Assessment of a Rubidium ESFADOF Edge-Filter as ... - tuprints

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32 3 (Excited State) Faraday Anomalous Dispersion Optical Filters Fig. 3.1: Schematic drawing of an ESFADOF together with the relevant Rubidium transitions; with kind permission from Springer Science+Business Media [93]: P and A denote crossed polarizers, B an homogeneous magnetic field and the pump radiation is injected with the help of an dichroic mirror. The polarization vector experiences a rotation of its direction, when passed through the atomic vapor, due to the fact that its circular polarized components, E ± , are subject to different dispersions near the absorption lines of the atomic vapor, which itself is influenced by the magnetic field. The pump radiation populates the lower ESFADOF level, here the 5P 3/2 level, such that the ESFADOF transition 5P 3/2 → 8D 5/2 becomes accessible. In contrast, ground state FADOFs do not need this additional pump radiation. As long as transitions emerging from the ground state are accessible to the probing light, proper FADOF operation can be guaranteed. by an additional laser source. The inset of Fig. 3.1 summarizes the relevant Rubidium transitions, upon which the experimental realization of the ESFADOF device relies. The implemented ESFADOF operates on the Rb 5P 3/2 → 8D 5/2 transition (543.30 nm), while being optically pumped on the Rb D 2 transition 5S 1/2 → 5P 3/2 (780.2405 nm). This choice has several advantages: (1) The ESFADOF transition wavelength is close to the absorption minimum of water [18]. (2) Radiation at this wavelength can be generated by second harmonic generation of the output of a compact Yb–doped fiber amplifier [54, 59]. (3) The lower ESFADOF-state 5P 3/2 can be optically pumped on the 5S 1/2 → 5P 3/2 transition by very efficient and robust semiconductor devices [94–100], making the employment of highly sophisticated solid state or dye lasers obsolete. The presentation of the experimental setup as well as a thorough discussion of the obtained results are the subject of the following chapters, where the current chapter focuses on the underlying physics of FADOFs and ESFADOFs.
3.1 Historical Overview 33 3.1 Historical Overview The following historical overview is intended to give a brief insight on the broad research field, concerning dispersive magnetic filters and their potential applications. It is not intended to be exhaustive and the author regrets having omitted any other important contribution. The first observation of the enhancement of the Faraday–effect close to absorption lines was made by Macaluso and Corbino in 1898. They detected the magnetic rotation in the Sodium D-lines [101]. Later on, Wood discovered a similar effect in the band spectrum of Na 2 [102]. However, over 50 years later, Öhman implemented and explored a first experimental realization of a FADOF device in 1956 [103]. He modestly entitles his pioneering works “A tentative monochromator for solar work based on the principle of selective magnetic rotation” [103], though it offers all the mentioned components which are essential for a FADOF: The atomic vapor cell placed in a homogeneous magnetic field and between two crossed polarizers. He demonstrated the working principle on the Sodium D-Lines in employing Sodium vapor and Sodium–flames inside the vapor cell. However, due to limitations concerning the optical quality of his setup, he was not able to operate his setup inside a telescope for solar observations, though he demonstrated the monochromatic band pass capabilities of this filter by imaging sunlight. It is obvious, that due to the lack of an appropriate narrow light source (Maiman invented the laser some years later in 1960 [104]), he was not able to record the spectral transmission characteristics of his device. Nevertheless, he was aware of the importance of this technique for astrophysics as a narrow bandpass filter. He stressed, the possibility of an enhanced investigation of the Hydrogen H α line in employing his apparatus. In addition, he also emphasized the importance of the quality of the employed polarizers for the achievable contrast. However, successive works of Cacciani et al. implemented the proposals of Öhman in 1968 and succeeded in investigating the solar emission spectrum with spectral narrow bandpass filters based on the Faraday–effect and circular dichroism [105]. These instruments are known as Magneto Optical Filter (MOF) within the astrophysical community and have been predominantly used in investigating solar oscillations through the Doppler–shift of selected atomic emission lines (cf. e.g. Ref. [106] and references therein). Roberts et al. investigated the Faraday effect and magnetic circular dichroism in atomic bismuth about 25 years later [107]. They implemented the first experimental setup, which allowed the measurement of the transmission spectrum of their implemented FADOF on a sub-GHz frequency scale. In addition, their publication presents a first theoretical description, which fits the presented data. Yeh published in 1981 a theoretical treatment of these dispersive magneto–optic filters, which is based on the fine–structure of the atomic Hamiltonian [108] and Chen et al. performed subsequent measurements on the Caesium D 2 transition line in 1987 [109]. The nomenclature Faraday Anomalous Dispersion Optical Filter with the acronym FADOF, which nowadays generally describes these kind
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6 Conclusion and Outlook The presen
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Appendix
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148 A Rubidium Atom 2. Relevant ato
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B Manufacturing process of Rb Vapor
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B Manufacturing process of Rb Vapor
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C Magnetic Field Strengths of the E
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D Tripod ECDL Fig. D.1: Schematic o
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160 References [10] G.L. Mellor and
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162 References [41] E.S. Fry, J. Ka
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164 References [69] Claude C. Leroy
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166 References [97] L. Goldberg, D.
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168 References [125] Cord Fricke-Be
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170 References [158] Triad Technolo
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172 References [186] M. Cheret, L.
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Curriculum Vitae Alexandru Lucian P
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178 1 Publications Conference Proce
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Supervised Theses Denise Stang, Wei
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184 1 Danksagung Bei Herrn Arno Wei
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