Laser-induced Fluorescence Lifetime Research Articles

Effective lifetime of Ni laser induced fluorescence excited at 336.9 nm during spark plug discharge

In this study, the laser induced fluorescence lifetime of Ni atoms in ambient air with presence of a plasma discharge was measured for the first time. Free Ni atoms were generated in air at a pressure of 1 bar by spark plug discharges driven by an inductive coil. The Ni atoms were excited at the 336.957 nm absorption line by a 336.96 nm, 90 ps laser pulse and the resulting temporally resolved decaying fluorescence signals were captured by a PMT. An effective fluorescence lifetime of about 1.1 ns was observed for the fluorescence signal within a 7.4 nm detection window centered at 345 nm. Further analysis also revealed that the lifetime of the transition showed statistically insignificant change throughout the duration of the discharge. The peak intensity of the fluorescence signal was found to be proportional to the integrated signal intensities. This in turn suggests that the integrated fluorescence signals in the aforementioned spectral region are proportional to the population density of ground state Ni atoms in the detection volume. The number density of free Ni atoms in the spark gap was measured over time during the plasma discharge, showing an accumulating trend in the beginning phase of the discharge followed by a slow decrease until the termination.

Laser-induced fluorescence and its effect on the damage resistance of fluoride-containing phosphate-based glasses

A series of multi-component fluoride-containing phosphate-based glasses prepared in a reducing atmosphere showed improved resistance to high-energy ultraviolet (UV) laser-induced damage and strong laser-induced fluorescence (LIF) within the glass bulk. The UV optical absorption, photoluminescence, and fluorescence decay properties of these glasses were investigated to explore the defect-related LIF mechanism and its underlying effect on the glasses’ laser-induced damage threshold (LIDT). Seven laser wavelengths ranging from 253 nm to 532 nm were used to excite the LIF, and two characteristic fluorescence bands peaking at approximately 414 nm and 780–800 nm occurred in all three types of glasses. The LIF band at 414 nm was attributed to PO3-EC defects in the second harmonic frequency (2ω) absorptive glass and third harmonic frequency (3ω) transparent glass, but Fe2+ ions in the fundamental frequency (1ω) absorptive glass. A later fluorescence band at 780–800 nm occurred due to POHC defects in the 2ω absorptive and 3ω transparent glasses and Fe3+ ions in the 1ω absorptive glass. A detailed study on the dynamic decay processes of two additional dominant fluorescence peaks at 450 nm and 780 nm under 266 nm excitation revealed the potential effect of LIF on LIDT improvement. The relatively longer LIF lifetime, higher LIF intensity, and larger LIF peak area corresponded with and contributed to a higher LIDT, especially in the 3ω transparent glass with a low UV absorption coefficient. This study provides strong evidence for the prior hypothesis between strong LIF and LIDT.

Upper-laser-level lifetime measurement of rear earth dopant in active fiber

The upper-laser-level lifetime (fluorescence lifetime) of the rear earth dopant in the active fiber is a key parameter which indicates the performance of the fiber, and takes an important role in designing the laser system. However, the accurate measurement of fluorescence lifetime in active fiber remains challenging, which mainly rely on the direct measurement of laser induced fluorescence lifetime of the active fiber or lifetime measurement of bulk laser glass. The former method suffers the error due to the amplified spontaneous emission and the reabsorption process, while the latter ignores the influence of high temperature and tension produced during the fiber drawing on the emission behavior of the material. Therefore, the accuracy of these measurements can become a problem. In this work, we propose a new approach to measuring the upper-laser-level lifetime of the rear earth dopant in the active fiber based on the power/energy performance of the fiber amplifier. The population inversion, i. e. the energy storage, in the active fiber of a fiber amplifier is a function of upper-laser-level lifetime. Therefore, the upper-laser-level lifetime can be derived by measuring the average power or output pulse energy of the amplifier, given that the energy storage in the active fiber is extracted adequately by a seed laser. Using the rate equations, we model the population inversion and energy storage in the active fiber each as a function of pump power and time, and the resulting relationship between the upper-laser-level lifetime and the average output power. The upper-laser-level lifetimes of several commercial Yb-doped active fibers are experimentally measured by this method through using the fibers as the gain media of the amplifier operated at 1064 nm. The convenience of experimental data processing is also discussed. The measured lifetime and evolution trend of the lifetime with dopant concentration exhibitthat they are in good agreement with those from other reports and the theoretical model, which verifies the feasibility of this method.

Fe i Oscillator Strengths for Transitions from High-lying Odd-parity Levels

Abstract We report new experimental Fe i oscillator strengths obtained by combining measurements of branching fractions measured with a Fourier Transform spectrometer and time-resolved, laser-induced fluorescence lifetimes. This study covers the spectral region ranging from 213 to 1033 nm. A total of 120 experimental -values coming from 15 odd-parity energy levels are provided, 22 of which have not been reported previously and 63 of which have values with lower uncertainty than the existing data. The radiative lifetimes for 60 upper energy levels are presented, 39 of which have no previous measurements.

Lifetime measurements using two-step laser excitation for high-lying even-parity levels and improved theoretical oscillator strengths in Y ii

We report new time-resolved laser-induced fluorescence lifetime measurements for 22 highly excited even-parity levels in singly ionized yttrium (Y II). To populate these levels belonging to the configurations 4d6s, 5s6s 4d5d, 5p2, 4d7s and 4d6d, a two-step laser excitation technique was used. Our previous pseudo-relativistic Hartree-Fock model (Biemont et al. 2011) was improved by extending the configuration interaction up to n = 10 to reproduce the new experimental lifetimes. A set of semi-empirical oscillator strengths extended to transitions falling in the spectral range λλ194-3995 nm, depopulating these 22 even-parity levels in Y II, is presented and compared to the values found in the Kurucz's data base (Kurucz 2011). (Less)

Study of laser-induced chlorophyll fluorescence lifetime measurement and its correction

A novel method for laser-induced fluorescence lifetime measurement and correction are presented to improve precision of chlorophyll fluorescence lifetime measurement. Laser was used as excitation source for exciting chlorophyll fluorescence. According to the measured signals characteristics, the fluorescence and background signals were detected respectively by photomultiplier. The chlorophyll fluorescence lifetime can be estimated from deconvolution of the fluorescence and background signals. Based on a number of retrieved results from simulations, a rule of inherent error with deconvolution was found. Therefore, the calibration formula was obtained through the comparison of ideal fluorescence lifetimes and retrieved ones. In actual measurements, the intrinsic fluorescence decay can be separated from the measured signals by deconvolution, and thus, the retrieved fluorescence lifetimes were substituted into a calibration formula to calculate the corrected values. Both simulations and experiments show that the method is a high precision and real-time measurement technique for chlorophyll fluorescence lifetime.

Laser-induced chlorophyll fluorescence lifetime measurement and characteristic analysis

A laser-induced fluorescence lifetime measurement method is presented to evaluate living status for plant growth and the environmental monitoring. A 355 nm laser is used as excitation source for exciting chlorophyll fluorescence, and the fluorescence signals are received by a photomultiplier. Because the measured signal is the convolution of the reliable fluorescence decay signals, laser pulse and instrument response function, according to their characteristics, the time-resolved measurement method is used to estimate the chlorophyll fluorescence and background signals separately; the real fluorescence decay signals are separated by combining a novel deconvolution method, and the chlorophyll fluorescence lifetime can be retrieved. Experiment shows that the method proves to be a high accuracy and real-time monitoring chlorophyll fluorescence lifetime technique; and the chlorophyll solution fluorescence lifetime is measured for different concentrations. The result can prove that the chlorophyll concentration is related to its fluorescence lifetime, and the calibration curves of chlorophyll concentration and fluorescence lifetime is fitted.

Instrumentation for X-ray Excited and Laser Induced Fluorescence Lifetime Spectroscopy Using Two-Dimensional Photon Counting

A table top picosecond pulsed X-ray and laser induced fluorescence spectrometer using two-dimensional photon counting is presented. With this streak camera system it is possible to measure fluorescence events in a wavelength range from 200-850 nm. Measuring results are full time resolved fluorescence spectra with a temporal resolution up to 20 ps after deconvolution. The instrumental response function (IRF) of the system is around 60 ps for laser excitation and 80 ps for X-ray excitation. For a performance test well known inorganic (CsI, CsI:Tl) and organic scintillators (anthracene) as well as rhodamine 6G for laser induced fluorescence are measured and evaluated. The easily manageable system shows satisfying results in agreement with literature values.

Fluorescence lifetimes of rhodamine dyes in vacuo

Abstract Laser-induced fluorescence lifetimes are reported for several mass-selected gas-phase rhodamine cations, which were generated using electrospray ionization. A recently developed instrument consisting of a quadruple ion trap mass spectrometer coupled to a tunable laser excitation source is used for ion storage and irradiation, respectively. Time-resolved fluorescence measurements are carried out using time-correlated single photon counting (TCSPC), with a Single Photon Avalanche Diode (SPAD) for efficient detection of the light. The time-resolved data are well fit using single exponential decays. Measured lifetimes are 5.65 ± 0.04 ns for gaseous cationic rhodamine 575 (also known as rhodamine 19), 5.83 ± 0.06 ns for rhodamine 590, 5.87 ± 0.05 ns for rhodamine 6G and 6.92 ± 0.06 ns for rhodamine 640 (also known as rhodamine 101). These values are the first reports of the lifetimes of gaseous cationic rhodamine 575, 590 and 6G, while the uncertainty for the reported lifetime of 640 is an order of magnitude smaller than the previously reported value. The reported gas-phase fluorescence lifetimes for these rhodamines are all longer than their measured lifetimes in solution. Photo-physical processes leading to the increase in the fluorescence lifetimes of molecules in the gas phase compared to their solution behavior are discussed. Knowledge of the intrinsic lifetimes of rhodamines, as provided in this work, will aid the development of fluorescence resonance energy transfer as a structural probe of gaseous ions. It will also form a basis from which to better understand how interactions with solvent influence the properties of fluorescent dyes.

Transition probabilities and lifetimes in gold (Au I and Au II)

Radiative lifetimes of three odd-parity levels of neutral gold (Au I) and one odd-parity level of singly ionized gold (Au II), measured using the time-resolved laser-induced fluorescence technique, have allowed the testing of the reliability of a relativistic Hartree–Fock model of the atomic structure taking configuration interaction and core-polarization effects into account. The importance of the inclusion of the latter effects in the calculations is emphasized. The laser-induced fluorescence lifetimes, combined with the theoretical branching fractions, have allowed us to deduce oscillator strengths for six 5d96s2–5d96s6p and 5d106s–5d96s6p transitions of Au I and for sixty-three 5d96s–5d96p, 5d96p–5d97s and 5d10–5d96p UV transitions of Au II.

Time-resolved laser-induced fluorescence lifetime measurements and relativisticHartree–Fock calculations of transition probabilities in Sm II

Radiative lifetime measurements were performed with time-resolved laser-inducedfluorescence techniques for 47 levels of the astrophysically important ionSm1+ over theenergy range 21 000–36 000 cm−1. The new results have been compared with previous measurements but also withtheoretical calculations taking configuration interactions and core-polarization effects intoaccount, and a satisfying agreement has been found for many levels of this complex ion.New calculated transition probabilities are deduced from the experimental lifetimes andfrom the theoretical branching fractions for 162 transitions of astrophysical interest. Theseresults will help astrophysicists in the quantitative investigation of the chemicalcomposition of CP stars.

Nanoscale thermometry via the fluorescence of YAG:Ce phosphorparticles: measurements from 7 to 77°C

The laser-induced fluorescence lifetime of 30 nm particles of YAG:Ce was measuredas a function of temperature from 7 to 77°C. Thefluorescence decay lifetimes for the nanoparticles of this phosphor varied from ≈18 to 27 ns, i.e.≈33%relative to the longest lifetime measured. This large variation in lifetime, coupledwith the high signal strength that was observed, suggest that YAG:Cenanoparticles will be useful thermographic phosphors. We describe the materialand the apparatus used to characterize its fluorescence, present the results ofmeasurements made over the range of temperatures tested and comment on somepossible applications for this novel material.

Time-resolved laser-induced fluorescence lifetime measurements and theoretical transition probabilities in Tb III

Lifetimes of four short-lived levels belonging to the ${4f}^{8}{(}^{7}F)6p$ configuration of Tb III have been measured using a two-step excitation time-resolved laser-induced fluorescence technique. They agree quite well with multiconfigurational relativistic Hartree-Fock calculations performed with inclusion of core-polarization effects. Using the experimental lifetimes and the theoretical branching fractions, a set of transition probabilities has been deduced for this ion.

Detection of In-Vivo Plant Leaves Damage Process Irradiated by UV-B Using Time-Resolved Laser-Induced Fluorescence Method.

We used a laser-induced fluorescence (LIF) method to monitor plant damage caused by environmental changes. A time-resolved LIF measurement system which can monitor rapid fluorescence phenomena was developed with a 200-fs and 660-nm laser source and a spectroscopic detection system with a time resolution of 30 ps. Leaf samples of a morning glory irradiated by UV-B were prepared for investigating the capability of the system for monitoring the damage process. The chlorophyll fluorescence lifetime of the leaves was monitored at 685 nm and 735 nm. At those wavelengths, the LIF lifetimes became shorter during UV-B irradiation, tending to recover to the control values after quitting the irradiation, and then finally exhibiting shorter lifetimes again. Relationships between the lifetimes and the plant's activities are discussed.

Influence of polarization effects and magnetic fields on time-resolved laser-induced fluorescence measurements.

The theory of time-resolved laser-induced fluorescence (LIF) in a static magnetic field is reformulated by means of the graphical method of angular momentum theory. Invariant general geometrical relations of the time-resolved fluoresence signal are obtained in an explicit form for arbitrary polarization and propagation directions of the primary and secondary radiation and for any direction of the magnetic field. On this basis an extensive experimental study was carried out to find general conditions for lifetime experiments using laser-induced fluorescence, under which the direction of polarization in the excitation and the observation channel and the influence of external magnetic fields does not change the time evolution of the fluorescence signal. It is shown that besides the well-known ``magic-angle'' excitation also measurements at very low pressures (p\ensuremath{\approxeq}${10}^{\mathrm{\ensuremath{-}}4}$ mbar) provide conditions where laser-induced alignment is negligible and does not disturb the time evolution of the decay signal. Furthermore the experiments confirm that the magnitude of laser-induced alignment depends very sensitively on the chosen transition scheme, on the value of the cross section for alignment destroying collisions, and on the geometry of the experiment. Interferences on the time-resolved fluorescence signal by external magnetic fields are also discussed. It is shown that the presence of a strong magnetic field can lead to lifetime results systematically too short under conditions typical for LIF lifetime experiments.

Theoretical study of the radiative lifetime of the A 1∏u state of C2

We have studied the Phillips (A 1∏u–X 1∑+g ) band system of C2 in order to help resolve the discrepancy between the best theoretical lifetimes and those deduced recently from laser-induced fluorescence (LIF) studies. Our calculated lifetime for the A 1∏u(v′=0, J′=1) state is 13.0 μs, in excellent agreement with the recent calculations of ONeil et al., but considerably shorter than the direct experimental measurements. A measure of the accuracy of the complete-active-space self-consistent-field (CASSCF) multireference configuration-interaction (MRCI) results in this work is obtained by a series of calibration calculations. Convergence in the n-particle space is demonstrated by comparison with full configuration interaction calculations in a double-zeta plus polarization basis, while the convergence of the one-particle basis set is demonstrated by systematically expanding the one-particle basis set up through g angular momentum functions. Furthermore, a coupling of the one- and n-particle spaces is shown to be unimportant by systematically expanding the active space in the CASSCF/MRCI treatment. Given that our theoretical results are estimated to be accurate to about 5%, the LIF lifetimes would appear to contain some systematic error.

Pressure dependence of the 2.3 μm laser-induced fluorescence (LIF) of room temperature PuF6

When PuF6 is excited in the 800 nm region, fluorescence peaked at 2.296 μm with less intense peaks at 2.207 and 2.126 μm is observed. Unlike the previous works that reported no self-quenching of the 2.3 μm LIF of PuF6, our data indicate a pressure dependence for the 2.3 μm LIF lifetime with a self-quenching rate constant of 162±4 Torr−1 s−1 and a collision-free lifetime of 218±5 μs. Both fluorescence and excitation spectra are in good agreement with the previously reported absorption spectrum of PuF6.

Temperature dependence of the laser-induced fluorescence of UF6 in the A–X̃ band

The temperature dependence of the time-resolved laser-induced fluorescence (LIF) of gaseous UF6 has been investigated in 10 °C increments from −30 to 80 °C over the 0.005–85 Torr pressure range. The UF6 was excited to the A state with a pulsed dye laser at 392.1 nm and the fluorescence emission peaked at 421 nm and was monitored to determine the LIF lifetime. The pressure/lifetime data at each temperature have been fit by computer with our LIF kinetic expression reported previously in this journal [J. Chem. Phys. 69, 2181 (1978)]. The six quenching rate constants of our kinetic model have been evaluated in terms of their temperature dependences. Each rate constant has been represented with an Arrhenius type expression; pre-exponential A factors and activation energies are presented.