Two-photon Laser-induced Fluorescence Research Articles

Enhancing selective production of atomic oxygen through nanosecond pulse-burst driven mode in a He/O2 dielectric barrier discharge

In this study, the temporal evolution of O atoms in a nanosecond burst-pulsed dielectric barrier discharge (DBD) is measured by two-photon absorption laser-induced fluorescence spectroscopy. The experiment is conducted at burst conditions of 50, 100, and 200 kHz pulse frequency, 10 Hz burst frequency, and 20–400 pulses in 0.1%–2% O2 + He mixtures. The accumulation effect of O atoms in the burst mode is observed and the density gradually saturates at around 100 pulses. Increasing the pulse frequency effectively enhances the O saturation density. The 0-dimensional kinetic model reveals that the saturation effect is primarily balanced by the formation and loss characteristics of O atoms. Similar saturation effect is also observed in the typical continuous periodic pulse mode (one pulse each cycle), but with a saturation density about one order of magnitude lower than that in the burst case, highlighting the burst excitation mode as an effective method for enhancing the instantaneous peak production of O atoms. Further investigations into the influence of O2 proportion on the selective production of O atoms are also performed. The results suggest that a low O2 proportion (<2%) and pulse-burst driven mode for the He/O2 DBD facilitates the selective production of O atoms while competing with O3 formation.

Instantaneous thermometry imaging using two-photon laser-induced fluorescence.

Measuring temperature in complex two-phase flows is crucial for understanding the dynamics of heat and mass transfer. In this Letter, we introduce a novel, to the best of our knowledge, optical approach based on the combination of two-photon laser-induced fluorescence (2p-LIF) imaging and two-color laser-induced fluorescence (2CLIF) for instantaneous temperature mapping of complex liquid media. Using Kiton Red (KR) and Rhodamine 560 (R560), a temperature sensitivity of 1.54%/∘C has been achieved over a range of 17-60°C. The monitoring of two-dimensional transient temperature dynamics in the heating and degassing of water shows the efficiency of the 2p-2CLIF. This new approach contributes to the toolkit of optical temperature measurement techniques, providing a robust solution for studying transient scattering media and high-speed two-phase flows.

Spatially resolved TALIF investigation of atomic oxygen in the effluent of a CO2 microwave discharge

A diagnostic setup for one-dimensionally spatially resolved two-photon absorption laser-induced fluorescence (TALIF) detection of ground state oxygen atoms ( 2p43P2,1,0 ) is developed. The goal of this study is to investigate the evolution of temperatures and absolute number densities of oxygen atoms along the effluent of a low-pressure CO2 microwave discharge in order to gain insights into some of the mechanisms governing the post-discharge regime. The plasma source is operated at conditions of 600 W– 1200 W of absorbed power with flow rates of 74 sccm and 370 sccm pure CO2 at pressures between 1.2 mbar and 5 mbar with specific energy inputs up to 111.9 eV/molecule. These operating conditions exhibit high CO2 conversions (up to 90%) at low energy efficiencies (2%–7.4%), due to direct electron impact dissociation driving the conversion process resulting in splitting of CO2 into CO and metastable oxygen atoms. The TALIF measurements yield spatially resolved translational temperatures between 1000 K– 1600 K for most operating conditions and axial positions along the effluent. Reference measurements with xenon 6p′[3/2]2 are used for absolute number density calibration. The resulting axially resolved number density profiles of ground state atomic oxygen increase along the effluent, even at considerable distances of several centimeters from the active discharge, before they reach a maximum between 5×1020 m−3 and 2.2×1021 m−3 depending on the condition, and decrease after that. This behavior indicates the potential significance of quenching of metastable oxygen atoms within the post-discharge regime of the investigated CO2 discharges. The measured spatially resolved number density evolutions are qualitatively consistent with quenching via wall collisions being the dominant deactivation mechanism, underlining the importance of particle-wall interactions.

Absolute calibration of the ratio of Xe/O two-photon absorption cross-sections for O-TALIF applications

The paper presents a calibration of the ratio of two-photon absorption cross-sections, σXe(2)/σO(2) , necessary for the absolute O-atom density measurements by two-photon absorption laser-induced fluorescence (TALIF) technique. To calibrate the ratio of the cross-sections, a special discharge with 100% dissociation of molecular oxygen, and so with a known ‘reference’ density of O-atom [O] ref=2⋅ [O2] was suggested. This is a nanosecond capillary discharge in N2:O2 mixtures with a few percent of oxygen at a reduced electric field of a few hundred of Townsend and specific deposited energy of about 1 eV mol−1. Voltage at the electrodes, electrical current in the plasma, longitudinal electric field and energy delivered to the gas were measured with 0.2 ns synchronisation. Additionally, radial distribution of emission of excited nitrogen molecules and gas temperature in the discharge and afterglow were obtained experimentally. Detailed 1D kinetic modeling was suggested to confirm complete O2 dissociation and to analyse the main reactions. By comparing the data measured by TALIF technique with the ‘reference’ density of oxygen atoms [O] ref , the ratio of the two-photon absorption cross-sections σXe(2)/σO(2) was determined.

Concentration measurements of atomic nitrogen in an atmospheric-pressure RF plasma jet using a picosecond TALIF

The absolute concentration and spatial distribution of ground-state atomic nitrogen (N) in an atmospheric pressure plasma jet were measured using the two-photon absorption laser-induced fluorescence. The jet was ignited by radio frequency voltage in argon (or argon with nitrogen admixture) flowing through a silica tube. The spatially resolved measurements of atomic nitrogen concentration were realized in the effluent of the jet. In a pure argon plasma, the N concentration was increased with the distance from the silica tube and reached the maximum value ( 3.5⋅1014 cm−3) at the distance of 15 mm, and then sharply decreased at the end of the plume. On the contrary, plasma ignited in Ar with nitrogen admixture, the maximum N concentration was located directly at the end of the silica tube, where plasma starts to blow out into the ambient air. The highest N concentrations for 0.5% and 2% of N2 in the feed gas were 1.3⋅1015 cm−3 and 4⋅1015 cm−3, respectively.

Effects of elevated pressure on thermochemical states of turbulent flame-wall interaction studied by multi-parameter laser diagnostics

Effects of increased pressure on the thermochemistry of turbulent flame-wall interaction (FWI) were investigated within this study. Quantitative, pointwise measurements of three state parameters, i.e., gas-phase temperature, CO2 and CO mole fraction, were performed by means of dual-pump coherent anti-Stokes Raman spectroscopy (CARS) and two-photon laser-induced fluorescence (LIF) of CO. The flame front was simultaneously tracked by planar OH-LIF imaging. The measurements were carried out in a fully premixed methane-air flame in an enclosed side-wall quenching burner test rig under atmospheric and pressurized conditions (3 bar absolute pressure). An evaluation of near wall flame front topologies showed that the interaction of the flame with the wall is predominantly characterized by one single, extended reaction zone, similar to a so-called head-on quenching configuration. The dominance of this quenching scenario occurred most likely due to the confined burner configuration preventing an unhindered expansion of the hot exhaust gases. Thermochemical states were studied using pairwise correlations of temperature, CO2 and CO mole fraction. Regarding the measurements at atmospheric pressure, an overall good agreement with other studies on atmospheric FWI in a similar unconfined burner was observed considering differences concerning the flow field and the burner configuration. For the thermochemistry measurements at elevated pressure, similar trends as for the atmospheric measurements were identified. A comparison of both operating cases suggested that FWI processes were more strongly affected by heat losses at elevated pressure, but differences are moderately pronounced. To the authors’ best knowledge, these experiments are the first attempt to explore the near-wall thermochemistry of FWI processes at elevated pressure using multi-parameter measurements. As the near-wall measurements were further complicated by effects arising with increasing pressure, e.g., intensified beam steering and reduced length scales, implications on the application of the laser diagnostics are reported.

‘Self-calibration’ method for TALIF measurement of O atoms by full photofragmentation of O3 using a 226 nm UV laser

Quantification of atomic oxygen through the method of two-photon absorption laser-induced fluorescence (TALIF) is common in the fields of plasma fundamental research and application treatments. Fluorescence signal calibration is required to absolutely quantify the O amount and normally achieved with the help of TALIF measurement of a known-density Xe gas. In this study, an alternative calibration method is proposed based on the full photofragmentation (FPF) of O3 with a known density in a known gas composition by the same UV laser beam as that of the TALIF detection of atomic O. This is achieved by an equivalent amount of O fragment contributing the same fluorescence intensity as that of the O3 FPF-TALIF process under the same experimental conditions. The validity of this calibration method is proved by comparing it to the TALIF measurement of the Xe gas. It provides a ‘self-calibration’ method for the TALIF detection of O atoms without any need to change the laser optical arrangements including the laser wavelength. In addition, it only requires a gas flow with known O3 density through the studied medium reactor or chamber (such as plasma discharges). Detailed theoretical and practical principles of this self-calibration approach are presented and discussed in this study.

Nitriding Effects of Ammonia Flames on Iron-based Metal Walls

Effects of NH3/O2/N2 premixed flame/mixture on iron-based metal walls have been investigated experimentally. A premixed NH3/O2/N2 flame or mixture formed by a quartz tube burner impinged on the disc-shaped metal test plate, of which the temperature was kept at 550 oC by an infrared lamp heater. As materials for the test plate, SACM645, SUS304 and SUS310S, which are widely used as industrial steels, were examined. After being exposed to either the NH3/O2/N2 flame or mixture for 5 hours, the surface hardness was measured by using a nano indenter. Distributions of nitrogen atom diffused into the metal wall were measured by means of the Electron Probe Micro Analyzer (EPMA) and Secondary Ion Mass Spectrometry (SIMS). In addition, spatial distributions of the NH3 concentration in the NH3/O2/N2 flame and mixture were measured by employing a two-photon absorption laser-induced fluorescence (TALIF) technique. It was found that the surface hardness of the test plates increased significantly after being exposed to the NH3/O2/N2 flame/mixture. The distributions of surface hardness and nitrogen atom concentration show that nitriding occurred by the present NH3/O2/N2 flame/mixture with the equivalent level of the conventional gas nitriding method. Moreover, it is also found that NH3 concentration in the vicinity of the wall plays an important role in the surface hardness increase, and a wider distribution of NH3 can result in a broader surface hardness distribution.

Characterization of the intermolecular vibrational levels bound within the Ar + I2(E, v) potential energy surfaces

Two-color, two-photon laser-induced fluorescence experiments were performed to probe the intermolecular interactions within the Ar + I2(E, vE = 0–3) potential energy surfaces. Spectra were recorded using the lowest-energy T-shaped level and an excited intermolecular vibrational level with bending excitation within the Ar + I2(B, vB = 23) potential as intermediate levels to guide the spectral assignments. Progressions of intermolecular stretching and bending levels bound within the Ar + I2(E, vE) potentials were identified, and their vibrational frequencies were determined. The harmonic frequency and anharmonic constant for the bending vibrational mode were determined to be ωe(b) ∼ 34.8 cm−1 and ωeχe(b) ∼ 0.3 cm−1. The frequency and anharmonic constant for the stretching mode were found to be the same as reported previously [V.V. Baturo, et al. Chem. Phys. Lett. 647 (2016) 161], ωe(s) = 37.2(1.1) cm−1 and ωeχe(s) = 1.8(2) cm−1.

Ammonia thermal decomposition on quartz and stainless steel walls

Ammonia has been proposed as a promising solution for hydrogen carriers as well as clean fuels. However, the reaction kinetics is still not robust in many engineering applications, where the deviation is mainly caused by the surface reactions of ammonia on the wall. To examine the ammonia surface reaction on engineering materials, in the present study, the thermal decomposition of ammonia is systematically investigated in uniformly heated quartz/SUS304 tubular flow reactors with the prescribed heating length. A decrease in the inner diameter of the quartz tubular reactor leads to an increase in the ammonia thermal decomposition rate, showing that the thermal decomposition reaction occurs even on quartz surfaces, which is usually believed to be inert. The thermal decomposition on the SUS304 reactor surface starts from as low as 700 K, indicating it is much more reactive than the quartz surface. One-step surface reaction models of ammonia for quartz/SUS304 surfaces are proposed, with which the reaction rates are estimated based on the experimental data. The inner surface of the SUS304 tubular reactor after the thermal decomposition experiments is examined by X-ray photoelectron spectroscopy. The formation of iron nitride on SUS304, which in turn facilitates ammonia thermal decomposition, reveals the positive feedback between ammonia decomposition and nitriding. Moreover, the present one-step surface reaction on stainless steel has been validated by measuring ammonia distributions in the preheat zone of NH3/O2/N2 premixed flame impinging on a stainless steel plate through a two-photon absorption laser-induced fluorescence (TALIF) technique.

O3 full photo-fragmentation TALIF spectroscopy for quantitative diagnostics of non-thermal O2-mixed plasmas

In this study, we explore the potential of using laser-induced photo-fragmentation of O3 by UV radiation as a quantitative diagnostic tool in non-thermal O2-mixed plasmas. We analyze the optical processes of O3 using a comprehensive kinetic model with a 226 nm laser, which is typically used in the two-photon absorption laser-induced fluorescence (TALIF) measurement of O atoms. Our model demonstrates that the fluorescence intensity from atomic O fragments produced by the same laser is directly proportional to the population of precursor O3. This makes various diagnostic purposes achievable through the proposed O3 full photo-fragmentation (FPF) TALIF spectroscopy, including calibration of TALIF signals of O atoms and quantification of both O and O3 in O2-mixed plasmas. We present detailed theoretical principles, technical requirements, and successful examples of implementation for different diagnostic aims using the proposed O3 FPF-TALIF spectroscopy. However, we also specify the limitations of the developed diagnostic methods, particularly under low E/N conditions (&amp;lt;30 Td), where other interferential species such as the vibrationally excited ground-state O 2 ( X 3 Σ g − , v ≠ 0 ) are abundantly produced.

Simultaneous single-shot imaging of H and O atoms in premixed turbulent flames using femtosecond two-photon laser-induced fluorescence.

A method based on femtosecond two-photon excitation has been developed for simultaneous visualization of interference-free fluorescence of H and O atoms in turbulent flames. This work shows pioneering results on single-shot simultaneous imaging of these radicals under non-stationary flame conditions. The fluorescence signal, showing the distribution of H and O radicals in premixed CH4/O2 flames was investigated for equivalence ratios ranging from ϕ = 0.8 to ϕ = 1.3. The images have been quantified through calibration measurements and indicate single-shot detection limits on the order of a few percent. Experimental profiles have also been compared with profiles from flame simulations, showing similar trends.

Temperature measurements in heated gases and flames using carbon monoxide femtosecond two-photon laser-induced fluorescence

Temperature measurements in heated gases and flames using carbon monoxide femtosecond two-photon laser-induced fluorescence

Two-dimensional laser-induced fluorescence thermometry in a medium- to high-enthalpy CO2 flow

Ground-based experimental facilities are needed to qualify materials subjected to aerothermodynamic loads during an entry into the Martian atmosphere. In the present work, the focus is on quantifying the temperature field in a medium- to high-enthalpy CO_{2} flow (from 4.5 to {10.5}, hbox {MJ}/hbox {kg}) of a plasma wind tunnel using one- and two-dimensional two-photon absorption laser-induced fluorescence (CO-TALIF) thermometry at a CO number density in the range of 1–2 times 10^{17} cm^{-3}. However, the measurement method developed here can also be used to study satellite propulsion systems. Due to absorption by air, a two-photon excitation scheme of the CO molecule at 115 nm (VUV) was used. Experimental and simulated excitation spectra are compared for temperature determination. For spectrum simulation in the B^1varSigma ^+leftarrow X^1varSigma ^+ system, an existing program was extended and a polynomial regression correlation was developed for signals with low signal-to-noise ratios. After the first one-dimensional temperature measurements using CO-TALIF in the free-stream to quantify the radial temperature profile for three conditions in the medium- to high- enthalpy range, respectively, two-dimensional measurements in a steady state test chamber at room temperature were carried out. For the two-dimensional investigations, a light sheet optic was designed to generate a light sheet free of divergence in width and thickness. The results of the one- and two-dimensional temperature measurements performed at medium- to high-enthalpy conditions provided plausible results concerning both the values and the course in radial and axial direction, the latter being, to the authors’ knowledge, the first two-dimensional temperature measurements under such conditions using CO-TALIF.

Species structures in preheated ammonia micro flames

Species structure of ammonia (NH3) micro flames stabilized on a preheated 2-mm diameter tube is investigated using laser-induced fluorescence (LIF) measurements and numerical simulations with detailed reaction mechanisms. Nitric oxide (NO) and hydroxyl (OH) radicals are measured using single-photon absorption laser-induced fluorescence (LIF), while hydrogen atoms (H) are measured using two-photon absorption LIF (TPLIF). NO and OH are measured using nanosecond excitation pulses while both nanosecond and femtosecond methods are employed for TPLIF of H. 1-D and 2-D flame simulations are performed using Cantera and ANSYS FLUENT, separately, and the results are compared with the experimental data. It was observed that experimental H-atom signals increased with increasing equivalence ratio (ϕ), while the model predicted an opposite trend. Compared to the model predicted a rapid drop of OH as a function of ϕ, experimentally measured OH profiles exhibit opposite trends in different height locations of the flame. It is conjectured that the thermal dissociation of NH3 to generate reactive radicals such as H and OH is enhanced with preheating rich mixtures. Measured NO-LIF signal decreases with increasing ϕ, which agrees with the predicted trend by the simulation. NO reduction in fuel-rich flames is expected to be due to NHi radicals generated from excess NH3. A negative correlation is observed between NO and H/OH as a function of ϕ, which contradicts with the simulation that shows a positive relationship. This discrepancy implies that the effect of NH3 thermal dissociation has to be considered in the simulation of rich NH3 flames. This study helps to fulfill the fundamental knowledge gap of NH3 dissociation kinetics and the role of reactive intermediates in oxidation and NO formation pathways, hence an important step towards realizing practical combustion devices operating of NH3 as an energy carrier.

Spatio-temporal profile of atomic oxygen in a 1 kHz repetition atmospheric-pressure plasma jet in He–O2–H2O mixture

Atomic oxygen (O) is one of the essential reactive species in plasma oxidation processes. We investigated the behavior of atomic oxygen in a 1 kHz-repetition pulsed plasma jet in atmospheric-pressure He/O2/H2O mixture. By two-photon absorption laser-induced fluorescence, the spatio-temporal profiles of O density were measured under various conditions. In the dry ([H2O] 100 ppm) condition, the rate of O production did not depend on the [O2] fraction in the range of [O2] = 275–8600 ppm. The analysis of the O-production rate indicates that the atomic oxygen in this plasma jet arises from electron-impact dissociation and quenching of O(1 D), similar to the O-production mechanism in radio-frequency plasma jet. The dependence of O-production in each discharge pulse (Δ[O]) on the discharge energy and [O2] in the plasma region at dry condition is formulated as . The decay rate of atomic oxygen was not explained by self-recombination or ozone-generation reactions; it was consistent with the reaction rate of O + OH O2 + H at [OH] = cm−3. This result suggests that the small amount of [OH] with 1013 cm−3 density is more responsible for O behavior than [O2] with large fraction of 1015 cm−3. We conducted a chemical reaction simulation considering the measured results of [O] and [OH] production, resulting in good agreement with the spatial distribution of [O]. Chemical reaction analysis revealed that the cyclic reproduction of OH via chain reaction with O and O2 is important, therefore a small amount of OH catalytically consumes atomic oxygen with two-order higher density.

Absolute N-atom density measurement in an Ar/N2 micro-hollow cathode discharge jet by means of ns-two-photon absorption laser-induced fluorescence

In this work, nanosecond two-photon absorption laser-induced fluorescence (TALIF) is used to probe the absolute density of nitrogen atoms in a plasma generated using a micro-hollow cathode discharge (MHCD). The MHCD is operated in the normal regime, and the plasma is ignited in an Ar/N2 gas mixture. First, we study a MHCD configuration having the same pressure (50 mbar) on both sides of the electrodes. A good agreement is found between the density of N atoms measured using TALIF in this work and previous measurements using vacuum ultraviolet Fourier transform absorption spectroscopy. Then, we introduce a pressure differential between the two electrodes of the MHCD, creating a plasma jet. The influence of the discharge current, the percentage of N2 in the gas mixture, and pressures on both sides of the MHCD is studied. The current has a small impact on the N-atom density. Furthermore, an optimal N-atom density is found at around 95% of N2 in the discharge. Finally, we demonstrate that the pressure has a different impact depending on the side of the MHCD: the density of N atoms is much more sensitive to the change of the pressure in the low-pressure side when compared to the pressure change in the high-pressure side. This could be due to several competing phenomena: gas residence time in the cathodic region, recirculation, or recombination of the N atoms at the wall. This study contributes to the optimization of MHCD as an efficient N-atom source for material deposition applications.

Femtosecond two-photon LIF imaging of atomic hydrogen in high-pressure methane-air flames

Atomic hydrogen (H) imaging studies in combustion systems have been limited thus far to atmospheric- or low-pressure flames. The commonly used excitation scheme for two-photon laser-induced fluorescence (TPLIF) of H involves 205-nm deep-ultra-violet (DUV) laser pulses generated using nanosecond (ns), picosecond (ps), or femtosecond (fs) laser systems. Ultrashort pulse, fs excitation schemes are more attractive because of the efficient two-photon excitation and interference-free kHz-rate imaging capability. In this work, we implemented a home-built, direct fourth harmonic generation (FHG) laser system to generate high-energy fs pulses for H imaging in CH4/air flames at pressures up to 10 bar. The high-energy FHG output was capable of overcoming transmission losses of DUV laser pulses through thick optical windows of the pressure vessel. Signal interferences such as photoionization, photolytic production, amplified spontaneous emission, and background chemiluminescence were avoided or minimized during data acquisition and subsequent data processing steps. A quadratic dependence of the H TPLIF signal on the laser energy was observed. The increase in the pressure from 1 to 10 bar showed a rapid decay of the fs H TPLIF signal although it should scale linearly with increasing H number density with pressure ideally at equilibrium conditions. Besides a detailed quenching correction, laser absorption and fluorescence signal trapping remain major issues at elevated pressures. The measured fluorescence signals are compared with the equilibrium H number densities and local H concentrations calculated using the Cantera (0D) and UNICORN (2D) flame codes, respectively, for a range of equivalence ratios, and possible reasons for discrepancies are discussed. Experimentally obtained 1D and 2D spatial distributions of H are well predicted by the UNICORN flame model. Steps towards quantitative single-shot H TPLIF imaging measurements in high-pressure flames are also discussed. Overall, the fs TPLIF imaging technique coupled with a high-efficiency home-built FHG system is a promising diagnostic approach for H imaging in high-pressure flames.

Simultaneous detection of three chemical species (NO, O, O2) using a single broadband femtosecond laser

Simultaneous nitric oxide (NO) laser-induced fluorescence (LIF), atomic oxygen (O) two-photon LIF (TPLIF), and molecular oxygen (O2) LIF were demonstrated using a single broadband femtosecond (fs) laser in methane- and hydrogen-fueled flames. An amplified Ti:Sapphire laser with ∼80-fs pulse duration was used to pump an optical parametric amplifier (OPA) to generate 226.1-nm pulses having 2.3 nm (∼450 cm−1) bandwidth to excite all three species simultaneously. The specific excitation transitions are NO A-X (0,0) system, O 3p3P←←2p3P two-photon transition, and O2B3Σu−−X3Σg− Schumann-Runge system. Detailed emission characterization was performed using a 1D imaging spectrometer to identify suitable emission bands for interference-free detection of each species. A simultaneous detection system consisting of a visible and a UV camera provided the optimal detection of all three species. Imaging studies revealed high concentrations of NO, O, and O2 at the edge of the flame cone of Bunsen flames because NO and O are produced at the hot flame front. O2 LIF signal was present only at the flame front because of the strong temperature dependence of the O2 Schumann-Runge system. Direct imaging of O TPLIF enabled single-shot as well as high-fidelity shot-averaged line images in stable laminar flames. Equivalence ratio scans in the CH4/air Hencken flames showed good agreements for O and O2 with Cantera equilibrium predictions performed using GRI-Mech 3.0. Although the NO measurements deviated from the equilibrium calculations on the fuel-rich side, it agreed well with previously reported NO LIF measurements in a similar flame. This discrepancy is likely due to Prompt NO, which was not considered in the simulation. NO LIF measurements as a function of height-above-the-burner in the H2/air Hencken flames agreed well with calculated NO mole fractions using the UNICORN flame code. The present study lays the foundation for single-laser imaging of three critical flame species in NO formation pathways in combustion systems.

Evaluation of LIF thermometry technique using Krypton as a tracer: Impact of laser lineshape and collisional bandwidth

In recent years, two-photon laser-induced fluorescence (TPLIF) of inert gas krypton (Kr) has received much attention as a potential non-intrusive flow diagnostic, thermometry, and velocimetry technique. However, the interaction between the laser bandwidth and the atomic excitation transition at varying pressures, and the variation of the fluorescence quantum yield due to spatially varying collisional quenching of Kr are not fully understood. The resulting lineshape and quenching corrections become especially important when the temporal scales of excitation laser pulses vary from nanosecond (ns) to femtosecond (fs) timescales. In this study, we report a comprehensive investigation of Kr line broadening and quenching effects, in particular, with respect to TPLIF-based temperature (T) measurements in flames. Experiments were conducted in both low-pressure and atmospheric-pressure flames and in two different burner configurations, using conventional ns and ultrafast fs duration laser sources. When using ns pulses, the results suggest no lineshape corrections are necessary at low pressure; however, a T-dependent empirical model was needed for atmospheric-pressure flames. In contrast, broadband fs pulses have linewidths in excess of 400 cm−1, which are significantly larger than sub-cm−1 spectral transitions, hence requiring no lineshape corrections at any pressure. Quenching measurements in low-pressure flames were found to be scaled by T−0.5 using previous low-pressure thermometry data and 1D flame model predictions. The Kr TPLIF temperature profiles measured using ns pulses (low and atmospheric pressures) and fs pulses (atmospheric pressures) agreed well with model predictions. In the absence of the necessity for lineshape corrections, fs Kr-TPLIF provides an easy way to extract T simply by taking the inverse square of the fluorescence signal. T-line imaging using fs-pulses are presented for several flame heights. The present study establishes a simplified approach for Kr TPLIF-based thermometry in flames.