Joseph-Albert Miehe

Evaluation of nitrogen fertilization effect on apple-tree leaves and fruit by fluorescence imaging

The work aims to validate the laser-induced fluorescence imaging method for detecting nutrient deficiency of fruit- trees and testing the storage ability of the fruits. Measurements concerned apple-trees (Malus x domestica Borkh.cv.Jonagold 2361) submitted or not to nitrogen fertilization (60 kg/ha) via roots. Besides recordings of fluorescence images of fruits and of leaves at the characteristic emission wavelengths, images which always showed an effect of the nitrogen, chemical and physiological analysis have been performed. The essential results were: (1) For rosette leaves, with a total chlorophyll content significantly lower for nitrogen depleted leaves, and a Chl a/b ratio as well as (phi) po (PS II efficiency of open reaction centers) independent of the treatment, images recorded in the red and in the far-red (690 and 740 nm chlorophyll a emissions) showed red/far-red intensities ratios higher in the absence of fertilization, in agreement with the lower chlorophyll a content. (2) For leaves of one year shoots, having all similar chlorophyll content and PS II efficiency, nitrogen supply led to a slight decrease of the red/far-red ratio value for 532 nm excitation, and for 355 nm excitation to an important decrease of the blue fluorescence/chlorophyll emission ratio, that was not observed for rosette leaves. (3) For apple fruits, presenting a high K/Ca ratio (approximately equals 42) i.e. a bad storage ability, the chlorophylls content of the green face skin as well as (phi) po were the same for both samplings, with a dramatic decrease of (phi) po (0.68 till to 0.45) during conservation (6 months). Under 355 nm excitation, the fluorescence ratios the most sensitive to the nitrogen deficiency were for the green face the blue/red ratios which decreased with nitrogen supply and increased with time, and the blue/green ratio for the apple red face.

Near-field measurements of vegetation by laser-induced fluorescence imaging

In this paper, a validation of a new UV-A laser-induced fluorescence imaging system implemented in an all-road car for near-field remote sensing of vegetation will be presented. It has been developed as a part of a European Community Program INTERREG II and is consisting of three main parts: excitation, detection and control units. The excitation source is a frequency tripled Nd:YAG laser and the laser spot size is adjusted via a variable beam expander. Fluorescence images are recorded at four characteristic fluorescence bands: 440, 520, 690 and 740 nm with a gated intensified digital CCD camera. The laser head and camera are situated on a directed in site and azimuth platform which can be high up to 6 meters. The platform positioning, localization and distance detection, spot size determination and adjustment, focus, sharpness, selection of the filter, laser and camera synchronization, gain of the intensifier, real time visualization of images, acquisition time are controlled by a newly developed software which allows also image storage, analysis and treatment. Examples of remote sensing fluorescence images from several plant species recorded at a distance of 10 - 30 m will be given and discussed further in this paper.

Laser-induced fluorescence imaging for monitoring nitrogen fertilizing treatments of wheat

The laser-induced fluorescence imaging system allows the recording of spectrally selected fluorescence images of the whole leaves or plants which is better and in contrast to the so far applied spot spectrofluorometer measurements. The fluorescence images of leaves of winter wheat (Soissons variety, Alsace) have been recorded at the four characteristic emission bands (440, 520, 690 and 740 nm) with a high resolution imaging device consisting of a frequency triplet or doubled Nd:YAG source for 355 nm or 532 nm excitation and of an intensified and gated CCD digitized camera. The effect of four different nitrogen treatments (0, 100, 140 and 180 kg/ha) on the fluorescence parameters (intensities F440, F520, F690, F740 and ratios F440/F520, F440/F690, F440/F740 and F690/F740) obtained by image processing has been analyzed by statistical treatment, in a randomized blocks experiment. The measurements have been carried out on two leaf storeys weekly gathered during two months (May and June 1996). For 355 nm excitation, a significant decrease of the fluorescence ratios F440/F690 and F440/F740 was observed for increasing nitrogen concentration: the blue and green mean fluorescence intensities remained much the same, while the red and far-red chlorophyll fluorescence emissions were enhanced by the fertilization. The fluorescence results are in excellent correlation with the crop yields.

Analysis of heavy-metal-stressed plants by fluorescence imaging

Chlorophyll fluorescence has been widely applied as a non-invasive technique for the in vivo analysis of plant stress. In this work, the two-dimensional image analysis of the fluorescence signal was used to evaluate the physiological status of heavy metal stressed leaves, based on their photosynthetic capacity. Chlorophyll fluorescence (greater than 650 nm) emission of control and heavy metal treated plants registered at different times during the blue light illumination of the leaves show abnormal patterns of non- homogeneous spatial distribution of the fluorescence emission from metal-treated plants. This is correlated to an altered photosynthetic functionality in different parts of the leaves. Quantitative evaluation of the photosynthetic activity can be made on data extracted after simple arithmetical pixel-point processing of fluorescence images taken at different time during the illumination process. The altered fluorescence emission was observed in absence of other visual symptoms that could testify problems at the level of the photosynthetic apparatus. This indicates that chlorophyll fluorescence imaging is a suitable tool for the early, pre-visual detection of plant stress also in the case of heavy metal stress.

Stochastic analysis of synchroscan operations of a streak camera

This paper deals with a theoretical and experimental study of the picosecond synchronization of a streak camera used in conjunction with a cw actively mode-locked laser system. The temporal resolution of two synchronization set-ups, a passive device (sweep obtained directly from the mode-locker oscillator) and an active arrangement (deflection derived from the recurrent laser pulses through a photodiode and a tunnel diode) has been examined. On the basis of the stochastic analysis it has been possible to interpret the experimental results for both configurations: in particular, it has been demonstrated that even in the presence of phase noise in the laser signal, perfect synchronization can be achieved.

Applications of synchronously pumped and cavity-dumped dye-laser associated with streak camera operated at the repetitive mode to time-resolved spectroscopy

SummaryA picosecond streak tube optically coupled to an image intensifier is used in repetitive mode with a mode-locked synchronously oumped or cavity-dumped dye-laser. Time resolutions of 15 ps are obtained; reproducibility of the measurements on the amplitude and time scales makes the system particularly suitable for time-resolved spectroscopy.RiassuntoSi usa un tubo di flusso dell’ordine del picosecondo otticamente accoppiato ad un intensificatore d’immagine con modo ripetitivo con un laser a colorante a modi vincolati pompato in modo sincrono o con cavità svuotata. Si ottengono risoluzioni temporali di 15 ps; la riproducibilità delle misurazioni sulle scale di ampiezza e di tempo rende il sistema particolarmente adatto alla spettroscopia a risoluzione temporale.РезюмеВ повторяющемся режиме используется пикосекундная лампа-вспышка, оптически связанная с усилителем изображения в случае синхротронно-накачанного лазера на красителях. Получается временные разрешения 15 пс. Воспроизводимость измерений по амплитуде и временной шкале дает систему, особенно подходящую для разрешенной во времени спектроскопии.

Photoemissive thin film with strange property for laser pulse detection

A kind of photoemissive thin film which can be exposed or stored in the atmosphere and can be used again in a vacuum system without any activation process for laser pulse detection is presented. They are different from usual photoemissive materials, since they do not contain alkali elements. They consist of metallic oxide thin film or other material thin film embedded with metallic ultrafine particles. A main interesting material is barium oxide thin film embedded with Ag ultrafine particles. This thin film can detect single laser pulse or laser pulses with high repetition frequencies (approximately 108 pulses/sec.), pulse duration ns to ps, and energy mJ to nJ per pulse.

Temporal and spectral analysis of the synchronization of synchroscan streak cameras

A stochastic model has been developed to explain the well-known experimental results in synchroscan measurements with actively mode-locked lasers demonstrating that in the configuration where the synchronization is carried out by means of the ultrastable oscillator exciting the acoustooptic mode-locker of the laser, the overall temporal resolution is considerably worse than in the case where the deflection is performed by the electric signal directly derived from the optical recurrent pulses. The calculations including both random period fluctuations of the laser pulses and temporal jitter due to the electronic trigger system are corroborated by experimental investigations. The study shows that even in the presence of the phase noise in the laser beam, a jitter free synchronization can be achieved.