Measured Fluorescence Decay Time Research Articles

Peculiarities of measuring fluorescence decay times by a streak camera for ps-TALIF experiments in reactive plasmas

We present a detailed methodology for (i) correctly configuring a streak camera to capture raw picosecond two-photon absorption laser induced fluorescence signals (ps-TALIF) of H-atom in low- and atmospheric-pressure plasmas, and (ii) properly processing the recorded raw experimental data with a dedicated mathematical signal processing method to infer actual ps-TALIF signals of H-atom. The goal is the accurate determination of the decay time of the recorded ps-TALIF signals of H-atom. A ps-laser is used to excite atomic hydrogen produced in both plasmas and the raw fluorescence signals are detected by the streak camera using different time windows/ranges (TR). It is shown that the choice of the TR affects the shapes and the decay times of the recorded raw TALIF signals. This is defined as the instrumental function of the streak camera and has a Gaussian profile as determined by recording the ultrafast laser pulse at different TR. To remove this instrumental distortion and extract the actual shape of the TALIF signals, the captured raw TALIF signals were fitted using the mathematical procedure developed in this study, which involved an exponentially modified Gaussian function. The application of our methodology leads to more reliable measurements of hydrogen atoms decay times after respecting the following acquisition conditions: (i) the TR of the streak camera should be sufficiently large to capture the complete (raw) TALIF signal, and (ii) the time width of the instrumental function of the streak camera should be as small as possible compared to the actual decay time of the fluorescence, while ensuring an optimal signal-to-noise ratio. This work demonstrates the remarkable potential of the combination of ps-TALIF and streak cameras in state-of-the-art optical plasma diagnostics.

Spectroscopy of Yb-doped tungsten–tellurite glass and assessment of its lasing properties

Glasses of the TeO2-WO3-Yb2O3 system are synthesized for wide range of Yb3+ concentrations of up to 6.0 × 1021 ions/cm3. The spectral-luminescent properties of lightly doped samples are investigated at room temperature and at the boiling point of liquid nitrogen. The energies of the Stark levels of the ground and excited states of Yb3+ ions incorporated into tungsten–tellurite glass are determined by analyzing the low-temperature spectra. The absorption, emission, and gain cross section spectra are obtained. The excess of the measured fluorescence decay time over the radiative lifetime ∼0.3 ms derived from the absorption spectra is attributed to the reabsorption effect in bulk samples. Measurements of lightly doped glass powder in the immersion liquid are made to reduce the effect of reabsorption. The fluorescence decay time of the powder is very close to the calculated radiative lifetime. Compared with phosphate, silicate, and other Yb3+-doped glasses, the tungsten–tellurite glass has a promising potential as a gain medium for lasers and amplifiers.

Bright, water-soluble CeF3 photo-, cathodo-, and X-ray luminescent nanoparticles

Bright, water-soluble CeF3 nanoparticles with small size and narrow size distribution have been synthesized using a simple co-precipitation method without any ligands. Size control of nanoparticles from 13 ± 2 to 9 ± 2 nm was achieved by varying the reaction time. Colloidal properties have been found to vary with pH and, independently, with dilution. The photoluminescence of the as-synthesized nanoparticles shows a highly photostable UV/Visible fluorescence band due to allowed 5d–4f transitions, also observed in the X-ray luminescence spectrum. This band is suitable for X-ray excitation of a range of photosensitizers. The photoluminescence quantum yield of nanoparticles was also determined to be 31 %. Using the measured fluorescence decay time of 25 ns, the radiative lifetime of Ce in CeF3 was found to be 80.6 ns. Both photoluminescence and cathodoluminescence emission are affected by the reaction time and measurement temperature. Electron-beam-induced defect annealing is also observed.

Yb^3+ spectroscopy in (Nb or Ta):RbTiOPO_4 single crystals for laser applications

Single crystals of Yb:RbTiOPO(4) codoped with Nb(5+) or Ta(5+) were grown by the top seeded solution growth slow-cooling technique. The ytterbium concentration in the crystals varies as a function of the molar ratio of the precursor oxides and of the codopant, reaching a maximum value of 1.9x10(20) Yb(3+) ions/cm(3). The broad band near 1 mum in absorption and emission spectra at room temperature is due to the large splitting of the Yb(3+) ground state. The ytterbium (2)F(5/2) level radiative lifetime in Nb:RbTiOPO(4) (tau(rad) = 2.7 ms), was calculated and then compared to the measured fluorescence decay time (tau(em) = 2.2 ms), giving an intrinsic quantum efficiency of 81%. To evaluate the potentiality of these crystals for self-frequency doubling, preliminary results of Yb(3+) laser operation and fundamental wavelength measurements for type-II non-critical second harmonic generation ( lambda(NCPM)) are also reported.

Synthesis and spectroscopic characterization of CaF2:Er3+ single crystal for highly efficient 1.53 μm amplification

A CaF2:Er3+ single crystal was grown by the Tammann–Stober method. The potential of this material as a laser crystal for 1530 nm emission was established by quantitative analysis of the optical absorption and emission spectra. Assuming the tetragonal symmetry of the Er3+ sites, the Bkq crystal field parameters, Racah parameters, spin–orbit interaction parameters, and configuration interaction parameters were derived by fitting the experimental absorption band positions with the model energy Hamiltonian. Judd–Ofelt parametrization was done to compute the radiative decay time and fluorescence branching ratio of various meta stable transitions. Using the measured fluorescence decay time and computed radiative decay time, 100% quantum efficiency is obtained for the 1530 nm band, which is reasonable due to the low multiphonon relaxation, and absence of nonradiative energy transfer processes at the 0.01 at.% Er3+ concentration. The narrow bandwidth (13 nm) and high stimulated emission cross section (3.2×10−20 cm2) support the suitability of CaF2:Er3+ for use in high gain optical amplifiers.

The influence of average photon number on the measured fluorescence decay time of scintillator

Measurement of the light decay time by the delayed single-photon coincidence method requires that the average number of photons detected by photomultiplier tube be much less than one. The probability that multiple photons will be detected during the measurement always exists and makes the measured time decay spectrum appear to be faster than the true one. By using the probability density function of detected fluorescence photon, Monte-Carlo simulations and numerical calculation, the quantitative relationship between the deviation of measured fluorescence decay time and the average photon number is obtained. It is found that the deviation is directly proportional to the average photon number and inversely proportional to the time range of TAC. The methods to determine the average photon number are discussed.

Analysis of the fluorescence of a Nd-doped 50% CaO–50% Al_2O_3 glass, pumped at 810 nm, between 1050 and 1100 nm

We report on the first observations, to our knowledge, of the 4F3/2→ 4I11/2 (1060-nm) induced fluorescence in a Nd-doped CaO–Al2O3 glass pumped by an 810-nm diode laser. This new doped glass is produced as a 3-mm-diameter sphere by heating and melting in an aerodynamic containerless trap and is rapidly solidified by radiative cooling (>350 K/s). This glass has an interesting Nd3+ emission maximum at 1067 nm (not many doped glasses have their emission maxima close to 1067 nm). The measured fluorescence decay time of the 4F3/2 level is short (0.3 ms) when the ion is excited by a narrow-band pulsed dye laser.

Development of UV saturable absorber acridine and its application for a short pulse KrF laser.

A derivative of the linear tri-cyclic compound acridine in several different solvents is shown to be as an effective saturable absorber for short pulse KrF lasers. Acridine dissolved in ethanol showed the best bleaching characteristics for a 20 ps laser pulse, the ratio of primary to the excited absorption cross-section of 7.3:1 and the low saturation fluence of 1.1mJ/cm2 due to the large absorption cross-section of 5.6 × 10-16cm2 at 249nm. Temporal behavior of the absorption recovery showed two time constants of 0.4ns and 115ns, the fast component corresponded to the measured fluorescence decay time of 0.43ns for the first excited singlet state. The ASE free operation (less than 0.1% of the laser energy) and the pulse compression in a saturated amplifier have been demonstrated. The laser pulse width was compressed by a factor of 4 in an absorber-amplifier arrangement.

Measuring fluorescence decay times by phase-shift and modulation techniques using the high harmonic content of pulsed light sources

In the present work we discuss the possibility to measure fluorescence lifetimes by coupling pulsed excitation with phase-shift and amplitude-modulation detection techniques. We show that, because of the high harmonic content of narrow light pulses, the sample may be considered as simultaneously excited with a set of modulation frequencies up to the GHz region with noticeable power. By measuring then the phase-shift and modulation ratio of fluorescence with respect to the exciting light in the high-frequency region, impressive time resolutions may be achieved. On the other hand, since we dispose of a wide range of modulation frequencies, the problem of the multiexponential decay may be easily handled and has an exact analytical solution, provided the signal-to-noise ratio is good enough. We anticipate the possibility to introduce cross-correlation methods in order to perform the experiment in the very-low-frequency region. A short discussion about the notion of time resolution for this kind of measurement is also included.

An improved technique for measuring fluorescence decay times in the nanosecond and sub-nanosecond range

A new method for accurately recording scintillation pulse contours and for determining their decay times is reported. The novelty of this technique centers around the averaging, storing, and analyzing capabilities that are provided by an on-line, 8K mini-computer. Decay time measurements can be made by employing either pulsed UV, or ionizing radiation such as α or β particles, as excitation sources. Programs have been developed to convolute time resolved spectra with a single decay time.

Estimation of quantum efficiencies and Arrhenius parameters of organic laser dyes by measuring fluorescence decay times down to T = 115 K

The fluorescence decay times of several organic dyes in alcoholic solution in the temperature range between 300 K and 115 K are measured. These measurements offer the possibility to determine Arrhenius parameters and to estimate quantum efficiencies.

Pulsed UV laser for fluorescence decay measurements

Second harmonic generation in a non-linear optical crystal is utilized to obtain pulsed UV emission (λ = 2573 Å) which exhibits peak powers of greater than 1 W at repetition rates ranging from single pulse to 1 MHz. Such a system is useful for measuring fluorescence decay times in UV excitable materials which are longer than 10 ns in duration.

Measurement of fluorescence decay time in living cells

This paper reports a simple technique for measuring fluorescence decay times of intracellular compounds. The data can be obtained from suspensions of living cells or, using a microscope, from single cells. The method employs a TRW, Inc. nanosecond spectral source and decay time computer which have been used previously for measuring decay times of aqueous solutions. Ascites tumor cells, liver cells, fibroblasts, bacteria, and cell fractions, after incubation with a fluorochrome and appropriate washing, can be suspended in a cuvette (or in the case of single cells, placed on a microscope slide) and the fluorescent decay time can be read out digitally in nanoseconds. The instrument is most accurate where actual decay values are > 2 ns, and under these conditions reads to a precision of ±0.5 ns in clear solutions, and ±1.0 ns for intracellular work. Results obtained using the fluorescent probes, anilinonaphthalene sulfonate (ANS), toluidinyl naphthalene sulfonate (TNS), 3,4-benzpyrene (BP), and 2-aminonaphthalene (2-AN) are presented as examples.

Versatile Technique for Measuring Fluorescence Decay Times in the Nanosecond Region

A new method of accurately recording scintillation pulse contours over several decades is described. Scintillation pulses are analyzed by an apparatus which combines the very fast rise time of a pulse sampling oscilloscope and the digital storage capacity of a multichannel analyzer. A special feature of this technique is its ability to accept, within limits, pulses random in time and amplitude so that fluorescence from samples excited either by pulsed uv radiation, β, or α particles may be analyzed. This apparatus, in combination with a hydrogen flash tube and a monochromator, has been used to measure the decay time of fluorescent solutions as a function of the wavelength of the exciting radiation. Decay time measurements have also been made for various modes of excitation: α particle, β particle, and pulsed uv.