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

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92 5 Discussion of the Experimental Results 60 50 Normalized intensity 1.0 0.5 200°C Gaussian fit 2σ σ / Pixel 40 0.0 -100 0 100 Position / Pixel 30 20 150 200 250 300 T Cell / °C Fig. 5.2: Temperature dependence of the trapping volume: The confinement of the trapped radiation upon the increase of the number density is clearly visible for temperatures >160 ◦ C. The inset shows a cross section through one corresponding radial profile and a Gaussian fit to the data. The dashed line is a cubic spline fit and underlines the confinement. Please note that the presented measurement estimates the radial profile by imaging the energy-pooling fluorescence of the vapor cell. The surrounding oven did not allow a perpendicular access, so that the fitted profile widths σ can only be compared relative to each other. circles mark the measured full width half maximum of an arbitrary cross section through the imaged fluorescence and the dashed line a cubic spline fit through these points. The shrinking of the trapping volume, when increasing the cell temperatures beyond 160 ◦ C, is clearly apparent. The employed technique gives only a rough estimate of the absolute diameter, however the values can be compared relatively, which proves that the confinement of the trapped radiation has to be taken into account for temperatures beyond 160 ◦ C. For the sake of completeness, it has to be mentioned that for pump intensities, which exceed the saturation intensity of the vapor by orders of magnitude, nonlinear radiation trapping effects appear. Stacewicz et al. and Scholz et al. performed extensive measurements on this topic [172–174]. By exciting sodium vapor with laser pulses of several kW/cm 2 in intensity, they have been able to demonstrate the saturation of the vapor far beyond the pumped volume. The fact that subnatural decays, i.e. decays faster than the natural lifetime of the excited atoms, result from the nonlinearity of these high pumped vapors, is striking. However, the available intensities of the employed cw pump laser do not reach values to observe this effect.
5.1 Overview of the Experimental Parameters 93 2. The energy pooling quenching rate: The energy pooling√ quenching rate depends on the mean velocity of the Rb atoms, v RMS = 3kB T m Rb , which itself has a square root dependency on the local vapor temperature. However, the small cross section of this process, σ EP 5P 3/2 ↔5D = 3×10-14 cm 2 [140], will only extract a minor amount of Rb atoms from the 5P 3/2 state (cf. Sec. 3.6.2). √ 2 ln2 kB T 3. The Doppler width: The Doppler width, ν D = 2ν , is also proportional to the square root of the local vapor temperature and affects the width of mc 2 the ESFADOF spectra directly. However, the exponential increase of the Rb vapor density covers this effect as long as the vapor remains saturated. 5.1.2 Pump Geometry Besides the vapor cell temperature, the choice of the implemented pump geometry has the strongest effect on the ESFADOF transmission spectrum and offers some distinct control parameters, such as the pump laser intensity, its detuning from the D2 line center, its spectral width and its polarization. These parameters allow to tailor the ESFADOF spectra within certain limits as they directly influence the population of the lower ESFADOF state: 1. The pump intensity: The amount of excited state atoms is directly influenced by the pump intensity. Saturating the vapor is advantageous in order to obtain the maximum ESFADOF transmission. In addition, as the energy-pooling quenching rate is proportional to the square of the excited state population (cf. Sec. 3.6.2), increasing the 5P 3/2 population also increases the losses. However, this loss channel saturates also with the saturation of the vapor. A quite more advantageous effect when increasing the pump intensity emerges from the imprisonment of the pump radiation within the vapor cell (cf. Sec. 3.6.3). Trapped photons can undergo a high number of absorption and reemission cycles within the highly opaque vapor before they eventually reach the initially pumped region again or escape from the vapor cell [139]. Meanwhile they experience a significant change in frequency and polarization [138, 139, 175]. These photons can be absorbed again by atoms within the initially pumped region and hence populate excited states, whose spectral overlap with the initial pump laser almost vanishes. This effect is of particular importance, as the confinement of the trapped radiation reinjects a significant amount of the trapped radiation back into the interaction volume. Hence, this effect can be regarded as an advantage and Sec. 5.2.2 further elaborates on this discussion. 2. The detuning of the pump laser: The spectral overlap between the pump laser and the 5S 1/2 → 5P 3/2 pump transition influences the amount of absorbed radiation. Due to the spectrally narrow laser source, this additional degree of freedom potentially offers the possibility to tailor the ESFADOF spectral characteristics to some extent. However, it can not be uncoupled from radiation trapping effects and the inhomogeneous magnetic fields. Its influence will be examined in Sec. 5.2.3.
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INSTITUT FÜR ANGEWANDTE PHYSIK TEC
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Abstract Global and local climate c
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Pentru Alexandru şi Florina
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II Contents 4.3 Measurement Unit .
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2 1 Introduction wide sea currents
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2 Remote Sensing of the Water Colum
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2.1 Measurement Principle 7 highly
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2.1 Measurement Principle 9 Fry and
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2.2 System Requirements 11 operatin
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2.2 System Requirements 13
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2.2 System Requirements 15 Table 2.
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2.2 System Requirements 17 1. Rayle
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2.2 System Requirements 19 wave. Th
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2.2 System Requirements 21 cent pro
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2.2 System Requirements 23 Fig. 2.6
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2.2 System Requirements 25 Both the
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2.3 Ideal Edge-Filter 27 of the Bri
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2.3 Ideal Edge-Filter 29 respective
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32 3 (Excited State) Faraday Anomal
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6 Conclusion and Outlook 143
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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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