Skip to main content
Sandbox Physics
Quantum physics: reading the evidence

Nobel A · Evidence and control · 1897–2022

The Stark effect: an electric field changes the spectrum

Sandbox Physics ·

What distinguishes a field-induced splitting from an ordinary drift or an unresolved broad line?

The report includes polarization, not just broadening

Stark’s 1913 announcement describes splitting hydrogen spectral lines in a strong electric field. With the observation direction transverse to the field, resolved components also had a stated polarization relation to that field. The observation was richer than a single peak moving to a new position.

The electric-field axis, viewing direction and polarization analyzer define different parts of the measurement. A line profile that omits them can erase the very structure being tested. The 1919 award also names the Doppler effect in canal rays; that contribution should not be confused with the field-induced splitting itself.

Read the evidence: J. Stark (1913), Observation of the Separation of Spectral Lines by an Electric Field, Nature 92, 401Nobel Prize in Physics 1919 — official award record

A line records a difference between two perturbed levels

An applied field changes atomic states and their energies. A spectral component corresponds to a difference between an upper and lower level, together with an allowed transition and its polarization. It is not a direct picture of one electron being pulled sideways.

Two levels can both move while their transition changes little. Conversely, several allowed transitions can produce a multiplet. Counting visible components without a model of both levels, selection rules and instrument resolution does not determine a complete atomic level scheme.

Read the evidence: J. Stark (1913), Observation of the Separation of Spectral Lines by an Electric Field, Nature 92, 401J. A. Sherman et al. (2012), High accuracy measure of atomic polarizability in an optical lattice clock

Linear and quadratic effects have different conditions

For an isolated nondegenerate parity state with no permanent electric dipole, the leading weak static-field shift is usually quadratic. A scalar convention is given below: the symbols specify the polarizability and the field magnitude. Tensor contributions and hyperfine structure are omitted in this expression.

Hydrogen’s ideal degenerate excited manifolds require degenerate perturbation theory and can show a linear effect. Thus this quadratic formula is a contrasting limit, not a fit to Stark’s original resolved hydrogen components. Fine structure, the Lamb splitting and strong-field mixing determine when a simplified limit is appropriate.

ΔE=−12αF2\Delta E=-\frac{1}{2}\alpha F^2

Read the evidence: J. A. Sherman et al. (2012), High accuracy measure of atomic polarizability in an optical lattice clockNIST TN 1524, Trapped ions and laser cooling V — quadratic Stark shifts and polarizability

Vary the field, and test the measuring system too

A quadratic shift is even under reversal of a uniform applied field. Stray fields can offset the minimum of a scan against applied voltage. Field nonuniformity can broaden the ensemble signal; electrode spacing, voltage calibration and spatial sampling therefore enter a field-shift measurement.

Sherman and collaborators measured the differential static polarizability of an optical clock transition. The relevant quantity for a transition is the difference of the two level responses. Their precision result is a modern experiment with its own species and apparatus, not a numerical refinement of the 1913 plate.

Read the evidence: J. A. Sherman et al. (2012), High accuracy measure of atomic polarizability in an optical lattice clock

Link the line-reading skills, not a nonexistent Stark apparatus

The hydrogen Lab supplies an unperturbed reference, and the coupled-spin Lab supplies a different example of resolving several spectral lines. Neither includes the real electric-field geometry and Stark coupling needed to reproduce the historical measurement.

Read the Lamb article alongside this one: an unwanted electric field can mix states and alter a metastable signal, while a deliberate field can be a spectroscopic control. The same interaction can be a tool or a systematic effect, depending on the experiment. A complete model must say which role it plays.

Read the evidence: Lamb and Retherford (1947), original paper scan hosted by the University of Maryland, pp. 241–243J. A. Sherman et al. (2012), High accuracy measure of atomic polarizability in an optical lattice clock

Sources and reading notes

Stark’s short 1913 announcement is available as an indexed publisher abstract; direct access redirected during preparation. Its wavelength-component and polarization observations are kept distinct from later perturbation theory. Sherman and collaborators provide a modern, independently measured quadratic Stark example. No early plate or field map is reconstructed.

  1. Lamb and Retherford (1947), original paper scan hosted by the University of Maryland, pp. 241–243
  2. J. Stark (1913), Observation of the Separation of Spectral Lines by an Electric Field, Nature 92, 401
  3. Nobel Prize in Physics 1919 — official award record
  4. J. A. Sherman et al. (2012), High accuracy measure of atomic polarizability in an optical lattice clock
  5. NIST TN 1524, Trapped ions and laser cooling V — quadratic Stark shifts and polarizability