ALP - applied laser and photonics group

Research Focus

Laser processing of technical ceramics, semiconductors and superconductors

The AG alp pursues three approaches in this area which are based on different laser technologies. On the one hand, these are the application of fiber lasers in continuous wave and pulsed operation for processing ceramics such as aluminum nitride, aluminum oxide and semiconductors such as silicon carbide. The classical machining methods of cutting, drilling and structuring are investigated and optimized for specific applications. In addition, alternative annealing processes to improve the electrical transition between metallic layers and the semiconductor SiC are being researched in the field of silicon carbide. On the other hand, innovative ultrashort pulse technology is also used for material processing, which permits particularly gentle processing due to its short pulse lengths. This applies not only to ceramics and semiconductors but also to superconductors. In addition, water jet guided laser cutting with pulsed laser systems is used to process semiconductors and superconductors in particular.

Monitoring of laser material processing

Reliable online process monitoring plays a key role in the development of fully automated laser manufacturing processes. The focus of research here is on the development and implementation of optical systems and algorithms for online monitoring of cut-offs and quality features when cutting metals with high-power fiber lasers and powder deposition welding with these beam sources. Different sensor concepts are developed and qualified under industrial conditions.

Design of the laser cutting system with detailed illustration of the sensor system.

Nanostructuring of conductive and non-conductive materials

Laser-induced nanostructuring and the associated functionalization of technical surfaces are currently revolutionizing applications in medical technology, biotechnology, tribology and electronics. A prominent example is the targeted adjustment of hydrophilic and hydrophobic properties of surfaces. In this field, the AG alp is researching fundamental questions concerning the production of these nanostructures on conductive and non-conductive materials, the production of high-quality flat nanostructures and the optimization of these processes for various applications according to requirements.

Laser-induced periodic surface structures (LIPSS) on sapphire

Glass processing with ultrashort laser pulses

Due to their excellent physical and chemical properties, glasses are a versatile class of materials. Applications range from optics to electronics, telecommunications and biomedicine. Due to their high transparency in the visible and near infrared, technical glasses only become accessible through the use of ultra-short pulse lasers for high-quality laser micro material processing.
The AG alp deals with the ultrashort pulse processing of glasses in the creation of free forms for the production of optical components. By means of an internal laser modification of the substrates, three-dimensional structures can also be removed from the material in a selective etching process.
In the field of nanostructuring, AG alp is researching the creation of laser-induced periodic surface structures on dielectrics. The large-area, homogeneous structuring of glasses with structure periods < 1 µm enables a broad application spectrum from optical diffraction gratings to the control of biological cell growth.

Metal processing with high power fiber lasers

In the field of metal processing, AG alp focuses on high-power fiber lasers. In combination with innovative system technology (e.g. 5-axis capable), AG alp uses high-power fiber lasers with an output of up to 4 kW to process metals in cutting and welding processes. In addition to classical fusion cutting, laser remote cutting is also being investigated here. Using high-speed galvanometer scanners, high cutting speeds can be achieved with low heat influences and thus high process quality. In the field of laser welding, the focus is on laser metal depositioning. By introducing metal powders of the same or dissimilar type into the laser beam, free forms can be applied in 3 dimensions. In addition, modulated laser radiation is used to investigate the welding of foreign material connections for applications such as electromobility.

Application of a 3D protective layer by means of laser metal depositioning.

Laser manufacturing processes for plastics

In practice, laser material processing of plastics primarily takes place in the form of plastic welding, in particular laser transmission welding of partially transparent components. In addition to this classical process with diode lasers, the AG alp also deals with the introduction of fiber lasers using diffractive beam shaping optics. The innovative welding of transparent joining partners with the ultrashort pulse laser also opens up new applications, for example in medical technology. Remarkable results are achieved in terms of process speed and process quality.
With a revolutionary approach, ultrashort pulse laser technology enables the three-dimensional laser direct structuring of microfluidic channels in transparent polymer substrates. For a complete functionalization of plastic substrates in microsystem technology, further laser-based processes complement the technological approach:

Laser direct structuring with pulsed laser systems for the metallization of plastics
Generation of microoptical functional elements by refractive index modification by ultrashort pulse and excimer lasers.

Laser direct writing of three-dimensional microchannels

Beam shaping to increase process efficiency and quality of machining processes

Through innovative beam shaping concepts, the energy and process efficiency as well as the quality of a laser material processing can be increased many times. In addition, beam shaping concepts enable completely new applications. In the field of beam shaping, AG alp researches the calculation and use of diffractive optical elements and spatial light modulators.

Planar polymer optical Bragg sensors

The classical Bragg sensor technology relies on fiber Bragg gratings for measuring temperatures and tensile stresses. Compared to Bragg gratings in fibers, planar processing allows a more effective integration of the sensor elements into photonic systems on the one hand, and a broader range of applications, e.g. multiaxial tension and compression stress measurements or shapesensors on the other. At the AG alp, planar polymer Bragg gratings and waveguides are produced by a single-stage excimer laser process (single writing step). Optical structures are generated by mask exposure in different optical standard polymers. Current research is carried out in the field of temperature, humidity, compression and tensile stress, shape and refractive index sensors with specially manufactured and assembled sensor elements.

Fabrication of planar Bragg grating sensors based

Surface functionalization of inorganic Bragg sensors

The sensory analysis of liquids and gases is of significant interest for many technology areas such as medical technology, chemistry, production engineering or food processing. In this context, AG alp has been dealing with optical sensor technology based on planar Bragg gratings for several years. Sensors based on this concept make it possible to make qualitative statements about the refractive index of an applied analyte and to describe biotechnological processes. The sensitivity and selectivity of the sensor structure can be influenced by the targeted modification of the sensor surface and at the same time the sensory functionality can be considerably extended. The modification of the surface enables the use of the sensor structure in the field of chemical, biochemical, immunological and molecular biological analysis.

Functionalized Bragg sensor on silicon substrate

Integrated Optics / Optofluidics

The production of integrated optical elements is based on technologies of the semiconductor industry. The AG alp uses appropriate photolithographic methods as well as wet and dry chemical etching processes for the production of integrated optical and microfluidic components (optofluidics) in photopolymers.
The aim of this research is the sensor technology of technical fluids and biological components for applications in process engineering, biotechnology and medical technology.

Section of a microfluidic channel with free-standing waveguide and integrated Bragg grating.

3D laser direct writing

The research work of the AG alp in the field of 3D laser direct writing focuses firstly on process optimization for the production of photonic components. The local selective exposure of positive and negative photoresists as well as hybrid polymers enables new designs of optical components such as polarization rotators, refractive and diffractive lenses or diffraction gratings. Secondly, new components can be realized and the effective build-up rate increased by linking them with photolithographic processes.

Microreflector fabricated by 3D laser direct write process

Selective Laser Melting (Metal)

Selective laser melting enables the generative production of three-dimensional structures from metals. In this technological field, AG alp has equipment that is unique in Europe. In particular, this includes a hybrid production machine that combines selective laser melting and micro milling to produce surfaces of the highest quality. In addition, a hot isostatic press with quenching is available. Based on this, one of the research focuses of the AG alp is the optimization of the manufacturing processes for different alloys, taking into account the complete process chain. This also includes the consideration of powder quality as well as downstream machining processes. On the application side, research focuses on the individualized adaptation of material properties such as the modulus of elasticity for generatively manufactured medical devices and implants.

Example of a 3D printed metal grid structure

Two-photon absorption (photopolymers)

The production of three-dimensional microscopic components with resolutions in the nanometer range on the basis of two-photon polymerization in photopolymers is a key technology for medical and microoptical applications. In this field, AG alp is working on the optimization of process speed through innovative beam guidance and beam shaping concepts as well as a hybrid approach of different laser-based processes to generate macroscopic components with nanoscopic properties.