# Advances in High-Power, Ultrashort Pulse DPSSL Technologies at HiLASE
## 1 Introduction  
Compact, kW-class, near-infrared pulsed lasers are becoming highly important for both science and industry. In particular, picosecond and sub-picosecond lasers have turned out to be indispensable tools in laser material processing. They are beneficial primarily for their highly accurate and special processing of many materials, such as the micro-patterning of large surfaces [1; 2; 3], or the processing of carbon-reinforced plastics [4]. Specifically, Yb:YAG lasers have lately reached a magic value of an average output power of 1 kW while their pulse energy exceeded 1 ] [5], both in burst mode [6] and continuous pulsing [7; 8], although often with a pulse length exceeding 10 ps.  
Rapid progress is also expected in mid-infrared and UV spectral regions. The growth of large volume conversion crystals and the advent of new kinds of nonlinear crystals enables efficient conversion of high average power and high energy picosecond near-infrared (near-IR) pulses with a wavelength of 1 \(\upmu\)m to deep ultraviolet (UV) [9; 10] or mid-infrared (mid-IR) spectral regions [11; 12]. This broadens the application potential of near-infrared ultrashort-pulse lasers in high-tech applications. For example, high-power picosecond laser pulses of fundamental and harmonic (up to fifth) frequencies will enable high-speed, high-precision micro- and nano-structuring of large surface areas on various materials with flat-top beams using diffraction optics and interference techniques [13]. Ultrashort laser pulses in the mid-IR spectral range can also open ways for 3D direct laser writing inside biologicalsamples, polymer materials, and narrow-bandgap semiconductors which are opaque for visible and near-IR laser light [14]. Furthermore, tunable spectral sources from near-IR to mid-IR at enhanced laser power can improve the sensitivity of infrared spectroscopy in applications for monitoring trace gases in atmosphere and biomedicine [15]. Besides industrial applications, near-IR picosecond pulses are also essential, for example, in THz waves generation [16; 17], attosecond science [18], or femtosecond optical parametric chirped pulse amplification (OPCPA) pumping [19].  
Near-IR thin-disk lasers also proved their ability to generate high average power short pulses, which are suitable for laser produced plasma-based (LPP) [20], free electron laser-based (FEL) [21; 22], or inverse Compton scattering-based (ICS) [23] extreme UV radiation sources. It helps, for example, to construct new stations for semiconductor lithography at 13.5 nm or 6.7 nm and to support evolution in electronics. An important requirement for application in lithography is stability of all laser parameters and compactness in the actual application field. Intensive study has been performed at the HiLASE Center to confirm the high beam quality thin-disk laser with good pointing stability [24; 25]. Higher conversion efficiency from pump pulse to amplified pulse energy is the key to realizing these characteristics. Mid-IR, compact, high average power diode-pumped sources based on Ho-doped materials also have potential to directly pump powerful CO\({}_{2}\) lasers, which would make the CO\({}_{2}\) lasers more compact for lithographic stations [26].  
In this paper, we report on progress in the development of ultrashort pulsed laser technology and laser components development since 2015, when a first review paper was published [27]. The technology of Yb:YAG thin-disk lasers Perla A, B, and C emitting in near-infrared ranges has matured, and goals have been updated to finally exceed 1 kW of average power and 1 J of pulse energy in following years (Figure 1). Nowadays, up to 500 W of average power can be generated. Together with the frequency conversion of these lasers and the construction of a new mid-IR disk laser beamline, the spectral range from UV (200 nm) to mid-IR (10 \(\upmu\)m) in picosecond and sub-picosecond temporal range should be covered (Figure 1). This progress, in development since 2015, is summarized in Tables 1 and 2.