With the rapid development of additive manufacturing to an established industrial manufacturing process, arises an increasing demand for process control. Especially industrial sectors with stringent safety regulations like aerospace, automotive or medicine, require a high level of quality monitoring. The limited space and the variety of possible beam incidence angle and position configurations inherent to laser scanning systems, constitute special framework conditions, only inadequately provided by state of the art beam diagnostic devices. To meet these requirements we developed a novel and compact measuring instrument capable of addressing scanner specific measurement tasks, including quantities so far inaccessible to conventional beam diagnostics. These involve for example the examination of the field flatness, pincushion distortion, position dependent focal shift, or accuracy of position and marking speed. Even more sophisticated issues like the accurate stitching of two overlapping exposure schemes are feasible. The working principle is based on a pattern of scattering structures within a glass plate. When scanned across the pattern, a small fraction of the laser beam is scattered and the light is collected with a photo-diode, allowing the reconstruction of the light path and derivation of the beam width. All above mentioned quantities are measured with high resolution and reproducibility. The current state of the experiments is presented, and the prospects of this novel measuring technology for scanner system diagnostics discussed.
In today’s industrial mass production, lasers have become an established tool for a variety of processes. As with any other tool, mechanical or otherwise, the laser and its ancillary components are prone to wear and ageing. Monitoring of these ageing processes at full operating power of an industrial laser is challenging for a range of reasons. Not only the damage threshold of the measurement device itself, but also cycle time constraints in industrial processing are just two of these challenges.
Power measurement, focus spot size or full beam caustic measurements are being implemented in industrial laser systems. The scope of the measurement and the amount of data collected is limited by the above mentioned cycle time, which in some cases can only be a few seconds.
For successful integration of these measurement systems into automated production lines, the devices must be equipped with standardized communication interfaces, enabling a feedback loop from the measurement device to the laser processing systems. If necessary these measurements can be performed before each cycle.
Power is determined with either static or dynamic calorimetry while camera and scanning systems are used for beam profile analysis. Power levels can be measured from 25W up to 20 kW, with focus spot sizes between 10μm and several millimeters. We will show, backed by relevant statistical data, that defects or contamination of the laser beam path can be detected with applied measurement systems, enabling a quality control chain to prevent process defects.
Modern high brilliance near infrared lasers have seen a tremendous growth in applications throughout the world. Increased productivity has been achieved by higher laser power and increased brilliance of lasers. Positive impacts on the performance and costs of parts are opposed to threats on process stability and quality, namely shift of focus position over time. A high initial process quality will be reduced by contamination of optics, eventually leading to a focus shift or even destruction of the optics.
Focus analysis at full power of multi-kilowatt high brilliance lasers is a very demanding task because of high power densities in the spot and the high power load on optical elements. With the newly developed high power projection optics, the High-Power Micro-Spot Monitor High Brilliance (HP-MSM-HB) is able to measure focus diameter as low as 20 μm at power levels up to 10 kW at very low internal focus shift.
A main driving factor behind thermally induced focus shift is the absorption level of the optical element. A newly developed measuring system is designed to determine the relative absorption level in reference to a gold standard. Test results presented show a direct correlation between absorption levels and focus shift.
The ability to determine the absorption level of optical elements as well as their performance at full processing power before they are put to use, enables a high level of quality assurance for optics manufacturers and processing head manufacturers alike.
KEYWORDS: Cameras, Signal attenuation, High power lasers, Thermography, Optical design, Diagnostics, CCD cameras, Head, Fiber lasers, Solid state lasers
The objective of the Materials International Space Station Experiment (MISSE) is to study the performance of novel
materials when subjected to the synergistic effects of the harsh space environment for several months. In this paper, a
few laser and optical elements from NASA Langley Research Center (LaRC) that have been flown on MISSE 6 mission
will be discussed. These items were characterized and packed inside a ruggedized Passive Experiment Container (PEC)
that resembles a suitcase. The PEC was tested for survivability due to launch conditions. Subsequently, the MISSE 6
PEC was transported by the STS-123 mission to International Space Station (ISS) on March 11, 2008. The astronauts
successfully attached the PEC to external handrails and opened the PEC for long term exposure to the space
environment. The plan is to retrieve the MISSE 6 PEC by STS-128 mission in August 2009.
The result in laser material processing is controlled mainly by the properties of the focused laser beam. Very special requirements have to be taken into account to characterize such a laser beam, which is finally used for laser micromachining. These specific aspects for the design of a beam diagnostics system ready to measure small spots (down the 10 micrometer range) at power densities up to several GW/cm2 will be discussed. Based on a CCD-camera concept, care has to be taken to magnify and to attenuate the beam properly. A special electronics design and algorithms are necessary to optimize the performance and finally to realize such a technical measuring system. Some applications of beam diagnostics within industrial processes (drilling holes, cutting wafers etc.) are demonstrated.
The ISO Standard 11146 has joined the various company specific standards into one set of procedures to determine laser beam propagation parameters. Due to the implementation of the standard, a lot of smaller and some critical measurement problems become visible.
The main part of beam parameter calculation is the determination of the beam width based on the second order moments of the power density distribution. Due to the mathematical definition, the second order moments are sensitive to incorrect determination of the zero level of the detector. The signal to noise ratio also plays an important role.
Other critical points are non-linearity and artifacts of the detector and the optical system itself. An example for an implementation of the ISO 11146 within the design of a real measuring tool is demonstrated. The PRIMES MicroSpotMonitor is a camera-based beam diagnostic system. It is ready to measure automatically even high power beams with dimensions down to the range of several micrometers. The constraints between the demands of the standard and practical application will be discussed.
By insertion of a fast mechanical Q-switch into the resonator, continuous discharge CO2 lasers can yield high peak power pulses at multi-kHz repetition rate. First experiments have been done with diffusion-cooled low-pressure CO2 lasers. For this type of laser the pulse energy can only be increased by increasing the length of the active medium. A limit is given by the onset of uncontrolled self oscillation which prevents regular Q-switched operation. Single pulse energies can apparently not exceed 30 mJ at 250 ns pulse duration for this type of laser. Fast gas-flow convection-cooled laser discharges allow us to increase the stored energy by increasing diameter and pressure of the active medium as well as the electrical power density. We present the results of Q-switching of a 5 kW industrial laser. Our Q-switch is scalable in optical power. It is based on a fast chopper and a conical mirror. In some experiments we tuned the laser over a wide range by a diffraction grating. The influence of gas pressure and mixtures as well as discharge parameters has been studied. Single pulse energies of 100 mJ have been found, limited by the electrical input power density.
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