Modeling biological fluorescence emission spectra using Lorentz line shapes and nonlinear optimization

Using the Levenberg-Marquardt nonlinear optimization algorithm and a series of Lorentzian line shapes, the fluorescence emission spectra from BG (Bacillus globigii) bacteria can be accurately modeled. This method allows data from both laboratory and field sources to model the return signal from biological aerosols using a typical LIF (lidar induced fluorescence) system. The variables found through this procedure match individual fluorescence components within the biological material and therefore have a physically meaningful interpretation. The use of this method also removes the need to calculate phase angles needed in autoregressive all-pole models.     

Unmixing coral fluorescence emission spectra and predicting new spectra under different excitation conditions

An algorithm was developed that uses prototype spectra and least-squares minimization to unmix the relative contributions of individual pigments to the composite fluorescence emission spectrum of reef corals. Field measurements indicated that it was necessary to include allowance for spectral shift of the wavelength peak of the prototype emission spectra. The unmixed spectra are used to predict the shape and amplitude of composite spectra that would be expected under different excitation conditions. We found that, for cases in which the pigments occur singly or with significant spectral separation, it is necessary to consider the properties of the excitation light sources, only, to make accurate predictions. In cases with spectral overlap the contribution of interpigment coupling cannot be neglected.     

Correction of phase anomalies of atmospheric emission spectra by the double-differencing method

Atmospheric emission measurements with the cryogenic airborne Michelson Interferometer for Passive Atmospheric Sounding revealed strongly disturbed phase and magnitude spectra. They were corrected with the double-differencing method: The phase information implied in the line structure of atmospheric spectra is used to specify a phase shift with respect to an instrumental phase spectrum, which was determined once from calibration measurements with the differencing method of Revercomb et al. [Appl. Opt. 27, 3210 (1988)].     

Correction of optical phase aberrations using binary-amplitude modulation

We show that phase aberrations in an imaging system can be mitigated using binary-amplitude masks that reduce destructive interference in the image spatial frequency domain. Appropriately designed masks increase the magnitude of the optical transfer function and prevent nulls. This offers a low-cost, transmission-mode alternative to phase correction as used in active and adaptive optics, without a restriction on the waveband of operation.     

State-of-the art comparability of corrected emission spectra. 2. Field laboratory assessment of calibration performance using spectral fluorescence standards

In the second part of this two-part series on the state-of-the-art comparability of corrected emission spectra, we have extended this assessment to the broader community of fluorescence spectroscopists by involving 12 field laboratories that were randomly selected on the basis of their fluorescence measuring equipment. These laboratories performed a reference material (RM)-based fluorometer calibration with commercially available spectral fluorescence standards following a standard operating procedure that involved routine measurement conditions and the data evaluation software LINKCORR developed and provided by the Federal Institute for Materials Research and Testing (BAM). This instrument-specific emission correction curve was subsequently used for the determination of the corrected emission spectra of three test dyes, X, QS, and Y, revealing an average accuracy of 6.8% for the corrected emission spectra. This compares well with the relative standard uncertainties of 4.2% for physical standard-based spectral corrections demonstrated in the first part of this study (previous paper in this issue) involving an international group of four expert laboratories. The excellent comparability of the measurements of the field laboratories also demonstrates the effectiveness of RM-based correction procedures.     

海洋浮游植物生长过程中溶解有机物质的三维荧光光谱研究

利用三维激发-发射矩阵荧光光谱技术,监测了赤潮异弯藻和中肋骨条藻培养过程中产生的溶解有机物,分析了三维荧光光谱图中的荧光峰位置、数量及荧光强度的变化情况.结果表明,微藻生长过程中会产生类蛋白和类腐殖质两类荧光有机物质,这两类有机物的荧光峰的位置及荧光强度有较大差异.在不同生长期,两类荧光有机物的产生机制不同.在指数生长期,两类有机物的荧光强度与藻密度成正相关,说明浮游植物释放了一定量的荧光物质;在平稳期和衰亡期,两类有机物的荧光强度迅速增加,这可能由于衰老、死亡藻细胞的破碎释放出大量的荧光有机物质所致,此外细菌对非荧光有机物进一步降解,也可能是产生该现象的一个原因.     

Measurement of radio-frequency temporal phase modulation using spectral interferometry

We present an optical method to measure radio-frequency electro-optic phase modulation profiles by employing spectrum-to-time mapping realized by highly chirped optical pulses. We directly characterize temporal phase modulation profiles of up to 12.5 GHz bandwidth, with temporal resolution comparable to high-end electronic oscilloscopes. The presented optical set-up is a valuable tool for direct characterization of complex temporal electro-optic phase modulation profiles, which is indispensable for practical realization of deterministic spectral-temporal reshaping of quantum light pulses     

Spatial amplitude and phase modulation using commercial twisted nematic LCDs

We present a method for full spatial phase and amplitude control of a laser beam using a twisted nematic LCD combined with a spatial filter. By spatial filtering we combine four neighboring pixels into one superpixel. At each superpixel we are able to independently modulate the phase and the amplitude of light. We experimentally demonstrate the independent phase and amplitude modulation using this novel technique. Our technique does not impose special requirements on the spatial light modulator and allows precise control of fields even with imperfect modulators.     

Wavefront watermarking of technical and biological samples using digital random phase modulation and phase retrieval

A technique for digital watermarking of smooth object wavefronts using digital random phase modulation and multiple-plane iterative phase retrieval is demonstrated experimentally. A complex-valued watermark is first encrypted using two random phase masks of known distributions before being superposed onto a set of host wavefront intensity patterns. Encryption scaling factor and depth of randomization of the masks are optimized such that the amplitude and phase watermarks are decrypted successfully and are not distorting the host wavefront. Given that the watermarked intensity patterns and the numerous decryption keys are available (i.e. distances between recording planes, light source wavelength, pixel size, random phase masks and their distances to the planes are all known), increasing the number of watermarked patterns used results in enhanced quality of decrypted watermarks. The main advantage of wavefront watermarking via the phase retrieval approach compared to the holographic approach is the avoidance of reference wave-induced aberration. Watermarking of wavefronts from lenses and unstained human cheek cells demonstrate the effectiveness of the technique.     

Transmission functions of an energy-mass spectrometer and energy spectra vs. emission angle data for silicon secondary ions

Results of a computer simulation of the propagation of ions through an energy mass analyzer comprising 90° and 180° spherical deflectors, transport lenses, and a quadrupole mass spectrometer are reported, which give the apparatus function of the analyzer for two operating modes. These functions were used to improve the experimental energy spectra for silicon secondary ions Si⁺, Si²⁺, and Si₂⁺ measured under 10 keV Ar ion bombardment of a silicon surface. The observed shift of energy spectra maxima with angle of emission was explained in terms of the concept of a local electron excitation in the collision cascade region. This model, developed earlier for metals, was shown to adequately describe the principal regularities of the secondary ion emission from semiconductors.     

Assessing phytoplankton using a two-rank database based on excitation-emission fluorescence spectra

The feasibility of using a two-rank database of reference spectra based on in vivo fluorescence excitation-emission matrix (EEMs) spectra to assess dominant groups of phytoplankton was explored. Twenty-six species belonging to 20 genera of seven divisions were studied. First, fluorescent characteristics of these EEMs were extracted using Daubechies-7 wavelet analysis. Second, the optimal characteristic spectra of scale vectors (SOCS) and time-series vectors (TOCS) were selected; phytoplankton of different genera were classified using Fisher linear discriminant analysis. Third, SOCS and TOCS reference spectra databases were obtained by hierarchical cluster analysis. Using non-negative least squares as the method to assess the phytoplankton, a two-rank reference spectra database was established according to their respective ability to identify the 2818 single-species samples. Using this fluorimetric technique, the correct identification rates (CIRs) for single-species samples were 88.8-100% at the genus level and 98.8-100% at the division level. Dominant species in the 465 laboratory mixtures had corresponding CIRs of 85.6% and 96.1%. Moreover, 15 of the 19 species used as dominants were correctly identified at the genus level. In 27 natural seawater samples, Prorocentrum donghaiense, Thalassiosira nordenskioldi, and Chaetoceros socialis (bloom-forming species with a density of about 10(7) cell L(-1)), and Alexandrium sp. (dominant species with abundance of about 10(6) cell L(-1)) were qualitatively identified at the genus level; other dominant species, with densities of 10(5) to 10(6) cell L(-1), were identified at the division level. The quantitative identification was relatively poor in the natural water samples, and several potential resolutions, including trying both new measuring methods and calculating methods, for future study are given.     

Superluminescent diode interferometer using sinusoidal phase modulation for step-profile measurement

We propose an interferometer in which the relationship between the degree of coherence (DCH) and the optical path difference (OPD) is utilized for determining an OPD longer than a wavelength. A superluminescent diode is employed as the source of the interferometer, and sinusoidal phase-modulating interferometry is used to detect the DCH and the phase of the interference signal. The combination of the OPD determined from the DCH and the phase of an interference signal enables us to measure an OPD longer than a wavelength with a high accuracy of a few nanometers. Experimental results show clearly the usefulness of the interferometer for a step-profile measurement.     

Electrochemical monitoring of the fluorescence emission of tetrazine and bodipy dyes using total internal reflection fluorescence microscopy coupled to electrochemistry

A very sensitive technique where an electrochemical cell is coupled to a total internal reflection fluorescence microscopy setup is described and applied for the first time to the electrochemical monitoring of the fluorescence of organic dyes in solution. It is shown that this setup basically allows both spatial and time resolution for the recorded fluorescence signal as a function of the electrode potential: indeed the variations of the emission intensity are recorded within the diffusion layer for a classical cyclic voltammetry or chronoamperometry experiment inducing the redox conversion of an emissive form into a non emissive one (and conversely). Simultaneously, the variations of the emissive state lifetime are measured to discriminate between a mechanism involving only the conversion into a non emissive form from one involving a quenching between the emitter and the electrogenerated species. The results concerning the investigation of the electrochemical monitoring of the fluorescence properties for two types of original dyes are presented, demonstrating the possibility to switch on and off the emission in a fully reversible way and to investigate in depth the mechanisms associated to this switch.     

Interferometric measurement of fluorescence excitation spectra

A Michelson interferometer has been adapted as an excitation source for fluorescence spectroscopy. A moving fringe pattern was generated by linear displacement of the movable mirror of the Michelson interferometer coupled to a xenon-arc lamp. This spectrally modulated source was monitored by a reference photomultiplier and used for exciting a Rhodamine B solution. The fluorescence emission at >645 nm was detected by a second photomultiplier. The two interferograms were acquired by a dual-channel digital oscilloscope, and their discrete Fourier transforms and corresponding power spectra were generated in a computer. The power spectrum of the emission signal represented the excitation spectrum, as was confirmed by comparison with the absorption spectrum of Rhodamine B. Thisoptical arrangement is well suited for acquiring fluorescence excitation spectra in the optical microscopy of biological specimens.     

Interlaboratory comparisons of acoustic emission spectra

A procedure has been developed whereby acoustic emission frequency spectra can be corrected for the variable effects of specimen geometry, couplant, and transducer characteristics. The results of several experiments on 7039 Al show that quantitative agreement can be obtained between laboratories for the spectral shapes and amplitudes of acoustic emissions emanated during a carefully specified mechanical test.     

Full-field phase modulation characterization of liquid-crystal spatial light modulator using digital holography

A direct quantitative phase measurement method to characterize intrinsic phase modulation from an entire active area of transmissive twisted-nematic liquid-crystal spatial light modulator (TN-LCSLM) is presented using digital holography (DH). The change in birefringence of liquid crystal material with respect to addressed gray scale produces phase modulation of wavefront transmitted through TN-LCSLM. Existing methods for phase modulation characterization of LCSLM mainly provides point measurement on its total active region. In this paper, the DH method is evolved to extract quantitative phase information of an entire active area from a single digital hologram formed using the complex wavefront transmitted through TN-LCSLM.     

含稀土配合物的聚丙烯酸酯的荧光可调控性能研究

用化学络合的方法制得含弱荧光稀土离子镨Pr(Ⅲ)和铒Er(Ⅲ)的单体,并经自由基聚合方法制得含Pr(Ⅲ)和Er(Ⅲ)的聚丙烯酸酯聚合物.通过对聚合物薄膜的荧光分析发现,敏化离子La(Ⅲ)、Y(Ⅲ)、Yb(Ⅲ)的引入,使含弱荧光稀土离子镨Pr(Ⅲ)和铒Er(Ⅲ)的聚丙烯酸酯表现出了明显的荧光发射特性,且通过引入这些敏化离子,可实现对上述聚合物的特征荧光发射光谱的调控作用;同时发现敏化离子Yb(Ⅲ)对上述两种聚合物的荧光调控作用都较为明显.