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...

Single-shot CARS Imaging of Near-Wall Turbulent Reacting Flows

In practical combustion devices featuring high power densities, the interaction between flames and walls may have a significant impact on the thermodynamic efficiency and the formation of pollutants (e.g. unburned hydrocarbons and carbon monoxide). The common understanding is that at the region near the wall ~ 1 mm, where the solid metal surface...

Development of Robust Ultrafast CARS Thermometry and Species Detection (PPT)

Development of two-beam femtosecond/picosecond CARS for high-fidelity thermometry in flames

We develop simultaneous ultrafast CARS thermometry and species detection as a unique tool to investigate combustion modes with reduced emissions of NOx, particulates, CO and unburned hydrocarbons. Coherent anti-Stokes Raman spectroscopy (CARS) has been developed over the last 4 decades for various gas-phase-, plasma-, flame- and combustion...

Flame-wall interaction at enhanced turbulence intensities as characterized by ultrafast 1d-cars thermometry

In practical combustion-based devices, such as internal combustion (IC) engines and gas turbines for power generation, there exists significant interaction between gas-phase combustion and metal surfaces. The nature of this heterogeneous interaction is complex, involving both physical and chemical effects. The metal surface is generally much...

A small porous-plug burner for studies of combustion chemistry and soot formation

We have developed and built a small porous-plug burner based on the original McKenna burner design. The new burner generates a laminar premixed flat flame for use in studies of combustion chemistry and soot formation. The size is particularly relevant for space-constrained, synchrotron-based X-ray diagnostics. In this paper, we present...

Development of simultaneous hyperspectral coherent Raman imaging for advancing reduced emission combustion technology

Overall aim and key objectives Advances in optical imaging techniques over the past decades have revolutionized our ability to study chemically reactive flows encountered in air-breathing combustion systems. Emerging technology for unravelling clean- and efficient heat release is needed for advancing new reduced...