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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Saturated absorption spectroscopy ： ウィキペディア英語版 Saturated absorption spectroscopy In experimental atomic physics, saturated absorption spectroscopy or Doppler-free spectroscopy is a set-up that enables the precise determination of the transition frequency of an atom between its ground state and an optically excited state. The accuracy to which these frequencies can be determined is, ideally, limited only by the width of the excited state, which is the inverse of the lifetime of this state. However, the samples of atomic gas that are used for that purpose are generally at room temperature, where the measured frequency distribution is highly broadened due to the Doppler effect. Saturated absorption spectroscopy allows precise spectroscopy of the atomic levels without having to cool the sample down to temperatures at which the Doppler broadening is no longer relevant (which would be on the order of a few millikelvins). It is also used to lock the frequency of a laser to the precise wavelength of an atomic transmission in atomic physics experiments. ==Doppler broadening of the absorption spectrum of an atom== (詳細はelectromagnetic field, the absorption of light by the atom depends on the frequency of the incident photons. More precisely, the absorption is characterized by a Lorentzian of width Γ/2 (for reference, Γ≈2π×6 MHz for common Rubidium D-line transitions〔(【引用サイトリンク】title=Alkali D line Data )〕). If we have a cell of atomic vapour at room temperature, then the distribution of velocity will follow a Maxwell–Boltzmann distribution :$n(v)\; dv=\; N\; \backslash sqrt\}e^\}\; dv,$ where $N$ is the number of atoms, $k\_B$ is the Boltzmann constant, and $m$ is the mass of the atom. According to the Doppler effect formula in the case of non-relativistic speeds, :$\backslash omega\_=\backslash omega\_0\backslash left(1\backslash pm\backslash frac\backslash right),$ where $\backslash omega\_0$ is the frequency of the atomic transition when the atom is at rest (the one which is being probed). The value of $v$ as a function of $\backslash omega\_0$ and $\backslash omega\_$ can be inserted in the distribution of velocities. The distribution of absorption as a function of the pulsation will therefore be proportional to a Gaussian with full width at half maximum :$\backslash Delta\backslash omega\_\; =\; \backslash omega\_0\; \backslash sqrt\}$ For a Rubidium atom at room temperature, :$\backslash Delta\backslash omega\_\backslash approx\; 2\backslash pi\backslash cdot\; 500\; \backslash mbox\backslash gg\backslash Gamma/2\backslash approx\; 2\backslash pi\backslash cdot\; 3\; \backslash mbox$ Therefore, without any special trick in the experimental setup probing the maximum of absorption of an atomic vapour, the uncertainty of the measurement will be limited by the Doppler broadening and not by the fundamental width of the resonance. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Saturated absorption spectroscopy」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.