Sección Especial: Óptica No Lineal / Special Section: Non-linear Optics
Research areas of the Plasma Spectroscopy Group at the University of
Valladolid
Líneas de investigación del Grupo de Espectroscopia de Plasmas de la
Universidad de Valladolid
S. Mar
(1,*,S), J. A. Aparicio
(1,S), A. Calisti
(2), M. Ćirišan
(3), M. I. de la Rosa
(1), J. A. del Val
(4),
S. Djurović
(3), L. M. Fuentes
(1), M. A. Gigosos
(1,S), M. Á. González
(5), A. B. Gonzalo
(4),
K. Grützmacher
(1), M. Ivković
(6), N. Konjević
(6), R. J. Peláez
(1,S), C. Pérez
(1,S)and B. Talin
(2)1. Departamento de Física Teórica, Atómica y Óptica, Facultad de Ciencias, Universidad de Valladolid, 47011 Valladolid, Spain.
2. UMR6633, Université de Provence, Centre Saint Jérôme, 13397 Marseille Cedex 20, France 3. Faculty of Sciences, Department of Physics, Trg Dositeja Obradovića 4, 21000 Novi Sad, Serbia
4. Departamento de Física Aplicada, EU Politécnica, Universidad de Salamanca, 05071 Ávila, Spain
5. Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Valladolid, 47011 Valladolid, Spain. 6. Institute of Physics, University of Belgrade, 11081 Belgrade, P.O. Box 68, Serbia.
(*) Email: [email protected] S: miembro de SEDOPTICA / SEDOPTICA member
Recibido / Received: 30/10/2010. Aceptado / Accepted: 15/12/2010
ABSTRACT:
Research lines of the Plasma Spectroscopy Group at the University of Valladolid are presented in this work. The first one is devoted to atomic parameters determination, the second to laser spectroscopy, and the third is calculation and spectral analysis by computer simulation.
Keywords: Optics, Spectroscopy, Plasma, Laser, Diagnostic.
RESUMEN:
Se presenta las líneas de investigación del grupo de Espectroscopia de Plasmas de la Universidad de Valladolid. La primera de las líneas se centra en la determinación de parámetros atómicos, la segunda, en la espectroscopia láser y la tercera, en cálculo y análisis de espectros mediante simulación por computador.
Palabras clave: Óptica, Espectroscopia, Plasma, Láser, Diagnóstico.
REFERENCES AND LINKS
[1]. W. L. Wiese, N. J. Konjević, “Regularities and similarities in plasma broadened spectral line widths (Stark widths)”, Quant. Spectrosc. Radiat. Trans.28, 185-198 (1982).
[2]. J. A. del Val, S. Mar, M. A. Gigosos, I de la Rosa, C. Pérez, V. González, “Design and characterization of a pulsed plasma source”, Jpn. J. Appl. Phys.37, 4177-4181 (1998).
[3]. S. Djurović, R. J. Peláez, M. Ćirišan, J. A. Aparicio, S. Mar, “Stark widths of Xe II lines in a pulsed plasma”, J. Phys. B - At. Mol. Opt.39, 2901-2916 (2006).
[4]. H. R. Griem, Spectral Line Broadening by Plasmas, New York, Academic (1974).
[5]. M. A. Gigosos, S. Mar, C. Pérez, M. I. de la Rosa, “Experimental Stark widths and shifts and transition probabilities of several Xe II lines”, Phys. Rev. E49, 1575-1585 (1994).
ÓPTICA PURA Y APLICAD
[7]. S. Mar, M. A. Gigosos, “Central structure of the H-beta line at low electron densities”, Atti della Fondazione Giorgio Ronchi37, 429-436 (1982).
[8]. F. Torres, M. A. Gigosos, S. Mar, “Study of the Balmer-beta core in a pulsed plasma”, J. Quant. Spectrosc. Ra.31, 265-271 (1984).
[9]. J. Hernández, M. A. Gigosos, F. Torres, S. Mar, “The Balmer-alpha profile corrected of strong self-absorption”, J. Quant. Spectrosc. Ra.33, 35-38 (1985).
[10]. S. Mar, A. Czernichowski, J. Chapelle, “Experimental Stark parameters for some spectral lines in SF6 plasma”, J. Phys. D19, 43-50 (1986).
[11]. M. A. González, V. R. González, S. Mar, “Precise measurement of the Balmer-alpha core”, J. Quant. Spectrosc. Ra.42, 247-251 (1989).
[12]. C. Pérez, M. I. de la Rosa, A. M. de Frutos, V. R. González, S. Mar, “Stark broadening of several Si II lines”, Ann. Phys.15, 115-116 (1990).
[13]. C. Pérez, M. I. de la Rosa, A. M. de Frutos, S. Mar, “Calibration of the Stark-broadening parameters in some He I lines”, Phys. Rev. A44, 6785-6790 (1991).
[14]. C. Pérez, M. I. de la Rosa, A. M. de Frutos, S. Mar, “Stark broadening of some C I and C II lines”, Phys. Rev. A44, 6948-6950 (1991).
[15]. C. Pérez, M. I. de la Rosa, A. M. de Frutos, S. Mar, “Temperature dependence of Stark broadening for several Si II lines”, Phys. Rev. E47, 756-759 (1993).
[16]. M. A. Gigosos, S. Mar, M. C. Pérez, “Medidas del ensanchamiento Stark en la línea del He I de 5016 Å”,
Opt. Pura Apl.26, 104-109 (1993).
[17]. C. Pérez, J. A. Aparicio, M. I. de la Rosa, S. Mar, M. A. Gigosos, “Calibration of the Stark broadening parameter of the 728.1 nm He I line”, Phys. Rev. E51, 3764-3766 (1995).
[18]. C. Pérez, I. de la Rosa, J. A. Aparicio, S. Mar, M. A. Gigosos, “Calibration of the Stark-broadening parameters of two He I lines with forbidden components”, Jpn. J. Appl. Phys.35, 4073-4076 (1996). [19]. J. A. Aparicio, M. A. Gigosos, S. Mar, “Transition probability measurement in an Ar II plasma”, J. Phys. B
- At. Mol. Opt. 30, 3141-3157 (1997).
[20]. J. A. Aparicio, M. A. Gigosos, V. R. González, C. Pérez, M. I. de la Rosa, S. Mar, “Measurement of Stark broadening and shift of singly ionized Ar lines”, J. Phys. B - At. Mol. Opt.31, 1029-1048 (1998).
[21]. J. A. Aparicio, C. Pérez, J. A. del Val, M. A. Gigosos, M. I. de la Rosa, S. Mar, “Measurement of Stark broadening and shift parameters of several Ar I lines”, J. Phys. B - At. Mol. Opt.31, 4909-4918 (1998). [22]. J. A. del Val, J. A. Aparicio, S. Mar, “Experimental Stark widths and shifts of several Ne I spectral lines”,
Astrophys. J.513, 535-541 (1999).
[23]. J. A. del Val, J. A. Aparicio, V. R. González, S. Mar, “Measurement of Stark widths in singly ionized oxygen”, Astron. Astrophys Suppl. Ser.140, 171-176 (1999).
[24]. S. Mar, J. A. Aparicio, M. I. de la Rosa, J. A. del Val, M. A. Gigosos, V. R. González, C. Pérez, “Measurement of Stark broadening and shift of visible N II lines”, J. Phys. B - At. Mol. Opt.33, 1169-1184 (2000). [25]. S. Mar, C. Pérez, V. R. González, M. A. Gigosos, J. A. del Val, M. I. de la Rosa, J. A. Aparicio, “Experimental
transition probabilities in N II lines”, Astron. Astrophys Supp. Ser.144, 509-515 (2000).
[26]. J. A. del Val, J. A. Aparicio, S. Mar, “Stark width measurements of Ne II lines”, Astrophys. J.536, 998-1004 (2000).
[27]. J. A. del Val, J. A. Aparicio, V. González, S. Mar, “Experimental transition probabilities of several Ne I lines”, Astron. Astrophys. 357, 1137-1142 (2000).
[28]. V. R. González, J. A. Aparicio, J. A. del Val, S. Mar, “Stark width and shift measurements of visible Si III lines”, Astron. Astrophys. 363, 1177-1185 (2000).
[29]. F. Rodríguez, J. A. Aparicio, A. de Castro, J. A. del Val, V. R. González, S. Mar, “Measurement of several transition probabilities in singly-ionized krypton”, Astron. Astrophys. 372, 338-345 (2001).
[30]. J. A. del Val, J. A. Aparicio, V. R. González, S. Mar, “Transition probabilities measurement in Ne II”, J. Phys. B - At. Mol. Opt.34, 2513-2525 (2001).
[32]. A. de Castro, J. A. Aparicio, J. A. del Val, V. R. González, S. Mar, “Measurement of Stark broadening and shift constants of singly-ionized krypton lines”, J. Phys. B - At. Mol. Opt.34, 3275-3286 (2001).
[33]. V. R. González, J. A. Aparicio, J. A. del Val, S. Mar, “Stark broadening and shift measurements of visible Si II lines”, J. Phys. B - At. Mol. Opt.35, 3557-3573 (2002).
[34]. F. Rodriguez, J. A. Aparicio, V. R. González, J. A. del Val, S. Mar, “Measurement of Stark parameters of He II P-alpha, P-beta and P-gamma spectral lines”, Astron. Astrophys. 409, 771-780 (2003).
[35]. C. Pérez, R. Santamarta, M. I. de la Rosa, S Mar, “Stark broadening of neutral helium lines and spectroscopic diagnostics of pulsed helium plasma”, Eur. Phys. J. D27,1, 73-75 (2003).
[36]. R. J. Peláez, C. Pérez, V. R. González, F. Rodríguez, J. A. Aparicio, S. Mar, “Experimental measurements of shifts and asymmetries of He II P-alpha and P-beta spectral lines”, J. Phys. B - At. Mol. Opt.38, 2505-2517 (2005).
[37]. R. J. Peláez, F. Rodríguez, V. R. González, C. Pérez, J. A. Aparicio, S. Mar, “Stark parameters of neutral helium 318.8 nm line”, Astron. Astrophys. 453, 751-754 (2006).
[38]. R. J. Peláez, M. Ćirišan, S. Djurović, J. A. Aparicio, S. Mar, “Stark broadening measurements of Xe III spectral lines”, J. Phys. B - At. Mol. Opt.39, 5013-5022 (2006).
[39]. S. Mar, J. A. del Val, F. Rodríguez, R. J. Peláez, V. R. González, A. B. Gonzalo, A. de Castro, J. A. Aparicio, “Measurement of transition probabilities in Kr II UV and visible spectral lines”, J. Phys. B - At. Mol. Opt.
39, 3709-3721 (2006).
[40]. M. Ćirišan, R. J. Peláez, S. Djurović, J. A. Aparicio, S. Mar, “Stark shift measurements of Xe II and Xe III spectral lines”, J. Phys. B - At. Mol. Opt.40, 3477–3490 (2007).
[41]. M. Ćirišan, R. J. Peláez, S. Djurović, J. A. Aparicio, S. Mar, “Stark broadening measurements of low-intensity Xe II lines in pulsed discharge”, J. Res. Phys.31, 11-18 (2007).
[42]. J. A. del Val, R. J. Peláez, S. Mar, F. Rodríguez, V. R. González, A. B. Gonzalo, A. de Castro, J. A. Aparicio, “Stark widths, shifts and regularities for Kr II visible spectral lines”, Phys. Rev. A77, 012501 (2008). [43]. R. J. Peláez, S. Djurović, M. Ćirišan, F. Rodríguez, J. A. Aparicio, S. Mar, “Ne II Stark width and shift
regularities”, Astrophys. J.687, 1423-1431 (2008).
[44]. S. Djurović, R. J. Peláez, M. Ćirišan, J. A. Aparicio, S. Mar, “Stark widths and shifts of Kr II UV spectral lines”, Phys. Rev. A78, 042507 (2008).
[45]. R. J. Peláez, S. Djurović, M. Ćirišan, J. A. Aparicio, S. Mar, “Irregularities of Stark parameters of Xe II spectral lines”, J. Phys. B - At. Mol. Opt.42, 125002 (2009).
[46]. R. J. Peláez, M. Ćirišan, S. Djurović, J. A. Aparicio, S. Mar, “Stark broadening measurements of low intensity singly and doubly ionized xenon spectral lines”, Astron. Astrophys. 507, 1697–1705 (2009). [47]. R. J. Peláez, S. Djurović, M. Ćirišan, J. A. Aparicio, S. Mar, “Stark halfwidth trends along the homologous
sequence of singly ionized noble gases”, Astron. Astrophys. 518, 1-12 (2010).
[48]. M. S. Dimitrijević, N. Konjević, “Stark widths of doubly- and triply-ionized atom lines”, J. Quant. Spectrosc. Radiat. Transfer24, 451-459 (1980).
[49]. W. Demtröder, Laser Spectroscopy, Basic Concepts and Instrumentation, Springer Berlin, Second Enlarged Edition (1996).
[50]. K. Kohse-Höinghaus, J. B. Jeffries, Applied Combustion Diagnostics, Taylor & Francis, New York (2002). [51]. V. P. Gavrilenko, “Laser-spectroscopy methods for diagnostics of electric fields in plasma (Review)”,
Instrum. Exp. Tech.49, 149-206 (2006).
[52]. K. Muraoka, M. Maeda, Laser-Aided Diagnostics of Plasmas and Gases, Institute of Physics Series in Plasma Physics IOP (2001).
[53]. J. Seidel, "Theory of two-photon polarization spectroscopy of plasma broadened hydrogen Lα line",
Phys. Rev. Lett. 57, 2154-2156 (1986).
[54]. K. Danzmann, K. Grützmacher, B. Wende, “Doppler-free two photon polarization spectroscopic measurement of the Stark- spectroscopy of plasma broadened hydrogen Lα line”, Phys. Rev. Lett.57, 2151-2153 (1986).
ÓPTICA PURA Y APLICAD
[56]. K. Grützmacher , M. I. de la Rosa, A. B. Gonzalo, M. Steiger, A. Steiger, “Two-photon polarization spectroscopy applied for quantitative measurements of atomic hydrogen in atmospheric flames”,
Appl. Phys. B76, 775-785 (2003).
[57]. A. B. Gonzalo, M. I. de la Rosa, M. C. Pérez, S. Mar, K. Grützmacher, “Absolute atomic hydrogen density distribution in a hollow cathode discharge by two-photon polarization spectroscopy”, Plasma Sources Sci. T.12, 150-155 (2003).
[58]. A. B. Gonzalo, M. I. de la Rosa, C. Pérez, S. Mar, K. Grützmacher, “Fundamentos de la espectroscopia de polarización por absorción de dos fotones aplicada al estudio de plasmas”, Opt. Pura Apl.35, 7-20 (2002).
[59]. M. I. de la Rosa, C. Pérez, K. Grützmacher, L. M. Fuentes, “Determination of two-photon absorption cross-section of noble gases for calibration of laser spectroscopic techniques”, Spectral Line Shapes
15, 18-20, American Institute of Physics (2008).
[60]. M. I. de la Rosa, C. Pérez, K. Grützmacher, A. B. Gonzalo, A. Steiger, “Electric field measurements in a hollow cathode discharge by two-photon polarization spectroscopy of atomic deuterium”, Plasma Sources Sci. T.15, 105-111 (2006).
[61]. M. I. de la Rosa, C. Pérez, K. Grützmacher, L. M. Fuentes, “Electric field strengths in a hollow cathode measured by Doppler-free two-photon optogalvanic spectroscopy via Stark splitting of the 2S level of deuterium”, Plasma Sources Sci. T. 18, 015012 (2009).
[62]. C. Pérez, M. I. de la Rosa, K. Grützmacher, “Hollow cathode fall field strength measured by Doppler-free two-photon optogalvanic spectroscopy via Stark splitting of the 2S level of hydrogen”, Eur. Phys. J. D56, 369-375 (2010).
[63]. J. Seidel, Private Communication (2000).
[64]. M. I. de la Rosa, C. Pérez, K. Grützmacher, A. B. Gonzalo, J. A. del Val, “Determination of electric field strength and kinetic temperature in the cathode fall region of a hollow cathode discharge”, J. Phys. - Conf. Ser.227, 012038 (2010).
[65]. A. Steiger, K. Grützmacher, M. I. de la Rosa, “Efficient generation of pulsed single-mode radiation tunable in the UV-C region”, Laser in Research and Engineering, Edts. W. Waidelich et al. Springer Verlag, Berlin (1996).
[66]. A. Bustillo, K. Grützmacher, A. Steiger, L. Werner, “UV-laser spectrometer for the generation of pulsed single longitudinal mode radiation down to 200 nm”, Proceedings of the 10th International Symposium
on Laser-Aided Plasma Diagnostics (Fukuoka, Japan) pp. 247-252 (2001).
[67]. M. A. Gigosos, J. Fraile, F. Torres, “Hydrogen Stark profiles: a simulation-oriented mathematical simplification”, Phys. Rev A31, 3509-3511 (1985).
[68]. M. A. Gigosos, V. Cardeñoso, “Study of the effects of ion dynamics on Stark profiles of Balmer-alpha and -beta lines using simulation techniques”, J. Phys B20, 6005 (1987)
[69]. V. Cardeñoso, M. A. Gigosos, “Computer simulation technique applied to the study of hydrogen Stark broadening by plasmas”, Phys. Rev. A39, 5258-5267 (1989).
[70]. M. A. Gigosos, V. Cardeñoso, “Ion dynamics effects in the Balmer gamma line: computer simulation calculations”, J. Phys. B - At. Mol. Opt.22, 1743-1749 (1989).
[71]. V. Cardeñoso, M. A. Gigosos, “Study of the Stark broadening of the Paschen alpha line in hydrogen”, J. Phys. B - At. Mol. Opt.30, 3361-3368 (1997).
[72]. M. A. Gigosos, V. Cardeñoso, F. Torres, “Stark-broadening simulation in hydrogen: study of the binary and complete binary collision hypotheses”, J. Phys. B - At. Mol. Opt. 19, 3027-3033 (1986).
[73]. A. Barbes, M. A. Gigosos, M. A. González, “Analysis of the coupling between impact and quasistatic field mechanisms in Stark broadening”, J. Quant. Spectrosc. Ra.68, 679-688 (2001).
[74]. L. Godbert-Mouret, T. Meftah, A. Calisti, R. Stamm, B. Talin, M. Gigosos, V. Cardenoso, S. Alexiou, R. W. Lee, L. Klein, “Accuracy of Stark broadening calculations for ionic emitters”, Phys. Rev. Lett.81, 5568 (1998).
[76]. M. A González, M. A. Gigosos, “Analysis of Stark line profiles for non-equilibrium plasma diagnosis”,
Plasma Sources Sci. T.18, 034001 (2009)
[77]. M. A. Gigosos, M. A. González, N. Konjevic, “On the Stark broadening of Sr+ and Ba+ resonance lines in ultracold neutral plasmas”, Eur. Phys. J. D40, 57-63 (2006)
[78]. S. Ferri, A. Calisti, C. Mosse, B. Talin, M. A. Gigosos, M. A. González, “Line shape modeling in warm and dense hydrogen plasmas”, High Energ. Dens. Phys.3, 81-85 (2007)
[79]. M. A. Gigosos, V. Cardeñoso, “New plasma diagnosis tables of hydrogen Stark broadening including ion dynamics”, J. Phys. B - At. Mol. Opt.29, 4795-4838 (1996).
[80]. M. A. Gigosos, M. Á. González, “Calculations of the polarization spectrum by two-photon absorption in the hydrogen Lyman-alpha line”, Phys. Rev. E58, 4950 (1998).
[81]. M. A. González, M. A. Gigosos, “Tables of dipolar emission and two photon absorption Lyman-alpha profiles”, Astron. Astrophys. Suppl. Ser.145, 491-494 (2000).
[82]. B. Talin, E. Dufour, A. Calisti, M. A. Gigosos, M. A. González, T. del Rio Gaztelurrutia, J. W. Dufty, “Molecular dynamics simulation for modelling plasma spectroscopy”, J. Phys. A: Math. Gen.36, 6049-6056 (2003).
[83]. E. Dufour, A. Calisti, B. Talin, M. A. Gigosos, M. A. González, J. W. Dufty, “Charge correlation effects in electron broadening of ion emitters in hot and dense plasmas”, J. Quant. Spectrosc. Ra.81, 125-132 (2003).
[84]. E. Dufour, A. Calisti, B. Talin, M. A. Gigosos, M. A. González, T. del Rio Gaztelurrutia, J. W. Dufty, “Charge-charge coupling effects on dipole emitter relaxation within a classical electron-ion plasma description”, Phys. Rev. E71, 066409 (2005).
[85]. M. A. Gigosos, M. A. González, B. Talin, A. Calisti, “Exact expression of the impact broadening operator for hydrogen Stark broadening”, Astron. Astrophys.466, 1189–1196 (2007).
[86]. M. A. Gigosos, M. A. González, “Comment on 'A study of ion-dynamics and correlation effects for spectral line broadening in plasma: K-shell lines'”, J. Quant. Spectrosc. Ra.105, 533-535 (2007). [87]. L. Godbert-Mouret, J. Rosato, H. Capes, Y. Marandet, S. Ferri, M. Koubiti, R. Stamm, M. González, M.
Gigosos, “Zeeman-Stark line shape codes including ion dynamics”, High Energ. Dens. Phys.5, 162-165 (2009).
[88]. J. Torres, J. M. Palomares, M. A. Gigosos, A. Gamero, A. Sola, J. J. A. M. van der Mullen, “An experimental study on the asymmetry and the dip form of the Hbeta line profiles in microwave produced plasmas at atmospheric pressure”, Spectrochim. Acta B63, 939-947 (2008).
[89]. J. M. Palomares, J. Torres, M. A. Gigosos, J. J. A. M. van der Mullen, A. Gamero, A. Sola, “Balmer-b line asymmetry characteristics in a high pressure, microwave-produced argon plasma”, Appl. Spectrosc.
63, 1223-1231 (2009).
[90]. S. Djurović, M. Ćirišan, A. V. Demura, G. V. Demchenko, D. Nikolic, M. A. Gigosos, M. A. González, “Measurements of H-beta Stark central asymmetry and its analysis through standard theory and computer simulations”, Phys. Rev. E79, 046402 (2009).
[91]. J. M. Palomares, J. Torres, M. A. Gigosos, J. J. A. M van der Mullen, A. Gamero, A. Sola, “Experimental characterization of the Hbeta line profiles in microwave-produced plasmas at atmospheric pressure”,
J. Phys. – Conf. Series207, 012013 (2010).
[92]. M. A. Gigosos, M. A. González, “Stark broadening tables for the helium I 447.1 line”, Astron. Astrophys. 503, 293-299 (2009).
[93]. M. Ivkovic, M. A. González, S. Jovicevic, M. A. Gigosos, N. Konjevic, “A simple line shape technique for electron number density diagnostics of helium and helium-seeded plasmas”, Spectrochim. Acta B65, 234-240 (2010).
[94]. R. Zikic, M. A. Gigosos, M. Ivkovic, M. A. González, N. Konjevic, “A program for the evaluation of electron number density from experimental hydrogen Balmer beta line profiles”, Spectrochim. Acta B
57, 987-998 (2002).
ÓPTICA PURA Y APLICAD
[96]. P. Bruggeman, T. Verreycken, M. A. González, J. L. Walsh, M. G. Kong, C. Leys, D.C. Schram, “Optical emission spectroscopy as a diagnostic for plasmas in liquids: opportunities and pitfalls”, J. Phys. D - Appl. Phys.43, 124005 (2009).
1.
Introducción
The Group of Plasma Spectroscopy of Valladolid University was created 30 years ago. Today it is a Recognized Research Group (Grupo de Investigación Reconocido (GIR)) in Valladolid University, with the name of Grupo de Técnicas Ópticas de Diagnóstico (TOD). The main activity of this Group is the development and application of experimental and theoretical techniques of Plasma Diagnostic: Emission Spectroscopy and Laser Spectroscopy.
2.
Research areas in atomic
parameters determination
Advances in atomic structure knowledge in terms of the spectral profiles of the lines emitted by plasma have great importance, not only for theoretical purposes, but also for its impact on industrial plasma diagnostics, fusion or astrophysics. Stark broadening is a widely employed technique for diagnostics as a tool for electron density determination. However, calibration of certain spectral profiles is very difficult. In these cases, the knowledge of the regularities in the sequence of Stark broadening or shift of lines corresponding to the same atomic transition of the homologous series of the atoms involved provides us the indirect determination of the Stark broadening or shift coefficient and, from them, the electron density.
Moreover, the knowledge of transition probabilities has great importance in the diagnostics of any radiation source, as conventional lamps, lasers, industrial and fusion plasmas, or in astrophysics. This circumstance becomes more outstanding in ionized atoms by the lack of experimental data in the bibliography. Transition probabilities can be obtained experimentally with relative simple procedures from the spectral line emission, if excitation temperature is measured in a precise way. However, the determination of the temperature in plasmas shows, as it is well known, big difficulties, especially under conditions of strong self absorption.
One of the most challenging features in study and plasma diagnostic is to get a plasma source with good reproducibility. Measurements obtained from the same or different plasma sources should be comparable to each other. However, when trying to compare spectroscopic data obtained from different plasma sources or experiments, strong discrepancies are observed not easily explained from the error bars provided by the authors. This is a particularly delicate point when the electron temperature is involved. The theoretical models involved in the determination of this parameter are very conditioned by the thermodynamic state of the plasma, which is sometimes difficult or even impossible to be established. When the pursued atomic parameters are not severely influenced by temperature, their determination is not a so serious problem. This is the case of the Stark widths or shifts. Otherwise, when temperature plays a significant role in the atomic parameters determination procedure, this becomes a delicate problem, as in fact happens for atomic transition probabilities.
In the last thirty years, the Spectroscopy Plasmas Group at the University of Valladolid has developed plasma generation and diagnostic techniques which allow an accurate determination of transition probabilities, as well as Stark widths and shifts in plasmas, whose electron densities and temperatures are in the range of 0.2 to 2.0×1023 m-3 and from 16000 to 45000 K respectively. Measurements can be performed with the same plasma source and with such reproducibility levels that the intensity of one spectral line, generated in different discharges under the same experimental conditions, differs in less than 5%. Differences in electron densities measured at the same instant of the plasma life in consecutive pulses are less than 10%.
Wiese and Konjević [1] established three types of regularities or systematic behaviour of Stark parameters: i) regularities within a spectrum, which are either systematic trends along the spectral series of atoms and ions of simple structure or similarities within multiplets, supermultiplets and transition arrays for emitters with a more complex structure; ii) similarities for analogous transitions of homologous atoms and ions; and iii) systematic trends for a fixed transition of ions within an isoelectronic sequence.
In this paper the short overview of the experimental results of Stark halfwidths and shifts and transition probabilities is given. The emphasis is placed on the analysis of analogous spectral line halfwidths of homologous ions along the homologous sequence of singly ionized noble gases. "Analogous" indicates the same type of transition with only the principal quantum number changed, while "homologous" indicates ions with the same electric charge and similar energy levels structure in the outer shells. Due to these similarities, a gradual increase of the spectral line halfwidths i.e. systematic trends should be expected.
2.1. Experimental setup
All measurements have been made from the plasma produced in a pulsed discharge lamp. The experimental arrangement is shown in Fig. 1. Experimental apparatus and plasma diagnostics are described elsewhere [2,3]. Only a short description of the experiment and data treatment will be given here.
The excitation unit contains a capacitor bank of 20 μF charged up to approximately 9 kV. The mixture of helium, as a working gas, and several percents of the analysed gas at a pressure of about 3 kPa continuously flows through the discharge lamp. The lamp is a cylindrical tube of Pyrex glass, 175 mm in length and 19 mm in internal diameter.
The percentage of the analysed gas mixed with the helium was adjusted to get sufficiently high spectral line intensities and at the same time have minimal or null self-absorption effect. The self-absorption was checked by means of a mirror placed behind the discharge lamp. Spectra were recorded with a spectrometer
equipped with an optical multichannel analyzer (OMA) detector and later with an intensified charge-coupled device (ICCD).
The spectrometer’s instrumental function was estimated by introducing a laser beam (632.85 nm) into its entrance slit. The halfwidth of this line, approximately 12.5 pm (4.1 pm/channel) for the OMA and 7 pm (2.3 pm/channel) for the ICCD, was taken into account as the instrumental broadening. An incandescent calibrated lamp and a deuterium lamp were used to obtain the spectrometer’s transmittance.
A two wavelengths interferometric method was used for the electron density determination. The electron density was in the range of (0.2-2.0)×1023 m−3 with an estimated experimental
uncertainty of about 10%. To verify these results, the profile of the He I 388.86 nm line in conjunction with Griem’s theoretical model [4] was used, in most cases. The electron temperature was determined by a Boltzmann-plot of appropriate spectral lines and was in the range of (16000 − 45000) K for all experiments. The estimated uncertainties were about 15%.
The experimental data treatment is explained in detail in our previous work [3]. A fitting procedure [5] was applied to the experimentally obtained spectrum to determine the total line halfwidth, the central position and the area of each spectral line profile. In order to obtain the Stark halfwidth from the total experimental halfwidth of the spectral line, a standard deconvolution procedure was employed [6]. Other broadening mechanisms, like Doppler and instrumental broadening were taken into account, while on the other hand van der Waals and resonance broadening were negligible for the plasma conditions in these experiments. 2.2. Results
In Table I the references concerning to the publications performed by the group for different atomic parameters and elements during the last years have been included [7-48].
ÓPTICA PURA Y APLICADA. www.sedoptica.es
Fig. 1. Experimental arrangement.
Stark regularities. In this field two works are worthy to mention here. First, the good repeatability of the plasma source employed has allowed, for instance, to evaluate and compare spectral profiles of different lines belonging to the transition (3P)3p(4Po)-(3P)3d(4D) in Ne II [43], and this has allowed to obtain levels of intramultiplet Stark regularity below the theoretical predictions. In Fig. 2 the measured lines are shown once normalised in area. Second, the great number of measured Stark halfwidths along the homologous sequence of singly ionised noble gases has allowed to analyse the experimental Stark halfwidth behaviour for the (3P)ns−(3P)np and (3P)np−(3P)nd transitions along this homologous series [47]. These results are shown in Figs. 3 and 4. It is obvious from these figures that Stark halfwidth regularities do exist. At the same time there is a significant dispersion of the experimental data. We showed that even dispersed experimental halfwidth results follow the regular behaviour for
multiplets, supermultiplets or transition arrays as established by Wiese & Konjević [1].
TABLE I
Publications performed by the group for different atomic parameters and elements
Element Stark Widths Stark
Shifts Probabilities Tr. H [7,8,9,11]
He [13,16-18,34,35,37] [34,36,37]
Ne [22,26,43,47] [22,43] [27,30] Ar [20,21,47] [20,21] [19] Kr [32,42,44,47] [32,42,44] [29,39] Xe [5,3,38,41,45,46,47] [5, 40, 45] [5]
S [10]
F [10]
Si [12,15,28,33] [28,33]
C [14]
O [23] [31]
Fig. 2. Experimental profiles of Ne II lines belonging to the multiplet (3P)3p(4Po)-(3P)3d(4D), normalized in area.
Fig. 3. Evolution of the Stark halfwidths for different homologous multiplets of the (3P)ns − (3P)np transition. The linear fit of experimental results is presented by a full line and the MSE calculations [48] by a dotted line.
Fig. 4. Evolution of the Stark halfwidth for different homologous multiplets in the (3P)np − (3P)nd transition. The linear fit of experimental results is presented by a full line and the MSE calculations [48] by a dotted line.
3.
Research areas in laser
spectroscopy
The main goal of experimental plasma physics is to obtain a complete characterisation of the plasma state; this means the determination of plasma parameters such as particle density, electric field strength, temperatures etc... This task becomes quite difficult when the plasma is far off the thermodynamic equilibrium, which is nevertheless the case of numerous plasmas of laboratory and technological interest [49,50]. Those plasmas are typically characterized by high electron excitation temperature and low kinetic temperatures of neutrals and ions. The dynamic of these discharges, which includes collisional phenomena, radiative emission, recombination in the presence of electromagnetic fields…, is rather complex and not always well understood. For this reason, many techniques have been developed for plasma diagnostic, among these techniques non intrusive methods, like laser spectroscopy, are preferred, see [51,52] and references therein. One of the advantages of using laser spectroscopy is to perform measurements of high temporal and spatial resolution. This kind of experimental work requires pulsed UV laser radiation of sufficient peak power and single longitudinal mode (SLM).
In our laboratory we have established a high precision two-photon polarization spectroscopy technique, this is a powerful tool for plasma diagnostic; it allows determining atomic ground densities, kinetic temperatures, electric field strength, electron densities etc....As hydrogen plays an important role in technological processes, this technique has been specially worked out for the 1S-2S transition of atomic hydrogen or deuterium.
The schematic set-up for measuring two-photon absorption by polarization spectroscopy is shown Fig. 5. A circularly polarized pump beam of high irradiance is focused into the investigated medium, where it overlaps with a weak linearly polarized signal beam. The signal beam experiences the two-photon resonant optical anisotropy induced in the medium by the circularly polarized pump beam. As a consequence, the linear polarization of the signal beam is rotated by the dispersion part and 2 3 4 5 6 7 8 9 10 11 12 ω (1 0 s ) -1 11
Ne II Ar II Kr II Xe II
2P-2Do 2P-2Po 2P-2So
4P-4Po 4P-4So 4P-4Do
de l V al e t a l. [2 6] Pel aez et a l. [4 3] de l V al e t a l. [2 6] Pel aez et a l. [4 3] A pa ric io e t a l. [ 20 ] A pa ric io e t a l. [ 20 ] de C as tro e t a l. [ 32] de C as tro e t a l. [ 32] D jur ovi c e t a l. [ 44 ] G igos os e t a l. [ 5] D jur ovi c e t a l. [ 3] G igos os e t a l. [ 5] D jur ovi c e t a l. [ 3] ' ' ' ' 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Ne II Ar II Kr II Xe II
de l V al e t a l. [2 6] Pel aez et a l. [4 3] A pa ric io e t a l. [ 20 ] de C as tro e t a l. [ 32] D jur oc ic e t a l. [ 44] G igos os e t a l. [ 5] D jur ovi c e t a l. [ 3]
-4Do 4F
-4Do 4D 4Po-4D
4So-4F 4So-4P
ÓPTICA PURA Y APLICAD
becomes slightly elliptic by the absorption part. The polarization change can most sensitively be detected behind a analyzer set at a right angle with respect to the original polarization direction [53, 54].
The signal irradiance behind the analyzer, Es,
is found to be for weak absorption and for the 1S-2S transition, with no angular moment transfer (ΔL=0) [55]:
( ) P
( )
Rh l E N E
E
p p
R
S ∆ +
〈 〉
= ν
ν σ
2 2
4
1 , (1)
here, N is the number density of the absorbing species, 〈Epl〉 is a suitably defined mean value for the product of the pump irradiance EP and
the length l of the overlap volume including the correlation function g(2). R denotes the residual transmittance of the crossed polarizers, i.e. ES/ER
as measured without pump beam. The polarization line shape function P(Δν) is given by the sum of the squares of the absorption line shape and the related dispersion as well, both are connected by the Kramers-Kronig relation. Where Δν = νs+νp-ν0, is the frequency difference between the sum of the laser-frequencies νs+ νp
(of the signal and pump beam), and the resonance frequency ν0. The signal is not affected by background radiation and/or quenching; and can be applied therefore without limitation at elevated pressures. In the case of counter-propagating beams, like in Fig. 5, the first order Doppler shift cancels and there is no Doppler-broadened background at all, because only absorption of one photon from each beam causes the signal. Additionally, collinear beams allow to measure Doppler broadened profiles, hence the determination of kinetic temperatures.
Fig. 5. Schematic set-up of two-photon polarization spectroscopy.
3a. Absolute density and two-photon cross section determination
For the determination of absolute number densities using Eq. (1), the value of 〈Epl〉 and the atomic cross section σ(2) had to be known. Even if σ(2) is available as in the case of hydrogen,
〉
〈Epl still depends on a number of parameters,
which can hardly be measured, i.e. the spectral, spatial and temporal irradiance distribution of both laser beams in the measurement volume. Therefore, direct use of the Eq. (1) does not give precise determination of the atomic number density. However, if 〈Epl〉 can be kept constant with sufficient long term stability, high accuracy can be reached by comparing measurements in the studied medium with a two-photon absorption standard. Such a standard is given by an absolute known two-photon absorption cross section and a well defined number density. In reference [55] the non-resonant two-photon polarization signal of xenon gas at room temperature, at the wavelength of the hydrogen transition, was chosen as an easy and reliable calibration reference, i.e. for the determination of absolute hydrogen densities. We have demonstrated that this technique is working well in different hydrogen media: arc plasmas (10 kPa) [55], flames at atmospheric pressure [56], and hollow cathode discharges (HCD) [57,58]. The uncertainty in all of these measurements is about 10%. The same standard can be applied to the determination of two-photon absorption cross section to other elements in different media of known number density. Now, we are applying this technique to the Xe transition: 5p61S0-5p56p[1/2]0 [59]. 3b. Local electric field strength
determination
in a plasma, far off the thermodynamic equilibrium, generated in a HCD operated either H or D in a wide range of plasma parameters: currents from 50 to 200 mA, pressures from 270 to 1350 Pa, and different cathode diameters [60-62]. The determination of the local E-field is based on measurements of the Stark spectrum of the 1S-2S transition of the hydrogen isotopes and the comparison of the measured frequency shift of the Stark components with the calculated ones [63]. For measuring the Stark splitting of the 2S level we have used two different laser spectroscopic methods. The first one is the above mentioned two-photon polarization spectroscopy, and the second one is based on two-photon excitation follows by optogalvanic detection, in this way we have been able to compare the accuracy of both methods. However, the optogalvanic signal created in our case is somehow different compared to optogalvanic signals measured in saturation spectroscopy. The irradiance, up to 1 GW/cm2, in the excitation region of the laser beams provides, in a first step, the two-photon excitation and the absorption of a third laser photon results in subsequent photo ionization. Hence, the charged particles created in the overlap volume of the laser beams are accelerated by the E-field and the corresponding variation of the discharge impedance can be measured. The high spatial resolution in the experiment is given by the overlap volume of the two laser beams, i.e. 200 µm. We plan to improve the detection sensitivity by at least one order of magnitude, using Doppler-free two-photon optogalvanic spectroscopy applied to the 1S - 3S/3D transition of hydrogen isotopes instead of the 1S-2S transition.
3c. Temperature determination
As already mentioned in the principle of two-photon polarization spectroscopy, the pump beam direction can be chosen either collinear or counter-propagating with respect to the signal beam, allowing measurements of Doppler-broadened and Doppler-free profiles. The deconvolution of the Doppler-free from the Doppler-broadened spectra yields the kinetic temperature of the hydrogen atoms. The temperature in the hydrogen flame was determined with an uncertainty about 10% [56].
We have also obtained the kinetic temperature distribution in the HCD operated with atomic hydrogen using optogalvanic spectroscopy [64]. 3d. UV-laser spectrometers
All of these measurements require tuneable UV-laser spectrometers, providing sufficient pulse energy with a very narrow spectral bandwidth, good pulse to pulse reproducibility and scan linearity. Because commercial laser systems can not provide such a radiation, we started more than one decade ago to develop advanced pulsed SLM UV-laser spectrometers, especially suited for laser-aided plasma diagnostic [65,66].
ÓPTICA PURA Y APLICAD
Tuneable laser radiation at 205 nm, which is required for the 1S-3S/3D two photon transition of atomic hydrogen is provided by a similar modular concept as the laser at 243 nm. The 205 nm radiation is generated by a Nd:YAG laser (Continuum, Powerlite 9000), a seeded KTP-OPO, two Ti:sapphire amplifiers, and by stepwise SFG via Second Harmonic Generation (SHG), Third Harmonic Generation (THG) and Four Harmonic Generation (FHG) using BBO-crystals. The short resonator consists of a KTP crystal placed in a plane mirror optical cavity, pumped by the second harmonic of the Nd:YAG laser. SLM pulsed operation is achieved by seeding with a tuneable external cavity cw diode laser. The special feature of the OPO is its linearity frequency tuning performed by changing the cavity length in a controlled way: one resonator mirror is mounted on a translator stage with nanometer precision, and the diode laser is frequency locked to one cavity mode. The pulse energy of the OPO output at 820 nm is about 1 mJ, and tuneable over a range of about 50 GHz. The OPO pulse is amplified in two Ti:sapphire crystals pumped also by the second harmonic of the Nd:YAG laser. The first Ti:sapphire crystal provides six pass amplification while the second crystal serves as two pass amplifier, generating pulse energies of about 60 mJ. Finally, in order to obtain the best conversion efficiency, the amplified 820 nm radiation is converted into the UV by stepwise SHG, THG and FHG using three BBO crystals. The radiation at 205 nm has up to 5 mJ pulse energy in about 4 ns and a spectral bandwidth around 300 MHz. In addition to the high pulse energy and the narrow bandwidth, the system provides good pulse-to pulse reproducibility and excellent scan linearity.
4.
Research area in line broadening
calculations
The experimental activities are complemented with the theoretical calculations and with the development of techniques for experimental data processing. The research group dedicates an especial effort to the calculation of the shapes of spectral lines in order to elaborate tables of line profiles to be used in plasma diagnostics. This line of work is kept since 30 years ago.
Nowadays the most important part of the calculation of line profiles is done using computer simulation techniques.
using the He I 447.1 nm line [92,93]. Our results have been included in some computer applications [94] to ease the plasma diagnostic and are widely used by different laboratories [95,96].
As has been mentioned before, the group works usually with researchers from other groups, both Spanish and foreigners. Currently we keep contact with the two only european groups working on plasma simulation applied to the calculation of line profiles. With the group from the University of Provence in Marseille, pioneer in this field, we have usual exchanges of researchers from Marseille in Valladolid and vice versa. The group, besides, has been working for several years in the study of line shapes with professors from Belgrade, Novi Sad and Moscow. Between the Spanish collaborations, it must emphasized the work with the group of research in plasmas at the University of Córdoba, that has used the results of our simulations to do plasma diagnostics in some of their works.
The group has currently a cluster of computers (294 CPUs) with which computer simulation calculations that would require a large supercomputation facility can be carried out. These equipments have been financed both with national and regional grants along the last 13 years.
Acknowledgements
