utilized a CPA MOPA laser scheme, consisted of master oscillator, regenerative amplifier, and stretchercompressor module. It was capable of delivering 15 W of average output power with a pulse

This level of output power and quality of a laser beam are practically the same as the output power of Yb:KGW/Yb:KYW thin-disk lasers with medium level of output power [6, 9].

~1.2) at pulse

biomedical devices, microfluidics, displays, and solar applications.

configuration, that is manifest in reduction of output power fluctuations.

duration down to 182 fs high in a nearly diffraction limited output beam (*M*<sup>2</sup>

smoother hole.

50 High Energy and Short Pulse Lasers

**5. Conclusion**

repetition rates of 50–500 kHz.

Parts of this chapter are reproduced from authors' previous publications [15, 25, 26].
