The ro-vibrational ν ₂mode spectrum of methane investigated by ultrabroadband coherent Raman spectroscopy

We present the first experimental application of coherent Raman spectroscopy (CRS) on the ro-vibrational ν2 mode spectrum of methane (CH4). Ultrabroadband femtosecond/picosecond (fs/ps) CRS is performed in the molecular fingerprint region from 1100 to 2000 cm-1, employing fs laser-induced filamentation as the supercontinuum generation...

High-temperature rotational-vibrational O_2^[sbnd]CO₂ coherent Raman spectroscopy with ultrabroadband femtosecond laser excitation generated in-situ

We present ultrabroadband two-beam femtosecond/picosecond coherent Raman spectroscopy on the ro-vibrational spectra of CO₂ and O₂, applied for multispecies thermometry and relative concentration measurements in a standard laminar premixed hydrocarbon flame. The experimental system employs fs-laser-induced filamentation...

Coherent Raman spectroscopy on hydrogen with in-situ generation, in-situ use, and in-situ referencing of the ultrabroadband excitation

Time-resolved spectroscopy can provide valuable insights in hydrogen chemistry, with applications ranging from fundamental physics to the use of hydrogen as a commercial fuel. This work represents the first-ever demonstration of in-situ femtosecond laser-induced filamentation to generate a compressed supercontinuum behind a thick optical...

Water vapor in hydrogen flames measured by time-resolved collisional dephasing of the pure-rotational N₂ CARS signal

We present a novel diagnostic technique to probe water vapor (H₂O) concentration in hydrogen (H₂) combustion environments via the time-resolved measurement of the collisional dephasing of the pure-rotational coherent anti-Stokes Raman scattering (CARS) signal of nitrogen (N₂). The rotational Raman coherence of...

Coherent N₂⁺ emission mediated by coherent Raman scattering for gas-phase thermometry

We report on the generation of coherent emission from femtosecond (fs) laser-induced filaments mediated by ultrabroadband coherent Raman scattering (CRS), and we investigate its application for high-resolution gas-phase thermometry. Broadband 35-fs, 800-nm pump pulses generate the filament through photoionization of the N₂...

Cascaded coherent anti-Stokes Raman scattering for high-sensitivity number density determination in the gas phase

Cascaded coherent anti-Stokes Raman scattering (CARS) signals can be efficiently generated from CARS signals when propagating collinearly with the pump/Stokes and probe beams. This effect can be seen as the CARS beam acting as the probe beam and being inelastically scattered a ‘second time’ from the Raman coherence induced along the focus of...

Coherent Raman imaging thermometry with in-situ referencing of the impulsive excitation efficiency

Simultaneous detection of resonant and non-resonant femtosecond/picosecond coherent anti-Stokes Raman spectroscopy (CARS) signals has been developed as a viable technique to provide in-situ referencing of the impulsive excitation efficiency for temperature assessments in flames. In the framework of CARS thermometry, the occurrence of both a...

Pure-rotational 1D-CARS spatiotemporal thermometry with a single regenerative amplifier system

We report spatiotemporal pure-rotational coherent anti-Stokes Raman spectroscopy (CARS) in a one-dimensional imaging arrangement obtained with a single ultrafast regenerative amplifier system. The femtosecond pump/Stokes photon pairs, used for impulsive excitation, are delivered by an external compressor operating on a ∼35% beam split of the...