Péter Richter

Optimizing Phytoremediation of Heavy Metal-Contaminated Soil by Exploiting Plants' Stress Adaptation

Soil phytoextraction is based on the ability of plants to extract contaminants from the soil. For less bioavailable metals, such as Pb, a chelator is added to the soil to mobilize the metal. The effect can be significant and in certain species, heavy metal accumulation can rapidly increase 10-fold. Accumulation of high levels of toxic metals may result in irreversible damage to the plant. Monitoring and controlling the phytotoxicity caused by EDTA-induced metal accumulation is crucial to optimize the remedial process, i.e. to achieve maximum uptake. We describe an EDTA-application procedure that minimizes phytotoxicity by increasing plant tolerance and allows phytoextraction of elevated levels of Pb and Cd. Brassica juncea is tested in soil with typical Pb and Cd concentrations of 500 mg kg−1 and 15 mg kg−1, respectively. Instead of a single dose treatment, the chelator is applied in multiple doses, that is, in several small increments, thus providing time for plants to initiate their adaptation mechanisms and raise their damage threshold. In situ monitoring of plant stress conditions by chlorophyll fluorescence recording allows for the identification of the saturating heavy metal accumulation process and of simultaneous plant deterioration.

High-efficiency dielectric barrier Xe discharge lamp: theoretical and experimental investigations

A dielectric barrier Xe discharge lamp producing vacuum-ultraviolet radiation with high efficiency was investigated theoretically and experimentally. The cylindrical glass body of the lamp is equipped with thin strips of metal electrodes applied to diametrically opposite sides of the outer surface. We performed a simulation of discharge plasma properties based on one-dimensional fluid dynamics and also assessed the lamp characteristics experimentally. Simulation and experimental results are analysed and compared in terms of voltage and current characteristics, power input and discharge efficiency. Using the proposed lamp geometry and fast rise-time short square pulses of the driving voltage, an intrinsic discharge efficiency around 56% was predicted by simulation, and more than 60?lm?W?1 lamp efficacy (for radiation converted into visible green light by phosphor coating) was demonstrated experimentally.

High frequency excitation waveform for efficient operation of a xenon excimer dielectric barrier discharge lamp

The application of a high frequency (~2.5 MHz) burst (amplitude-modulated sinusoidal) excitation voltage waveform is investigated for driving a fluorescent dielectric barrier discharge (DBD) light source. The excitation waveform presents a novel method for generating spatially stable homogeneous Xe DBD possessing a high conversion efficiency from electrical energy to VUV excimer radiation (~172 nm), even at a significantly higher electrical energy deposition than realized by pulsed excitation. Simulation and experimental results predict discharge efficiencies around 60%. Lamp efficacy above 74 lm W−1 has been achieved. VUV emission and loss mechanisms are investigated extensively and the performance of burst and pulsed waveforms is compared both theoretically and experimentally.

Improved design method for acousto-optic light deflectors

Abstract The purpose of this work is to find a reliable approach for one- and two-dimensional acousto-optic deflector design. The design method is based on an improved theoretical model of anisotropic acousto-optic interaction. The new feature of this model is the application of new approximations together with the inclusion of effects that were previously neglected, such as optical beam divergence, second order diffraction and optical activity. Configurations for maximum efficiency and maximum resolution are shown. Optimization of the two-dimensional deflector design is presented. The reliability of the model is demonstrated at wavelengths of 633 and 1064 nm through experimental results with devices designed based on the new model for TeO 2 deflectors.

Realization of true-time delay lines based on acoustooptics

A true-time optical delay line for short radiofrequency (RF) pulses using path length dispersion is proposed. It is an optical implementation of the linear phase-shift theorem of the Fourier transformation. Acoustooptic signal processing is used for conversion into the optical frequency domain and for spatial Fourier decomposition of the pulse. The processing of the pulse is obtained by differentially phase shifting the particular frequency components, followed by a heterodyne reconversion into the RF domain. The optical system is intended to be used for delaying, but also for shaping and filtering of RF pulses, mainly in phased array radar antennas. Theoretical analysis of the system principle is given together with experimental results, demonstrating 2-/spl mu/s time delay of 0.5-/spl mu/s-long pulses with maximum optical phase shift of 1.2/spl pi/. A detailed theoretical and experimental bandwidth analysis is carried out, pointing to the main technical problems and their solutions.

Two-wavelength, multipurpose, truly portable chlorophyll fluorometer and its application in field monitoring of phytoremediation

In this paper a compact, portable instrument is presented for the measurement of full chlorophyll fluorescence kinetics of plants at two different wavelengths. The instrument uses a 635 nm laser diode as a light source with variable gain driving that allows excitations at selectable actinic levels. The plant fluorescence is detected, at 690 nm and 735 nm, through a specially mixed three-branch optical fibre bundle. Large scale field monitoring of vegetation is made possible by the utilization of PC/104-form embedded electronics including a low power, IBM PC/386-compatible single board computer (SBC) with non-volatile flash memory. Application of a general purpose SBC and task oriented programming offers in situ data evaluation making process control possible. The capabilities of the instrument were demonstrated in monitoring soil phytoremediation processes.

Improving the efficiency of a fluorescent Xe dielectric barrier light source using short pulse excitation

Operation of a Xe dielectric barrier discharge lamp producing 147–172 nm VUV radiation is investigated both theoretically and experimentally. Xe gas pressure varies between 100 and 300 mbar, and the glass body of the lamp is coated with LAP (green) phosphor to convert radiation into the visible part of the spectrum. Simulation results predict improved discharge efficiencies reaching 67% when excited by a fast rise-time, short pulse (~200 ns) driving waveform. In this case most power deposited into the plasma efficiently produces excimers, while other energy dissipation processes (ion heating, e–Xe elastic collision) are kept at a low rate. Simulation and experimental results are compared in terms of discharge efficacy and show good agreement. A lamp efficacy value as high as 80 lm W−1 is demonstrated experimentally.

A secure data storage system based on phase-encoded thin polarization holograms

A novel secure data storage architecture based on phase-encoded, thin film, Fourier-type polarization holograms is reported. Efficient data encryption and verification can be obtained by phase modulation of the reference wave introduced by a phase-type spatial light modulator that is imaged onto the hologram plane. A physical model is formulated including phase-encoding, non-linear storage medium behaviour and features of the proposed optical system. A method is proposed and implemented in the form of a custom modelling tool for generating code sets optimal in terms of code number and security level. The utility of the architecture and the achievable security level are experimentally demonstrated.

Thermal behavior of acousto-optic devices: Effects of ultrasound absorption and transducer losses

In the present paper we analyze the electric and acoustic losses in acousto-optic devices, especially in their ultrasonic transducers and the related thermal effects. We include electric and acoustic losses into the classical electric equivalent model of the transducer, to explain the characteristics of the measured electric and thermal behavior. Measured temperature distributions on the acousto-optic crystal faces serve visualization of the conversion efficiency of the radio-frequency input to bulk acoustic waves. We show that the pronounced acoustic frequency dependence of the temperature distribution is in correlation with the frequency dependent losses in the transducer and in the bulk. We also demonstrate experimentally the effectiveness of our active and passive heat removing and temperature stabilization methods.

Investigation of acousto-optic tunable filter parameters for fast spectrometer application

Ideally an acousto-optic tunable filter is capable for selecting a single optical wavelength from a broadband polychromatic light beam simply by its electronic tuning. In practice, however, both the wavelength resolution and the operating wavelength range of the filter are limited by its electric and optical properties. An experimental configuration of a computer-controlled, fast acousto-optic spectrometer, based on an acousto-optic tunable filter operating in the 400- to 800-nm visible range with an average resolution of 10 nm is constructed and studied. The spectrometer has been operated in broadband optical measurements, such as determination of transmission spectra of complex, multilayer optical thin films and also real-time, in situ monitoring of evaporation processes. During the experiments, an anomalous behavior of the filter was observed that seriously limited the performance of the filter in the blue region. Some requirements necessary for spectrometer application are summarized and theoretical and experimental results are given illustrating the existence and also the elimination of this anomalous behavior.