Using a Kretschmann configuration-based setup, surface-enhanced Raman scattering (SERS) experiments have been performed on a monolayer of Nile blue. The experiment has been optimized to achieve reproducible conditions. Laser excitation resulted in a fast decay of the Raman line intensities ending at a stable signal level. We have analyzed this intensity variation mode specifically. The Raman deactivation rate was found to be different for different vibrational modes where high-wavenumber vibrations showed slower decay than the group of low-wavenumber modes. SERS spectra were obtained excluding the contribution of this deactivation process for different angles of incidence of the exciting laser beam. The variation of the surface plasmon excitation in the thin silver film coated onto the prism surface of the Kretschmann configuration resulted in drastically different relative enhancements of the different Raman modes pointing to a major contribution of the chemical enhancement mechanism in the single-layer SERS experiment. The enhancement was found to be mode-specific. High-wavenumber modes showed a stronger enhancement than the low-wavenumber group.

Different mechanisms contribute to the increase of the inelastically scattered signal observed in surface-enhanced Raman spectroscopy (SERS). The so-called electronic (chemical) enhancement mechanism has been studied using a Kretschmann configuration by switching the electronic contribution on and off. For this, the direct coupling of the analyte molecules to the metal surface was prevented with the help of different intermediate layers between molecules and metal consisting of self-assembled monolayers or a metallic oxide layer. It has been observed that for a separation from the metal, despite the only very small (a few nanometers) distance from the metal surface introduced by the interlayers, the ratio between the enhancements determined for in-resonance and preresonance conditions is drastically reduced compared to the situation where the molecules can chemisorb on the metal surface. It was also observed that while in the case of direct contact to the metal surface, the resonance/preresonance enhancement ratio was strongly mode-dependent, such dependence did not occur when the analyte molecule was kept away from direct access to the surface. This confirms the transition to a pure electromagnetic enhancement when the molecules are separated from the metal surface and allows for the characterization of the two mechanisms.

A relatively simple experimental procedure is proposed for the simultaneous detection and quantitative assessment of moxifloxacin (Moxi) as an example for an antibiotic using surface‐enhanced Raman spectroscopy (SERS) performed in a Kretschmann configuration (KC). The example of Moxi shows the advantage of this approach, such as high sensitivity and relatively simple experimental procedure. The Moxi was reliably detected at levels of 100 nM using excitation laser powers as low as a few milliwatts. We also demonstrate that in the KC, the direct coupling between the electronic systems of analyte molecules and metal substrate contributing to the chemical enhancement mechanism in SERS plays a major role. For this, we have performed simulations based on density functional theory (DFT). The line profile of the SERS spectra can be explained by the direct coupling of molecular sites to the metal. This adds to the molecular specificity of SERS when using the KC.

A Toffoli logic gate (CCNOT gate) is a universal reversible logic gate from which all other reversible gates can be constructed. It has a three-bit input and output. The goal of our work was to realize a Toffoli gate where all inputs and outputs are realized optically, which allows for ultrafast switching processes. We demonstrate experimentally that a Toffoli logic gate can be created based on nonlinear multi-wave interactions of light with matter. Using femtosecond laser pulses, the all-optical Toffoli gate is based on the coherence of the optical signals produced via the nonlinear optical processes. Sum frequency (SF) and second harmonic (SH) generations are combined in such a way so as to yield the complete truth table of the universal reversible logic gate.

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