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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 Optical autocorrelation ： ウィキペディア英語版 Optical autocorrelation In optics, various autocorrelation functions can be experimentally realized. The field autocorrelation may be used to calculate the spectrum of a source of light, while the intensity autocorrelation and the interferometric autocorrelation are commonly used to ''estimate'' the duration of ultrashort pulses produced by modelocked lasers. The laser pulse duration cannot be easily measured by optoelectronic methods, since the response time of photodiodes and oscilloscopes are at best of the order of 200 femtoseconds, yet laser pulses can be made as short as a few femtoseconds. In the following examples, the autocorrelation signal is generated by the nonlinear process of second-harmonic generation (SHG). Other techniques based on two-photon absorption may also be used in autocorrelation measurements,〔Roth, J. M., Murphy, T. E. & Xu, C. ''Ultrasensitive and high-dynamic-range two-photon absorption in a GaAs photomultiplier tube'', Opt. Lett. 27, 2076–2078 (2002).〕 as well as higher-order nonlinear optical processes such as third-harmonic generation, in which case the mathematical expressions of the signal will be slightly modified, but the basic interpretation of an autocorrelation trace remains the same. A detailed discussion on interferometric autocorrelation is given in several well-known textbooks.〔J. C. Diels and W. Rudolph, ''Ultrashort Laser Pulse Phenomena'', 2nd Ed. (Academic, 2006).〕〔W. Demtröder, ''Laserspektroskopie: Grundlagen und Techniken'', 5th Ed. (Springer, 2007).〕 ==Field autocorrelation== For a complex electric field $E(t)$, the field autocorrelation function is defined by : $A(\backslash tau)\; =\; \backslash int\_^E(t)E^$ *(t-\tau)dt The Wiener-Khinchin theorem states that the Fourier transform of the field autocorrelation is the spectrum of $E(t)$, i.e., the square of the ''magnitude'' of the Fourier transform of $E(t)$. As a result, the field autocorrelation is not sensitive to the spectral ''phase''. The field autocorrelation is readily measured experimentally by placing a slow detector at the output of a Michelson interferometer. The detector is illuminated by the input electric field $E(t)$ coming from one arm, and by the delayed replica $E(t-\backslash tau)$ from the other arm. If the time response of the detector is much larger than the time duration of the signal $E(t)$, or if the recorded signal is integrated, the detector measures the intensity $I\_M$ as the delay $\backslash tau$ is scanned: : $I\_M(\backslash tau)\; =\; \backslash int\_^|E(t)+E(t-\backslash tau)|^2dt$ Expanding $I\_M(\backslash tau)$ reveals that one of the terms is $A(\backslash tau)$, proving that a Michelson interferometer can be used to measure the field autocorrelation, or the spectrum of $E(t)$ (and only the spectrum). This principle is the basis for Fourier transform spectroscopy. 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「Optical autocorrelation」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.