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.
In QED, the Lamb Shift is understood as based on electron self-interaction, in which the electron “continuously emits and absorbs virtual photons, and as a result its electric charge is spread over a finite volume instead of being pointlike.” Eides, Grotch, and Shelyuto, 2007 But QED is focused on computing the energy levels in a momentum space treatment using perturbation analysis, and appears to be silent on how exactly the charge is spread over that small volume in position space. Definition of lamb shift in the Definitions.net dictionary. Meaning of lamb shift. What does lamb shift mean? Information and translations of lamb shift in the most comprehensive dictionary definitions resource on the web. Understanding the Lamb shift is one of the milestones of QED and atomic physics. We revisit this central effect from a new angle: after being led to the hypothesis that the Lamb shift may be. For the Lamb-shift and for the anomalous part of the magnetic moment of the electron the agreement is within some parts in one hundred thousand respectively in a million and no disagreement has yet been found. Quantum electrodynamics is indeed one of the most accurate of all the theories of physics. Lamb shift, ﬁne structure and hyperﬁne structure in helium-like ions by fast-beam laser spectroscopy E.G. Thompson a, H.S. Margolis b,J.D.Silverb and M.R. Tarbutt b a Department of Physics, Florida State University, Tallahassee, FL 32306, USA b Clarendon Laboratory, University of.
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|
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Lamb shift[′lam ¦shift] (atomic physics)
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