The metal halide indium iodide (InI) is used as an important additive to mercury discharge lamps. The aim of this paper is to prepare resonant coherent anti-Stokes Raman scattering (RECARS) experiments for measuring concentration and temperature profiles of InI in commercially available metal halide lamps. The spectral positions of possible RECARS lines of InI (double and triple resonances) are calculated up to rotational quantum number J = 280 and vibrational quantum number v = 10. There is evidence for triple resonances leading to strong RECARS signals at J = 174 and J = 231. Dipole transition moments are calculated, which are important input data for the determination of the RECARS spectra. A degenerate-folded BOXCARS setup with a frequency-tripled Nd:YAG laser at 355 nm pumping two dye-laser systems oscillating near 411 nm is utilized to detect RECARS signals of the rovibronic transitions between X:(1)Sigma(+) and A:(3)Pi(0)(0(+)) states of InI. The laser output is attenuated to prevent saturation of the spectra. The tunable dye-laser systems have good beam-pointing stability and a small spectral width (<0.07 cm(-1)). Measured RECARS spectra from a pure InI vapor quartz cell at p = 120 Pa and T = 880 K are compared with theoretical data and good agreement is obtained with respect to the spectral position and RECARS intensity. The scatter signals are achieved with laser-pulse energies of less than 1 µJ. A collision-constant Gamma = 0.0025 cm(-1) describes the line broadening best. The experiments are also performed at a partial InI pressure of 1.12 kPa, a partial Hg pressure of 112 kPa, and a temperature of T = 1073 K and could be interpreted with a broadening constant Gamma = 0.23 cm(-1). Temperature measurements were performed between 900 and 1200 K with an accuracy of 7%. Copyright 2000 Academic Press.

A coherent anti-Stokes Raman scattering (CARS) set-up has been developed to study the reduction of nitric oxide (NO) by a microwave-generated nitrogen plasma under atmospheric pressure. A frequency-doubled Nd:YAG laser provides two pump beams at nm and excites a dye laser, which is tunable between 588 and 615 nm. Density and temperature profile measurements of in the cylindrical microwave discharge by the common CARS technique deliver an axis temperature of 7000 K at P = 800 W input power. The detection of a minority of NO in under atmospheric pressure by CARS is limited to a concentration of 2500 ppm. By applying polarization-sensitive CARS the detection limit can be scaled down to 200 ppm. This technique is used to examine the reduction of NO in a reaction chamber fed by vibrationally excited and N entering the chamber through a nozzle. Behind the nozzle most of the NO is decomposed. An overall reduction efficiency for NO of 65-85% was found, decreasing with growing NO concentration.

A coherent, anti-Stokes Raman scattering (CARS) setup has been developed to detect contamination of atmospheric nitrogen by nitric oxide (NO). To allow spatially resolved measurements and the possibility of utilizing windows close by the test volume, we chose the folded BOXCARS setup with a CARS lens of focal length 0.5 m and a diameter of 80 mm. A frequency-doubled Nd:YAG laser (lambda = 532 nm; E-L = 50 mJ; tau(L) = 10 ns; repetition rate, 10 s(-1); bandwidth, 0.05 cm(-1)) serves as pump for a dye laser (E-p = 25 mJ; E-L = 2 mJ; bandwidth, 0.03 cm(-1)), which is tunable between 585 and 615 nm. Nitric oxide CARS spectra including the first hot band have been measured with high spectral resolution in a temperature range from 300 to 800 K. The detection limit of NO is on the order of 0.25% in nitrogen under atmospheric pressure. With suppression of the nonresonant background in the application of polarization CARS, the detection limit could not be scaled down in a desirable manner, The comparison between measured and calculated CARS spectra of NO in an N-2 surrounding confirms the reliability of the energy matrix elements and the Lorentzian width of the type Gamma(p,T = 0.06(298 K/T)(0.6)p/p(0) cm(-1).

Resonance enhanced CARS and LIF have been applied to the CH radicals in a microwave excited Ar/H\(_2\)/CH\(_4\) plasma (\(p = 21\) Pa, \(P_{\rm Mikro} = 2.7\) kW). Both techniques yield similar nonthermal rotational population distributions of CH(X\(^2\Pi_r\)) in its vibrational ground state (\(v=0\)), which can be described by two rotational temperatures, \(T_{\rm rot,1} \approx 600\) K being in the order of the gas temperature for rotational states with \(N \le 7\), and a considerably higher \(T_{\rm rot,2}\) for the higher rotational states. This result is in goodagreement with previous resonance CARS and LIF measurements in similar plasmas. With resonance CARS additional measurements on CH in the \(v=1\) state could be performed yielding a vibrational temperature of 2440 K, the total CH density was about \(1.6 \times 10^{18}\) m\(^{-3}\). The detection limits of both techniques are determined, in our case about \(2 \times 10^8\) CH radicals per quantum state in the detection volume, and their advantages and disadvantages are discussed.

Methyl (CH3) is generated by photodissociation of methyliodide (CH3I) applying an excimer laser operating at 248 nm. The CH3 is detected using coherent anti-Stokes Raman spectroscopy (CARS). The CH3 density is deduced by monitoring simultaneously the reduction of the CARS signal of the parent molecule CH3I. CARS spectra of CH3 (v = 3005 cm−1) are recorded and the rotational temperature is evaluated. The CARS signal intensities are compared with those of deuterium and methane in order to obtain an absolute calibration of the Raman cross section. The measurements yield a Raman cross section of dσ/dΩ = 7 × 10−31cm2/sr at λP = 532 nm.

Resonance enhanced coherent anti-Stokes Raman scattering (RECARS) is applied to the CH radical produced in a microwave (2.45 GHz) excited ArCH4 plasma. The electronic A2Δ − X2Πr transition of the CH radical is used to obtain a resonance enhancement of the rotational CARS lines. With this technique rotational lines up to N = 15 and up to v = 2 are measured. In good agreement with earlier LIF measurements in similar plasmas we obtain two rotational temperatures for CH(X2Πr), Trot,1 = 671 ± 32 K for N < 8, and Trot,2 = 1400 ± 91 K for N ≥ 8. The vibrational temperature is about 2800 K and the CH density is estimated to be in the range of 1010 to 1011 cm−3.

Coherent anti-Stokes Raman scattering (CARS) is applied to a microwave (2.45 GHz) excited plasma used for plasma enhanced chemical vapor deposition. The applicability of CARS to low pressure (2 Pa) plasmas is verified, and the absence of saturation is carefully checked. Ground state concentration profiles as well as rotational temperatures of CH4 are presented with high spatial and temporal resolution. The measurements show a decrease of the CH4 ground state density under the influence of the plasma down to ≊25% (nCH4=1.0×1020 m−3) of its initial value. The rotational temperature is nearby room temperature across the total discharge volume. A straightforward modeling of the plasma explains the decrease of CH4 ground state densities as an effect of electron collisions and delivers an approximate value of the electron temperature of about 3 eV.

A narrow-band BOXCARS system has been used for spatially resolved diagnostics of a microwave discharge in an axial-flow CO2 laser module. Axial and transverse distributions of the vibrational and rotational temperatures of N2 and CO as well as those of the CO2 dissociation degree have been determined. They have been used as a reference for a vibrational kinetic model for the laser medium. This allowed determination of an approximate electron density distribution along the discharge tube. A CCD camera has been used for visualizing the intensity distribution in the beam overlap region and checking its effect on the CARS saturation behaviour.

Concerns experimental investigations of the glow to arc transition in a transverse-flow CO2 laser discharge in a pressure range of 30-100 hPa. Constriction development was recorded with a high-speed film camera and storage oscilloscope, and the maximum density of the electric power deposited in the glow discharge below the instability threshold was determined. Spatially resolved diagnostics of the discharge prior to the instability onset were carried out with an electric probe and a boxCARS set-up. Constrictions start to develop in discharge regions characterized by high plasma density or density gradient, large pressure pulsations or high density of negative ions. They propagate towards the electrodes at velocities in the range of 100-800 m s-1. The electric field inside a constriction is of the order of 104 V m-1. The probable mechanism of their development involves avalanche ionization at the constriction head without thermalization in the filament. The influence of discharge and flow conditions on the instability threshold was investigated. The favourable effect of preionization and flow turbulence on the discharge stability was confirmed. Also the possibility of raising the instability threshold by using an uncooled cathode was ascertained. An adjustment of the cathode profile is proposed as a simple and effective means of ensuring a uniform current distribution over the discharge channel width, which is a prerequisite of a stable discharge operation and laser action at increased electric power densities.

CARS (Coherent Anti-Stokes Raman Scattering) has developed into a powerful tool for studying molecular systems. One of its possibilities is to derive vibrational and rotational temperatures as well as concentrations of molecules from measurements of the energy level population differences. A very good spatial resolution of CARS technique is one of its important advantages. This feature has been utilized for making spatially resolved measurements of the vibrational and rotational temperatures of N2 in a d.c.-excited transverse-flow CO2 laser discharge. Apart from that also spectra of CO2, CO and O2 in the discharge have been taken, which allowed us to evaluate the spatial distributions of those components in the discharge. Additionally first investigations of a microwave-excited CO2 laser module have been performed for comparison.