Random Lasing via Plasmon-Induced Cavitation of Microbubbles

Fluorescence enhancement of organic dyes by femtosecond laser-induced cavitation bubbles for crystal imaging

Fluorescence from organic dyes can be applied in many research fields such as imaging, bio-sensing and diagnosis. One shortcoming of fluorescence imaging is the limitation in emission intensity. Amplification of fluorescence signals can be achieved by the enhancement of localized electromagnetic fields. Metallic nanoparticles are widely applied to produce plasmon resonance, but they cause thermal damage to fragile bio-materials. In this study, we propose a method for nanoparticle-free fluorescence enhancement by ultrafast laser-induced cavitation bubbles in organic dye solutions. Fluorescence enhancement without the use of nanoparticles prevents potential hazards including thermal effects and biotoxicity. In order to achieve fluorescence enhancement in neat dye solution, cavitation bubbles were induced by focusing an 800 nm ultrafast laser beam. Another 400 nm laser beam was used to pump the gain medium. Fluorescence enhancement was observed in various dye solutions. The intensity and spectra of the fluorescence emission can be controlled by changing the power and focus of the excitation laser. According to time-resolved microscopy and simulation results, the cavity formed by the laser-induced bubbles results in the enhancement of the localized electromagnetic field and induces the amplification of the fluorescence signal. The bubble-enhanced fluorescence emission was used for imaging of protein crystals without causing thermal damage to the samples. This study provides an effective method for bio-compatible fluorescence enhancement and has application prospects in fields such as bio-imaging.

Ultra-bright and narrow-band emission from Ag atomic sized nanoclusters in a self-assembled plasmonic resonator

We have proposed, implemented and investigated a novel, efficient quantum emitter based on an atomic-sized Ag nanocluster in a plasmonic resonator. The quantum emitter enables the realization of: (1) ultra-bright fluorescence, (2) narrow-band emission down to 4 nm, (3) ultra-short fluorescence lifetime. The fluorescence cross-section of a quantum emitter is on the order of σ ∼ 10^-14 cm², which is comparable to the largest fluorescence cross-sections of dye molecules and quantum dots, and enables a light source with a record high intensity known only for plasmon nanolasers. The results presented suggest a unique method for fabricating nanoprobes with high brightness and wavelength-tunable spectrally narrow fluorescence, which is needed for multiplex diagnostics and detection of substances at extremely low concentrations.