Il Nuovo Cimento D

, Volume 1, Issue 4, pp 519–539 | Cite as

Two-photon transitions in two-electron systems: The 11 S–21 S transition in2He

  • F. Bassani
  • G. Vignale


The two-photon transition probability between the 11 S and the 21 S states of atomic He has been computed in the one-electron approximation by using simple approximate wave functions. The results with thee E·r interaction and with the— (e/mc)A·p interaction differ by less than 20%, but the former is shown to give more consistent results. The values of the absorption coefficients for a laser radiation of varying frequency are shown to be experimentally accessible and experiments are suggested with sinchrotron radiation and a laser beam. The Einstein relation between absorption and spontaneous emission can be extended to two-photon processes and the natural lifetime of the 21 S-state of He is computed and found to be ∼25 ms, in reasonable agreement with experiment and with other calculations.


Oscillator Strength Einstein Relation Resonance Ionization Spectroscopy Velocity Gauge Transition Probability Rate 
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Si calcola la probabilità di transizione a due fotoni tra gli stati 11 S e 21 S dell’He atomico nell’approssimazione a elettroni indipendenti, usando semplici funzioni d’onda. I risultati ottenuti con l’interazione della formae E·r e con l’interazione della forma —(e/mc)A·p differiscono per meno del 20%, ma si mostra che la prima forma conduce a risultati piú attendibili. Si calcolano i valori dei coefficienti di assorbimento con luce laser di varia frequenza, e si suggerisce la possibilità di esperimenti in cui si utilizzi luce laser e radiazione di sincrotrone. La relazione di Einstein tra assorbimento ed emissione spontanea può essere estesa ai processi a due fotoni e da essa si calcola il tempo naturale di vita dello stato 21 S dell’elio, per il quale si ottiene il valore di ∼25 ms, in ragionevole accordo con risultati sperimentali ed altri risultati teorici.


Рычисляется вероятность двухфотонного перехода между состояниями 11 S и 21 S в атоме He в одно-злектронном приближении, используя простые приближенные волновые функции. Результаты, полученные дляe E·r взаимодействия и для—(e/mc)A·p взаимодействия, отличаются менее, чем на 20%, но первая форма взаимодействия дает более непротиворечивые результаты. Проводятся вычисления коэффициентов поглошения для лазерного излучения различных частот. Предлагаются эксперименты с исполязованием синхротронного излучения и лазерного пучка. Соотношение Эйнштейна между поглощением и спонтанным излучением может быть обобщено на случай двухфотонных процессов. Вычисляется естественное время жнзни 21 S состояния He, которое составляет ∼25 мс, что находится в разумном согласии с экспериментом и другими вычислениями.


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Copyright information

© Società Italiana di Fisica 1982

Authors and Affiliations

  • F. Bassani
    • 1
    • 2
  • G. Vignale
    • 3
  1. 1.University of Illinois at Urbana-ChampaignUrbanaUSA
  2. 2.Scuola Normale SuperiorePisaItalia
  3. 3.Scuola Normale SuperiorePisaItalia

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