Investigation of oscillator strength enhancement of electric dipole forbidden transitions in optical near field

点击翻译按钮获取中文摘要

1 Estimation of electric dipole forbidden transition efficiency in optical near fields generated by a sub-wavelength slit arrayOptical near fields generation by a periodically structured 50 nm width slit array of a 50 nm thick gold film were calculated with the FDTD (Finite Difference Time Domain) method, which was developed in this project. The efficiencies of the electric quadrupole (E2) and magnetic dipole (M1) transitions, which are modified by the gradient of the excitation light field, were evaluated for the calculated optical fields. The E2 transition efficiency is largely enhanced in the case where the light polarization of the incident light is perpendicular to the slit direction while such enhancement is not seen for the M1 transition in this polarization. The large enhancement of the E2 transition efficiency mainly originates from the field concentration and the large spatial modulation at the slit edge. In the case where the incident light is parallel to the slit, the enhan … More cement is small for both the E2 and Ml transition, which is consistent with the modification factor of (k_0ld)^<-2>, where K_0 and d are the wavenumber of the homogenously propagating light in vacuum and the slit width, respectively. The enhancement of the E2 excitation efficiency was also calculated for the 1s-ortho exciton in Cu_2O in the optical near field generated by a sub-wavelength slit array. It was suggested that the enhancement is affected by the surface plasmon resonance.2 Observation of emission spectra of the 1s-ortho exciton in Cu_2O through a sub-wavelength slit arrayWith an electron beam lithographic method, a periodically structured gold slit array with 50 nm thickness was fabricated on a Cu_2O crystal surface. We confirmed that the emissions of the electric quadrupole (E2) and dipole (El) transitions of the 1s-ortho excitons in Cu_2O can be observed through the slit array. So far, effects of the slit array to the E2 emission have not been detected. The polarization and slit-period dependences of the emission intensities were observed.3 Observation of the magnetic dipole transition of O_2We developed a spectroscopic system with a dipole laser to observe the light absorption due to the magnetic dipole (M1) transition of O_2 (A-band, 763 nm). In order to make the system high sensitive, we merged the system with an off-axis cavity. It was confirmed that the absorption spectrum can be measured with sufficient spectral resolution. The effect of multi-reflection in the cavity for the increase in the sensitivity was also confirmed. Less