Pumping-power-dependent photoluminescence angular distribution from an opal photonic crystal composed of monodisperse Eu3+/SiO2 core/shell nanospheres.

High quality opal photonic crystals (PhCs) were successfully fabricated by self-assembling of monodisperse Eu(3+)/SiO(2) core/shell nanospheres. Angular resolved photoluminescence (PL) spectra of a PhC sample were measured with different pumping powers, and its PL emission strongly depended on spectroscopic position of the photonic stop band and the optical pumping power. Suppression of the PL occurred in the directions where the emission lines aligned with the center of the photonic stop band. Suppression and enhancement of the PL were observed at low- and high-pumping powers, respectively, in the directions where the emission lines were located at the edges of the photonic stop band. When pumping power exceeded 6 µJ/pulse, a super-linear dependence was found between the pumping power and PL intensity. The dramatic enhancement of PL was attributed to the amplification of spontaneous emission resulted from the creation of large population inversion and the slow group velocity of the emitted light inside the PhC. The opal PhC provided highly angular-selective quasi-monochromatic PL output, which can be useful for a variety of optical applications.

Photoinduced multimode coherent acoustic phonons of metallic nanoprisms and the effects of shape-induced anisotropic electronic stresses.

In this work we reported experimental measurements of ultrafast structural dynamics in metallic nanoprisms induced by a femtosecond laser pulse. The main focus of this study of anisotropic heating in nanoprisms is about laser fluence effects on photoexcitation of two planar coherent acoustic phonon modes, namely, the breathing mode and the totally symmetric mode. We presented a combined two-temperature model and 2-D Fermi-Pasta-Ulam model to explain both the dependence of the initial phases and the mode weight on the excitation power. Our transient optical absorption data for both the initial fast monotonic decay and the subsequent coherent acoustic oscillations clearly indicate the presence of anisotropic thermal expansion in nanoprisms.

Suppression of spatial hole burning in a solid-state laser with the degenerate resonator configuration.

Under degenerate resonator configuration and tightly focused pump beam in a linear-cavity solid-state laser, the spatial hole-burning effect can be suppressed. This laser can attain very high intensity in the gain medium due to shrinkage of its beam waist to match the pump beam and therefore most of its gain is depleted even by a standing wave. This was demonstrated by a simulation with spatial dependent rate equations and experiment results of a plano-concave Nd:YVO4 laser. The suppression effect was observed up to 20 times the pump threshold.

Bottle beam from a bare laser for single-beam trapping.

We demonstrate that a laser beam converging from a specific transverse mode is a bottle beam, as described in J. Opt. Soc. Am. B 20, 1220 (2003). To our knowledge, this is the first time that a bottle beam has been generated directly from a laser. By calculating the radiation forces on a dielectric Rayleigh sphere in the bottle beam, we show that the single beam can trap high-refractive-index particles at the multiple axial sites of intensity maxima, and it can confine low-index particles on a transverse plane within the bottle regions. Such a novel laser beam may have other applications.

Direct generation of optical bottle beams from a tightly focused end-pumped solid-state laser.

We demonstrate that various optical bottle beams can be directly generated from a tightly focused end-pumped Nd:YVO4 laser. By controlling the size of pump beam and intracavity aperture in a planoconcave cavity, we obtain well contrasting optical bottles with semiconfocal, 1/3-, and 1/5-degenerate cavity configurations. These beams result, respectively, from the superposition of the fundamental mode and the corresponding lowest degenerate transverse eigenmode, which is in-phase at their beam waists. Unlike that of our previous simulation model, this new observation is universal; it is suitable for any kind of gain media in tightly end-pumped lasers.