33 research outputs found
Modeling nonlinear optical interactions of focused beams in bulk crystals and thin films: A phenomenological approach
Coherent nonlinear optical micro-spectroscopy is a frequently used tool in
modern material science, as it is sensitive to many different local
observables, which comprise, among others, crystal symmetry and vibrational
properties. The richness in information, however, may come with challenges in
data interpretation, as one has to disentangle the many different effects like
multiple reflections, phase jumps at interfaces, or the influence of the
Guoy-phase. In order to facilitate interpretation, the work presented here
proposes an easy-to-use semi-analytical modeling ansatz, that bases upon known
analytical solutions using Gaussian beams. Specifically, we apply this ansatz
to compute nonlinear optical responses of (thin film) optical materials. We try
to conserve the meaning of intuitive parameters like the Gouy-phase and the
nonlinear coherent interaction length. In particular, the concept of coherence
length is extended, which is a must when using focal beams. The model is
subsequently applied to exemplary cases of second-harmonic and third-harmonic
generation. We observe a very good agreement with experimental data and
furthermore, despite the constraints and limits of the analytical ansatz, our
model performs similarly well as when using more rigorous simulations. However,
it outperforms the latter in terms of computational power, requiring more than
three orders less computational time and less performant computer systems
Characterization of human and rodent native and recombinant adenosine A2B receptors by radioligand binding studies
Adenosine A2B receptors of native human and rodent cell lines were investigated using [3H]PSB-298 [(8-{4-[2-(2-hydroxyethylamino)-2-oxoethoxy]phenyl}-1-propylxanthine] in radioligand binding studies. [3H]PSB-298 showed saturable and reversible binding. It exhibited a KD value of 60 ± 1 nM and limited capacity (Bmax = 3.511 fmol per milligram protein) at recombinant human adenosine A2B receptors expressed in human embryonic kidney cells (HEK-293). The addition of sodium chloride (100 mM) led to a threefold increase in the number of binding sites recognized by the radioligand. The curve of the agonist 5′-N-ethylcarboxamidoadenosine (NECA) was shifted to the right in the presence of NaCl, while the curve of the antagonist PSB-298 was shifted to the left, indicating that PSB-298 may be an inverse agonist at A2B receptors. Adenosine A2B receptors were shown to be the major adenosine A2 receptor subtype on the mouse neuroblastoma x rat glioma hybrid cell line NG108-15 cells. Binding studies at rat INS-1 cells (insulin secreting cell line) demonstrated that [3H]PSB-298 is a selective radioligand for adenosine A2B binding sites in this cell line
Nonlinear optical interactions in focused beams and nanosized structures
Thin-film materials from μm thickness down to single-atomic-layered 2D materials play a central role in many novel electronic and optical applications. Coherent, nonlinear optical (NLO) μ-spectroscopy offers insight into the local thickness, stacking order, symmetry, or electronic and vibrational properties. Thin films and 2D materials are usually supported on multi-layered substrates leading to (multi-) reflections, interference, or phase jumps at interfaces during μ-spectroscopy, which all can make the interpretation of experiments particularly challenging. The disentanglement of the influence parameters can be achieved via rigorous theoretical analysis. In this work, we compare two self-developed modeling approaches, a semi-analytical and a fully vectorial model, to experiments carried out in thin-film geometry for two archetypal NLO processes, second-harmonic and third-harmonic generation. In particular, we demonstrate that thin-film interference and phase matching do heavily influence the signal strength. Furthermore, we work out key differences between three and four photon processes, such as the role of the Gouy-phase shift and the focal position. Last, we can show that a relatively simple semi-analytical model, despite its limitations, is able to accurately describe experiments at a significantly lower computational cost as compared to a full vectorial modeling. This study lays the groundwork for performing quantitative NLO μ-spectroscopy on thin films and 2D materials, as it identifies and quantifies the impact of the corresponding sample and setup parameters on the NLO signal, in order to distinguish them from genuine material properties