Hassen Ghalila

Spectroscopy and metastability of BeO

The potential energy curve of the ground electronic state of BeO and those of the lowest electronic states of the BeO+ cation are computed using the CASSCF/MRCI methods and a large basis set. For the cation, the spin–orbit coupling and the transition momentum integrals are also evaluated. These data are used later to deduce an accurate set of spectroscopic constants and to investigate the spin–orbit-induced predissociation of the lowest electronic excited states of BeO+. Our calculations show that the high-rovibrational levels of the BeO+ (12Σ+) electronic state exhibit rapid predissociation processes forming Be+(2S) + O(3P). Our curves are also used for predicting the single ionization spectrum of BeO.

Field enhancement and target localization impact on the biosensitivity of nanostructured plasmonic sensors

Surface plasmon resonance (SPR) biosensors using field enhancement in nanograting surfaces can overcome sensitivity limitations of conventional SPR biosensors. Nevertheless, the correlation of the local field enhancement established in such structures with sensitivity enhancement has not been extensively studied. We present a numerical study of the coupling effect between the various plasmon modes present in nanograting structures with various structural parameters. We give here a quantitative demonstration of the improvement in sensing performance of SPR biosensors by selective localization of the target molecules in the regions where the electromagnetic field intensity is locally enhanced.

Excitation-emission matrix fluorescence coupled to chemometrics for the exploration of essential oils.

Excitation-emission matrix fluorescence (EEMF) coupled to chemometrics was used to explore essential oils (EOs). The spectrofluorometer was designed with basic and inexpensive materials and was accompanied by appropriate tools for data pre-treatment. Excitation wavelengths varied between 320 nm and 600 nm while emission wavelengths were from 340 nm to 700 nm. Excitation-emission matrix (EEM) spectra of EOs presented different features, revealing the presence of varying fluorophores. EOs from the same species but from different origins presented almost the same spectra, showing the possibility that EEM spectra could be used as additional parameters in the standardisation of EOs. With the aid of unfold principal component analysis (UPCA), resemblances obtained by spectral analysis of EOs were confirmed. A five components parallel factor analysis (PARAFAC) model was used to find the profiles of fluorophores in EOs. One of those components was associated to chlorophyll a.

Active learning in physics a way for rational thinking, a way for development

Science Development leads to new concepts, new tools and new techniques. It leads to a society development with new Truth. This Truth is shared by the Society which development is built on Knowledge, on rationality thinking and scientific behavior. This takes its origin in the experimental approach introduced by Ibn Al Haythem in optics at the Xth century. By the end of the last millennium, this approach-known as Active Learning in Physics- has been adopted in most developed countries in physics education programs. Active Learning in Optics and Photonics- ALOP- is extended actually to some developing countries through a UNESCO program. A French edition of ALOP takes place through many workshops over Morocco and Tunisia. It aims to build Truth on evidence and not on intuition or personal authority.

Optics simulations with Python: diffraction

Python is an easy open source software that can be used to simulate various optical phenomena. We have developed a suite of programs, covering both geometrical and physical optics. These simulations follow the experimental modules used in the ALOP (Active Learning in Optics and Photonics) UNESCO program in the sense that they complement it and help with student prediction of results. We present these programs and the student reactions to these simulations.

Fluorescence Spectroscopy Combined with Chemometrics for the Investigation of the Adulteration of Essential Oils

Artificial neural networks (ANNs) were built with excitation-emission matrix fluorescence (EEMF) spectra of essential oils for the investigation of their adulteration. With self-organized maps (SOMs), the clusters formed by all the types of essential oils were visualized. Pure essential oils were globally separated from their adulterated samples. The nature of the adulterant (vegetable oil, essential oil, solvent) in adulterated essential oils was revealed by a multilayer perceptron (MLP) network which classified them with a percentage of correct classification of 92.31%. In the case of the adulteration of neroli essential oil by sunflower vegetable oil, with another multilayer perceptron network, the level of adulteration was globally well evaluated. The correlation coefficient between true and evaluated adulteration percentages was 0.951. The samples corresponding to the adulteration percentage of 5% were the worse evaluated.

A simple wavelength division multiplexing system for active learning teaching

The active learning project consists in a series of workshops for educators, researchers and students and promotes an innovative method of teaching physics using simple, inexpensive materials that can be fabricated locally. The objective of the project is to train trainers and inspire students to learn physics. The workshops are based on the use of laboratory work and hands-on activities in the classroom. The interpretation of these experiments is challenging for some students, and the experiments can lead to a significant amount of discussion. The workshops are organized within the framework of the project ‘‘Active Learning in Optics and Photonics” (ALOP) mainly funded by UNESCO, with the support of ICTP (Abdus Salam International Centre for Theoretical Physics) and SPIE. ALOP workshops offer high school, college or university physics teachers the opportunity to improve their conceptual understanding of optics. These workshops usually run for five days and cover several of the topics usually found in any introductory university physics program. Optics and photonics are used as subject matter because it is relevant as well as adaptable to research and educational conditions in many developing countries [1]. In this paper, we will mainly focus on a specific topic of the ALOP workshops, namely optical communications and Wavelength Division Multiplexing technology (WDM). This activity was originally developed by Mazzolini et al [2]. WDM is a technology used in fibre-optic communications for transmitting two or more separate signals over a single fibre optic cable by using a separate wavelength for each signal. Multiple signals are carried together as separate wavelengths of light in a multiplexed signal. Simple and inexpensive WDM system was implemented in our laboratory using light emitting diodes or diode lasers, plastic optical fibres, a set of optical filters and lenses, prism or grating, and photodiodes. Transmission of audio signals using home-made, simple, inexpensive electronic circuits was also demonstrated. The experimental set-up was used during national ALOP workshops. Results are presented and discussed in this paper. Current explorations to further develop these and other closely-related experiments will also be described.

Using mobile camera for a better exploitation and understanding of interference and diffraction experiments

To deduce the wave nature of light, explain its behavior when it interacts with material obstacles (diffraction) or its behavior when light from two coherent sources interfere with each other (interference), we need to explain what are waves and what are their properties (wavelength, frequency, mathematical relationship between wavelength and frequency, superposition principle, …). Two principal approaches are generally used to introduce waves: 1/ An experimental approach (the example commonly used approach): to observe the water waves pattern obtained when drops of water (with an eye dropper, two eye droppers, or equivalent) fall -at a steady rate- on a calm pool of water surface. 2/ A theoretical approach: Wave coming from one source is represented by a sinusoidal function; Superposition of waves coming from two coherent sources is done by a sum of two sinusoidal functions with constant phase difference. In Tunisia, different workshops on “wave nature of light based on interference and diffraction” using Active Learning process have been organized for about 150 secondary school teachers in 2009. These workshops are based on UNESCO Active Learning in Optics and Photonics (ALOP) project. This paper will show how taking water wave’s pattern using some participant’s mobile camera helps to make some misconceptions resolved and includes at the same time other more complex phenomena.

Hands-on experimental and computer laboratory in optics: the Young double slit experiment

Teaching optics to small groups of students allows them to share ideas and leads to discussions, which will enable them to understand concepts better. This is a form of peer teaching/evaluation. This group dynamic favors creativity and inhibits obstacles to learning and understanding due to shyness, and other psychological factors. In addition, this paradigm allows the learner to be an active participant in the learning process rather than a passive recipient of knowledge as in the traditional lecture based teaching methodology. The project proposed here is based on both experimental and numerical approaches. Groups of students will be using simple and inexpensive equipment in a hands-on way. Additionally using numerical tools with open source environments such as the Python programming language allows one to perform numerical experiments. These two approaches are perfectly complementary; indeed the experiments favor observations and measurements and on the other hand numerical modeling favors abstraction and familiarization of mathematical formalisms of the optical phenomena. We propose a pedagogical methodology “Active Learning in Simulating Optics” (ALSO), where the active learning method is used not only for hands on experimentation while numerical modeling facilitates development of computer codes wherein students can design their own experiments. Mixing these two approaches, experimentation and simulation, is also very well adapted in working within projects for the elaboration of a new tools for teaching. This ALSO methodology will be presented along with results from workshops utilizing this technique.

Role of simulations in optics education

Simulations can play an important role in science education. Simulations (enabled by powerful numerical and visualization methods) are excellent tools for teaching optical phenomena. The advantages of using simulations as a tool for teaching optics include, amongst others, (1) giving students an engaging, hands-on active learning experience, (2) helping in understanding equations as physical relationships among experimental measurements and (3) allowing students to investigate phenomena that would not be possible to experiment on in a laboratory or classroom setting. We illustrate the utility of simulations in optics by describing some examples from geometric and physical optics using the open source programming language Python.