Zhenhuan Yi

Ultralow-power local laser control of the dimer density in alkali-metal vapors through photodesorption

Ultralow-power diode-laser radiation is employed to induce photodesorption of cesium from a partially transparent thin-film cesium adsorbate on a solid surface. Using resonant Raman spectroscopy, we demonstrate that this photodesorption process enables an accurate local optical control of the density of dimer molecules in alkali-metal vapors.

Pulsed cooperative backward emissions from non-degenerate atomic transitions in sodium

We study backward cooperative emissions from a dense sodium atomic vapor. Ultrashort pulses produced from a conventional amplified femtosecond laser system with an optical parametric amplifier are used to excite sodium atoms resonantly on the two-photon 3S?4S transition. Backward superfluorescent emissions (BSFEs), both on the 4S?3P and 4S?3P transitions, are observed. The picosecond temporal characteristics of the BSFE are observed using an ultrafast streak camera. The power laws for the dependencies of the average time delay and the intensity of the BSFEs on input power are analyzed in the sense of cooperative emission from nonidentical atomic species. As a result, an absolute (rather than relative) time delay and its fluctuations (free of any possible external noise) are determined experimentally. The possibility of a backward swept-gain superfluorescence as an artificial laser guide star in the sodium layer in the mesosphere is also discussed.

Surface-Enhanced Raman Scattering on Template-Embedded Gold Nanorod Substrates

Surface-enhanced Raman scattering (SERS) of rhodamine 6G was investigated on template-embedded gold nanorods produced by anodic aluminum oxide template-assisted nanofabrication. A signal enhancement of about 106 was obtained. Two-dimensional arrays of gold nanospheres with different diameters and gap sizes were used as simplified model systems. SERS substrate design principles were investigated in order to achieve maximum electromagnetic enhancement of both the incident and Raman scattered fields.