Two-Photon Ionization and Three-Photon Above-Threshold Ionization of Argon

Studies of nonlinear laser-matter interaction have been so far limited to wavelengths from the near ultraviolet to infrared, because of the low brightness of currently available sources outside this range. However nonlinear processes in the VUV/Soft X-ray domain would initiate multiphoton innershell spectroscopy, XUV nonlinear optics and applications of such processes to metrology. The probability of multiphoton transitions decreases rapidly with the number of photons involved. A typical two-photon bound-free transition has a rate of the order of .1 ps{sup {minus}1} at 10{sup 12} W.cm{sup {minus}2} and scales as the square of the intensity. Such an intensity is therefore required to saturate a two-photon transition with a 100 fs pulse. This is difficult to achieve with the present state-of-the-art techniques for producing intense XUV pulses. To the authors knowledge, only two cases of such transitions have been reported so far. The first one is a two-photon ionization of argon by the third harmonic of a KrF laser. Since the photon energy (15 eV) is just below the ionization energy (15.75 eV) for argon, the transition is quasi-resonant. The second case is a two-photon ionization of helium by the 9th harmonic of a Ti:S laser. In the latter case an autocorrelation measurement of the harmonic pulse has been reported. In the present work, the authors report on two-photon ionization of argon at 133 nm (9.3 eV) from the third harmonic of a frequency doubled Ti:S laser, and a three-photon above-threshold ionization involving two 9.3 eV photons and one 3.1 eV photon

Time-Frequency Characterization of Femtosecond Extreme Ultraviolet Pulses

A measurement of chirp and pulse duration of fifth harmonic of a frequency-doubled Ti:sapphire laser was presented. The photoelectron signal due to cross correlation of harmonics generated by 400 nm blue light and an 800 nm infrared probe pulse, was measured using energy resolved cross-correlation method. Results demonstrated that the technique could be used to characterize the time-frequency behavior of much higher-order harmonics

Experimental Study and CFD Thermal Assessment of Horizontal Hot Water Storage Tank Integrating Evacuated Tube Collectors with Heat Pipes

International audienceThis paper presents an experimental study and a set of CFD simulations applied to a horizontal tank storing hot water. Hence, the main purpose of this work is to suggest a new and optimal design of the studied horizontal tank which is considered as the main device in individual solar water heaters integrating Evacuated Tube Collectors (ETC) with heat pipes. An experimental study was carried out to measure the maximum temperature of the heat pipes using a thermal camera. Subsequently, CFD simulations were performed using the previously recorded experimental results. The numerical studies aimed to assess the effect of the heat pipe's number, integrated on the lateral internal shell of the tank, on its energetic performances such as the discharging efficiency. In fact, four cases were studied according to the number of the used heat pipes (n). Several performance indicators were defined to identify the optimal configuration, such as the heat transfer coefficient assessed at the heat pipe, temperature contours and streamlines, temperature evolution according to specific paths defined inside the storage tank and the discharging efficiency\ldotsIt was found that the average temperature of the horizontal tank is increased by the rise in the heat pipe's number. On the other hand, the laminar structure of the flow field is disturbed and the outlet temperature of the hot loaded water is also affected. Otherwise, the HTC calculated for the heat pipe close to the outlet of the storage tank for n = 6 achieved 212.5W/K m2, while it is 300 W/K m2 and 230 W/K m2 for n = 8 and n = 10, respectively. Moreover, the discharging efficiency of the horizontal storage tank depends mainly on the instantaneous variation of the water's temperature

Heat Transfer inside Cavities Heated by Discrete Sources: Solar Systems

International audienceIn this paper, we studied numerically laminar natural convection in two types of configurations: the first a square enclosure with four types of discrete sources (Plane, Circular, Square and Triangular) with partial heating of the bottom wall while the rest is maintained constantly adiabatic. The second configuration a rectangular enclosure in which we increased the number of discrete sources for each geometric shape. This study simulates the case of heat generation in a storage tank of hot water or in an electronic component mounting enclosure. The light source is considered to be located in the lower wall with a heated fixed width. This heating will be introduced either as an isothermal or uniform flow. For the purposes of this analysis, the length of the source is set at 20% of the total length of the lower wall. The upper wall, the unheated portion of the bottom wall, the right and left walls will be considered adiabatic. For all configurations the Rayleigh number was fixed at 106. The streamlines and isotherms are presented for various combinations of forms of the heated zone. The results will also be presented in a number of local Nusselt on heated wall

Energy and Parametric Analysis of Solar Absorption Cooling Systems in Various Moroccan Climates

International audienceThe aim of this work is to investigate the energetic performance of a solar cooling system using absorption technology under Moroccan climate. The solar fraction and the coefficient of performance of the solar cooling system were evaluated for various climatic conditions. It is found that the system operating in Errachidia shows the best average annual solar fraction (of 30%) and COP (of 0.33) owing to the high solar capabilities of this region. Solar fraction values in other regions varied between 19% and 23%. Moreover, the coefficient of performance values shows in the same regions a significant variation from 0.12 to 0.33 all over the year. A detailed parametric study was as well carried out to evidence the effect of the operating and design parameters on the solar air conditioner performance

Design and Thermal Performance Optimization of a Forced Collective Solar Hot Water Production System in Morocco for Energy Saving in Residential Buildings

International audienceThis paper presents a comprehensive study that aims to assess the energetic performances of a solar hot water collective system under a realistic load consumption profile in Morocco. The case study which has been considered in this work is a residential building located in Fez city. Several parameters are involved into the performance assessment of the collective system. Hence, it was essential to identify the parameters on which we will act in order to carry out the parametric study. In fact, the technology of evacuated tube collectors (ETC) with heat pipes were selected as a fixed study parameter, while a set of other indicators were investigated contributing to the collective hot water system design and optimization, such as the solar collector panel total area, the connecting methods between the collector's field which could be serial, parallel or mixed connection, the collective hot water storing volume configurations in addition to the intrinsic optical efficiencies of the world's manufacturers solar collectors. In order to achieve the assessment of the energetic performances of the collective system, four parametric studies were described and carried out to ensure its design and optimization during the dynamic mode operation. The most relevant findings from this research paper are presented as follows. Incrementing the collector's field area to 120 m2 optimizes the thermal efficiency of the collective system, and the hydraulic booster consumption is reduced. Besides, it would be advantageous to use a total area of 80 m2 to satisfy the hot water need demand over the four seasons, since the overall collective system thermal efficiency remain above 60%. Moreover, is was possible to ensure a seasonal solar fraction which is greater than 50% by connecting a collective storage tank with a volume of 1500 l and a solar collector panel with an area of 100 m2. Last but not least, the effect of the row's number as well as the number of collectors connected per row on the overall collective system's solar fraction was also investigated through this study