arXiv subjects

Matthias Bickermann

Publications and source records attributed to Matthias Bickermann.

5 recordsLinked to original sources

arXiv2026

Redetermination of the second-order nonlinear optical coefficients of BaMgF4

BaMgF4 (BMF) has the potential to serve as a platform material for vacuum-ultraviolet (VUV) nonlinear optics owing to its ferroelectricity and high UV transparency down to 130 nm. However, the second-order nonlinear optical coefficients reported for BMF span approximately one order of magnitude, hindering a reliable assessment of its potential for nonlinear optical applications. Here, we redetermined these coefficients by combining Maker fringe, wedge, and single-pass second-harmonic-generation measurements at a fundamental wavelength of 1064 nm. Our results establish that all the second-order nonlinear optical coefficients of BMF lie in the range of 0.01-0.04 pm/V. We determined d31 to be 0.035 pm/V, which is among the largest coefficients of BMF, while it has been underestimated relative to the other coefficients in previous studies. Although d31 is not the largest coefficient, the use of its long corresponding coherence length is beneficial for quasi-phase matching, particularly for VUV generation, where the fabrication of lower-order quasi-phase-matching structures is crucial.

physics.optics↗

arXiv2026

Generation of continuous-wave laser light at 148.4 nm using cavity-enhanced second harmonic generation in $BaMgF_4$

The development of a nuclear optical clock based on \textsuperscript{229}Th is expected to influence the next generation of time and frequency standards. At its heart is the need for a continuous wave (CW) at laser at 148.4~nm to drive the clock transition between the ground and excited isomeric state. In this work we experimentally investigate the potential of BaMgF\textsubscript{4} crystals to create a CW solid state laser at the vacuum ultraviolet (VUV) wavelength of 148.4~nm via cavity-enhanced second harmonic generation. For this purpose, a BaMgF\textsubscript{4} crystal was grown, optically polished and periodically poled. The crystal was inserted into a power-enhancement cavity, resonant at the fundamental wavelength of 296.8~nm and the generated laser light at 148.4~nm was characterized. Within this proof-of-concept investigation, a VUV output power of typically ($16\pm1$)~pW is obtained. This marks the first time that this type of crystal is used to generate VUV laser light. The experimental findings are compared to theoretical expectations and provide a clear path for future improvements, which could have implications not only for compact laser sources in the VUV but also solid-state as well as single-ion based \textsuperscript{229}Th nuclear clocks.

physics.optics↗

arXiv2024

Evaluation and thermodynamic optimization of phase diagram of lithium niobate tantalate solid solutions

The phase diagram of the lithium niobate and lithium tantalate solid solutions was investigated using experimental data from differential thermal analysis (DTA) and crystal growth. We used XRF analysis to determine the elemental composition of crystals. Based on the Neumann-Kopp rule, essential data of end members lithium niobate (LN) and lithium tantalate (LT) was created. The heats of fusion of end members given by DTA measurements of LN (103 kJ/mol at 1531 K) and LT (289 kJ/mol at 1913 K) were given as input parameters to generate the data. This data served as the basis for calculating a phase diagram for LN and LT solid solutions. Finally, based on the experimental data and thermodynamic solution model, the phase diagram was optimized in the Calphad Factsage module. We also generated thermodynamic parameters for Gibb's excess energy of the solid solution. A plot of segregation coefficient as a function of Ta concentration was derived from the phase diagram.

cond-mat.mtrl-sci↗

arXiv2021

Photochromism and influence of point defect charge states on optical absorption in aluminum nitride (AlN)

In this work, we study the absorption properties of AlN in the range of 1.5 - 5.5 eV, as well as the meta-stable change in absorption induced by ultraviolet (UV) irradiation (photochromism), and the restoration of the initial state under the action of irradiation of 2 - 4 eV or elevated temperatures. UV irradiation results in a decrease of the absorption coefficient from 110 cm$^{-1}$ to 55 cm$^{-1}$ at 4.7 eV while in the visible range the absorption coefficient increases from values below 5 cm$^{-1}$ to ~35 cm$^{-1}$. Measurements with two linear polarizations, parallel and perpendicular to the optical axis, provide determination of several different absorption bands at 2.6, 2.8, 3.4, 4.0, 4.5, and 4.8 eV. The bands at 2.6 eV and 3.4 eV identify the defect levels near to the valence band, while the band peaking at 2.8 eV is related to the conduction band. The photochromism allows controlling the absorption of light in two related spectral ranges because the decrease of UV absorption and increase of the visible absorption are related to switching the charge state of the same defects.

cond-mat.mtrl-sci↗

arXiv2020

Phase diagram studies for the growth of (Mg,Zr):SrGa$_{12}$O$_{19}$ crystals

By differential thermal analysis a concentration field suitable for the growth of Zr, Mg codoped strontium hexagallate crystals was observed that corresponds well with experimental results from Mateika and Laurien, J. Crystal Growth 52 (1981) 566-572. It was shown that the melting point of doped crystal is ca. 60 K higher than that of undoped crystals. This higher melting points indicates hexagallate phase stabilization by Zr, Mg codoping, and increases the growth window, compared to undoped SrO-Ga$_2$O$_3$ melts.

cond-mat.mtrl-sci↗