Filament-Driven Impulsive Raman Spectroscopy

Abstract

Vibrational Raman spectroscopy is performed in the gas phase using a femtosecond laser pulse undergoing filamentation as an impulsive excitation source. The molecular coherence induced by the filamentary pulse is subsequently probed using a narrowband, sub-picosecond laser pulse to produce Raman spectra of gas phase species in a few tens of milliseconds (~10 laser shots). Pulse shortening with concomitant spectral broadening during filamentation results in a pulse that is both sufficiently short and of sufficient spectral power density to impulsively excite the highest energy ground state vibrations (up to 4158 cm(-1) corresponding to H(2)). Gas phase detection of chloroform, methylene chloride, cyclohexane, toluene, pentane, triethylamine, ammonia, nitromethane, and gasoline is performed.

Roles of Free Electrons and H2O2 in the Optical Breakdown-Induced Photochemical Reduction of Aqueous [AuCl4]−

“…The interactions of intense, ultrashort laser pulses with condensed media give rise to nonlinear optical phenomena, enabling applications including: white light lasers, 1 remote optical sensing, 2,3 nanostructure writing onto solid surfaces, 4,5 and cellular nanosurgery. [6][7][8] The initial process of laser-energy deposition involves the generation of a localized, weakly ionized plasma, [8][9][10][11][12] which leads to supercontinuum emission (SCE), optical breakdown (OB) of the medium, or both.…”

“…The interactions of intense, ultrashort laser pulses with condensed media give rise to nonlinear optical phenomena, enabling applications including white light lasers, remote optical sensing, , nanostructure writing onto solid surfaces, , and cellular nanosurgery. − The initial process of laser-energy deposition involves the generation of a localized, weakly ionized plasma, − which leads to supercontinuum emission (SCE), optical breakdown (OB) of the medium, or both. , SCE results in a significant broadening of the initial input spectrum, and propagation of the white light as filaments in the medium, , while OB produces a dense, opaque microplasma when a sufficiently high free-electron density is achieved. , …”

The extreme nonlinear optics of gases and femtosecond optical filamentation

“…A different remote sensing approach, with molecular specificity, has been achieved by exploiting the extreme bandwidths and short pulses generated in filaments to impulsively pump characteristic vibrational states and then probe them with a narrower bandwidth, nonfilamenting pulse to generate a stimulated Raman spectrum for analysis. 25 The same group also directly measured the extreme optical pulse shortening, which takes place inside a filament core. 26 Since the first demonstration of femtosecond filamentation in air, 27 filaments typically have been generated using millijoule-level k ¼ 0.8 lm pulses of duration $100 fs from Ti:Sapphire lasers.…”

Absolute measurement of the ultrafast nonlinear electronic and rovibrational response inH2andD2

“…For example, h/∆t rot ∼ 0.03 eV in N 2 , where j max ∼ 10 at room temperature. However, for femtosecond pulse filamentation in gases, significant pulse self-shortening and spectral broadening can occur so as to excite vibrational modes even in H 2 (in which hΩ v ∼ 0.5 eV), driven by pulse spikes thought to be as short as several femtoseconds [14,15]. Nevertheless, to our knowledge there has never been a controlled experiment directly measuring the full, time-resolved electronic and rovibrational nonlinear response of a light molecule.…”