It was performed a Time of Flight (TOF) study for the plume produced by laser ablation of cooper by 355 nm, 23 ns
duration laser pulses, in vacuum. The plume sensor was made of a piezoelectric PVDF film associated with a pair of
electrodes. By varying the electrodes polarization we evaluated the fraction of neutral atoms, which ranged from 8 to
30 % of the plume. By adjusting a TOF function to the PVDF electric signal we obtained the center of mass velocity and
the translational temperature. It was observed that product vCM × Tz remains constant with the electrodes potential and
that the accelerating potential to which the plume is submitted has practical limits.
KEYWORDS: Aluminum, Fiber lasers, Aerospace engineering, Solids, Surface plasmons, High power fiber lasers, Corrosion, Process control, Resistance, Laser development
This work intends to contribute towards the knowledge of AA6013 aluminum alloy weldability, autogenously welded
with a high-power fiber laser. The quality and metallurgical characterization of the welds were done considering laser
speed and power as process parameters. The present study shown that is possible to obtain welds with good macroscopic
quality; i.e. with regular welds borders and without the presence of holes, cracks or porosities in speeds around 5 m/min
using 1 kW laser power. Additionally, it had been verified that the liquation zone is well confined around 50 μm. The
presence of porosities in longitudinal cuts was linked to keyhole instabilities, which could be appropriately controlled by
the process parameters. Although this alloy is known for some propensity for solidification cracking, any cracking was
verified. This could be linked to an appropriate thermal cycle during welding due to the high quality laser beam, which
produces short solidification interval. The present results indicate that other difficult-to-weld Al-based alloys could be
properly joined using the fiber laser.
It is presented a new method that allows real-time measurement of the laser beam quality from a single lateral image of a
beam propagating in a scattering medium. The development of this method involved studies of an adequate scattering
medium and the design of an image acquisition optical system. Comparing with traditional methods, this new method is
faster and less exhaustive, providing multiple beam diameters measurements with the same (or even better) accuracy
from a unique image in real time. For a single mode HeNe laser beam, it was obtained the value M2 = 1.1 ± 0.1.
The pulse parameters of a Cu-HyBrID laser were measured in a large range of discharge conditions. It was shown that the laser efficiency is determined by an adequate pre-pulse electron density. Almost constant laser average power and efficiency can be obtained in very different pulse repetition rates provided other discharge parameters were adjusted in order to maintain the optimal pre-pulse electron density. We observed that the pulse width depends mainly on the HBr concentration while the pulse energy is mainly dependent on the absolute HBr pressure and repetition rate.
In this work we present the results of CVD-diamond processing using a copper vapor laser. With a self filtering unstable resonator the laser produces an average power of 9 watts in a 3.5 times limited diffraction beam at a 10 KHz repetition rate. The laser beam is focused on the diamond surface using a lens with a 150 mm focal distance producing a spot size of 70 microns. The laser intensity achieves 2 GW/cm2 on the focus. Electronic microscopy of the processed samples showed clean cut and drill with the whole diameter coincident to the laser beam spot size. Since diamond has a very high thermal diffusivity the temperature rise due to the average power would not be enough to promote evaporation, thus it was concluded that the diamond processing is only die to the laser peak power. Diamond burr with 1.0 mm diameter were cut with the same apparatus at a linear velocity of 200 mm/hour showing a clear and shape cut.
A theoretical model has been developed to study the XeCl phototriggered lasers developed in the frame of the Eureka EU205 program: one of small active volume studied at LPGP, and a larger one at LASERDOT. Over a large range of experimental parameters, a pretty good agreement is obtained for the evolution of the electric parameters and the laser output characteristics -- energy and power. At moderate pressures (2 - 3 bars), and high energy loading (400 - 600 J/l), the temporal evolution of the laser power exhibits the successive emission of several laser pulses. This feature is also predicted by the model, but the calculations largely overestimate the energy included in the later pulses. The physical reasons for this disagreement have been established on the LPGP device, for which optical spectroscopic studies have shown the development of discharge instabilities.
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