Coherent Anti-stokes Raman Research Articles

Determination of temperature and concentration of molecular nitrogen, oxygen and methane with coherent anti-stokes raman scattering

Temperature and concentration measurements by Coherent Anti-Stokes Raman Scattering (CARS) of molecular nitrogen, oxygen and methane were carried out. A comparison of corrected thermocouple and CARS temperature measurements in a high-temperature furnace up to 2000 K is presented. The temperature dependent CARS spectra of N2 and O2 are evaluated by a simulation program. Agreement between CARS and thermocouple temperatures is obtained within 40 K for N2 and 80 K for O2. Good agreement is found between measurements and calculations of the decrease of CARS intensity with temperature. Various “quick-fit” methods for N2-and O2-temperature measurements from temperature sensitive spectral parameters were tested. Temperature dependent CARS spectra of thev1-fundamental of methane are recorded and the methane CARS intensity as function of temperature is measured.

High-resolution coherent anti-stokes raman spectroscopy measurements of carbon monoxide linewidths in a flame

We have used a high-resolution (0.005 cm −1 ) coherent anti-Stokes Raman spectroscopy (CARS) experiment to obtain fully resolved CARS spectra in a flame. Spectra of Q -branch transitions of CO and O -branch transitions of N 2 were analyzed to obtain J-dependent Raman linewidths. The CO linewidths are compared to infrared P- and R-branch linewidths measured by other workers in similar rich methane/air flames. The results demonstrate the utility of high-resolution CARS for providing spectral information needed for applying conventional CARS to combustion environments.

Analytical expressions for coherent anti-stokes raman spectral (CARS) profiles

Analytical expressions are presented that allow the calculation of coherent anti-Stokes Raman spectra (CARS) of gas phase molecules with nonoverlapping lines. The results of the evaluation of Kataoka-Teets and Yuratich convolution integrals are given for six cases: scanning and multiplex CARS where the pump and Stokes laser intensity spectral profiles are Gaussian, Lorentzian, and the mixed configuration of Lorentzian pump and Gaussian Stokes profiles. Useful approximations to these expressions are discussed.

Coherent anti-stokes raman spectroscopic measurements of temperature and acetylene spectra in a sooting diffusion flame: Colloquium on combustion diagnostics

We report coherent anti-Stokes Raman spectroscopy (CARS) measurements of nitrogen and acetylene Q-branch spectra in a sooting laminar ethylene/air diffusion flame, previously characterized by thermocouple and laser scattering/extinction measurements. Good agreement between CARS and thermocouple temperature measurements was obtained throughout the flame. Effects of the presence of heavy soot-loading on the CARS measurements were minimized by reducing the acceptance angle and spectral bandwidth of the CARS detection system. We also present the first known CARS measurements of flame-generated acetylene. The acetylene spectra are in good agreement with preliminary calculated spectra.

Neutral radical detection in silane glow-discharge plasma using coherent anti-stokes raman spectroscopy

RF glow discharges of silane have been investigated using CARS technique, and a weak signal assigned to the ν 1 Q-band of SiH 2 has been observed at around 2030 cm −1 for the first time. The number density of SiH 2 in the plasma has been estimated and is discussed in relation to the magnitude of SiH 4 dissociation rate independently determined also by CARS.

Polarization suppression of the nonresonant background in three-wave coherent anti-stokes raman spectroscopy (CARS)

Polarization suppression of the nonresonant background in three-wave coherent anti-stokes raman spectroscopy (CARS)

Coherent anti-stokes raman scattering (cars) of large C 2H 4Ar clusters

CARS spectra from a supersonic molecular beam of ethylene/argon mixtures show a strong signal close to the Q branch of the ν 2 vibration of ethylene. The pressure dependence and scaling laws for a condensing molecular beam indicate that it is due to large C 2H 4Ar clusters. The experiment did not permit the identification of the clusters.

Observation of coherent anti-stokes continuum resonance raman scattering in iodine vapor

High-resolution CARS spectra of molecular iodine were recorded with excitation frequencies in resonance with the absorption continuum of the B( 3∏ o+ u) and the repulsive 1∏ iu state. Band-shapes are explained by a calculation of the third-order non-linear susceptibility for CARS x (3)(μ AS). There is semi-quantitative agreement between the observed and calculated spectra.

Collision-free coherent anti-stokes raman spectroscopy (cars) of molecular photofragments

Collision-free CARS spectra of molecular oxygen produced in the viable photodissociation of ozone have been obtained. The nascent rotational and vibrational state distributions of the oxygen have been extracted from these spectra.

Observation of saturation broadening of the coherent anti-stokes raman spectrum (cars) of acetylene in a pulsed molecular beam

Reported is the first observation of saturation broadening in a high-resolution coherent Raman spectrum of the v 2 Q-branch of acetylene. The measured saturation broadening of 1050 MHz is significantly greater than the calculated ac Stark broadening of less than 100 MHz.

CARS法による拡散火炎中の水素濃度の測定

A simple system of CARS (Coherent AntiSTOKES RAMAN Spectroscopy) was constructed and applied to measurements of the distribution of the concentration of hydrogen in a hydrogenair diffusion flame. The apparatus is similar to that used by TARAN et al.: The incident beam from a giant pulse ruby laser into a cell filled with high pressure hydrogen generates stimulated RAMAN emissions. The first order STOKES light selected from the emissions together with the original ruby laser light is focused in the system containing hydrogen and the intensity of CARS light thus generated is measured. Using the method similar to that for estimating the density distribution of a axially symmetric system from a shadowgraph, the distribution of hydrogen concentration in the flame could be determined quantitatively. The results were compared with that of the calculation using the BURKE-SCHUMANN's model and the problems which should be considered in experiments with this technique were discussed.

Resonance Raman and coherent anti-stokes Raman scattering spectra of flavin derivatives. Vibrational assignments and the zwitterionic structure of 8-methylamino-riboflavin.

Resonance Raman and coherent anti-stokes Raman scattering spectra are reported for flavins modified by deprotonation at N3 and by CH substitution for N1, N3 and N5, using laser excitation in resonance with the visible electronic transition. Vibrational shifts are used to make qualitative assignments of the observed vibrational modes. Both 8-CH3NH- and ionized 8-OH-riboflavin were found to give markedly different spectra patterns form flavin itself; this observation supports a partial zwitterionic structure for the 8-CH3NH derivatives.

Coherent anti-stokes raman scattering in gaseous nitrogen with picosecond pulses

The use of CARS as a prove of gas phase molecular concentration has been extended into the picosecond regime. A double-beam configuration employing single pulses from a mode-locked Nd:glass laser has allowed measurement of N 2 ( 1Σ g, ν = 0) pressures on accuracy of better than 10% with 8 ps time resolution. This technique shows promise for the study of dynamics of gas phase photodissociation processes.

An approach to rotational temperatures of nitrogen in diffusion flames using coherent anti-stokes raman scattering

An approach to rotational temperatures of nitrogen in diffusion flames using coherent anti-stokes raman scattering

Temperature and concentration measurements in reactive media by coherent anti-stokes raman scattering

We present the application of Coherent anti-Stokes Raman Scattering (CARS) to the investigation of the diffusion flame on a wetted spherical burner. The theory is reviewed briefly, together with instrumental considerations. The setup is described. Temperatures and concentrations were measured from spectral contours of N 2 ; CO was also detected and its concentration profile was plotted.