We present an analysis of the advantages and disadvantages of recording and monitoring of nonlinear strain waves in a solid waveguide made of a nonlinearly elastic material (polystyrene) using three techniques: off-axis digital holography with observation ‘in-transmission’ and ‘in-reflection’ and acoustical diagnostics utilizing piezoelectric transducers. Holographic ‘in-transmission’ recording was shown to provide more reliable determination of wave parameters owing to both higher resolution and sensitivity to longitudinal waves only. When monitoring the wave process by piezoelectric sensors attached to the lateral surface of the waveguide, the sensor sensitivity to shear waves did not allow us to isolate the contribution of longitudinal waves in a prolonged input part of the waveguide.
We present detection of strain solitary waves in polystyrene waveguides using pump-probe digital holography. Analysis of spectral components of the detected longitudinal strain waves was performed at several locations of the waves inside the waveguide in the course of their propagation. The data obtained allowed us to evaluate attenuation of relatively short- and long-wavelength components and to demonstrate much faster decay of high-frequency wavelets in comparison with the long solitary wave. Along with the spectral analysis monitoring of variations of solitary wave shape in the course of its propagation was performed. The dependence of spectral composition of the strain wave on the energy of the initial shock wave showed an increase in the relative contribution of long-wave components with the strain wave energy.
The influence of solution polarity and viscosity on fluorescence decay parameters in free and protein-bound NADH was studied. The fluorescence in NADH dissolved in water, methanol, ethanol, propylene glycol, and alcohol dehydrogenase-containing solution was two-photon excited by femtosecond laser pulses at 720 nm and recorded by means of the time-correlated single photon counting (TCSPC) method. Fluorescence decay times and corresponding weighting coefficients were determined by fit from polarization-insensitive fluorescence decay experimental signals. The fluorescence decay times τ1 and τ2, and weighting coefficients a1 and a2 were found to depend significantly on the solution type. A model describing the dependence of the fluorescence decay parameters on the microenvironment in solutions with different polarity and viscosity has been developed. According to the model, the heterogeneity in the measured fluorescence decay times in NADH and the time values were closely related with the charge distributions in the cis and trans configurations of the nicotinamide ring that result in different electrostatic field and different non-radiative decay rates. The influence of solution polarity and viscosity on the measured fluorescence decay times was investigated. As shown in high viscous solutions the increase of fluorescence decay times in NADH was mostly due to slowing down of the nuclei motions during the vibrational relaxation and intramolecular nuclear rearrangement whereas in low viscous solutions the fluorescence decay times follow the change of solution polarity.
Accounting for nonlinear elasticity of modern materials becomes very important due to their rising operation at high dynamic loads. Generation of strain solitary waves (solitons for brevity) is one of the processes of interest, however details of a transformation of an initial impact into the soliton are not completely clear yet. In this paper we demonstrate the advantages of a combination of classical and digital holographic recording for investigation of the early stages of soliton formation. While classical realization of holographic interferometry allowed for visualizing sharp phase gradients representing, in particular, shock waves, digital recording supplied quantitative data on parameters of smoother disturbances evolving in the course of soliton formation. The applied holographic techniques allowed us to monitor the entire process of soliton formation, to visualize intermediate wave patterns and to obtain quantitative data on the resulting soliton.
We studied polarized fluorescence in biological coenzyme NADH in water-methanol solutions upon two-photon excitation with femtosecond laser pulses at 720 nm. The polarized fluorescence decay was recorded by a time correlated single photon counting (TCSPC) system. Fluorescence decay times, rotational diffusion time, fluorescence anisotropy, and the ratio of two pre-exponential factors have been determined and studied as a function of methanol concentration. The results obtained were interpreted on the basis of a model of NADH denaturation processes in solutions and can be used for modeling of NADH binding with various dehydrogenases in living cells.
In this paper we present a comprehensive description of the pump-probe holographic arrangement and data processing procedure optimized for reconstruction of long smooth strain wave patterns in transparent solids. The approach was tested on detection of nonlinear strain waves generated in a uniform PMMA bar by initial shock pulses of different energies. Phase images representing these waves in the bulk of the waveguide are demonstrated. The strain wave parameters and evolution were shown to be substantially dependent on the initial shock pulse amplitude.
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