Geminate recombinations in photolysis of carboxy-hemoglobin studied by photoacoustic calorimetry

Enthalpy and conformational volume changes in photo-dissociation of carboxy-hemoglobin of human, bovine, pig, horse and rabbit are investigated by photoacoustic calorimetry (PAC). Considering the time scale of the experimental system, the results should be related to geminate recombinations in photolysis dynamics. The results show that the enthalpy and conformational volume changes for different species are different, and can be correlated with the protein structures.     

Determination of Reaction Enthalpy and Conformational Volume Changes by Photoacoustic Spectroscopy

The reaction enthalpy and conformational volume changes can be qualitatively estimated by means of the temperature-dependent pulsed photoacoustic spectroscopy. The curves for heat-releasing fraction and conformational volume changes with different temperatures are presented. The simultaneous equations for determination of the enthalpy and volume changes are established based on temperature-dependent measurements, and applied to study the photolysis of coenzyme system.     

三线态形成的量子产率研究

本文利用脉冲激光光声微量量热方法，以蒽为标准化合物，尝试求几种有机化合物，如吖啶，二苯酮，吩噻嗪及菲的三线态形成量子产率ХＴ。结果发现吖啶的ХＴ值与文献（１）吻合得很好；由于实验所用传感器时间响应的限制，所求其他三种化合物的ХＴ值与文献值有较大的偏差，为此，利用解卷带积方法，扣除传感器的响应后，即可求得较满意的ХＴ值。     

Single-wavelength functional photoacoustic microscopy in biological tissue

Recently, we developed a reflection-mode relaxation photoacoustic microscope, based on saturation intensity, to measure picosecond relaxation times using a nanosecond laser. Here, using the different relaxation times of oxygenated and deoxygenated hemoglobin molecules, both possessing extremely low fluorescence quantum yields, the oxygen saturation was quantified in vivo with single-wavelength photoacoustic microscopy. All previous functional photoacoustic microscopy measurements required imaging with multiple-laser-wavelength measurements to quantify oxygen saturation. Eliminating the need for multiwavelength measurements removes the influence of spectral properties on oxygenation calculations and improves the portability and cost-effectiveness of functional or molecular photoacoustic microscopy.     

Quenching effects on pulsed photoacoustic signals in NO2–air samples

A theoretical expression for the pulsed photoacoustic signal amplitude from NO₂–air mixtures is deduced based on a two-level system and the inhomogeneous wave equation, in the limit where the V-T relaxation time is longer than the laser pulse width (low buffer pressure). In this time limit, the photoacoustic signal from NO₂, at constant pressure, after excitation by pulses from a Nd:YAG laser at 532 nm, is measured at different buffer pressures. The relaxation rates are obtained by measuring the quenching of visible fluorescence induced by the same laser. The experimental dependence of the photoacoustic signal amplitude on air pressure shows a very good agreement with the model, where the measured relaxation rates are included.     

Simultaneous determination of the spatial profile of the laser beam and vibrational-to-translational relaxation time by pulsed photoacoustics

Measuring the vibrational-to-translational relaxation time τ_V-T in gases is one of the applications of pulsed photoacoustic spectroscopy. Unfortunately, the spatial profile of the laser beam can significantly influence the accuracy of these measurements. Namely, minor changes in the spatial profile of the laser beam cause significant errors in the τ_V-T measuring. We present a method for simultaneous determination of the spatial profile of the laser beam and vibrational-to-translational relaxation time. It is based on the temporal shape of the photoacoustic pulse and utilizes a mathematical algorithm developed for photoacoustic tomography. PACS 39.30.+w; 82.80.Kq; 07.57.Ty     

External cavity quantum cascade laser for quartz tuning fork photoacoustic spectroscopy of broad absorption features

We demonstrate mid-infrared spectroscopy of large molecules with broad absorption features using a tunable external cavity quantum cascade laser. Absorption spectra for two different Freons are measured over the range 1130-1185 cm(-1) with 0.2 cm(-1) resolution via laser photoacoustic spectroscopy with quartz tuning forks as acoustic transducers. The measured spectra are in excellent agreement with published reference absorption spectra.     

基于中红外量子级联激光器和石英增强光声光谱的CO超高灵敏度检测研究

采用石英增强光声光谱(QEPAS)技术对CO痕量气体展开检测研究. 为了实现超高灵敏度探测, 采用输出波长为4.6 μm的新颖中红外高功率分布反馈量子级联激光器为光源, 实现了对CO气体基频吸收带的激发与测量. 在优化了调制深度、气体压强和提高了CO分子的振动-转动弛豫速率后, 获得了1.95 ppbv的优异探测极限. 在分析检测结果的过程中, 讨论了能级寿命对信号强度的影响, 并对QEPAS信号强度的表达式进行了修正.     

Photoacoustic phase shift as a chemically selective spectroscopic parameter

The phase information obtained in photoacoustic experiments can be used to separate the signals originating from chemical species with overlapping absorption spectra. This approach was applied to quantify parts per million CO levels in propylene using quartz-enhanced photoacoustic spectroscopy and a quantum cascade laser as an excitation source. The experimental data were used to evaluate V–T relaxation rates of CO and N₂O in propylene. PACS 42.62.Fi; 43.35.Sx     

Energy relaxation time in a gas mixture measured by a photothermal probe beam deflection technique

The deflection of a cw probe laser beam, which occurs in a gas mixture after the absorption of a short laser pump pulse, was experimentally studied inside the irradiated region in order to characterize the generation of photothermal and photoacoustic effects. The time varying component of the probe deflection was detected, and the results are presented as functions of pumping fluences, laser wavelengths and gas pressures. Numerical modelling of the thermo-acoustic dynamics leads to the definition of an effective energy relaxation time for SF₆/Ar gas mixtures. An interesting nonlinear behaviour of this energy relaxation time is reported.