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- Laser (10)
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Articles 1 - 23 of 23
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 …
Using An Expectation‐Maximization Algorithm To Obtain Dielectric Relaxation Time Spectra Ofaqueous Montmorillonite Clay Suspensions, Stephen E. Bialkowski, Lynn Dudley, Dani Or
Using An Expectation‐Maximization Algorithm To Obtain Dielectric Relaxation Time Spectra Ofaqueous Montmorillonite Clay Suspensions, Stephen E. Bialkowski, Lynn Dudley, Dani Or
Stephen E. Bialkowski
Determination of relaxation-time distributions from dielectric spectra of complex impedance or dielectric permittivity remains a challenge. This problem is one of a wider class of ill-posed inverse problems where the measurement is a superposition or convolution of functions containing the sought-after information. An expectation-maximization (EM) algorithm is shown to be useful for obtaining dielectric relaxation-time distributions from impedance data. This algorithm is stable and converges to realistic relaxation-time spectra without the need for constraints or initial values. The implementation used herein updates expectations in an iterative multiplication step. The models and basic assumptions of impedance spectroscopy are outlined in the …
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. …
Overcoming The Multiplex‐Disadvantage Using Maximum‐Likelihood Inversion, Stephen E. Bialkowski
Overcoming The Multiplex‐Disadvantage Using Maximum‐Likelihood Inversion, Stephen E. Bialkowski
Stephen E. Bialkowski
A maximum-likelihood estimator, derived under quantum-noiselimited measurement conditions, is used to obtain wavenumber-ordered spectra produced by a model Michelson interferometer. The estimator is tested on a number of synthetic interferograms, and results are compared to similar spectra obtained by using the Fourier (cosine) transform. It is found that the maximum-likelihood inversion method does not result in white noise in the spectrum estimate when the spectrum is sparse. It thus may be used to circumvent the main disadvantage in multiplexed spectrometer measurements using quantum-noise-limited detectors for emissionbased measurements. It is also found that maximum-likelihood inversion methods can be used to obtain …
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 …
Detection Of Dityrosine In Apoferritin, Stephen E. Bialkowski
Detection Of Dityrosine In Apoferritin, Stephen E. Bialkowski
Stephen E. Bialkowski
Laser-excited fluorescence spectroscopy was adopted for dityrosine detection in horse spleen apoferritin. Dityrosine was identified in horse spleen apoferritin. Fractionation of acid-hydrolyzed horse spleen apoferritin showed fluorescence attributed to dityrosine, and other compounds, excited by 325-nm laser radiation. The other fluorescent compounds resulted in a broad fluorescence emission spectrum of horse spleen apoferritin. The broad emission band overlapped with the fluorescence emission spectrum of pure dityrosine. Fractionation of horse spleen apoferritin acid hydrolysate prior to laser-excited fluorescence detection was necessary for dityrosine quantitative analysis. The concentration of dityrosine in horse spleen apoferritin was 2.5% (mol/mol), estimated from the method of …
Laser Excited Fluorescence Of Dityrosine, Sahar F. Mahmoud, Stephen E. Bialkowski
Laser Excited Fluorescence Of Dityrosine, Sahar F. Mahmoud, Stephen E. Bialkowski
Stephen E. Bialkowski
In this research, laser-excited fluorescence was examined for sensitive detection of aqueous dityrosine. Samples were excited with a 6.3-mW, 325-nm helium-cadmium laser focused into a small volume-fluorescence cell with a 10-cm lens. The resulting fluorescence emission was collected perpendicular to the excitation and detected with two different schemes. An optical bandpass filter was used with a photomultiplier tube for sensitive quantitative measurement, while a photodiode array detector was used in conjunction with a spectrograph for qualitative characterization of fluorescence emission spectra. Dityrosine detection on the order of 2 × 10-11 M was obtained with the use of the photomultiplier …
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 …
Optimized Spectroscopic Signal Estimates Using Integration And Matched Filters, Stephen E. Bialkowski
Optimized Spectroscopic Signal Estimates Using Integration And Matched Filters, Stephen E. Bialkowski
Stephen E. Bialkowski
This paper examines theories of signal processing as applied to peak magnitude estimation in absorption and emission spectroscopy. Signals obtained from Fourier transform, fixed wavelength, and scanning dispersive instruments are modeled in terms of the time required to obtain a spectrum. The differences between these techniques and the signal processing procedures that should be used for each technique are characterized for a Lorentzian spectral feature. Including the time required to scan over a range of optical frequencies results in optimal signal processing procedures that are different from those previously supposed. In particular, it is found that the optimal matched filter …
Simple Scheme For Variable High Power Laser Beam Attenuation, Stephen E. Bialkowski
Simple Scheme For Variable High Power Laser Beam Attenuation, Stephen E. Bialkowski
Stephen E. Bialkowski
A venetian style infrared attenuator placed prior to a pinhole spatial filter results in variable high‐power laser attenuation. This attenuation scheme has a wide dynamic range, results in high‐quality Gaussian beams, does not introduce beam walk‐off error, and is independent of polarization.
Optimal Estimation Of Impulse‐Response Signals Through Digital Innovations And Matched Filtersmoothing, Stephen E. Bialkowski
Optimal Estimation Of Impulse‐Response Signals Through Digital Innovations And Matched Filtersmoothing, Stephen E. Bialkowski
Stephen E. Bialkowski
A real‐time digital filter is described which may be most useful for optimal determination of the magnitude of impulse‐response functions found in pulsed, repetitive experiments of low duty cycle. This filter is based on a matched filter but employs an interference orthogonalization step. This results in a signal magnitude estimate which is independent of coherent interference. The filter updates the signal magnitude estimate upon each repetition of the experimental cycle. Comparisons to signal estimation using gated sampling devices are given.
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.
A Statistical Interpretation Of The Rotational Temperature Of No Desorbed For Ru(001), Stephen E. Bialkowski
A Statistical Interpretation Of The Rotational Temperature Of No Desorbed For Ru(001), Stephen E. Bialkowski
Stephen E. Bialkowski
A simple model of the rotational state of NO prior to thermal desorption from Ru(001) surface is developed in terms of the rotational heat capacity. The predicted rotational temperature of the desorbed species is consistent with known data on this system. The model is extended to predict translational energy anisotropy in the desorbed NO.
A Quantitative Test Of Unimolecular Rate Theory In The Multi‐Photon Dissociation Of Cf2Cfcl, John C. Stephenson, Stephen E. Bialkowski, David S. King, Everet Thiele, James Stone, Myron F. Goodman
A Quantitative Test Of Unimolecular Rate Theory In The Multi‐Photon Dissociation Of Cf2Cfcl, John C. Stephenson, Stephen E. Bialkowski, David S. King, Everet Thiele, James Stone, Myron F. Goodman
Stephen E. Bialkowski
We have measured the distribution of total energy in reaction products for the CO2 laser‐induced MPD: CF2CFCl→CF2+CFC1. From a separate study of MPD rates as a function of laser intensity and inert buffer gas pressure, reliable estimates of the radiative pumping rates are known for this reaction. These results, when analyzed together, allow us to extract a unimolecular A factor from the MPD data. The determined value A = 3×1016 sec−1 agrees well with estimates based on independent thermal data.
Simple Parallel Interface Between An Optical Multichannel Analyzer And A Microprocessor, Stephen E. Bialkowski
Simple Parallel Interface Between An Optical Multichannel Analyzer And A Microprocessor, Stephen E. Bialkowski
Stephen E. Bialkowski
A simple circuit is given which will allow data transfer from a LSI‐11 DRV11 parallel interface unit to a PARC 1216 Optical Multichannel Detector Controller. The Circuit for OMA to LSI‐11 data transfer is slightly more complicated. Data buffering is used so that data transfer can occur without time‐out loss due to the dynamic memory refresh cycle of the LSI‐11. The circuit may be constructed and mounted within the PARC 1216 unit with only minor, noncritical, modifications to the controller unit. The unit is able to transmit data from the 1216 controller running at dwell times as short as 40 …
The Determination Of Mass Transport Coefficients And Vibrational Relaxation Rates Of Speciesformed In Laser Photolysis Experiments, Stephen E. Bialkowski, David S. King, John C. Stephenson
The Determination Of Mass Transport Coefficients And Vibrational Relaxation Rates Of Speciesformed In Laser Photolysis Experiments, Stephen E. Bialkowski, David S. King, John C. Stephenson
Stephen E. Bialkowski
A simple analytical solution of the equations which govern the formation, collisional relaxation, and mass transport rates of species produced in radially symmetric laser‐induced processes is given. These equations are specifically applied to the CO2 laser‐induced dissociations of CF2HCl and C2F3Cl dilute in argon. The concentration of the vibrational ground state of the CF2 radical product was probed as a function of time and pressure both during and after the photolyzing laser pulse by the laser‐excited fluorescence technique. From these measurements, the vibrational relaxation rate of ? CF2 in argon was …
Energy Partitioning In The Ir Multiphoton Dissociation Of Molecules: Energy Of Xcf2 And Xcfcl Fromcf2Cfcl, John C. Stephenson, Stephen E. Bialkowski, David S. King
Energy Partitioning In The Ir Multiphoton Dissociation Of Molecules: Energy Of Xcf2 And Xcfcl Fromcf2Cfcl, John C. Stephenson, Stephen E. Bialkowski, David S. King
Stephen E. Bialkowski
We have measured the vibrational (v), rotational (J,K), and translational energy, (ET), of the X̃ CF2 and X̃ CFCl fragments formed in the CO2 laser induced multiphoton dissociation of CF2CFCl (chlorotrifluoroethylene): CF2CFCl→CF2(v,J,K)+CFCl(v,J,K)+ET(v,J,K), which was the only detectable reaction path for CF2CFCl. More vibrational energy (Ev) appears in CF2 than in CFCl. Direct spectroscopicmeasurements of populations in levels 0<ν2<7 show that Ev is distributed statistically in the bending mode (ν2) of CF2 according to P(Ev)=exp(−Ev/k Tv), …
Gas Phase Laser Induced Fluorescence Spectroscopy Of Cfcl, Stephen E. Bialkowski, David S. King, John C. Stephenson
Gas Phase Laser Induced Fluorescence Spectroscopy Of Cfcl, Stephen E. Bialkowski, David S. King, John C. Stephenson
Stephen E. Bialkowski
The CFCl radical has been produced in the gas phase by both IR multiphotonphotolysis of C2F3Cl and He metastable reaction with C2F3Cl. Single vibronic level fluorescence and excitation spectra taken of this species have yielded sufficient information to determine certain vibronic constants. The excited state was found to have an origin of T0=25 283±5 cm−1 with vibrational frequencies: ω2′=394±3 cm−1 and ω3′=739±5 cm−1. In the ground state, the vibrational frequencies were found to be: ω3″=118±10 cm−1, ω2″=448±6 cm …
Collisionless Formation And Rovibronic Relaxation Of Ch And Oh From The Ir Multiphoton Photolysisof Ch3Oh, Stephen E. Bialkowski, William A. Guillory
Collisionless Formation And Rovibronic Relaxation Of Ch And Oh From The Ir Multiphoton Photolysisof Ch3Oh, Stephen E. Bialkowski, William A. Guillory
Stephen E. Bialkowski
A CO2 TEA laser has been used to initiate the collisionless multiphotondissociation of CH3OH between 1000 and 10 mtorr. The appearance of OH(X2Πi) 50±20 nsec after the laser pulse, independent of initial CH3OH pressure (50–200 mtorr), suggests the primary dissociative channel CH3OH+n hν→CH3 +OH(X2Πi); although CH3 could not be correspondingly confirmed. The appearance of CH(X2Πr) 70±20 nsec after the OH(X) appearance, independent of initial CH3OH pressure (70–400 mtorr), suggests secondary collisionless dissociation. Initial rovibronic distributions of OH(X) …