Frequency-domain photoacoustic technique formeasuring absolute optical absorption coefficient using three-chamber cell

Frequency-domain photoacoustic (PA) technique for immediate measuring absolute optical absorption coefficient is presented. It is based on determination of the ratio of the two spectrum amplitudes of the differential PA signal. The sample is placed into the lateral chamber of a three chamber PA cell. The difference of pressure variations (differential PA signal) excited in two other chambers as a result of laser pulse absorption by the sample is recorded. Presented PA technique was tested experimentally by measuring water absorption coefficient at an IR wavelength.

Effect of size and indium-composition on linear and nonlinear optical absorption of InGaN/GaN lens-shaped quantum dot

Based on the Schr ¨odinger equation for envelope function in the effective mass approximation, linear and nonlinear optical absorption coefficients in a multi-subband lens quantum dot are investigated. The effects of quantum dot size on the interband and intraband transitions energy are also analyzed. The finite element method is used to calculate the eigenvalues and eigenfunctions. Strain and In-mole-fraction effects are also studied, and the results reveal that with the decrease of the In-mole fraction, the amplitudes of linear and nonlinear absorption coefficients increase. The present computed results show that the absorption coefficients of transitions between the first excited states are stronger than those of the ground states. In addition, it has been found that the quantum dot size affects the amplitudes and peak positions of linear and nonlinear absorption coefficients while the incident optical intensity strongly affects the nonlinear absorption coefficients.

Optical properties of core/shell spherical quantum dots

In this study,the effects of quantum dot size on the binding energy,radiative lifetime,and optical absorption coefficient of exciton state in both GaN/AlxGa1-xN core/shell and AlxGa1-xN/GaN inverted core/shell quantum dot structures are studied.For the GaN/AlxGa1-xN core/shell structure,the variation trend of binding energy is the same as that of radiation lifetime,both of which increase first and then decrease with the increase of core size.For AlxGa1-xN/GaN inverted core/shell structure,the binding energy decreases first and then increases with core size increasing,and the trends of radiation lifetime varying with core size under different shell sizes are different.For both structures,when the photon energy is approximately equal to the binding energy,the peak value of the absorption coefficient appears,and there will be different peak shifts under different conditions.

Measurement and feature analysis of absorption spectra of four algal species

Two methods for particulate pigments(i.e.,quantitative filter technique,QFT,and in vivo measurement,InVivo,respectively)and two methods for dissolved pigments(i.e.,Acetone Extracts,AceEx,and high-performance liquid chromatography,HPLC,respectively) were used to obtain the optical absorption coefficient spectra for cultures of four typical algal species.Through normalization and analysis of the spectra,it is shown that(1) the four methods are able to measure optical absorption spectra of particulate and/or dissolved pigments;(2)that the optical absorption spectra of particulate and dissolved pigments were consistent in terms of the peak position in the blue wavelength,and the difference of the peak position in the near infrared wavelength was ~10nm between each other;and(3)that the leveling effect of the absorption spectra of particulate pigments was significant.These four methods can all effectively measure the absorption coefficients of phytoplankton pigments,while each one has its unique advantages in different applications.Therefore,appropriate method should be carefully selected for various application due to their intrinsic difference.