Q-Band Resonator for
Pulsed EPR Spectroscopy

Pulsed EPR spectroscopy using high-power microwave pulses or arbitrary waveform generated shaped broadband pulses requires a low-Q resonator to avoid truncation of the pulse shape and ensure the entire spectrum is excited by the microwave pulse. However, the large resonator bandwidth often comes at the cost of a reduced microwave conversion factor. Loop-Gap-Resonators (LGRs) have large bandwidths, but maintaining large B1e values and excellent field homogeneity along the length of the sample. This is a great advantage particularly when using AWG generated broadband pulses. The Bridge12 Q-Band resonator (B12TQLP) is the first commercially available Q-Band LGR for pulsed EPR spectroscopy combining all these highly desired features.
Bridge12 Q-Band LGR

Bridge12 Q-Band LGR

The Bridge12 Q-Band resonator (B12TQLP) is optimized for pulsed dipolar EPR spectroscopy (e.g. DEER/PELDOR, SIFTER, RIDME, DQC, etc) in cases where the sample amount is limited. The resonator can be operated from 4 K to room-temperature and is compatible with standard cryostats such as the Oxford Instruments CF935 or the Cryogen Ltd. Cryogen-Free Cryostat. The resonator is connected to the spectrometer using a standard WR-28 waveguide coupling. For pulsed EPR experiments the coupling is adjusted using a micrometer screw, no frequency adjustments are necessary when changing the resonator coupling from critical to overcoupled.

Compact Resonator

Compact Resonator

The Bridge12 B12TQLP was designed with small samples in mind. The resonator accepts standard Q-Band sample tubes with an OD of 1.6 mm (e.g. Wilmad WG-221T-RB).

The sample is mounted on a sample stick for easy inserting of the sample into the resonator and removing, even if the sample needs to stay frozen at all times.

The probe comes with an integrated temperature sensor for accurate measurements of the sample temperature.

Large Bandwidth ...

Sample: BDPA/PS.
Data courtesy of Prof. Song-I Han, UCSB

Large Bandwidth …

LGRs are an excellent choice for pulsed EPR experiments due to their low Q and therefore large bandwidth. Using the micrometer screw on top of the resonator to adjust the iris position, the B12TQLP resonator can be completely overcoupled. The Bridge12 B12TQLP has a loaded Q of about 400 when critically coupled, corresponding to a bandwidth of 85 MHz. By changing the iris coupling the resonator Q can be lowered to < 85, increasing the resonator bandwidth to > 400 MHz.

... and large B<sub>1e</sub> Fields

Sample: BDPA/PS.
Data courtesy of Prof. Song-I Han, UCSB

… and large B1e Fields

LGRs are known for their large microave conversion factors. The Bridge12 QLP resonator can achieve B1e field stregnths of > 125 MHz at a bandwidth of > 90 MHz. For a completely overcoupled resonator (bandwidth > 400 MHz) the experimentally achieved B1e fields are still > 70 MHz.

4-Pulse DEER/PELDOR Experiments

Sample: MS57-2/o-Terphenyl, 65 K.
Data courtesy of Prof. Song-I Han, UCSB

4-Pulse DEER/PELDOR Experiments

The Bridge12 QLP resonator was specifically developed for pulsed DEER/PELDOR experiments. The resonators large excitation bandwidth and microwave conversion factor guarantees high sensitivity and results in short acquisition times.

To the right, a single trace of a 4-pulse DEER experiment is shown on a ruler molecule with an average nitroxide distance of 2.84 nm. A trace with no averaging was recorded at a temperature of 65 K is shown. Data is analyzed using the SVD method developed by Madhur Srivastava (Cornell University) to determine the distance distribution as described here.

The Bridge12 QLP resonator was developed under a Small Business Innovation Research (SBIR) Grant by the National Institute of General Medical Sciencies (NIGMS) of the National Institutes of Health (NIH).

Below, find some general literature references for dipolar spectroscopy and the required instrumentation.

  1. Reviews/Books:
  2. Double-Quantum Coherence Spectrosocpy:
  3. PELDOR:
    • Milov, A. D., A. B. Ponomarev, and Yu. D. Tsvetkov. “Electron-Electron Double Resonance in Electron Spin Echo: Model Biradical Systems and the Sensitized Photolysis of Decalin.” Chemical Physics Letters 110, no. 1 (September 14, 1984): 67–72. https://doi.org/10.1016/0009-2614(84)80148-7.
  4. SIFTER:
    • Jeschke, G., M. Pannier, A. Godt, and H. W. Spiess. “Dipolar Spectroscopy and Spin Alignment in Electron Paramagnetic Resonance.” Chemical Physics Letters 331, no. 2 (December 1, 2000): 243–52. https://doi.org/10.1016/S0009-2614(00)01171-4.
  5. Q-Band LGR Resonators
    • Denysenkov, Vasyl, Philipp van Os, and Thomas F. Prisner. “Q-Band Loop-Gap Resonator for EPR Applications with Broadband-Shaped Pulses.” Applied Magnetic Resonance 48 (December 1, 2017): 1263–72. https://doi.org/10.1007/s00723-017-0930-9.
    • Tschaggelar, Rene, Frauke D. Breitgoff, Oliver Oberhänsli, Mian Qi, Adelheid Godt, and Gunnar Jeschke. “High-Bandwidth Q-Band EPR Resonators.” Applied Magnetic Resonance 48 (December 1, 2017): 1273–1300. https://doi.org/10.1007/s00723-017-0956-z.

Technical Specifications

  • Resonator Frequency (empty): 36 GHz
  • Resonator Frequency (with sample): 34 GHz
  • Conversion Factor (high Q): > 12 G/√W
  • Loaded Q (empty): 300 - 400
  • Bandwidth (high Q): 100 MHz
  • Conversion Factor (low Q): > 6 G/√W
  • Loaded Q (empty): < 100
  • Bandwidth (low) Q): 400 MHz
  • Maximum Sample OD: 1.6 mm (e.g Wilmad-Labglass, WG-221T-RB)
  • Typical Sample Height: 4.0 mm
  • Operating Temperature Range: cryogenic temperatures to Room Temperature
  • Sample exchange at all temperatures
  • Integrated temperature sensor for accurate determination of the sample temperature
  • Compatible with Oxford Instruments cryostat model CF935
  • Probe leak checked at the factory
  • Optical access (optional)

Any questions?