Germanium Crystal Undulator Realization through Pulsed Laser Melting Technique

Crystal-based undulators are breakthrough devices for developing new gamma-ray light sources. Operating at photon energies ranging from 100 keV to several tens of MeV, they offer a promising approach to high-brilliance gamma-ray generation. By exploiting the channeling phenomenon, a periodically bent crystal can be aligned with relativistic particle beams to produce high-energy photons. When particles are confined within atomic channels and follow a periodic trajectory due to the crystal’s curvature, directional light emission occurs. In this context, precise control over the manipulation of crystal planes to achieve a sinusoidal elastic deformation of the lattice is crucial for enabling this technology. This work investigates the induction of strain in monocrystalline semiconductor materials using the pulsed laser melting (PLM) technique, with the goal of meeting the bending requirements of such devices. PLM is an out-of-equilibrium process in which a high-intensity pulsed UV laser beam melts the crystal surface to a depth of several hundred nanometers within a few nanoseconds. During the rapid cooling phase, the crystal resolidifies epitaxially in less than a hundred nanoseconds. If a controlled layer of heterogeneous atoms is deposited on the surface beforehand, these atoms diffuse into the molten phase and become incorporated into the crystal during regrowth. As a result, large quantities of dopants or alloying elements can be introduced, often exceeding the limits of equilibrium-based techniques. This approach is particularly advantageous for hyperdoping applications in nanoelectronics, photonics, and radiation detector fabrication. By combining PLM with sputter deposition, strain can be induced in germanium monocrystals through the formation of a pseudomorphic alloy layer in the near-surface region. A range of laser parameters, such as pulse energy and pulse count, has been tested to optimize the induced strain. Moreover, different crystallographic orientations were explored, revealing a strong correlation between crystal direction and the lattice relaxation mechanisms that ultimately limit the maximum achievable strain. Finally, applying this technology within a carefully designed photolithographic process enables the practical fabrication of crystals with sinusoidally bent planes. Further characterization of the fabricated structures confirms the feasibility of this approach for realizing this type of advanced device. The fabricated devices were characterized using diffraction techniques, and their structure was simulated and optimized through finite element mechanical calculations. Based on the deformation of the crystal planes, the undulator dynamics of a 35 GeV positron beam and the spectral probability of gamma photon emission from the device were calculated.