Defining and controlling the absorption of the laser beam is important since all of the heating energy is brought to the material through absorption. Even small variations in the absorption change the laser power needed by hundreds of W. In this study the absorption of a diode laser beam to low alloy steel has been measured by a liquid calorimeter and the surface temperature has been measured with a dual wavelength pyrometer. The varied processing parameters were the power intensity of the beam, the interaction time, and the angle between the surface and the optical axis of the laser beam. Surface temperatures during hardening varied from the A c1 temperature to the melting point. Tests were done with a 3 kW diode laser with a 12ϫ5 mm hardening optic. The absorptivity of a machined clean steel surface ranged from 46% to 72% depending on the processing parameters. Aluminum oxide blasting of the surface increased the relative amount of energy absorbed to the work piece. The coupling rates for blasted surfaces varied from 66% to 81%. Best absorptivity was achieved by applying graphite coating on the surface. Absorptivity values in excess of 85% were measured.

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Fiber lasers in MOPA configuration are a very flexible tool for micromachining applications since they allow to independently adjust the pulse parameters such as pulse duration, repetition rates and pulse energy while maintaining a constant beam quality. The developed fiber laser provides an average power of 11 W and maximum pulse energy of 0.5 mJ for a wide range of pulse parameters at diffraction limited beam quality. Its pulse duration and repetition rate are continuously adjustable from 10 ns to cw and from 10kHz to 1MHz respectively. Ablation experiments were carried out on stainless steel, nickel and silicon with the goal of optimizing removal rates or surface finish using nanosecond pulses of different parameters. Maximum removal rates are achieved on all three materials using relatively similar pulse parameters. For silicon, pulse duration of 320ns at 100kHz and 45mJ resulted in optimum removal. In single shot experiments on silicon a significant influence of th e pulse duration was found with a distinct optimum for removal rate and surface finish. The optimum intensity at the work piece is in the range of 35MW/cm2 to 70MW/cm2. Lower values are below the ablation threshold, while the plasma shielding effect limits considerable increases in removal rates for intensities exceeding 70MW/cm2

Solar cells used in photovoltaic (PV) crystalline silicon modules commonly feature grid fingers and bus bars as front contacts. The grid fingers and bus bars partially block the sunlight from reaching the semiconductor layers of a solar cell and therefore reduce the efficiency of a solar module. In this paper, we present experimental results of different technologies to reduce the shadowing effect that bus bars and grid fingers impose. We focus on two technologies that can be easily integrated into standard PV module technology and help to increase the module's efficiency. In the first technology, a laser is used to create a scattering pattern on the front glass of the module. This pattern directs light away from the bus bars and grid fingers. In the second technology, the bus wires are coated with a diffuse reflective coating. The sunlight is diffusely reflected at this coating. A part of it is reflected at such angles that internal reflection at the front surface of t he cover glass occurs. From there the light is reflected back to the solar cell and contributes to the generated photocurrent

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