Granthamborch2309

We report on a compact, ultrahigh-vacuum compatible optical assembly to create large-scale, two-dimensional optical lattices for use in experiments with ultracold atoms. The assembly consists of an octagon-shaped spacer made from ultra-low-expansion glass, to which we optically contact four fused silica cavity mirrors, making it highly mechanically and thermally stable. The mirror surfaces are nearly plane-parallel, which allows us to create two perpendicular cavity modes with diameters ∼1m m. Such large mode diameters are desirable to increase the optical lattice homogeneity, but lead to strong angular sensitivities of the coplanarity between the two cavity modes. We demonstrate a procedure to precisely position each mirror substrate that achieves a deviation from coplanarity of d=1(5)µm. Creating large optical lattices at arbitrary visible and near-infrared wavelengths requires significant power enhancements to overcome limitations in the available laser power. The cavity mirrors have a customized low-loss mirror coating that enhances the power at a set of relevant visible and near-infrared wavelengths by up to 3 orders of magnitude..The coherent propagation and amplification of high-power laser radiation in a multicore fiber consisting of a square array of weakly bound cores are studied. Exact stable analytical solutions are found for the out-of-phase mode, which describes the coherent propagation of wave beams in such fibers. The analytical results are confirmed by direct numerical simulation of the wave equation. The stability conditions of the out-of-phase mode in the active medium are found.Optical frequency conversion in semiconductor nanophotonic devices usually imposes stringent requirements on fabrication accuracy and etch surface roughness. Here, we adopt the concept of bound-state-in-continuum (BIC) for waveguide frequency converter design, which obviates the limitations in nonlinear material nano-fabrication and requires to pattern only a low-refractive-index strip on the nonlinear slab. Selleck compound 991 Taking gallium phosphide (GaP) as an example, we study second-harmonic generation using horizontally polarized pump light at 1.55 µm phase matching to vertically polarized BIC modes. A theoretical normalized frequency conversion efficiency of 1.1×104 % W -1 c m -2 is obtained using the fundamental BIC mode, which is comparable to that of conventional GaP waveguides.We investigated the performance of electric-field-induced second-harmonic generation (E-FISHG) by spectroscopic measurement using high-intensity femtosecond laser pulses. The second-harmonic intensity increased quadratically versus the applied electric field, as expected from the theory, up to 15 kV/cm with the laser energy up to 2.5 mJ, which is ∼5 times higher than the observable optical breakdown threshold. In addition, when the laser energy was 2.8 mJ, ∼80 times signal intensity at 0.23 mJ was obtained. These results suggest that the electric-field measurement by E-FISHG with high-intensity second harmonics is expected by using high-intensity laser pulses above the observable optical breakdown threshold. Spectroscopic measurement shows no E-FISHG of white light generated by self-phase modulation in laser-induced filament.We propose a $2 \times 2$ thermo-optic switch with high switching performance. The switch is based on multimode interferometer (MMI) couplers and a Mach-Zehnder interferometer (MZI) structure, where the phase arms are designed as laterally supported suspended ridge waveguides (LSSRWs) with a metallic heater placed on the slab. It is experimentally demonstrated that this switch has a power consumption of 1.07 mW, a thermal time constant $\sim4.7\;\unicodex00B5 \rm s$, an extinction ratio $\sim30\;\rm dB$, and an insertion loss $\sim0.5\;\rm dB$. Particularly, the corresponding figure of merit (FOM) has been improved by 1 order magnitude compared with general thermo-optic switches. This $2 \times 2$ thermo-optic MMI-MZI switch may find potential application for network reconfiguration and on-chip optical information processing.The microscopic mechanism for ionic influence on the hydrogen bond network of water has not been fully understood. Here we employ the terahertz Kerr effect (TKE) technique to map the intermolecular hydrogen bond dynamics in a series of aqueous halide solutions at the sub-picosecond scale. Compared with pure water, the significantly enhanced bipolar TKE response associated with polarization anisotropy in an ionic aqueous solution is successfully captured. We decompose the measured TKE response into different molecular motion modes and demonstrate that the obviously increasing positive polarity response is mainly due to the anion-water hydrogen bond vibration mode with the resonant THz electric field excitation. Our measurement results provide an experimental basis for further insight into the effects of ions on the structure and dynamics of a hydrogen bond in water.The effective fifth-order susceptibility, $\chi_\rm eff^(5)$, of two-dimensional (2D) semiconducting layered transition metal dichalcogenide (LTMD) molybdenum disulfide ($\rm MoS_2$) is reported here for the first time, to the best of our knowledge. Using the $ Z $-scan technique with a laser operating at 800 nm, 1 kHz, 100 fs, we investigated the nonlinear behavior of $\rm MoS_2$ suspended in acetonitrile (concentration, 70 µg/ml). The effective nonlinear refractive index $n_4,eff = - (7.6 \pm 0.5) \times 10^- 26\; \rm cm^4/\rm W^2$, proportional to $\rm Re\chi_\rm eff^(5)$, was measured for monolayer $\rm MoS_2$ nanoflakes, prepared by a modified redox exfoliation method. We also determined the value of the nonlinear refractive index $n_2 = + (4.8 \pm 0.5) \times 10^- 16\;\rm cm^2/\rm W$, which is related to the material's effective third-order optical susceptibility real part, $Re\chi_\rm eff^(3)$. For comparison, we also investigated the nonlinear response of tungsten disulfide ($\rm WS_2$) monolayers, prepared by the same method and suspended in acetonitrile (concentration, 40 µg/ml), which only exhibited the third-order nonlinear effect in the same intensity range, up to $120\;\rm GW/\rm cm^2$. Nonlinear absorption was not observed in either $\rm MoS_2$ or $\rm WS_2$.