基于激光诱导叶绿素荧光寿命成像技术的植物荧光特性研究

针对植物荧光遥感探测中信号易受干扰的问题, 提出了一种用于评估植物生长状况及环境监测的荧光寿命成像技术. 采用凹透镜对355 nm波长的激光扩束, 再照射植物激发叶绿素荧光, 由增强型电荷耦合器件接收荧光信号. 采用时间分辨测量法, 连续用相同激光脉冲照射植物以激发相同的荧光信号, 同时不断改变激光脉冲触发探测器启动的延时时间, 从而能够得到完整的离散荧光信号分布图像. 对植物特定位置点产生的离散荧光信号进行拟合, 再运用一种改进型的迭代解卷积法可反演高精度的荧光寿命; 进而反演图像各点的荧光寿命以生成植物的荧光寿命分布图. 该方法所绘制的荧光寿命图比荧光强度图能更准确地反映植物内部的叶绿素含量, 并对活体植物叶绿素荧光寿命的物理特性进行了初步研究, 证明叶绿素荧光寿命与植物生理状态存在一定关联; 并且叶绿素荧光寿命与活体植物所处环境存在着复杂的关系. 未来将与生物物理学家们合作, 继续探寻叶绿素荧光寿命与植物生存环境的关系.     

Time-resolved chlorophyll fluorescence of spruce needles under various light conditions

Different branches of a declined spruce were exposed to full sunlight, reduced sunlight (using a fine wire mesh), and natural shadow. Subnanosecond decay kinetics and time-gated fluorescence spectra of individual needles were measured and compared with their chlorophyll concentration. Sunlight-exposed needles showed lower chlorophyll concentrations and higher intensitiesI ₃ of a long-lived fluorescent component (decay time about 3 ns) than shadow needles. This seems to be due to a reduced energy transfer from the chlorophyll antenna molecules to the reaction centres of Photosystem II. After light reduction to 15–20% during one summer season the chlorophyll concentration increased, whereasI ₃ decreased, thus proving some recovery of the photosynthetic apparatus.     

Spectral and kinetic properties of fluorescence of immunoactive steroids in the gas phase

We have used steady-state fluorescence spectroscopy and pulsed kinetic fluorimetry with high time resolution to experimentally study the spectral and temporal characteristics of luminescence of immunoactive 8-aza-D-homogona-1,3,5(10), 13-tetraene-12,17a-dione (8-aza-D-homogonane) molecules in the gas phase. We have established the existence of several centers emitting long-wavelength and short-wavelength fluorescence. The fluorescence of high-temperature 8-aza-D-homogonane vapor (T = 550 K) when excited by radiation with λ_ex = 266 nm is represented by two spectrally separated emission bands with maxima λ _max ^fl = 465 nm and λ _max ^fl = 365 nm. Analysis of the distribution of fluorescence decay times for 8-aza-D-homogonane showed that in the spectral range of the emission wavelengths 360–590 nm, the fluorescence decay kinetics contains three components with average lifetimes <200 psec, 2.8 nsec and 13.5 nsec. The multicenter nature of luminescence of 8-aza-D-homogonane was confirmed by direct measurements of instantaneous fluorescence spectra in different stages of luminescence decay. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 309–314, May–June, 2006.     

Spectral changes of diffracted polychromatic Gaussian beams in the far field

The spectral behavior of polychromatic spatially fully coherent Gaussian beams diffracted at an aperture in the far field is studied based on the propagation law of the cross-spectral density function. Detailed numerical calculation results are presented, and illustrated. It is shown that the spectral changes take place in the vicinity of zeros of the Airy pattern, and the spectral modifier depends on the truncation parameter δ and diffraction angle α. The critical diffraction angle α_c, at which the spectrum is split into two lines with equal height i.e., the spectral switch appears, varies with truncation parameter δ. The spectral switch vanishes if δ becomes large enough. A detailed comparison with the previous publications is given, showing somewhat extension made in our work.     

基于叶绿素荧光光谱分析的黄瓜霜霉病害预测模型

为了实现对黄瓜病害的快速无损准确预测,基于激光诱导叶绿素荧光光谱分析技术,建立了温室黄瓜霜霉病害的预测模型.通过测定健康叶片、病菌接种3d叶片和接种6d叶片的光谱曲线,采用一阶导数光谱预处理方法,结合主成分分析数据降维方法对三组光谱数据进行特征信息提取后,建立主成分得分散点图,依据累积贡献率选取10个主成分代替导数光谱...     

Spectral indices to assess the carotenoid/chlorophyll ratio from adaxial and abaxial leaf reflectance

The ratio between the carotenoid and chlorophyll concentrations can indicate the physiology and phenology of plants. Most of the vegetation indices related to the ratio between the carotenoid and chlorophyll contents only consider the reflectance from the adaxial leaf surface. In this study, it was found that the leaf reflectance from the abaxial surface is lower than that of the adaxial surface in the visible wavelength region. On the contrary, the reflectance is higher on the adaxial surface in the near-infrared wavelength region. The difference ratio index resulted in the best correlation with the carotenoid/chlorophyll ratio and was the most robust among all the spectral indices studied when the spectral information on the adaxial and abaxial surfaces was pooled. The result indicated that this index can accurately estimate the carotenoid/chlorophyll ratio because of the insensitivity to the differences between adaxial and abaxial leaf surfaces.     

Spectral hole burning and fluorescence in femtosecond laser induced Sm-doped glasses

The femtosecond laser was used to irradiate sol-gel derived Sm³⁺-doped Al₂O₃-SiO₂ glasses, in which the Sm³⁺ was reduced into Sm²⁺ ions. The fluorescence line narrowing was applied to investigate the coordination sphere of the Sm²⁺ ion. The spectral hole burning was performed on ⁷F₀→⁵D₀ transition of the Sm²⁺. The depth and width of the burnt holes were ∼27% and ∼4 cm⁻¹ FWHM at 7 K, respectively. Hole spectra were stable up to room temperature. The hole-burning efficiency was superior to that of Sm²⁺ in H₂ treated glasses and comparable to that in X-ray in terms of hole-burning dynamics.     

Spectral detection of resonance fluorescence as a generalized quantum measurement

Spectrally resolved detection of single atom resonance fluorescence in the limit of well-separated spectral lines is considered. By using a special type of correlation measurements over the fluorescent field, in which a filtered photon detection is followed by an unfiltered photon detection, we obtain a conditioned atomic state following the filtered photon detection. The properties of the atomic state following detection of the reflected photon are studied and interpreted on the basis of quantum interference between the dressed states. Measurement operators associated with the detection of the passed and reflected photons are derived and used to construct the master equation for the atomic density matrix subjected to continuous spectral detection, the filter tuning being arbitrary.     

Spectral and statistical properties of fluorescence from N atoms in a cavity

Spectral and statistical properties of fluorescence from N two-level atoms interacting with an intense cavity mode are discussed. Quite different results from collective resonance fluorescence in a free space are shown.     

Spectral changes in inhomogeneous media; a quasi-optical approach

Spectral changes in inhomogeneous media depending on the spatial coherence of the source can be described by a quasi-optical approach. Assuming a Gaussian-Schell model source the spectral changes are described by using a Gaussian beam and ABCD matrices for the propagation in the medium.     

Spectral changes in homogeneous media; a quasi-optical approach

In the past decade spectral changes depending on the spatial coherence of the source have been described by a cross-spectral density method. It is shown that for Gaussian-Schell model sources a quasi-optical approach is valid which uses Gaussian beams and ABCD matrices to describe the optical system.     

Spectral changes in El of Au-GaP diodes and negative resistance

Spectral changes in Au-GaP diodes at 77°K are observed when approaching the negative resistance region in forward bias. Both optical and transport behaviors are accounted for in terms of saturation of Si deep-acceptor recombination centers. An analytical model is proposed.     

利用高光谱植被指数监测紧凑型玉米叶绿素荧光参数F_v/F_m

为进一步评价遥感监测紧凑型玉米叶绿素荧光参数Fv/Fm的可行性,通过开展小区紧凑型玉米试验,分析紧凑型玉米整个生育期Fv/Fm与高光谱植被指数的相关关系,建立紧凑型玉米Fv/Fm高光谱监测模型。结果表明,紧凑型玉米Fv/Fm与选取的高光谱植被指数均呈极显著正相关,其中结构敏感色素指数(SIPI)与Fv/Fm的相关性最好,相关系数(r)为0.88。用SIPI建立紧凑型玉米Fv/Fm的监测模型,其决定系数(R2)为0.812 6,均方根误差(RMSE)为0.082。研究表明,利用高光谱植被指数可以有效地监测紧凑型玉米整个生育期的Fv/Fm。     

Spectral changes in stochastic light beams propagating in turbulent ocean

The behavior of the spectral composition of a typical stochastic beam in a turbulent ocean environ is revealed. The analysis is based on the extended Huygens–Fresnel principle and the coherence theory in the space-frequency domain. The optical source is assumed to be of the Gaussian Schell-model type with a single narrow Gaussian spectral line in the visible region. Optical turbulence in the ocean is assumed to be driven by temperature and salinity fluctuations. It is found that the well-known source correlation-induced spectral shift is compensated by turbulence at sufficiently large distances.