Search results for "induced fluorescence"
showing 10 items of 46 documents
Experimental studies of the NaRb ground-state potential up to thev″=76level
2002
Laser induced fluorescence spectra of the C {sup 1}{sigma}{sup +}-X {sup 1}{sigma}{sup +} system of {sup 23}Na{sup 85}Rb and {sup 23}Na{sup 87}Rb have allowed vibrational levels of the electronic ground state up to v{sup ''}=76, spanning 99.85% of the potential well to be observed. The ground-state term values have been fitted to a Dunham polynomial expansion, and also to a direct modified Lennard-Jones (MLJ) potential. The analytical MLJ construction allowed us to match previous measured term values for v{sup ''}{<=}30 with long-range behavior of the potential through the intermediate internuclear distance region covered by the present investigation.
Retrieval of sun-induced fluorescence using advanced spectral fitting methods
2015
Abstract The FLuorescence EXplorer (FLEX) satellite mission, candidate of ESA's 8th Earth Explorer program, is explicitly optimized for detecting the sun-induced fluorescence emitted by plants. It will allow consistent measurements around the O2-B (687 nm) and O2-A (760 nm) bands, related to the red and far-red fluorescence emission peaks respectively, the photochemical reflectance index, and the structural-chemical state variables of the canopy. The sun-induced fluorescence signal, overlapped to the surface reflected radiance, can be accurately retrieved by employing the powerful spectral fitting technique. In this framework, a set of fluorescence retrieval algorithms optimized for FLEX ar…
LIF intensity distribution as a deperturbation tool: application to the fully-mixed A1Σ+–b3Π complex of NaRb
2005
Abstract The intensity distribution in the NaRb A 1 Σ + ( v A ′ = 16 , J ′ = 30 ; v A ′ = 18 , J ′ = 66 ) ∼ b 3 Π → X 1 Σ + ( v X ′ ′ = 2 ÷ 44 , J ′ ′ = J ′ ± 1 ) fluorescence series induced by diode laser excitation from the ground state have been measured and directly applied to restore adiabatic potential energy curve for the A-state of the fully-mixed A 1 Σ + – b 3 Π complex. Relative intensities in the long non-diagonal A → X progressions have been proved to be much less influenced by strong spin–orbit interaction than the corresponding term values of the fully coupled A 1 Σ + – b 3 Π complex.
Fast thermometry for trapped ions using dark resonances
2015
We experimentally demonstrate a method to determine the temperature of trapped ions which is suitable for monitoring fast thermalization processes. We show that observing and analyzing the lineshape of dark resonances in the fluorescence spectrum provides a temperature measurement which accurate over a large dynamic range, applied to single ions and small ion crystals. Laser induced fluorescence is detected over a time of only $20\,\mu$s allowing for rapid determination of the ion temperature. In the measurement range of $10^{-1}-10^{+2}\,$mK we reach better than $15\,\%$ accuracy. Tuning the cooling laser to selected resonance features allows for controlling the ion temperatures between $0…
Fluorescence of rubidium in a submicrometer vapor cell: spectral resolution of atomic transitions between Zeeman sublevels in a moderate magnetic fie…
2005
It is experimentally demonstrated that use of an extremely thin cell (ETC) with the thickness of a Rb atomic vapor column of ∼400 nm allows one to resolve a large number of individual transitions between Zeeman sublevels of the D1 line of 87Rb and 85Rb in the sub-Doppler fluorescence excitation spectra in an external magnetic field of ∼200 G. It is revealed that due to the peculiarities of the Zeeman effect for different hyperfine levels of Rb, all allowed transitions between magnetic sublevels can be clearly resolved for 87RbF_g = 1 --> F_e = 1, 2 and F_g = 2 --> F_e = 1, 2 fluorescence excitation. Also, relatively good spectral resolution can be achieved for 85RbF_g = 2 --> F_e = 2, 3 flu…
Multi-sensor spectral synergies for crop stress detection and monitoring in the optical domain: A review
2022
Remote detection and monitoring of the vegetation responses to stress became relevant for sustainable agriculture. Ongoing developments in optical remote sensing technologies have provided tools to increase our understanding of stress-related physiological processes. Therefore, this study aimed to provide an overview of the main spectral technologies and retrieval approaches for detecting crop stress in agriculture. Firstly, we present integrated views on: i) biotic and abiotic stress factors, the phases of stress, and respective plant responses, and ii) the affected traits, appropriate spectral domains and corresponding methods for measuring traits remotely. Secondly, representative result…
Spontaneous lifetimes and relaxation cross-sections of the D1Π state of NaRb
2003
Abstract The time-resolved intensity of dispersed laser induced fluorescence following the Ar + -laser D 1 Π←X 1 Σ + excitation was measured for both 23 Na 85 Rb and 23 Na 87 Rb isotopomers in a thermal cell. Spontaneous radiative lifetime values determined for v ′ ( J ′ ) rovibronic levels of the D 1 Π state in the v ′ range from 0 to 17 and J ′ from 8 to 131 varied from 22.5 to 17.3 ns. Averaged collisional quenching cross-section values of (3–6)×10 −14 cm 2 were obtained for NaRb (D 1 Π, v ′ , J ′ ) + Rb collisions from the Stern–Volmer plots.
MIXING TIME IN UNBAFFLED STIRRED TANKS
2012
Unbaffled stirred tanks, despite their poorer mixing performance with respect to baffled vessels, are gaining a growing industrial interest as they provide significant advantages in selected applications, including a number of biochemical, food and pharmaceutical processes. There still is however a general lack of information on their mixing performance, that needs to be addressed in order to fully exploit their application potential. The present work is aimed at providing experimental information on mixing rates in an unbaffled vessel operated without top-cover (Uncovered Unbaffled Stirred Tank, UUST). The planar laser induced fluorescence (PLIF) technique was adopted for measuring the dis…
A LASER-INDUCED FLUORESCENCE (LIF) METHOD FOR MONITORING OXYGEN–ALKALI DELIGNIFICATION OF SOFTWOOD KRAFT PULP
2002
ABSTRACT A laser-induced fluorescence (LIF) method for monitoring the oxygen–alkali delignification of pine (Pinus sylvestris) kraft pulp was tested. The fluorescence intensity of the effluent was found to increase systematically during treatment as the lignin content of the pulp decreased. This emission method, compared, for example, to a UV/Vis absorption method, seems to have potential for large-scale applications. Owing both to the complex chemical nature of the effluent from oxygen–alkali delignification and to the complex nature of the fluorescence method, further work on this method is needed before it can be used for industrial purposes.
Frequency-modulation spectroscopy with blue diode lasers
2000
Frequency-modulation spectroscopy provides ultrasensitive absorption measurements. The technique is especially adaptable to diode lasers, which can be modulated easily, and has been used extensively in the near-infrared and infrared spectral regions. The availability of blue diode lasers now means that the accessible wavelength region can be increased. We successfully demonstrate wavelength-modulation spectroscopy and two-tone frequency-modulation spectroscopy for the weak second resonance line of potassium at 404.8 nm and for the transition at 405.8 nm in lead, starting from the thermally populated 6p(2) P-3(2) metastable level, information on the modulation parameters is obtained with a f…