In combustion and gasification diagnostics, the knowledge of temperature distribution and gas component concentration is crucial in order to understand or optimize such processes. In this study, we compare ultra‐broadband two‐beam femtosecond/picosecond coherent anti‐Stokes Raman scattering (fs/ps CARS) with spontaneous Raman scattering to retrieve temperature and concentration information. We show that two‐beam fs/ps CARS can be effectively used for concentration measurements down to 0.5% CO in gas mixtures of CO2 and N2. With two‐beam fs/ps CARS, thermometry from ~200°C to ~800°C based on CARS spectra of CO2 or H2 is shown. With spontaneous Raman scattering, concentration determination is well performed in gas mixtures of H2, N2, and CO2 with H2 content ranging from 16% to 0.5% at room temperature and from 16% to 7% H2 at ~900°C. Besides, thermometry in gas mixtures of N2 and CO2 from ~200°C to ~600°C based on spontaneous Raman scattering is also shown in this study.

The gasification of carbonaceous feedstocks usually takes place in high-pressure, high-temperature reactors, making it difficult to have direct access to the reaction site. Since the greenhouse gas CO2 is a major component in gasification, there is an urgent need for a better understanding of these processes. In this study, we investigate carbon gasification in a CO2 atmosphere using the ultrabroadband, coherent anti-Stokes Raman spectroscopy (CARS). In contrast to conventional three beam CARS, this approach allows the simultaneous determination of the temperature of the CO2 atmosphere and the concentration of the reaction product CO. We show that temperature drop and increase in CO are directly linked to the feedstock conversion measured by thermogravimetric analysis. Due to gasification, a considerable temperature drop of up to 200 K was measured, which was predicted by simulations in the literature but has not been confirmed experimentally yet.

We investigate the spectral properties of ps laser-induced filamentation in air using an ultrafast thin-disk based amplifier at a central wavelength of 1030 nm with a maximum pulse energy of 60 mJ at a repetition rate of 1 kHz. We show that the spectrum induced by filamentation in air is sufficiently broad to excite ro-vibrational Raman transitions in N2, O2 and CH4. The excitation is probed with the second harmonic (515 nm) to generate CARS signals in air. Furthermore, we investigate the influence of optical windows on the CARS signal for applications in combustion and gasification diagnostics.

Due to their large spectral bandwidth sub ∼20 fs pulses are a versatile tool in spectroscopy, but for applications in gases comparably high pulse energies are required. These pulses are easily subject to distortions of the spectral shape, phase and shot-to-shot stability. We investigate the excitation efficiency for two-beam ultrabroadband fs/ps coherent anti-Stokes Raman scattering (CARS) using a shot-to-shot stable BBO-based optical parametric chirped pulse amplifier (OPCPA). Up to 10 bar, quantitative concentration measurements with and without consideration of the excitation efficiency measured in argon are investigated for ternary gas mixtures with Raman shifts up to ∼3000 cm−1.

We investigate the coherent anti-Stokes Raman scattering (CARS) in air generated by the spectral broadening of laser induced filamentation at a pulse duration of ~1 ps and a central wavelength of ~1 μm.