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La première partie de ce travail présente une nouvelle méthode qui permet de détermination rapidement de la température et de la concentration en fer d'un plasma d'arc MAG utilisé dans la technologie de soudage par plasma. Le plasma est un mélange [Ar-CO2] en présence de fer, avec un rapport molaire entre Ar et CO2 constant de 82%-18%. La seconde partie s'intéresse au rayonnement d'un plasma d'argon utilisé dans la technologie soudage GTAW et pouvant conduire à des dangers photobiologique. Dans le chapitre 1, le contexte et la motivation de ce travail sont présentés. Les travaux déjà effectués et publiés dans ces deux axes scientifiques sont passés en revue. Dans le chapitre 2, les compositions à l'équilibre sont calculées par la méthode de la minimisation de l'énergie libre de Gibbs. Les densités et fonctions de partitions obtenues pour chaque espèces présente dans le plasma sont ensuite utilisées pour déterminer les pertes radiatives des plasmas [Ar-CO2]-Fe via la méthode du coefficient d'émission net (CEN). Cette estimation des pertes ne peut se faire sans le calcul préalable du coefficient d'absorption spectral que nous avons réalisé finement par la méthode " raie par raie ". Tous les mécanismes radiatifs prédominants dans le plasma ont été pris en compte: continua atomique et moléculaire, raies atomiques et moléculaires. Cette partie constitue la base de cette étude sur laquelle se fonde notre nouvelle méthode de diagnostic destinée à déterminer à la fois la température et la concentration en fer d'un plasma d'arc de soudage. Le chapitre 3 est dédié à l'étude expérimentale d'un plasma d'arc MAG constituée d'une analyse spectroscopique permettant de remonter au profil de température et tester l'hypothèse de l'Équilibre Thermodynamique Local. La température d'excitation est obtenue par la méthode de Boltzmann tandis que la mesure d'élargissement de Stark pour les raies de fer et d'argon permet de remonter à la température et la densité des électrons. / This PhD thesis introduces a method that allows the fast determination of temperature and iron concentration for MAG-P Arc. The MAG-P Arc is in fact [Ar-CO2]-Fe mixtures, with a constant molar ratio between Ar and CO2 [82%Ar-18%CO2]. In a second time, this thesis presents a study of the optical radiation associated to photobiological hazards for argon GTAW Arc. In chapter 1, the background and motivation of this work is introduced. The previous works published in this field are reviewed. In chapter 2, the equilibrium compositions are calculated firstly using the minimization of Gibbs free energy. Then the radiative properties of [Ar-CO2]-Fe plasmas are obtained in the frame of the net emission coefficient (NEC) approach, using the accurate "line by line" method. All significant radiative contribution mechanisms are taken into account in the calculation. This study will constitute a groundwork to build the diagnostic method that allows determination of temperature and iron concentration profiles in welding arc. In chapter 3, spectroscopic investigation of the LTE hypothesis across the MAG-P Arc is made. Excitation temperature is obtained with Boltzmann plot method while iron and argon lines Stark broadening measurements are used to get electron temperature and electron density. LTE hypothesis validity across the arc is discussed considering the agreement between the two temperatures, the electron density and iron content. Results show supporting evidence for the main part of the plasma, along radial and axial directions. Discrepancies occur only at the fringe of the arc, where the two temperatures differ by more than 2000 K. In chapter 4, a method allowing a fast determination of space- and time-resolved plasma temperature and iron concentration in MAG arcs during the high-current phase is introduced. This method consists in measuring the plasma spectral radiation of the arc with iron vapours using a high-speed camera filtered by narrow band filters in the spectral intervals of 570-590 nm and 606-627 nm respectively; calculating theoretically the dependence of the absolute emissivity e570-590 nm and relative emissivity e570-590 nm/e607-627 nm versus the plasma temperature and the iron concentration. This method has also been validated for a layer of plasma by adopting other existing diagnostics such as Stark broadening, which demonstrates the effectiveness of this new method. In chapter 5, a theoretical investigation of the UV (180-400 nm), UVA (315-400 nm) and blue light (300-700 nm) radiation associated with the photobiological hazards to workers for argon GTAW arcs is presented. The radiative properties of argon plasma are calculated for the three spectral regions, and a two-dimensional model of a GTAW arc is then developed to determine the local emissions in the arc, the total radiation escaping from the arc and corresponding effective irradiances. This study clearly supports the importance of undertaking an effective protection strategy for workers, particularly for skin and eyes, in the welding environment. Finally, a general conculsion is given in chapter 6.

Copper vapour laser (CVL) pumped high repetition rate narrow bandwidth dye laser is an important source of tunable radiation. It finds numerous applications in spectroscopic investigations and selective material processing like atomic vapour laser isotope separation (AVLIS). Being wavelength selective in these applications stability of the output wavelength and bandwidth are extremely important. The stability of these parameters depend upon the refractive index fluctuation of the dye medium, due to pump beam induced temperature gradients, dye solution flow, and mechanical stability of optical components. Precise measurement of wavelength and bandwidth of a dye laser and control over parameters governing the variations are important for any stable dye laser system. In this thesis, details of investigations carried out on a Rhodamine 6G dye laser for obtaining stable wavelength and output power are presented. Parameters that affect the stability were identified, monitored and put on close loop control to achieve the desired stability. Pump beam i.e. CVL optical power, dye flow rate and dye solution temperature are mainly these parameters. CVL power is mainly a function of input electrical power and pressure of the buffer gas inside the tube. To monitor and regulate these parameters, different sensors and actuators were selected and interfaced with a master slave topology based data acquisition and control system. The DAQ and control system is designed around a micro controller card based on advanced CPU P80552 and has on chip 8 channel 10 bit multiplexed analog input, 16 TTL digital inputs and 16 digital outputs. It works as slave and PC as master. Following closed loops were designed and incorporated to maintain a stable output: a. Average output of CVL was maintained constant by regulating the electric input power through closed loop control. b. The buffer gas pressure was monitored with a semiconductor pressure sensor and was regulated using pulse width modulation. c. Temperature of the dye solution was monitored with PT100 and was controlled using proportional controller. d. Flow rate of dye solution was controlled using a variable frequency drive (VFD) for the dye circulation pump. e. The dye laser wavelength was monitored by using a high resolution spectrograph and pixel position of the peak from CCD image obtained from spectrograph is used for feedback correction using a pico motor. In the present work with application of the above-mentioned input power and pressure loops, a stable output of CVL, is achieved. Variations in power and pulse width of CVL are got limited to within 2%, from 10% when CVL system was working unregulated. This control system does the line regulations and corrects the input electrical power if variations in discharge current occur due to pressure variation. Every dye cell has limits on flow rate because of its geometry. With flow and temperature control dye cell was characterized to work with lower linewidth. VFD (variable frequency drive) is used for flow regulation. Finally active control on set wavelength was also achieved with resolution of 0.01nm accuracy. Measurement of wavelength was done with 0.3 m, 0.054 nm resolution spectrograph. Closed loop pico motor with 30 nm per step linear resolution was used for wavelength control. The thesis is organized in four chapters. First chapter presents a brief introduction to high repetition rate CVL pumped dye laser, operation of a CVL and parameters affecting the dye laser stability and their control schemes. Literature survey in this chapter is focused on different control mechanisms used with such lasers. Second chapter describes the laser system and interfacing of data acquisition system used for experimental setup. Closed loop controls for different parameters are described in this chapter. It also describes the software algorithms developed for this work. Third chapter presents experimental results and analysis with discussion on performance of the control loops. Finally the conclusion is given and few suggestions are made for further work.