The Next Step in Electron-Electron Double Resonance

ELDOR Upgrade Unit

Electron-electron double resonance (ELDOR) spectroscopy became very common to measure electron-electron distances (DEER and PELDOR) . For more elaborated experiments like Soft ESEEM and TPPI, the two microwave sources need to be phase locked to each other, a setup referred to as Coherent ELDOR.

Coherent ELDOR: The Setup

On the excitation side, the ELDOR source is locked to the main microwave bridge source by a locking unit. The PatternJet pulse programmer provides the necessary external trigger for the lock.


The Coherent ELDOR setup is seemlessly integrated into Bruker's Intermediate Frequency (IF-)concept, readily providing Coherent ELDOR capabilities from 1 to 100 GHz.

Coherent ELDOR: Application Examples

2 frequency Soft-ESEEM (top) vs. high-power and low-power ESEEM (middle and bottom, resp.) demonstrating the increased resolution.

Coherent ELDOR has become commercially available only recently. Key pulsed EPR experiments are Soft ESEEM and TPPI detection. Further, pulsed EPR experiments with two phase-locked sources are also advantageous for Quantum Computing experiments.

Two Frequency Soft-ESEEM

Soft-ESEEM (cf. Schweiger & Jeschke, Principle of pulse electron paramagnetic resonance, ch. 11.3) has the advantage of selectively exciting allowed and forbidden transitions and thus requiring only low mw power levels. The comparision of the two frequency Soft-ESEEM (red, top trace) with the common one-frequency ESEEM (high and low power, green and blue, resp.) clearly demonstrates the increase in resolution and selectivity.