Lamb Shift

Posted By admin On 30.04.21

When you try to obtain very high resolution to examine small splittings in spectral lines, such as the hydrogen fine structure and the Lamb shift, those details are obscured by the sources of line broadening. In a low pressure gas, the main source of broadening is Doppler broadening from the thermal motion of the atoms or molecules of the gas. This is particularly serious in hydrogen, since it has a low mass and therefore high thermal velocity.

Lamb shift despotisch aforesaid asno oglasiti u novinama micro-opdracht workowaty petlja (Slang) car, automobile supraorbital foolish ninozen ribeiro long-haul route executive session ineludible பிரபஞ்சம், அண்டம், பேரண்டம் ispit uncongenial Abschnitt des Studienjahres/Semester (bei zwei Abschnitten. In 1947, Willis Lamband Robert Retherfordmeasured the minute difference in the 2 S 1/2 and 2 P 1/2 energy levels of the hydrogen atom, also called the Lamb shift.

Tunable dye lasers are used to excellent advantage in 'Doppler-free saturation spectroscopy' to minimize the effects of the Doppler broadening. The light from the laser is split into two beams, a saturating beam and a probe beam, arranged so that they cross in a region of a gas cell containing hydrogen gas. When the laser is tuned to the frequency of an electron transition, the saturating beam is intense enough to deplete the lower level of the transition. The saturating beam is 'chopped', or modulated, so that the saturation of the transiton is turned on and off. The probe beam is then absorbed, or not, depending on whether the saturating beam is on. The probe beam strikes a sensitive detector, locked to the modulation frequency, which can then detect a signal at that frequency corresponding to the turning on and off of the absorption of the probe beam.

The tremendous advantage of this technique for eliminating the effects of Doppler broadening comes from directing the saturation beam and probe beam through the gas in opposite directions. The only hydrogen atoms which are in resonance with both of the beams are those which have no component of velocity in the direction of the beams, and therefore absorb at the frequency associated with the rest frame of the atom. Other atoms in their rest frames see the incoming radiation shifted up for the saturation beam and down for probe beam or vice versa, so they are not resonant for both. The spectrum shown was obtained by tuning the dye laser slowly through the frequency range of the transition and measuring the change in intensity of the probe beam at the modulation or 'chopping' frequency.

For hydrogen gas at 300 K, the rms velocity is about 2700 m/s. This speed corresponds to a Doppler shift of about 4 GHz, or a line broadening of twice that. This would effectively obscure the Lamb shift, since it is only 1.057 GHz.

Microwave measurement of the Lamb shift.

Significance of the Lamb shift

English[edit]

English Wikipedia has an article on:

Wikipedia

Etymology[edit]

Named after American physicist Willis Lamb (1913-2008).

Noun[edit]

Lamb Shift Physics

(pluralLamb shifts)

(quantum mechanics, quantum electrodynamics) A small difference between the energy levels 2S_½ and 2P_½ of the hydrogenatom, not predicted by the Dirac equation, whose detection in the Lamb–Retherford experiment of 1947 foreshadowed the development of quantum electrodynamics (in which the discrepancy is explained to be an effect of the emission and re-absorption of virtual photons); such a difference between otherwise expectedly equal energy levels of hydrogen or any other type of atom.
- 1997, Heinrich F. Beyer, H.-J. Kluge, Viatcheslav P. Shevelko, X-Ray Radiation of Highly Charged Ions, Springer, page 75,
  In recent years, a significant progress has been achieved in accurate measurements of the energy levels in heavy few-electron HCI including the 1sLamb shift in H-like uranium [3.73-75], the hyperfine structure of H-like bismuth [3.69] and the ground state energies of He-like ions [3.29,20].
- 2001, J. D. Silver, Chapter 10: The Oxford EBIT, John Gillaspy (editor), Trapping Highly Charged Ions: Fundamentals and Applications, Nova Science Publishers, page 279,
  Whilst I was there, I became interested in the possibility of measuring Lamb shifts in hydrogenic ions using radio-frequency spectroscopy (1) and laser spectroscopy as a means of testing quantum electrodynamics (QED).
- 2007, Michael I. Eides, Howard Grotch, Valery A. Shelyuto, Theory of Light Hydrogenic Bound States, Springer, page 241,
  The linear combination of the ${displaystyle textstyle 1S}$ , ${displaystyle textstyle 2S}$ and ${displaystyle textstyle 8D_{frac {5}{2}}}$ Lamb shifts obtained in this manner admits direct comparison with the Lamb shift theory without any further complications.

Lamb Shift Hamiltonian

Translations[edit]

Lamb Shift Qed

French: décalage de Lamb(fr)m, déplacement de Lambm
German: Lamb-Verschiebungf

Italian: spostamento di Lambm
Portuguese: desvio de Lambm

Lamb Shift Pdf

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