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Laser transmission welding has become an established joining technique in series production of plastic components. Besides its unique process related properties, it also offers several monitoring methods to ensure a constant welding result. In most cases, pyrometry is the method of choice which contactless detects the heat emitted from the interface of the joining partners. Considering the transmission properties of polymers and the optical components between the workpiece and pyrometer, only a small fraction of the thermal process emission is able to penetrate to the detector of the pyrometer. Typically, in classic laser transmission welding, the thermal emission is measured in the spectral range 1.1–2.5 μm limited by the laser wavelength on the one side and the absorption capability of polymers/optical elements in the optical path on the other side. In absorber-free laser transmission welding, laser sources in the range of 1.6–2 μm are used in order to exploit the intrinsic absorption of thermoplastics. With the laser emitting in the sensitivity range of the pyrometer, optical filters have to be used to isolate the thermal radiation from the laser radiation which, however, attenuates the already weak thermal signature even further. An approach that does not require any optical filters is presented in this paper. The concept is operating the laser in a pulsed mode which enables detection of thermal emissions between two consecutive pulses without being overlaid by the laser radiation. Though laser radiation is not delivered continuously, the result demonstrates that it is still possible to obtain a nearly homogeneous seam when choosing an appropriate pulse regime. It is also shown how the detected signal can be utilized to adjust the focal position, which is an important but time-consuming aspect in absorber-free laser welding.

Within the plastic industry laser transmission welding ranks among the most important joining techniques and opens up new application areas continuously. So far, a big disadvantage of the process was the fact that the joining partners need different optical properties. Since thermoplastics are transparent for the radiation of conventional beam sources (800- 1100 nm) the absorbance of one of the joining partners has to be enhanced by adding an infrared absorber (IR-absorber). Until recently, welding of absorber-free parts has not been possible. New diode lasers provide a broad variety of wavelengths which allows exploiting intrinsic absorption bands of thermoplastics. The use of a proper wavelength in combination with special optics enables laser welding of two optically identical polymer parts without absorbers which can be utilized in a large number of applications primarily in the medical and food industry, where the use of absorbers usually entails costly and time-consuming authorization processes. In this paper some aspects of the process are considered as the influence of the focal position, which is crucial when both joining partners have equal optical properties. After a theoretical consideration, an evaluation is carried out based on welding trials with polycarbonate (PC). Further aspects such as gap bridging capability and the influence of thickness of the upper joining partner are investigated as well

Spatial and spectral emission characteristics and efficiency of high-power diode laser (HPDL) based pump sources enable and define the performance of the fundamental solid state laser concepts like disk, fiber and slab lasers. HPDL are also established as a versatile tool for direct materials processing substituting other laser types like CO2 lasers and lamp pumped solid state lasers and are starting to substitute even some of the diode pumped solid state lasers. Both, pumping and direct applications will benefit from the further improvement of the brightness and control of the output spectrum of HPDL. While edge emitting diodes are already established, a new generation of vertical emitting diode lasers (VCSELs) made significant progress and provides easy scalable output power in the kW range. Beneficial properties are simplified beam shaping, flexible control of the temporal and spatial emission, compact design and low current operation. Other characteristics like efficiency and brightness of VCSELs are still lagging behind the edge emitter performance. Examples of direct applications like surface treatment, soldering, welding, additive manufacturing, cutting and their requirements on the HPDL performance are presented. Furthermore, an overview on process requirements and available as well as perspective performance of laser sources is derived

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