We experimentally investigate the interaction of two collinearly counter-propagating filaments in air. The fluorescence is enhanced by 4 times due to the increase of the clamped intensity and electron (or plasma) density. The output energy at the end of a filament, the spectra of the excitation beams, and the fluorescent intensity are found to be dependent on the relative pulse delays between the counter-propagating pulses. The results indicate that the modulation of the filamentation-induced fluorescence intensity with another filament launched from the opposite direction is feasible, which provides a new perspective for studying the interaction of filaments and may improve the detection sensitivity for fluorescence sensing. 

Experimental study on counter-propagating filaments in air

We report on the experimental demonstration of the laser induced aerosol formation driven by fs high-energy mid-IR pulses and facilitated by resonance excitation and subsequent oxidation of the ambient volatile organic compounds.

Atmospheric Photochemistry of Volatile Organic Compounds Triggered by Mid-IR Filaments

Association reactions by femtosecond laser filamentation in gaseous C2H4 were studied by time-of-flight mass spectrometry of neutral reaction products. Direct sampling from the reaction cell to a mass spectrometer via a differential pumping stage allowed the identification of various hydrocarbon molecules C n H m with n = 3-7 and m = 4-7, which includes species not observed in the previous studies. It was found that products containing three and four carbon atoms dominate the mass spectrum with smaller yields for higher-mass species, suggesting that carbon chain growth proceeds through the reaction with C2H4 in the reaction cell. The product distribution showed a clear dependence on the laser pulse energy for filamentation.

Yukari Takeuchi

Papers

Association Reaction of Gaseous C2H4 in Femtosecond Laser Filaments Studied by Time-of-Flight Mass Spectrometry.