We investigate the accuracy of temperature measurements by coherent anti-Stokes Raman spectroscopy (CARS) of O₂ and use measurements taken with N₂ CARS and a thermocouple for comparison. Scanning vibrational CARS spectra of O₂ and N₂ were recorded over a broad range of temperatures: between 294 K and 1900 K in air that was heated in a tube furnace and at approximately 2450 K in a fuel-lean CH₄–O₂–N₂ flame. Temperatures were derived from least-squares fits of simulated and experimental spectra. Both the fundamental vibrational band and the first hot vibrational band were included in fitting. In the case of the tube furnace, the N₂ and the O₂ CARS temperature measurements agreed to within 3%, and results were similar with the thermocouple; in the flame the agreement was to within 1%. We conclude that, for cases in which O₂ is present in sufficient concentrations (≈10% or greater), the accuracy of O₂ thermometry is comparable with that of N₂.

Polarization-spectroscopy (PS) line shapes and signal intensities are measured in well-characterized hydrogen–air flames operated over a wide range of equivalence ratios. We use both low (perturbative) and high (saturating) pump beam intensities in the counterpropagating pump–probe geometry. The effects of saturation on the line-center signal intensity and the resonance linewidth are investigated. The PS signal intensities are used to measure relative OH number densities in a series of near-adiabatic flames at equivalence ratios (ϕ) ranging from 0.5 to 1.5. The use of saturating pump intensities minimizes the effect of pump beam absorption, providing more accurate number density measurements. When calibrated to the calculated OH concentration in the ϕ = 0.6 flame, the saturated PS number density measurements probing the P ₁(2) transition are in excellent agreement with OH absorption measurements, equilibrium calculations of OH number density, and previous saturated degenerate four-wave mixing OH number density measurements.

We assess the measurement of hyperspectral reflectance for outdoor monitoring of green algae and cyanobacteria cultures with a multichannel, fiber-coupled spectroradiometer. Reflectance data acquired over a 4-week period are interpreted via numerical inversion of a reflectance model, in which the above-water reflectance is expressed as a quadratic function of the single backscattering albedo, which is dependent on the absorption and backscatter coefficients. The absorption coefficient is treated as the sum of component spectra consisting of the cultured species (green algae or cyanobacteria), dissolved organic matter, and water (including the temperature dependence of the water absorption spectrum). The backscatter coefficient is approximated as the scaled Hilbert transform of the culture absorption spectrum with a wavelength-independent vertical offset. Additional terms in the reflectance model account for the pigment fluorescence features and the water-surface reflection of sunlight and skylight. For the green algae and cyanobacteria, the wavelength-independent vertical offset of the backscatter coefficient is found to scale linearly with daily dry weight measurements, providing the capability for a nonsampling measurement of biomass in outdoor ponds. Other fitting parameters in the reflectance model are compared with auxiliary measurements and physics-based calculations. The model-derived magnitudes of sunlight and skylight water-surface reflections compare favorably with Fresnel reflectance calculations, while the model-derived quantum efficiency of Chl-$a$ fluorescence is found to be in agreement with literature values. Finally, the water temperatures derived from the reflectance model exhibit excellent agreement with thermocouple measurements during the morning hours but correspond to significantly elevated temperatures in the afternoon hours.

A frequency-locked, injection-seeded, pulsed optical parametric generator (OPG) has been developed for short-range infrared differential absorption lidar (DIAL) applications. The periodically poled lithium niobate OPG is pumped by a passively Q-switched Nd:YAG microlaser and is seeded by a distributed feedback (DFB) diode laser. The OPG is designed for DIAL measurement of a narrow R-branch transition of methane at 3.2704 μm. The output of the OPG is a two-pulse sequence with a 100-μs temporal separation between the pulses, where the first pulse is absorbed by methane and the second pulse is not absorbed. The first pulse is actively locked to the methane absorption feature by use of the derivative of the transmission spectrum through a reference cell. Although the device was not optimized for output power, the 3.27-μm OPG output energies of the first and second pulses are 5.5 and 5.9 μJ, respectively, producing 21 mW when operated at 1818 Hz.

We demonstrate detection of nitro-containing compounds with laser photofragmentation (PF) coupled with resonance enhanced multiphoton ionization (REMPI) and ion mobility spectrometry (IMS). In PF-REMPI, a laser dissociates the parent molecules, producing fragments that can then be ionized by absorption of additional laser photons. The production of these ions strongly depends on the wavelength of laser light, with ion yields corresponding to the absorption spectrum of the fragments [nitric oxide (NO) in the present case]. Combining IMS with PF-REMPI provides further specificity, separating ions according to their mobilities through an atmospheric-pressure drift tube. In this work, we use a pulsed UV laser to examine the characteristics of atmospheric-pressure PF-REMPI, the chemistry occurring in the ionization region and drift tube, and the viability of detecting ions created by both resonance-enhanced and nonresonant ionization. Probing NO in a helium–nitrogen bath, we demonstrate that the detection of ions displays single-shot response to changes in ion generation, with an ion extraction-to-collection efficiency of $\sim 12\%$. We then evaluate the sensitivity and specificity of PF-REMPI/IMS as applied to the detection of both the explosive surrogate 2, 4-dinitrotoluene and the nuisance compound nitrobenzene.

Monitoring of cooling tower performance in a nuclear reactor facility is necessary to ensure safe operation; however, instrumentation for measuring performance characteristics can be difficult to install and may malfunction or break down over long duration experiments. This paper describes employing a thermodynamic approach to quantify cooling tower performance, the Merkel model, which requires only five parameters, namely, inlet water temperature, outlet water temperature, liquid mass flowrate, gas mass flowrate, and wet bulb temperature. Using this model, a general method to determine cooling tower operation for a nuclear reactor was developed in situations when neither the outlet water temperature nor gas mass flowrate are available, the former being a critical piece of information to bound the Merkel integral. Furthermore, when multiple cooling tower cells are used in parallel (as would be in the case of large-scale cooling operations), only the average outlet temperature of the cooling system is used as feedback for fan speed control, increasing the difficulty of obtaining the outlet water temperature for each cell. To address these shortcomings, this paper describes a method to obtain individual cell outlet water temperatures for mechanical forced-air cooling towers via parametric analysis and optimization. In this method, the outlet water temperature for an individual cooling tower cell is acquired as a function of the liquid-to-gas ratio (L/G). Leveraging the tight tolerance on the average outlet water temperature, an error function is generated to describe the deviation of the parameterized L/G to the highly controlled average outlet temperature. The method was able to determine the gas flowrate at rated conditions to be within 3.9% from that obtained from the manufacturer’s specification, while the average error for the four individual cooling cell outlet water temperatures were 1.6 °C, −0.5 °C, −1.0 °C, and 0.3 °C.