Master Oscillator Power Fiber Amplifier lasers (MOPFA) lasers have been available for several years but very short
nanosecond pulses along with low brightness, high repetition rates and high average power has only been achieved
recently. The different types of pulsed fiber lasers are described. These new fiber laser designs have characteristics that
allow them to challenge conventional laser technology in many application areas. Some data on industrially relevant
ablation rates is included and other applications are also presented.
The stochastic effects of assist gas in QCW and pulsed laser machining (percussion drilling) in steel are measured with a
novel in situ high speed low coherence imaging system. Real-time imaging is delivered coaxially with machining energy
and assist gas revealing relaxation and melt flow dynamics over microsecond timescales and millimeter length scales
with ~10 micrometer resolution. Direct measurement of cut rate and repeatability avoids post cut analysis and iterative
process development. Feedback from the imaging system can be used to overcome variations in relaxation and guides
blind hole cutting.
Global interest in solar power has created a huge increase in manufacturing capability for silicon based
photovoltaic devices. The consequent shortage of silicon has also led to increased interest in thin film solar technology
and many new manufacturing facilities are due to come on stream. Lasers are required for precision ablation, cutting and
welding tasks on both silicon and thin film based devices. The photovoltaic industry has not been slow to take advantage
of the benefits and capabilities of fiber lasers for these tasks. A brief review of these processes is presented along with
examples of high speed high quality silicon cutting and thin film ablation using fiber lasers.
Diffractive beam shaping, using a remapping approach, requires a laser source that is well characterized and stable. Recent advances in the development of fiber lasers have shown stable, high quality, TEM00 single mode performance at powers < 200 Watts for 1090 nm. This paper will give a detailed account of the design and experimental results for a 5.5 mm 1/e2 fiber lasers shaped by an off-axis diffractive beam shaper to produce tophat focused spots < 50 microns. One application of interest is in the area of micro welding of thin stainless steel sheets. Experimental data will be presented for this micro welding application.
Fiber-integrated high power fiber lasers (HPFLs) have demonstrated remarkable levels of parametric performance, efficiency, operational stability and reliability, and are consequently becoming the technology of choice for a diverse range of materials processing applications in the "micro-machining" domain. The design and functional flexibility of such HPFLs enables a broad operational window from continuous wave in the 100W+ power range, to modulated CW (to 50kHz prf and above), and to quasi-pulsed operation (kW/μs/mJ regime) from a single design of laser system. A long-term qualification program has been successfully completed to demonstrate the robustness and longevity of this family of fiber lasers.
In this paper we report for the first time on the power-scaling extension of SPI's proprietary side-coupled cladding-pumped GTWave<sup>TM</sup> technology platform to output power levels in the multi-hundred watt domain. Fiber and system design aspects are discussed for increasing both average power and peak power for CW and quasi-pulsed operation respectively whilst maintaining near-diffraction limited beam quality and mitigating non-linear effects such as Stimulated Raman Scattering. Performance data are presented for the new family of laser products with >200W CW output power, M<sup>2</sup> ~ 1.1 and modulation performance to 50kHz: Furthermore, the modular, flexible approach provided by GTWave<sup>TM</sup> side-pumped technology has been extended to demonstrate a two-stage MOPA operating at >400W.
Fiber-integrated high power fiber lasers are becoming the technology of choice for a diverse range of micromaterials processing applications due to their efficiency, operational stability and reliability. It is now clear that a much wider range of laser parameters are available when fiber lasers are compared to conventional solid-state lasers. Add to this the lack of additional variables associated with thermal lensing and process development is greatly simplified. Of even more importance, this parameter flexibility enables these lasers to perform well beyond the state-of-the-art in certain established applications where performance expectations are now very high. Similarly, due to its low M<sup>2</sup>, the
laser is shown here to perform well in applications and on materials that might not be immediately considered suitable for this type of continuous-wave modulated laser.
Sealed CO<sub>2</sub> lasers at <500 watts power are widely used for cuttng and drilling, but their welding performance is less well known. The welding trials reported here address this by identifying welding performance for certain widely used ferrous and non-ferrous materials. Welds were made at a fixed average power and a range of laser parameters over a range of weld speeds. Conventional metallographic techniques were used for assessing weld dimensions and weld quality.
The most widely used basic building block for high power diode lasers systems is a 19 emitter diode laser bar. For materials processing tasks, these may be used as single bars, can be built into vertical stacks or may be fiber coupled. For certain applications a line of light is preferred to a round beam and hence the use of fiber optic delivery may not be necessary. Straightforward optics can be used to convert the divergent output from this diode bar into a rectangle of line of focused light but the uniformity of the beam within this rectangle is a major problem. When diode bars are stacked vertically, this problem becomes 2 dimensional for anything other than a tightly focused beam. In particular, when a single bar line source is used to cover a large surface area by motion normal to the long axis of the beam, this non-uniformity creates fluctuations in intensity due to the separation between the individual emitters on the bar. This in turn causes processing problems when a laser line is used to seal multiple micro-fluidic devices. This work reports the use of a novel technique combined with conventional fiber delivered sources and novel laser line sources to tackle this problem.
In this paper, results of investigations on the shape of weld pool during High Power Diode Laser (HPDL) welding are presented. The results of tests showed that the shape of weld pool and mechanism of laser welding with a rectangular pattern of 808 nm laser radiation differs distinctly from previous laser welding mechanisms. For all power densities the conduction mode welds were observed and weld pool geometry depends significantly on the welding parameters.
Laser soldering systems have been available for many years but the recent arrival of high power direct diode systems has given a boost to the acceptance of these systems by industry. Diode lasers are now being employed in industry for a range of soldering applications, most of these are the more challenging soldering applications where the controllability of laser processing is required and the diode laser brings added benefit to these. Very little work has been published on the quality of laser soldered joints and this paper addresses this shortfall by exploring laser parameters and joint quality using a number of techniques.
Diode lasers are now being employed in industry for a range of applications, in particular they are starting to be used as alternatives to conventional techniques for thermal joining of plastics. This is being assisted by the use of improved reliability aluminum-free diodes and diode laser systems, partly due to a better understanding of failure mechanisms. The laser welding and related techniques are dependent on transmission of part of an infra-red beam through the upper layer of a joint and semi-quantitative assessment of this is required for specific applications. The technique is applicable not only to high average powers, but also to very low average power, in this regime delicate thin-walled components may be joined. Recent developments using derivatives of this technique have shown that a wide range of similar and dissimilar material combinations may be joined.
Experimental laser cutting work has been performed on a commonly used sheet aluminum alloy to establish an approximate relationship between maximum laser cutting speed and the thickness of an anodized layer on the surface of the material. Results show a very significant increase in maximum speed, which is maintained even with increasing thickness of the anodized layer well beyond that at which maximum beam absorption is thought to occur.
While coating automotive body steels with zinc has a beneficial effect on their corrosion properties it can give significant problems when individual panels are subsequently welded to form the body shell. This work shows that a pulsed Nd:YAG laser can be used as a precleaning tool to locally remove the zinc and then as a spot welding device to join 2 sheets in a lap weld configuration. Laser spot welding can produce joints having adequate strength at a range of conditions but the localized nature of the heat input can produce damage on the top surface, this is often not acceptable in structures such as an automotive body shell. In this work, conditions have been identified which are capable of precleaning the area to be welded and able to produce welds having adequate strength with cosmetically acceptable surfaces.
High power solid state lasers are increasingly being used for drilling and cutting of advanced materials. This is because of the difficulty in machining, in particular, drilling of small diameter holes, using conventional methods. The pulsed Nd YAG laser is an excellent tool for fine drilling and cutting of these materials because of its combination of high peak power pulse capability and its low beam divergence. A program of experimental work has therefore been carried out to examine the practical effects of key laser variables on the drilling of the Ceramic Matrix Composite material. The parameters used and the systematic approach to the trials is also presented along with information on how statistically significant and repeatable results were obtained.
Technology advances are described which have led to improved 1 kW average power
solid state lasers. These developments lead to genuine processing advantages in
terms of manufacturing flexibility, and in the case of welding, metallurgical
quality. Results of various brief welding trials are reported on a number of
different materials, with some preliminary mechanical weld test results.