We propose a method based on neural network training algorithms for the design of diffractive neural networks - with the aim to perform advanced laser beam shaping in the NIR/VIS spectrum for laser materials processing. The method enables the efficient design of systems including multiple cascaded diffractive optical elements (DOEs) and allows the simultaneous optimization for complex (intensity and phase) target field distributions in multiple target planes. The multi-target boundary condition in the optimization method offers great potential for advanced laser beam shaping.
Freeform optics generating specific irradiance distributions have been used in various applications for some time now. While most freeform optics design algorithms assume point sources or perfectly collimated light, the search for algorithms for non-idealized light sources with finite spatial as well as angular extent is still ongoing. In this work, such an approach is presented where the resulting irradiance distribution of a freeform optical surface is calculated as a superposition of pinhole images generated by points on the optical surface. To compute the required arrangement of the pinhole images for a prescribed irradiance pattern, the expectation maximization algorithm from statistics is applied. The result is then combined with a ray-targeting approach for finding the shape of the corresponding freeform optical surface. At its current state, the approach is applicable to Gaussian input irradiances, single-sided freeform optics and for the paraxial case. An example freeform optical surface for laser material processing is shown and discussed demonstrating the performance and the limitations of the presented approach.
Recently, freeform optics have been introduced for application adapted beam shaping in laser heat treatment. There, intensity distributions are generated that induce previously defined temporal and spatial temperature profiles. To this end, a two-step simulation strategy is necessary, where in the first step the intensity distribution must be derived for which in the second step the freeform optics is calculated. To provide a design that can successfully be integrated in an experimental setup, the incoming laser beam’s characteristics must be accounted for in the derivation of the adapted intensity distribution as well as in the freeform optics design. Here, the two most relevant quantities are the beam’s maximum output power as well as the divergence angle. In this work, strategies are presented that account for the beam’s maximum output power in the derivation of the adapted intensity distribution. Furthermore, stabilizing methods are introduced to enhance the performance of a previously introduced freeform optics design algorithm that takes into account the laser beam’s finite divergence angle but suffers from numerical noise and oscillation problems. A simulation example that uses both techniques is given for (nano)ceramic thin-film laser processing.
The origin of quantum physics was the discovery of the base unit of electromagnetic action h by Max Planck in 1900 when he analyzed the experimental results of the black body radiation. This permitted Albert Einstein a few years later to explain the photoelectric effect by the absorption of photons with an energy of E = h • f . We exploit the Planck-Einstein relation in a new type of fundamental spectroscopic measurements of direct transitions between two states with energy differences of about 10 neV and induced frequencies of a few MHz. Employing a Lamb-shift polarimeter and a Sona transition unit, featuring a relatively simple magnetic field configuration of two opposing solenoidal coils, we were able to determine f and measure E independently. Only resonances corresponding to integer multiples of Planck's constant h were observed in our setup, which can very well be explained quantitatively by the Schrödinger equation. This new method beautifully demonstrates the quantization in the micro-cosmos and allows one to measure the hyperfine splitting energies between the substates with F = 1 and mF = −1, 0, +1 of metastable hydrogen atoms as function of a magnetic field and, thus, to investigate the influence of QED corrections on the Breit-Rabi diagram.
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