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Steven T. Cundiff - One of the best experts on this subject based on the ideXlab platform.

  • Two-dimensional Fourier-Transform Spectroscopy of potassium vapor
    2020
    Co-Authors: X Dai, D. Karaiskaj, A D Bristow, Steven T. Cundiff
    Abstract:

    Optical two-dimensional Fourier-Transform (2DFT) Spectroscopy is used to study the coherent optical response of potassium vapor in a thin transmission cell. Rephasing and nonrephasing spectra of the D 1 and D 2 transitions are obtained and compared to numerical simulations. Non-perturbative calculations using the optical Bloch equations give very good agreement with the experimental peak strengths and line shapes. Nonradiative Raman-like coherences are isolated using a different 2DFT projection. Comparison between the optical and Raman linewidths shows that dephasing is due to partially correlated energy fluctuations. Density-dependent measurements show distortion of 2DFT spectra due to pulse propagation effects

  • Pulse Propagation Effects in Optical 2D Fourier-Transform Spectroscopy: Theory.
    The journal of physical chemistry. A, 2015
    Co-Authors: Steven T. Cundiff, Austin P. Spencer, David M. Jonas
    Abstract:

    A solution to Maxwell’s equations in the three-dimensional frequency domain is used to calculate rephasing two-dimensional Fourier Transform (2DFT) spectra of the D2 line of atomic rubidium vapor in argon buffer gas. Experimental distortions from the spatial propagation of pulses through the sample are simulated in 2DFT spectra calculated for the homogeneous Bloch line shape model. Spectral features that appear at optical densities of up to 3 are investigated. As optical density increases, absorptive and dispersive distortions start with peak shape broadening, progress to peak splitting, and ultimately result in a previously unexplored coherent transient twisting of the split peaks. In contrast to the low optical density limit, where the 2D peak shape for the Bloch model depends only on the total dephasing time, these distortions of the 2D peak shape at finite optical density vary with the waiting time and the excited state lifetime through coherent transient effects. Experiment-specific conditions are ex...

  • Pulse Propagation Effects in Optical 2D Fourier-Transform Spectroscopy: Experiment
    The journal of physical chemistry. A, 2013
    Co-Authors: Austin P. Spencer, Galan Moody, David M. Jonas, Andrew Kortyna, Steven T. Cundiff
    Abstract:

    In optical two-dimensional Fourier-Transform (2DFT) Spectroscopy, understanding how the spectral line shape is affected by pulse propagation in the sample is crucial for an accurate interpretation of spectra. We report an experimental study of pulse propagation effects in 2DFT Spectroscopy performed in a dense atomic vapor. The spectral line shape can be dramatically distorted due to high optical density as well as the physical thickness of a sample. The spectral distortion can be partially corrected by using a reference pulse copropagating with the signal combined with appropriate data processing.

  • Coupling in InGaAs double quantum wells studied with 2D Fourier Transform Spectroscopy
    CLEO: 2013, 2013
    Co-Authors: Gaël Nardin, Galan Moody, Rohan Singh, Travis M. Autry, François Morier-genoud, Steven T. Cundiff
    Abstract:

    We study asymmetric double InGaAs quantum well samples, featuring three different barrier widths, using optical two-dimensional Fourier Transform Spectroscopy. Depending on the barrier width, we observe different coupling mechanisms between the two wells.

  • revealing exciton dephasing and transport dynamics in semiconductor quantum well quantum dot systems using optical 2d Fourier Transform Spectroscopy
    Proceedings of SPIE, 2012
    Co-Authors: D. Karaiskaj, Alan D. Bristow, Daniel Gammon, Allan S. Bracker, Steven T. Cundiff, Xingcan Dai, Galan Moody, Mark E Siemens
    Abstract:

    Exciton dephasing and relaxation dynamics are studied in a GaAs quantum dot ensemble using optical twodimensional Fourier Transform Spectroscopy. We measure the temperature and excitation-density dependence of the exciton ground-state homogeneous lineshape of quantum dots within the ensemble and show that acoustic phonon sidebands are absent. The linewidth increases nonlinearly with temperature from 6 to 50 K and the behavior is well-described by an Arrhenius equation with an offset. The absence of a phonon-activation peak in the spectra reveals that elastic exciton-phonon scattering is the primary dephasing mechanism and the results can be explained qualitatively using an extension of the independent Boson model that includes quadratic coupling in the phonon displacement coordinates. At temperatures ≥ 35 K, spectral features associated with phonon-assisted population transfer of excitons out of the quantum dots and into quantum wells states begin to appear.

Nathalie Picque - One of the best experts on this subject based on the ideXlab platform.

Moschos G Polissiou - One of the best experts on this subject based on the ideXlab platform.

  • assessing saffron crocus sativus l adulteration with plant derived adulterants by diffuse reflectance infrared Fourier Transform Spectroscopy coupled with chemometrics
    Talanta, 2017
    Co-Authors: Eleftherios A Petrakis, Moschos G Polissiou
    Abstract:

    Abstract Saffron, the dried red stigmas of the plant Crocus sativus L., is well-known as one of the most important and expensive spices worldwide. It is thus highly susceptible to fraudulent practices that employ, among others, plant-derived adulterants. This study presents an application of diffuse reflectance infrared Fourier Transform Spectroscopy (DRIFTS) and chemometric techniques for evaluating adulteration of saffron with six characteristic adulterants of plant origin, i.e. C. sativus stamens, calendula, safflower, turmeric, buddleja, and gardenia. The proposed method involved a three-step process for the detection of adulteration as well as for the identification and quantification of adulterants. Partial least squares discriminant analysis (PLS-DA) was applied to perform authentication of saffron based on mid-infrared fingerprints (4000–600 cm−1), resulting in 99% correct classification of pure saffron and saffron adulterated at 5–20% (w/w) levels. Adulterant identification in positive samples was performed with high sensitivity and specificity by a six-class PLS-DA model, with spectroscopic data from the region 2000–600 cm−1. Subsequently, partial least squares (PLS) regression models were built for the quantification of each adulterant. By using synergy interval PLS (siPLS) for variable selection, models with improved performance were developed, with detection limits ranging from 1.0% to 3.1% (w/w). The results obtained illustrate that this strategy based on DRIFTS has the potential to complement existing methodologies for the rapid and cost-effective assessment of typical saffron frauds.

  • direct determination of rosmarinic acid in lamiaceae herbs using diffuse reflectance infrared Fourier Transform Spectroscopy drifts and chemometrics
    Analytical Abstracts, 2013
    Co-Authors: Dimitrios Saltas, Petros A Tarantilis, Christos S Pappas, Dimitra Daferera, Moschos G Polissiou
    Abstract:

    For the determination of rosmarinic acid (RA) directly in pulverized plant material, a method is developed using diffuse reflectance infrared Fourier Transform Spectroscopy (DRIFTS) without any physicochemical pretreatment of samples. The RA content of 11 samples of eight different Lamiaceae herbs, as determined by high performance liquid chromatography (HPLC), varied between 86 ± 1 mg/g (in lemon balm) and 12.0 ± 0.8 mg/g (in hyssop) of dried plant material. The 11 samples and 50 other additional samples, which were prepared by mixing initial samples with KBr, were measured using DRIFTS. The second derivative of the spectral region 1344-806 cm–1 was used and the corresponding data were analyzed using partial least squares (PLS) regression. The correlation between infrared spectral analysis and HPLC measurements shows that the DRIFTS method is sufficiently accurate, simple, and rapid. The RA content of the 11 Lamiaceae samples determined by DRIFTS ranged from 81 ± 4 mg/g (in lemon balm) to 12 ± 3 mg/g (in hyssop) of dried plant material.

  • direct determination of rosmarinic acid in lamiaceae herbs using diffuse reflectance infrared Fourier Transform Spectroscopy drifts and chemometrics
    Journal of Agricultural and Food Chemistry, 2013
    Co-Authors: Dimitrios Saltas, Petros A Tarantilis, Christos S Pappas, Dimitra Daferera, Moschos G Polissiou
    Abstract:

    For the determination of rosmarinic acid (RA) directly in pulverized plant material, a method is developed using diffuse reflectance infrared Fourier Transform Spectroscopy (DRIFTS) without any physicochemical pretreatment of samples. The RA content of 11 samples of eight different Lamiaceae herbs, as determined by high performance liquid chromatography (HPLC), varied between 86 ± 1 mg/g (in lemon balm) and 12.0 ± 0.8 mg/g (in hyssop) of dried plant material. The 11 samples and 50 other additional samples, which were prepared by mixing initial samples with KBr, were measured using DRIFTS. The second derivative of the spectral region 1344–806 cm–1 was used and the corresponding data were analyzed using partial least squares (PLS) regression. The correlation between infrared spectral analysis and HPLC measurements shows that the DRIFTS method is sufficiently accurate, simple, and rapid. The RA content of the 11 Lamiaceae samples determined by DRIFTS ranged from 81 ± 4 mg/g (in lemon balm) to 12 ± 3 mg/g (in...

  • identification and differentiation of goat and sheep milk based on diffuse reflectance infrared Fourier Transform Spectroscopy drifts using cluster analysis
    Food Chemistry, 2008
    Co-Authors: Christos S Pappas, Petros A Tarantilis, Ekaterini Moschopoulou, Golfo Moatsou, I Kandarakis, Moschos G Polissiou
    Abstract:

    Abstract A new methodology for identification and differentiation of goat and sheep milk was developed based on FT-IR Spectroscopy using hierarchical and discriminant analysis. Forty-nine goat and 38 sheep defatted and freeze-dried Greek milk samples were analyzed. FT-IR spectra were obtained in the diffuse reflectance infrared Fourier Transform Spectroscopy (DRIFTS) mode. The spectral region 1840–950 cm −1 was used to ‘fingerprint’ milk types. Main peak used for differentiation of goat/sheep milk is located at 1745 cm −1 , which is correlated to the degree of sugars carboxyl methyl esterification. Hierarchical and discriminant analyses were based on the absorptions of the above spectral region. These analyses showed that the samples of goat milk can be differentiated from the samples of sheep’s.

  • determination of the degree of esterification of pectinates with decyl and benzyl ester groups by diffuse reflectance infrared Fourier Transform Spectroscopy drifts and curve fitting deconvolution method
    Carbohydrate Polymers, 2004
    Co-Authors: Christos Pappas, Anna Malovikova, Zdenka Hromadkova, Petros A Tarantilis, Anna Ebringerova, Moschos G Polissiou
    Abstract:

    Pectinates with benzyl and decyl ester groups were prepared by alkylation of the tetrabutylammonium salt of pectic acid with benzyl and decyl bromides, respectively. The degree of esterification (DE) of the pectin derivatives was determined by diffuse reflectance infrared Fourier Transform Spectroscopy and the curve-fitting deconvolution method. A linear relationship between DE and the ratio of the peak area at 1745 cm−1 to the sum of the peak areas at 1745 and 1608 cm−1 was established with a high correlation coefficient 0.98. The deconvolution analysis using the curve-fitting method allowed the elimination of spectral interferences from pectin components and their degradation products. The limits of the method are given by DE 6 and 93%. The method was compared with chemical analysis and found to be equivalent in view of accuracy and repeatability (t-test, F-test). The method is applicable in analysis of natural or synthetic mixtures and/or crude pectin substances.

G Guelachvili - One of the best experts on this subject based on the ideXlab platform.

David M. Jonas - One of the best experts on this subject based on the ideXlab platform.

  • Vibrational and Nonadiabatic Coherence in 2D Electronic Spectroscopy, the Jahn-Teller Effect, and Energy Transfer.
    Annual review of physical chemistry, 2018
    Co-Authors: David M. Jonas
    Abstract:

    Femtosecond two-dimensional (2D) Fourier Transform Spectroscopy generates and probes several types of coherence that characterize the couplings between vibrational and electronic motions. These cou...

  • Pulse Propagation Effects in Optical 2D Fourier-Transform Spectroscopy: Theory.
    The journal of physical chemistry. A, 2015
    Co-Authors: Steven T. Cundiff, Austin P. Spencer, David M. Jonas
    Abstract:

    A solution to Maxwell’s equations in the three-dimensional frequency domain is used to calculate rephasing two-dimensional Fourier Transform (2DFT) spectra of the D2 line of atomic rubidium vapor in argon buffer gas. Experimental distortions from the spatial propagation of pulses through the sample are simulated in 2DFT spectra calculated for the homogeneous Bloch line shape model. Spectral features that appear at optical densities of up to 3 are investigated. As optical density increases, absorptive and dispersive distortions start with peak shape broadening, progress to peak splitting, and ultimately result in a previously unexplored coherent transient twisting of the split peaks. In contrast to the low optical density limit, where the 2D peak shape for the Bloch model depends only on the total dephasing time, these distortions of the 2D peak shape at finite optical density vary with the waiting time and the excited state lifetime through coherent transient effects. Experiment-specific conditions are ex...

  • Pulse Propagation Effects in Optical 2D Fourier-Transform Spectroscopy: Experiment
    The journal of physical chemistry. A, 2013
    Co-Authors: Austin P. Spencer, Galan Moody, David M. Jonas, Andrew Kortyna, Steven T. Cundiff
    Abstract:

    In optical two-dimensional Fourier-Transform (2DFT) Spectroscopy, understanding how the spectral line shape is affected by pulse propagation in the sample is crucial for an accurate interpretation of spectra. We report an experimental study of pulse propagation effects in 2DFT Spectroscopy performed in a dense atomic vapor. The spectral line shape can be dramatically distorted due to high optical density as well as the physical thickness of a sample. The spectral distortion can be partially corrected by using a reference pulse copropagating with the signal combined with appropriate data processing.