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A new method to measure true twophotoncorrelation of soft Xray synchrotronradiation
https://ir.soken.ac.jp/records/1287
https://ir.soken.ac.jp/records/1287b8d55cbde4fb4329a3fd3d4a0710465a
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要旨・審査要旨 / Abstract, Screening Result (292.4 kB)


本文 (4.5 MB)

Item type  学位論文 / Thesis or Dissertation(1)  

公開日  20100222  
タイトル  
タイトル  A new method to measure true twophotoncorrelation of soft Xray synchrotronradiation  
タイトル  
タイトル  A new method to measure true twophotoncorrelation of soft Xray synchrotronradiation  
言語  en  
言語  
言語  eng  
資源タイプ  
資源タイプ識別子  http://purl.org/coar/resource_type/c_46ec  
資源タイプ  thesis  
著者名 
〓, 仁忠
× 〓, 仁忠 

フリガナ 
タイ, レンズン
× タイ, レンズン 

著者 
TAI, Renzhong
× TAI, Renzhong 

学位授与機関  
学位授与機関名  総合研究大学院大学  
学位名  
学位名  博士（理学）  
学位記番号  
内容記述タイプ  Other  
内容記述  総研大甲第371号  
研究科  
値  数物科学研究科  
専攻  
値  X1 放射光科学専攻  
学位授与年月日  
学位授与年月日  19990324  
学位授与年度  
値  1998  
要旨  
内容記述タイプ  Other  
内容記述  Twophoton correlation measurement provides a promising way to experimentally demonstrate the statistical nature of a light source, which is very significant for the deep understanding of the photongenerating process and the diagnosing of the coherence property. Quantitatively two photon correlation is described by secondorder coherence. Usually the behavior of the secondorder coherence against any of the parameters <br />defining the phase volume is different for different photon statistics. The Poisson photon statistics for coherent light gives its secondorder coherence as a flat response; The BoseEinstein photon statistics for chaotic light gives its secondorder coherence as a bunching effect; While the SubPoisson photon statistics for nonclassical light gives its secondorder coherence as an antibunching effect. Therefore the measurement of twophoton correlation is proved to be a good finger print to check whether light is in coherent state or incoherent state such as thermal state or nonclassical state.<br />Historically the measurement of twophoton correlation was first performed by HanburyBrown and Twiss (HBT) in 1956. They used a linear mixer to realize the correlation of the two currents from the photoelectric detectors illuminated by a stationary thermal light souece, a mercury arc, and the photobunching effect was first successfully observed in the visible region of 435.8 nm.<br />HBT method is no doubt a good way to extract the small excess twophoton correlation for a stationary light because the background, that is the DC components, has been cut off automatically by the broad band amplifiers, which is in fact the key of the success of HBT experiment. However there exists a general problem, to which no attention has ever been paid, in measuring the twophoton correlation of nonstationary light such as synchrotron radiation (SR) by the HBT method. Here the "nonstationary" means a sense of classical mechanics that the observed intensity has some deterministic time structure. The systematic time structure of SR decided by the bunch distribution of the electric current in a storage ring will give rise to a large amount of unexpected accidental correlation, which in fact has nothing to do with the inherent photon statistics of light source and usually l000～l0000 times larger than the true twophoton correlation due to the short bunch separation length (2ns) and the short coherence time (～0.1ps) which is not comparable to the time resolution (1ns) of the measuring system. The existence of the accidental correlation would severely prevent us from observing the bunching effect of the true twophoton correlation.<br />Therefore to suppress the much larger accidental correlation and to extract the small true twophoton correlation, a novel intensity interferometer has been developed for soft Xray synchrotron radiation. This intensity interferometer consists of an optical vacuum chamber and an electric correlator. All the essential optical elements which includes a wire scanner, a precise diffraction slit, a grating monochromator with a coherence time modulator, a beam divider and two fastresponse photon detectors (microchannel plates) are mounted in this high vacuum chamber. The electric correlator completes the multiplication of the two broad band electric currents coming from the photoelectric detectors. The basic idea to suppress the much larger accidental correlation is to modulate the coherence time by modulating the entrance slit width of the monochromator by a piezoclectric translator. The two sets of light intensity are simultaneously modulated too. When the frequency of modulation is f, the third harmonics 3f is detected with a lochin amplifier because the 3f components include only the true twophoton correlation. Practically it is difficult to modulate with frequency f without any higher order harmonics distortion which might add some false 3f components. To overcome this difficulty we have used a sharp bandpass filter of l00～350 MHz in each branch of the correlator, which is lower than the RF frequency 500 MHz and much higher than 1.6 MHz, the revolution frequency of the stored beam of the 2.5 GeV storage ring.<br />This new apparatus has been operated successfully in the measurement of the horizontal twophoton correlation for the first harmonic of undulator radiation with photon energy of 70 eV at the Photon Factory, KEK. By narrowing the precise slit width which correspondingly changes the spatial coherence of the incident SR, a bunching effect of the normalized excess twophoton correlation has been clearly observed. This explicit bunching effect implies that synchrotron radiation is chaotic radiation.<br />Further investigation shows that although secondorder coherence is completely determined by the firstorder coherence for the case of chaotic light, the measured information from the light source is essentially different. The twophoton correlation of synchrotron radiation does not depend on the response time of the detectors but gives the information of instantaneous emittance of the stored beam with the time scale of coherence time τC. By fitting the experimental data, the horizontal instantaneous emittance of the stored beam is estimated to be 40nmrad.<br />This intensity interferometer can be utilized to characterize the coherence properties of incomplete FELs, such as SASE, because if they are fully coherent light sources the normalized excess twophoton correlation would have a flat response, but not showing a photonbunching effect.  
所蔵  
値  有  
フォーマット  
内容記述タイプ  Other  
内容記述  application/pdf 