Cover glass influence on high power fiber laser induced focus shift

Posted on October 30, 2009 by Steven Glover

By: D. Reitemeyer1, T. Seefeld1, F. Vollertsen1, J. P. Bergmann2
1 BIAS – Bremer Institut für angewandte Strahltechnik GmbH, Bremen, 28359, Germany
2 Jenoptik Automatisierungstechnik GmbH, Jena, 07745, Germany

In materials processing with solid state laser sources a fiber optical waveguide is used to transport the
beam to the work station where the beam is focused on the work piece by a processing head. The high
beam quality of state of the art diode pumped solid state lasers allows concentrating the high output
power in a small focus diameter. This forwards the advantage of laser beam welding, the locally
concentrated energy input which enables precise processing.
Along with today’s high beam quality new challenges arise in the systems technology with increasing
requirements for the processing head. The high energy density in the laser beam path heats up the beam
guiding and forming optics, despite the fact that they have an absorption level below 1%. The
temperature increases when fume and spatter from the welding process are locally enhancing the
absorption on the cover glass which protects the beam outlet of the welding head. Figure 1a shows the
measured temperature distribution on the surface, at 5 kW a maximum rise of 170 K was detected.
This temperature rise influences the refractive index and the surface shape. Figure 1b shows the surface
deformation of a contaminated cover glass at 5 kW laser power measured by the fringe reflexion
technique. This influences the optical properties of the optics and thus the beam geometry at the work
piece. Figure 2 shows the influence on the focus’ position and diameter in dependence of the laser
power. The so called focus shift effect may influence the precision of the process.
At ICALEO 2009 a new way to analyze the influences on the focus shift will be presented. This work is
part of a project where BIAS and Jenoptik Automatisierungstechnik GmbH are working on new
approaches for systems technology for material processing with high brightness laser sources.

The above brief overview was extracted from its original abstract and paper presented at The International Congress on Applications of Lasers & Electro-Optics (ICALEO) in Orlando, FL. To order a copy of the complete proceedings from this conference click here

Electrical-Mechanical-Systems

Posted on October 27, 2009 by Steven Glover

By: Norbert Lorenz

Over the past few years the interest in Micro-Electro-Mechanical-Systems (MEMS) and Micro-Optical-Electrical-Mechanical-Systems (MOEMS) from research institutions, industrial firms and the press has risen considerably. Of particular interest are lab-on-a chip devices where many subsystems (ICs and MEMS) are assembled to a functional system for medical and bio-photonic applications. To date the main focus has been on the devices themselves; the research and development of low cost, high reliability assembly and packaging has been rather limited, and as a result current MEMS packaging costs can reach up to 90% of the overall device costs.

MEMS are sensors and actuators on a micro- and nanometre scale incorporating mechanical elements and electronics. They are normally built on a common silicon substrate through microfabrication technology, although alternative technologies using different materials are being increasingly developed. MEMS are commonly known for the realisation of “lab-on-a-chip” devices where many subsystems (ICs and MEMS) are assembled together to make a functional system.

The Heriot-Watt group has demonstrated the feasibility of laser-based glass frit bonding of a range of miniature packages, important for MEMS and related applications. The laser provides localised heat energy, preventing damage to temperature-sensitive materials or dis-assembly of other components of the overall system. Glass frit is an ideal material to use, as it conforms well to the surfaces being joined, provides good hermeticity, and the temperatures required are relatively modest.

Adaptive Spatio-Temporal Techniques For Smart Ultrafast Laser Processing of Optical Glasses

Posted on October 25, 2009 by Steven Glover

By: Razvan Stoian

Among different laser processing techniques, photoinscription employing ultrashort laser pulses has
demonstrated increased potential for three-dimensional optical functionalization of bulk transparent materials.
The resulting refractive index changes can be viewed as building blocks for embedded optical functions, used for
example in waveguiding applications. The requirements of a desired photonic response involve precise adjustments of the refractive index which usually depend on the material relaxation paths. As mechanisms withdistinct characteristic timescales are involved, such as defect creation or thermo-mechanical compaction, byadjusting irradiation conditions a certain control of their competition may be established, resulting in a betterdesign of the material transformation. Advanced strategies are then necessary to improve the irradiation results.
Recently, beam manipulation concepts were developed which allow a modulation of the energy feedthrough
according to the material transient reactions, enabling thus a synergetic interaction between light and matter and, therefore, optimal results. The emerging idea is that suitable light time delivery can enable the control of the excitation and relaxation processes with consequences for the final modification. The photowriting technique
may therefore be conveniently tuned to determine suitable material behaviors, i.e. positive refractive index
changes in materials of optical interest, with both fundamental and technological consequences.

Figure 1 (a) Concept for spatial and temporal femtosecond pulse shaping assisted by a feedback loops. (b,c)
Phase-contrast microscopy refractive index flip in BK7 borosilicate under the action of temporally optimized
pulses as compared to standard short pulse illumination and (d,e) corresponding transverse traces. Black
color denotes a positive index change, required for guiding applications. (f-h) 2D bulk dividers based on
evanescent wave coupling in partial arrays and (i) 3D divider achieved using parallel processing.

This emphasis a fundamental question; how irradiation results can be improved taking into account various criteria for quality processing. Considering the complexity of processes occurring between the initial excitation and the final structural transformation, the task of defining the possible improvement factors is rather difficult, requesting more efficient optimization procedures. We consequently discuss structuring approaches based on adaptive spatio-temporal pulse manipulation using automated light modulators capable of influencing ultrafast laser-induced processes inside transparent materials towards better processing results. Two strategies for gaining
impact on material transformations under light exposure will be presented, adaptive temporal tailoring techniques and spatial beam forming, together with their integration in feedback-driven approaches. These strategies are discussed in the context of optical functionalization for delivering specific designs of the refractive
index, accompanied by concepts of efficient processing approaches. This also involves an engineering aspect related to simultaneous processing of structural modifications in 3D arrangements where a feasible solution is represented by dynamic spatial beam shaping techniques. The approach has a dual aspect and includes corrections for beam propagation errors and spatial intensity distributions in desired forms for parallel processing, mastering both the nonlinearity and the geometry of interaction. Photowritten structures can be arranged in patterns generating complex propagation effects. Offering then multiple opportunities for upgrading laser interactions and responding “intelligently” to material reactions, adaptive schemes in spatio-temporal domains can have an extended range of action, enabling applications that can largely benefit from light-matter synergies.

Emerging Laser Processes and Tool Technology in Solar Photovoltaics

Posted on October 25, 2009 by Steven Glover

By: Dave Clark

2009 has been a very turbulent year so far for both the commercial laser and the solar PV industry. We have witnessed a dramatic slow down in the industrial laser business worldwide and a significant turndown in the fortunes of many solar cell manufacturers and line equipment makers. In the midst of this PV industry shake-out however we are now seeing the emergence of some exciting new laser processes that promise to revolutionize the way we make solar cells and enable the drive to lower costs and higher efficiencies for the industry.

This presentation will discuss some of the current laser-based manufacturing techniques for crystalline silicon solar cells as well as thin-film solar panels. With an overview of laser processes, such as edge isolation, edge deletion, contact forming, and thin-film scribing. In addition laser processes that are currently in the R&D or pilot production stage will be reviewed and the author will offer an assessment of their respective prospects for adoption at the manufacturing level together with a perspective on what’s needed from the next generation solid state lasers to make this a reality.

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Category Archives: General

Cover glass influence on high power fiber laser induced focus shift

Electrical-Mechanical-Systems

Adaptive Spatio-Temporal Techniques For Smart Ultrafast Laser Processing of Optical Glasses

Emerging Laser Processes and Tool Technology in Solar Photovoltaics