氦狹窄共振線的光譜分析和鹼土族原子在直流電場下的反應; Spectral Analysis of Narrow Resonance and Responses of Alkaline-earth Atoms in DC Electric Field

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/43847

Title:	氦狹窄共振線的光譜分析和鹼土族原子在直流電場下的反應;Spectral Analysis of Narrow Resonance and Responses of Alkaline-earth Atoms in DC Electric Field
Authors:	羅仁佑;Jen-Iu Lo
Contributors:	物理研究所
Keywords:	都卜勒效應;壓力效應;光吸放;光游離;吏塔克效應;穿隧效應;column density effect;Fano;autoionization;Ryd自游離
Date:	2010-06-22
Issue Date:	2010-12-08 14:22:55 (UTC+8)
Publisher:	國立中央大學
Abstract:	對那些在解析度不夠的條件下被量得的狹窄共振線而言，除了原本熟知因解析度不夠所造成的問題外，還存在一個稱之為 column density 的效應。這個效應源自於處理實驗數據的式子無法正確的解釋所量得訊息 ; 因為處理數據式子是依據於實驗的方法而來，所以不同的實驗方法所得到的光譜將會不同。為了了解 column density effect 的影響，我們選擇了氦的這兩共振線 --- $(2,1_3)$ 和 $(2,1_4)$ --- 作為研究的對象。然而，因為這兩共振線的線寬都小於都卜勒效應所造成的線寬變化，因此都卜勒的效應必須加入理論模擬內以資比較。但也因都卜勒效應的出現，我們發現在模擬中必須依據一定的程序。經由與實驗的比較得知，此正確的程序是: 理論計算出來的共振線需與都卜勒效應先行作計算，所得的結果再與 column density effect 再做一次計算。基於實驗與經由這個正確的模擬程序模擬出來的結果作比較，我們可將氦的這兩共振線 $(2,1_3)$ 和 $(2,1_4)$ 完全解析出來。直流的電場效應(史塔克效應)會造成光譜上共振線的偏移、分裂、變寬和振子強度的消長，在我們對鎂、鈣、鍶和鋇測到的光游離譜中都可看到這些基本的現象。對鎂和鈣在各自的第一游離閥上的史塔克效應，可觀測到由許多波包所組成的振盪現象(electric field induced resonances);這些波包是由許多更細小的譜線所組成。當電場改變時，觀測到的波包和其內的小譜線都有相同特性的位移。但其中有一個特別的波包 --- 正在演化的波包，其內部小譜線所被觀測到的位移現象卻是與其他波包相反;只要下一個正在演化的波包的部份被觀測到時，這個波包內的譜線的位移現象就會和其他波包內的譜線相同。而在這正在演化的波包內且在游離閥位置上的小譜線，其游離截面會有突然增大的情況，這個現象在實驗中明顯的被觀察到。在低於第一游離閥的能量區域外，穿隧效應可在鎂和鈣的光譜中被發現。另外對於鈣、鍶和鋇在其本身的自游離態的史塔克效應，對被觀測到的能階移動情形大部分是呈現出紅位移的現象。藍位移只能偶爾被觀測到，而且位移的量並不明顯。而在游離閥上的振盪現象(electric field induced resonances)，在鈣和鍶第二游離閥上的光譜可被觀察到。而在自游離態的波段中能被觀測到的最明顯史塔克效應的現象是譜線的分裂與增長，在鈣和鍶的光譜上可明顯的被觀察到。在鍶的自游離態的史塔克光譜中，能階互避的現象可被量測到。 For those narrow resonances observed without a good resolution, in addition to the familiar problem due to a poor instrumental resolution itself, there is another effect called ``column density effect' which will profoundly change the observed spectrum. This effect stemmed from the discrepancy between the formula used in dealing with experimental data over-simplifies the actual interaction; also because mathematical formulas used in dealing with data relies on experimental method incidentally, the various spectra observed by different method will be different accordingly. In order to understand about the column density effect well, we chose two of He resonances --- $(2,1_3)$ and $(2,1_4)$ --- to be our targets. It is well known that the widths of the two resonances are both narrower than Doppler broadening, hence calculation of Doppler effect has to be included into convolution in order to expect a good agreement between theory and experiment. Because takeing into account of Doppler effect, we will found out a particular convoluting procedure which has to be taken in the first place. Judged by the comparison between simulation and experimental results, the proper procedure should be that convolute theoretical resonance with Doppler effect first and then convolute with column density effect afterwards. Based on the comparison between experimental results and simulation results convoluted by the proper convolution procedure, the resonances of He $(2,1_3)$ and $(2,1_4)$ were resolved fully in this work. The well known effects on spectral features such as --- shift, splitting, broadening and variation of oscillator strength --- due to DC electric field for the resonances, were observed in the Stark photoionization spectra of Mg, Ca, Sr and Ba. For the case of the Stark effects around the first threshold of Mg and Ca, the oscillation features (electric field induced resonances) on the ionization continuum were observed distinctly. The oscillation features were formed with many manifolds and these manifolds were constructed by a plurality of observed narrow peaks. All the similar movements for the manifolds and the narrow peaks within these manifolds were observed as field strength varied. There was a particular manifold --- evolving manifold, the movements of the narrow peaks in this manifold were different from these of another manifolds; once the part of the next evolving manifold is appeared, the movements of those narrow peaks in the manifold will be similar with these of another peaks in another manifolds. Incidently for a particular narrow peak just at the position of the apparent threshold, the cross section increased unexpectedly and soon return to a typical value as its neighboring peaks when field strength increases. This unexpected change in cross section for the particular peak can be observed clearly in our experiment. Below the first ionization limit tunneling effect was observed in spectra of Mg and Ca. For the case of Stark effects of Ca, Sr and Ba in their autoionization region, the movements for the mostly observed autoionization resonances were red shift, but blue shift was observed just for a few resonances. The oscillation features (electric field induced resonances) above the second threshold was observed in the Stark spectra of both Ca and Sr. The most distinct phenomena for the autoionization states were peak splitting and oscillator strength sharing observed in the Stark spectra of Ca and Sr. Effect of level anti-crossing were observed in Stark spectra for the autoionization states of Sr.
Appears in Collections:	[Graduate Institute of Physics] Electronic Thesis & Dissertation

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