Structuring of materials is the most general approach for controlling waves in solids. As spin waves-eigen-excitations of the electrons' spin system-are free from Joule heating, they are of interest for a range of applications, such as processing 1-5 , filtering 6-8 and short-time data storage 9 . Whereas all these applications rely on predefined constant structures, a dynamic variation of the structures would provide additional, novel applications. Here, we present an approach for producing fully tunable, two-dimensionally structured magnetic materials. Using a laser, we create thermal landscapes in a magnetic medium that result in modulations of the saturation magnetization and in the control of spin-wave characteristics. This method is demonstrated by the realization of fully reconfigurable oneand two-dimensional magnonic crystals-artificial periodic magnetic lattices.There are two general approaches in designing the properties of a material: changing its chemical composition and structuring. Structuring has been used to control mechanical 10 , optical 11 , and even magnetic properties 12,13 . Periodic variation of the magnetic material's parameters allows the realization of magnonic crystals with novel properties not found in the unstructured material. For example, the dispersion relation of spin waves can be controlled to achieve new schemes for spin-wave-based computing [1][2][3][4][5][14][15][16][17] . The spin-wave dispersion relation depends on many parameters, such as the geometry of the spin-wave waveguide (film thickness and waveguide width), external magnetic field H ext , and saturation magnetization M S . In fact, all of these parameters have already been used to fabricate magnonic crystals [6][7][8]12,13,[18][19][20] : arrays of metallic stripes, etched grooves or antidots, biasing magnetic field or periodic variation of the saturation magnetization using ion implantation.However, all available methods for the fabrication of such spintronic devices result in spatially constant magnetic materials. J. Topp et al. have shown that the parameters of magnetic materials can be changed locally after the rather time-consuming fabrication of the spintronic device 21 -but the functionality of the device stays the same. Here, we present an alternative method for structuring and use it for the manipulation of spin waves-namely fully tunable light patterns (computer-generated holograms), in which optically induced thermal patterns/landscapes modify the spinwave dispersion relation and, hence, the propagation. Thus, the proposed optically reconfigurable magnetic material allows the functionality of a magnetic element to be tuned on demand; the same element can be used as a conduit, a logic gate or a data buffering element.The set-up used for the realization of the light patterns consists of a continuous wave laser as light source, an acousto-optical modulator for temporal intensity control, and a spatial light modulator for spatial intensity control (see Fig. 1a). To study the influence of the thermal gradient ...

functional elements, chiral photonic crystals, photonic metamaterials and quasicrystals. With this technology becoming commercially available, [ 1 ] many novel ideas have been realized by scientists around the world. Some of these developments can already be seen as new research areas enabled by 3D µ-printing.Many excellent reviews of the underlying technology have recently been published, and we give here just a short selection. [2][3][4][5] With the present progress report we want to summarize the tremendous technological development during the last fi ve years as well as to give an overview over some vastly growing research fi elds enabled by this development. As the number of research papers based on 3D µ-printing as enabling technology is exploding, we intend to categorize the most recent developments to identify future research directions and possible novel fi elds for the years to come. Recent Technological Advances in 3D µ-PrintingFrom the fi rst proof-of-principle in 1997, [ 6 ] the µ-printing community has continuously been expanding the structuring capabilities of µ-printing systems overcoming limitations such as structuring speed, sample volume, complicated pre and post processing, as well as minimum feature size and resolution. Progress is made along two directions: First, extending the aforementioned benchmarks of µ-printing systems. Second, techniques that move µ-printed structures towards functional devices. These two directions obviously are intertwined and require interdisciplinary research efforts on new photocurable materials, complex light-matter interaction, reaction kinetics as well as processes on a molecular level infl uencing structure formation. The most infl uential technological advances are summarized in this section.Section 2.1. covers recent work leading to a tremendous increase of the capabilities of µ-printing systems. Section 2.2. describes superresolution concepts exploiting light-matter interactions to achieve smaller feature sizes and higher structural resolution. Section 2.3. reviews spatial light modulator (SLM) based laser lithography providing additional degrees of freedom by shaping the wavefront of the laser beam. Laser Sources, Scanning Devices, and Writing GeometryThe high complexity of ultrafast fs-lasers drives the community to look for alternative laser sources, leading to cost and In this progress report the development of three-dimensional µ-printing and its impact as an enabling technology onto different scientifi c fi elds is reviewed. Driven by direct laser writing via two-photon absorption, the technology has reached a level of maturity and ease of application such that 3D printing on the micrometer scale can now be considered. While the underlying technology is still developing towards higher resolution and increasing speed of fabrication, the last fi ve years have seen new fi elds rising that were obviously enabled by 3D µ-printing. Among the recent technological developments discussed in this progress report are the fi elds of super-resolution lithography ...

We control the point-spread-function of high numerical aperture objectives used for direct laser writing with a spatial light modulator. Combining aberration correction with different types of amplitude filters to reduce the aspect ratio of the point-spread-function enhances the structural and optical quality of woodpile photonic crystals. Here, aberration correction is crucial to ensure the functionality of the filters. Measured point-spread-functions compare well with numerical calculations and with structures generated by direct laser writing. The shaped point-spread-function not only influences the maximum achievable three-dimensional resolution but also proximity effect and optical performance of woodpile photonic crystals.

We review the fundamental concepts of direct laser writing (DLW) of 3D metallic structures via photoreduction and give an overview over the state-of-the-art. On the one hand, metallic microstructures and nanostructures play an important role in photonic applications such as resonators, antennas, metamaterials, and polarizers. On the other hand, DLW offers a flexible and fast way to fabricate microstructures. Because the underlying mechanisms from the first photoreaction to the final 3D microstructure are quite complex and not yet well controlled, we believe that a review of the photochemistry and photophysics of the direct writing process of metal structures helps to promote development in this field. To this end, we first summarize the principles of electroplating and electroless plating as this helps understand the photoresist’s components. Next, we describe the different photoreducing agents and photoreactions that lead to metal seeds and in consequence to nanoparticles. This is followed by insights into the physics of nanoparticle agglomeration to the desired microstructure. Finally, we give an overview over the state-of-the-art of DLW metallic 3D microstructures.

The generation of multi foci is an established method for high-speed parallel direct laser writing, scanning microscopy and for optical tweezer arrays. However, the quality of multi foci reduces with increasing resolution due to interference effects. Here, we report on a spatial-light-modulator-based method that allows for highly uniform, close to Gaussian spots with diffraction limited resolution using a wavelength of 780 nm. We introduce modifications of a standard algorithm that calculates a field distribution on the entrance pupil of a high numerical aperture objective splitting the focal volume into a multitude of spots. Our modified algorithm compares favourably to a commonly used algorithm in full vectorial calculations as well as in point-spread-function measurements. The lateral and axial resolution limits of spots generated by the new algorithm are found to be close to the diffraction limit.