## 1 Introduction  
Lens arrays have been demonstrated to be applied in numerous fields of optics such as, e.g., in sensor applications as in Shack-Hartman sensors for wave front detection [1], in imaging systems as for microscopy [2] or photolithography [3] or for increasing the light extraction efficiency in organic light-emitting diodes/devices [4, 5]. Furthermore, lens arrays are used for beam homogenization to ensure uniform illumination as being employed in, e.g., beam-shaping of excimer laser beam profile [6], petawatt-class Ti:sapphire amplifier [7], planar laser diagnostics [8] or illumination systems [9]. Two types of lens array based beam homogenizers are discussed in literature, the non-imaging applying one lens array and a Fourier lens and the imaging beam homogenizer including two lens arrays and a Fourier lens [10]. Figure 1 shows an imaging beam homogenizer with two lens arrays LA1 and LA2 as well as a Fourier lens. The first lens array is used to split the incoming light into several beamlets which are located on the second lens array and further focused and overlapped by a Fourier lens, forming a homogeneous intensity profile. The contour of the final beam profile is given by the footprint of the single elements within the lens arrays. Using Equation (1) [6], the size of the corresponding Top-Hat profile in the focal plane of the Fourier lens can be calculated with \(p\) being the lens pitch, \(a\) the distance between the two lens arrays, \(F\) the focal length of the Fourier lens, as well as \(f_{1}\) and \(f_{2}\) the arrays' focal lengths. \[D=p\frac{F}{f_{1}\cdot f_{2}}[(f_{1}+f_{2})-a] \tag{1}\]If the imaging condition (\(f_{2}\approx a\)) is fulfilled, the size of the Top-Hat can be calculated with the simplified Equation (2) while the distance \(b\) between the second lens array and the Fourier lens can be chosen freely due to not affecting the size of the formed Top-Hat (see Equation (2)) and will only influence its divergence [7,11]. \[D=p\frac{F}{a} \tag{2}\]  
While lens arrays are often fabricated via thermal reflow processes [22, 23, 24], several alternative methods such as ink-jetting [25], reactive ion etching [26] or hot embossing [27] have been demonstrated. Recently, femtosecond laser-based lens array fabrication techniques have been developed which are summarized in Table 1. [PERSON] et al. [12] demonstrated the usage of the femtosecond laser in a backside wet etching process for geometry generation, which is followed by thermal annealing to smoothen the surface to fabricate microlens arrays in silica. [PERSON] et al. [13] and [PERSON] et al. [14] showed the microlens array fabrication by femtosecond laser production of microholes and a subsequent wet etching step forming the lens geometry on silicon as well as silica and sapphire, respectively. [PERSON] et al. [15] modified photosensitive glass with a femtosecond laser which is further processed via thermal treatment, wet etching and annealing to fabricate the finalized optic. [PERSON] et al. [16] fabricated microlens arrays with femtosecond lasers, while a single pulse is sufficient to form a single lens in PDMS by the laser-induced plasma expansion and its mechanical