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Articles 1 - 9 of 9
Full-Text Articles in Physical Sciences and Mathematics
Continuous Laser‐Excited Photothermal Spectrometry Of CdsXSe1‐X Doped Glasses, Oluwatosin Dada, Matthew R. Jorgensen, Stephen E. Bialkowski
Continuous Laser‐Excited Photothermal Spectrometry Of CdsXSe1‐X Doped Glasses, Oluwatosin Dada, Matthew R. Jorgensen, Stephen E. Bialkowski
Stephen E. Bialkowski
Photothermal lens measurements and finite element modeling are used to examine the physical changes taking place in optical filter glasses. Colored glass and neutral density filters are found to have a strong positive temperature-dependent refractive index change. The overall positive refractive index change is thought to be a consequence of complex counteracting factors: stress-induced birefringence, polarizability, structural network, and temperature-dependent carrier density changes in the CdSxSe1–x microcrystals that produce optical properties of these glasses. Finite element analysis (FEA) modeling is used to examine the temperature profiles and the goodness of the semi-infinite thermal diffusion solution normally used …
Steady‐State Absorption Rate Models For Use In Relaxation Rate Studies With Continuous Laserexcited Photothermal Lens Spectrometry, Stephen E. Bialkowski
Steady‐State Absorption Rate Models For Use In Relaxation Rate Studies With Continuous Laserexcited Photothermal Lens Spectrometry, Stephen E. Bialkowski
Stephen E. Bialkowski
This paper examines the solutions of kinetic rate equations for prediction of the photothermal lens signals under irradiance conditions that can lead to optical saturation or bleaching. The relaxation kinetics resulting from forcing excited state populations in multiple levels by high excitation irradiance continuous lasers is examined and irradiance-dependent photothermal lens signals are predicted. The analyses described in this paper are based on simple kinetic models for optical excitation and subsequent excited state relaxation. Dark-state relaxation is assumed to be extremely fast compared to limiting kinetics resulting in simplified excited state models. Kinetic models are derived for two, four and …
Optical Bleaching In Continuous Laser Excited Photothermal Lens Spectrometry, Agnes Chartier, Stephen E. Bialkowski
Optical Bleaching In Continuous Laser Excited Photothermal Lens Spectrometry, Agnes Chartier, Stephen E. Bialkowski
Stephen E. Bialkowski
This paper presents methods for measuring and modeling optical bleaching that occurs, by using continuous laser sources for solution-phase organic dye molecule spectrometry. Photothermal lens experiments are used to measure the nonlinear optical absorption coefficients of eosin Y, erythrosin B, and pseudo-isocyanine iodide dyes in ethanol as a function of excitation irradiance. Excitation irradiance-dependent photothermal lens data are subsequently interpreted in terms of the photophysics and excited-state relaxation dynamics of the condensed-phase dye molecules under study. The model uses first-order kinetics for excitation and subsequent metastable-state relaxation back to the ground state and accounts for both ground- and metastable-state absorption. …
Photothermal Lens Spectrometry Of Homogeneous Fluids With Incoherent White‐Light Excitationusing A Cylindrical Sample Cell, Agnes Chartier, Stephen E. Bialkowski
Photothermal Lens Spectrometry Of Homogeneous Fluids With Incoherent White‐Light Excitationusing A Cylindrical Sample Cell, Agnes Chartier, Stephen E. Bialkowski
Stephen E. Bialkowski
A model for photothermal lens signal generation in a cylindrical sample cell under constant irradiance excitation is described and tested. The model is developed with and without the assumption that the sample cell does not change temperature over the irradiation time. In both cases, the photothermal lens is predicted to be parabolic in form with a strength that is independent of sample cell radius. The predicted irradiance independence suggests that incoherent illumination can be used to perform photothermal lens spectroscopy in low-volume cells. Experimental evidence is obtained using a Xe arc lamp to perform photothermal lens spectroscopy in a 6 …
Diffraction Effects In Single‐ And Two‐Laser Photothermal Lens Spectroscopy, Stephen E. Bialkowski, Agnes Chartier
Diffraction Effects In Single‐ And Two‐Laser Photothermal Lens Spectroscopy, Stephen E. Bialkowski, Agnes Chartier
Stephen E. Bialkowski
A simple method for calculating the effects of optical geometry on photothermal lens signals is shown. This method is based on calculating cumulative electric-field phase shifts produced by a series of Gaussian refractive-index perturbations produced by the photothermal effect. Theoretical results are found for both pulsed-laser and continuous Gaussian laser excitation sources and both single- and two-laser apparatuses commonly employed in photothermal lens spectroscopy. The effects of apparatus geometry on the resulting signal are shown. Analytical time-dependent signal results are found for small signals. Analytical pump–probe focus geometry results allow direct optimization for certain conditions. The calculations indicate that the …
Accounting For Saturation Effects In Pulsed Infrared Laser Excited Photothermal Spectroscopy, Stephen E. Bialkowski
Accounting For Saturation Effects In Pulsed Infrared Laser Excited Photothermal Spectroscopy, Stephen E. Bialkowski
Stephen E. Bialkowski
Equations that relate photothermal lens focal lengths and photothermal deflection angles to saturation absorption coefficients are derived. These equations are derived for two-level absorbers with both homogeneously and inhomogeneously broadened transitions. Initial and time-dependent photothermal lens signals are calculated. Equations describing the zero-time signals are exact to within the simplifying assumptions of the derivation, while the time-dependent signals are approximate. The approximation is performed by the use of a finite series of Gaussian functions to model the temperature change profile distorted by nonlinear absorption. The excitation irradiance-dependent signal behavior for rectangular and exponential excitation pulse time profiles for homogeneously and …
Pulsed‐Laser Excited Differential Photothermal Deflection Spectrometry, Stephen E. Bialkowski, Xu Gu, Pete E. Poston, Linda S. Powers
Pulsed‐Laser Excited Differential Photothermal Deflection Spectrometry, Stephen E. Bialkowski, Xu Gu, Pete E. Poston, Linda S. Powers
Stephen E. Bialkowski
This paper describes a differential photothermal optical absorbance apparatus that uses two excitation beams at different wave-lengths. A single probe beam monitors the difference in heats generated by the two wavelengths. The theory is developed for the operational principles of the apparatus, and theoretical signals are compared with those obtained with a conventional absorption spectrophotometer. The differential photothermal apparatus has a theoretical advantage over conventional spectrophotometry for samples with less than unit absorbance. Experiments are described which verify the operating principles and demonstrate the flexibility of the apparatus.
Application Of The Batio3 Beam Fanning Limiter As An Adaptive Spatial Filter For Signal Enhancementin Pulsed Laser Excited Photothermal Spectroscopy, Stephen E. Bialkowski
Application Of The Batio3 Beam Fanning Limiter As An Adaptive Spatial Filter For Signal Enhancementin Pulsed Laser Excited Photothermal Spectroscopy, Stephen E. Bialkowski
Stephen E. Bialkowski
A method for obtaining a high-contrast visible-light signal from infrared absorption in low-absorbance samples is described. This method is based on a beam-fanning optical limiter in photorefractive BaTiO3. The resulting signal is not linear but does exhibit an enhanced signal-to-background ratio that is 4 to 6 orders of magnitude better than that of conventional infrared absorption spectrophotometry in the shot-noise limit. A simple model for the beam-fanning, optical-limiter-based, pulsed-laser-excited photothermal spectroscopy detector is found to describe the experimental data adequately. This technique using photothermal spectroscopy detection may have advantages for rapid signal analysis and for two-dimensional visible imaging …
Photothermal Lens Aberration Effects In Two Laser Thermal Lens Spectrometry, Stephen E. Bialkowski
Photothermal Lens Aberration Effects In Two Laser Thermal Lens Spectrometry, Stephen E. Bialkowski
Stephen E. Bialkowski
A comparison of theories describing two laser photothermal lens signals is given. The aberrant nature of this lens is accounted for in a theory which treats the propagation of a monitor laser in terms of a phase shift in this laser beam wave front. The difference between theories are discussed in terms of the predicted signal strengths and temporal behavior. The aberrant theory results in smaller theoretical signal strengths and different functional relationships between signal and analyte level.