Second-order nonlinear optical properties of composite material of an azo-chromophore with a tricyanodiphenyl acceptor in a poly(styrene-co-methyl methacrylate) matrix

© 2017 Elsevier B.V.The composite material of new synthesized 4-((4-(N,N-n-dibutylamino) phenyl)diazenyl)-biphenyl-2,3,4-tricarbonitrile (GAS dye) in commercial poly(styrene-co-methyl methacrylate) (PSMMA) was prepared, poled and its nonlinear optical properties compared with DR1 dye were studied. High thermal stability of the composite material was revealed, and the maximal concentration of the chromophore was found to reach ∼20 wt%. The dipole moment, polarizability tensor, and first hyperpolarizability tensor of the investigated dyes were calculated by within the framework of the coupled perturbed density functional theory. A nanosecond second-harmonic generation Maker fringes technique was used which is capable of providing the magnitude of the second-order nonlinearity of optical materials at a wavelength of 1064 nm. For the tested GAS–PSMMA composite material, maximal coefficient d33 was found to be 50 pm/V. The nonlinear optical response, which was achieved here, shows possible usefulness of the GAS dye as a component for molecular design of nonlinear-optical materials with advanced characteristics

Searching for chameleon-like scalar fields with the ammonia method

(Abridged) The ammonia method, which has been proposed to explore the electron-to-proton mass ratio, mu = m_e/m_p, is applied to nearby dark clouds in the Milky Way. This ratio, which is measured in different physical environments of high (terrestrial) and low (interstellar) densities of baryonic matter is supposed to vary in chameleon-like scalar field models, which predict strong dependence of both masses and coupling constant on the local matter density. High resolution spectral observations of molecular cores in lines of NH3 (J,K) = (1,1), HC3N J = 2-1, and N2H+ J = 1-0 were performed at three radio telescopes to measure the radial velocity offsets, DeltaV = V_rot - V_inv, between the inversion transition of NH3 (1,1) and the rotational transitions of other molecules with different sensitivities to the parameter dmm = (mu_obs - mu_lab)/mu_lab. The measured values of DeltaV exhibit a statistically significant velocity offset of 23 +/- 4_stat +/- 3_sys m/s. When interpreted in terms of the electron-to-proton mass ratio variation, this infers that dmm = (2.2 +/- 0.4_stat +/- 0.3_sys)x10^{-8}. If only a conservative upper bound is considered, then the maximum offset between ammonia and the other molecules is |DeltaV| <= 30 m/s. This gives the most accurate reference point at z = 0 for dmm: |dmm| <= 3x10^{-8}.Comment: 23 pages, 11 figures, 6 tables. Accepted for publication in A&A. Title and text corrected, references update

Quantum cascade laser frequency stabilisation at the sub-Hz level

Quantum Cascade Lasers (QCL) are increasingly being used to probe the mid-infrared "molecular fingerprint" region. This prompted efforts towards improving their spectral performance, in order to reach ever-higher resolution and precision. Here, we report the stabilisation of a QCL onto an optical frequency comb. We demonstrate a relative stability and accuracy of 2x10-15 and 10-14, respectively. The comb is stabilised to a remote near-infrared ultra-stable laser referenced to frequency primary standards, whose signal is transferred via an optical fibre link. The stability and frequency traceability of our QCL exceed those demonstrated so far by two orders of magnitude. As a demonstration of its capability, we then use it to perform high-resolution molecular spectroscopy. We measure absorption frequencies with an 8x10-13 relative uncertainty. This confirms the potential of this setup for ultra-high precision measurements with molecules, such as our ongoing effort towards testing the parity symmetry by probing chiral species