Stimulated Raman Microscopy Implemented by Three Femtosecond Laser Sources

In this work, the implementation of a femtosecond Stimulated Raman Scattering microscope, equipped with three femtosecond laser sources: a Titanium-Sapphire (Ti:Sa), an optical parametric oscillator (OPO), and a second harmonic generator (SHG); is presented. Our microscope is designed so that it can cover all the regions of Raman spectra, taking advantage of two possible laser combinations. The first, Ti:Sa and OPO laser beams, which cover the C-H region (>2800 cm-1 ) in stimulated Raman gain (SRG) modality, whereas the second, Ti:Sa and SHG laser beams, covering the C-H region and the fingerprint region in stimulated Raman losses (SRL) modality. The successful realization of the microscope is demonstrated, reporting images of polystyrene beads using both SRL and SRG modalities.

Photon decaying in de Sitter universe

The interaction between three photons is studied in de Sitter ambient space formalism. As a special case, the half harmonic generator is considered, i.e., one photon decays to two same-energy photons. The scattering matrix elements are presented which define the indirect gravitational effect on quantum field theory. The null curvature limit of scattering matrix is obtained for comparing it with its Minkowskian counterpart. The Hamiltonian of this interaction, in Minkowski space–time, was presented by using the quantum vacuum fluctuation in the one-loop approximation.

Arylthienyl-vinyl-benzothiazoles as Efficient Second Harmonic Generators (SHG) for Nonlinear Optics

New push-pull second harmonic generation (SHG) chromophores 2 were synthesized in order to study their linear and nonlinear optical properties. The donor-acceptor π-conjugated systems 2 were prepared in good to excellent yields by a simple aldol-type condensation of the precursor aldehydes 1 with 6-nitro-2-methyl-1,3-benzothiazole in the presence of NaOH. Hyper-Rayleigh scattering in dioxane solutions was used to evaluate their second-order nonlinear optical properties. The experimental results showed that the optical (linear and nonlinear) properties are influenced by the electron-donor strength of the groups of the π-conjugated bridge. The vinyl-benzothiazole derivative 2b, with methoxyl as the donor group, exhibited the largest first hyperpolarizability β (1660 × 10−30 esu, 40 times greater than the standard reference pNA molecule) and the highest decomposition temperature (Td = 360 °C). The good balance between nonlinearity and thermal stability makes this compound a promising candidate as second harmonic generator (SHG) for nonlinear optics.