Search

The fundamental parameters of a laser beam, such as the exact position and size of the focus or the beam quality factor M² yield vital information both for laser developers and end-users. However, each of these parameters can significantly change on a short time scale due to thermally induced effects in the processing optics or in the laser source itself, leading to process instabilities and non-reproducible results. In order to monitor the transient behavior of these effects, we have developed a camera-based measurement system, which enables full laser beam characterization in online. A novel monolithic beam splitter has been designed which generates a 2D array of images on a single camera chip, each of which corresponds to an intensity cross section of the beam along the propagation axis separated by a well-defined spacing. Thus, using the full area of the camera chip, a large number of measurement planes is achieved, leading to a measurement range sufficient for a full beam characterization conforming to ISO 11146 for a broad range of beam parameters of the incoming beam. The exact beam diameters in each plane are derived by calculation of the 2nd order intensity moments of the individual intensity slices. The processing time needed to carry out both the background filtering and the image processing operations for the full analysis of a single camera image is in the range of a few milliseconds. Hence, the measurement frequency of our system is mainly limited by the frame-rate of the camera.

Laser processing of carbon fiber reinforce plastic (CFRP) is a very promising method to solve a lot of the challenges for large-volume production of lightweight constructions in automotive and airplane industries. However, the laser process is actual limited by two main issues. First the quality might be reduced due to thermal damage and second the high process energy needed for sublimation of the carbon fibers requires laser sources with high average power for productive processing. To achieve thermal damage of the CFRP of less than 10μm intensities above 10 8 W/cm² are needed. To reach these high intensities in the processing area ultra-short pulse laser systems are favored. Unfortunately the average power of commercially available laser systems is up to now in the range of several tens to a few hundred Watt. To sublimate the carbon fibers a large volume specific enthalpy of 85 J/mm³ is necessary. This means for example that cutting of 2 mm thick material with a kerf width of 0.2 mm with industry-typical 100 mm/sec requires several kilowatts of average power. At the IFSW a thin-disk multipass amplifier yielding a maximum average output power of 1100 W (300 kHz, 8 ps, 3.7 mJ) allowed for the first time to process CFRP at this average power and pulse energy level with picosecond pulse duration. With this unique laser system cutting of CFRP with a thickness of 2 mm an effective average cutting speed of 150 mm/sec with a thermal damage below 10μm was demonstrated.

We demonstrated for the first time, to the best of our knowledge a new intracavity pulse stretching design, employing a single grating-mirror based on a leaky-mode grating-waveguide design. The extremely compact and flexible layout allows for femtosecond pulses to be easily stretched up to nanosecond durations. The stretcher was implemented in a diode-pumped Yb:CALGO regenerative amplifier followed by a standard transmission grating compressor. We demonstrated sub-200 fs long pulses (stretched pulses ≈ 110 ps) with a maximum energy of 205 μJ at 20 kHz repetition rate. As a proof of the robustness and potential energy scaling of leaky-mode grating-waveguide intracavity stretcher, energies up to 700 μJ and 400 ps long pulses before compression at a lower repetition rate of 10 kHz, have been achieved. A simple model is proposed to investigate the cavity behavior in presence of induced spatial chirp.

We present first experimental investigations on Ytterbium-doped Sc 2 SiO 5 as a promising gain medium for thin-disk lasers. This oxyorthosilicate laser material combines good thermo-mechanical properties and a broad emission bandwidth suitable for high-power cw and mode-locked laser operation. The demonstrated average output powers of up to 75 W with a not yet optimized thin-disk crystal confirm the power capability of this new material and preliminary tests on passive mode-locking indicate the high potential for future ultrafast thin-disk laser oscillators.

The multi-core fiber laser is a promising fiber laser concept since it combines good beam quality and a high mode field diameter to reduce nonlinear effects especially for pulsed laser operation. Therefore this concept is a good candidate for high power fiber laser operation with a good beam quality. In the present paper we report on the characterization and the laser operation of a fiber laser with a hexagonal array of 19-cores. The near and the far field intensity distribution of the emitted beam as well as the bending-induced transversal mode selection have been investigated. The obtained experimental and simulation results and show a good agreement.