Where Is the Site of the “Oxygen Burst” Located During Light Induction in Dark-Adapted Leaves？ A Study Using Photoacoustic Techniques

: The “oxygen burst” phenomenon that appeared during the light-induction period of intact leaves could be monitored using a photoacoustic technique high time resolution. The relationship between oxygen bursts and dark-adapted time, far-red light pretreatment, photothermal signal, and chlorophyll a (Chl a) fluorescence kinetics were investigated in the present study. Using extraneous inhibitors or cofactors of electron transport, a modified vacuum-infiltration method was undertaken to locate directly the site at which oxygen bursts of intact leaves occurred. We found that the photothermal signal showed little evidence of oscillation during the light-induction period. The oxygen burst was resolved into two components if dark-adapted time lasted longer than 20 min. Methyl viologen (MV) or far-red light could not eliminate the first component, whereas formate-Na (pH 7.0,20 μmol/L) eliminated the first component but had no effect on the second one. Furthermore, the photochemical quenching, the electron transport rate of Chl a fluorescence, and the first component of the oxygen bursts approached lowest values simultaneously. This evidence indicates that the site at which the first component of oxygen bursts occurred was located between photo-system (PS)I and PSII (i.e. the PQ pool). The formate-Na experiment also showed a linkage between the first component and the S state of oxygen evolution at the donor side of PSII. Furthermore, elimination of the second component by far-red light and absorption of the second component by MV indicated that the site at which the second component of oxygen bursts may be located at the acceptor side of PSII.

Thermal diffusivity of light-emitting diode packaging material determined by photoacoustic piezoelectric technique

Thermal property is one of the most important properties of light-emitting diode （LED）. Thermal property of LED packaging material determines the heat dissipations of the phosphor and the chip surface, accordingly having an influence on the light-emitting efficiency and the life-span of the device. In this paper, photoacoustic piezoelectric （PAPE） technique has been employed to investigate the thermal properties of polyvinyl alcohol （]？VA） and silicon dioxide, which are the new and the traditional packaging materials in white LED, respectively. Firstly, the theory of PAPE technique has been developed for two-layer model in order to investigate soft materials; secondly, the experimental system has been set up and adjusted by measuring the reference sample; thirdly, the thermal diffusivities of PVA and silicon dioxide are measured and analysed. The experimental results show that PVA has a higher thermal diffusivity than silicon dioxide and is a better packaging material in the sense of thermal diffusivity for white LED.

Thermal Properties of Materials Characterized by Scanning Electron-Acoustic Microscopy

A modified technique of scanning electron-acoustic microscopy is employed to determine thermal diffusivity of materials. Using the dependence of the electron-acoustic signal on modulation frequency of the electron beam, the thermal diffusivity of materials is characterized based on a simplified thermoelastic theory. The thermal diffusivities of several metals characterized by the modified scanning electron-acoustic microscopy are in good agreement with the referential values of the corresponding materials, which proves that the scanning electronacoustic microscopy can be used to characterize the thermal diffusivity of materials effectively. In addition, for micro-inhomogeneous materials, such as biological tissues, the macro-effective （average） thermal diffusivities are characterized by the technique.

Study of vibrational relaxation of O_3 (001)using photoacoustic technique

The vibration- translational relaxation ime of ozone (001) was measured from phase delay of the photoacoustic detected signal with respect to signal of CO2-laser radiation in the binary mixtures of O3 with N2, O2, and Ar at the temperature 300°K. To eliminate the phase delay of the detected signal caused by inertia of the microphone membrane the technique of electrical activation was used.

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.