Claus Schnitzler

Dense Spatial Multiplexing Enables High Brightness Multi-kW Diode Laser Systems

The materials processing industry has recently mandated the need for more efficient laser systems with higher beam quality and longer life. Current multiplexing techniques, state-of-the-art laser diodes and novel cooling designs are now emerging as possibilities to meet the ever demanding industry needs. This paper describes the design and initial results of a direct diode system that is aimed at delivering 1.5 kW of output power and a beam divergence of 40 mm mrad on a long life macro-channel cooler. The design entails multiplexing 2 wavelength combined beams and 2 polarization combined beams. Each of the four branches of the direct diode system utilizes a novel stacking and cooling design. The results from one of these branches, 1 wavelength and 1 polarization, are presented where the light is coupled into a fiber with a 400 μm core diameter and a NA of 0.22. Each branch consists of 60 diode laser mini-arrays, where each mini-array consists of four 100 μm wide emitters and a lateral fill factor of 50%. An output power of 500W at 10°C water temperature and 420 W at 25°C are demonstrated through the 400 μm fiber.

Soldering techniques for the assembly of high power solid-state lasers

Soldering techniques are of increasing interest for the manufacturing of laser systems. High thermal conductance required for effective and long-term-stable cooling of laser components and a low sensibility to environmental influences like temperature changes and humidity are the main reasons to join components by soldering. Compared to conventional mounting techniques, soldering demands highly complex process control. Detailed knowledge about the influence of mechanical stress caused by thermal expansion mismatch is necessary to properly choose not only the process strategy but also the dimensions of the components. This paper reports on the development of soldering techniques for the surface-mounted assembly of laser components such as lenses, mirrors, laser-crystals and nonlinear crystals used for the assembly of a miniaturized marking laser system “MicroSlab”[1].

Highly flexible ultrafast laser system with 260W average power

A flexible ultrafast laser amplifier system based on Ytterbium Innoslab technology with an average power exceeding 200W is presented. The pulse duration of the system can be continuously tuned between 500fs and 6ps, limited only by the amplification bandwidth of Yb:YAG and the stretcher of the seed source. The repetition rate can be varied from 26.6MHz down to 1MHz. For the ps-regime more than 200μJ and for the fs-regime more than 50μJ are demonstrated without the need of temporal compression of the high power beam after the amplifier. Spectral bandwidth is close to the transform limit of the shortest measured pulses. Beam quality is measured to be near the diffraction limit (M2<1.3).

Highly efficient diode-end-pumped Nd:YAG slab laser

High power diode pumped solid state lasers are auspicious sources for various applications in material processing. The solid state laser we report on is a Nd:YAG slab laser, that is partially end pumped from two ends by the line focus of two diode laser stacks. The pumped volume has a rectangular cross section. The resonator is configured, so that it is stable in the plane of small dimension and off axis unstable in the plane of large dimension of the gain cross section. Unlike conventional slab laser design, in which the laser beam takes zick zack path inside the slab crystal, in the present design the beam goes straight through the crystal with perpendicular end faces.

Design of efficient freeform lenses for mass-market illumination applications using hybrid algorithms

We report on the development and experimental analysis of novel freeform polymer lenses for the uniform illumination of a target area using high-brightness LED. In a first step, the LED module was centered over the illuminated area and the two faces of a freeform lens were designed for homogeneous and efficient light distribution. In a second step, the system was extended for an off-axis target, the overall size was reduced and structures for automated alignment with respect to the LED were included. Photometric analyses were used for each system and were found to be in good agreement with simulations.

Femtosecond Innoslab amplifier with 300W average power and pulse energies in the mJ-regime

We demonstrate a femtosecond Yb:YAG InnoSlab laser amplifier producing <3mJ pulse energy at 100kHz pulse repetition rate. The minimal pulse duration is <1ps resulting in pulse powers <3GW. High energy and high average power could be obtained with the use of chirped pulse amplification on the power amplifier end. The laser setup consists of a seed laser with 10mW average power at pulse repetition rates of 100kHz to 1MHz, a pre-amplifier stage, a highpower InnoSlab-amplifier stage and a grating based pulse compressor. This laser source is suited for pumping of OPCPA setups und parallelisation of applications in materials processing.

Optical system design for a reflector-based LED food lighting module

We report on the development and experimental analysis of an LED lighting module for use in a high-end food lighting environment which puts high demands on color homogeneity and color rendering. The system is built from highly reflecting and partly scattering PVD coated metal reflector sheet that has limited deformability and uses RGBW LEDs. We develop an optical design that is adapted to allow for color mixing and to take into account manufacturing constraints and include this into a prototypical module. Results of measurements and field tests are in good agreement with simulations.