Q-Band Resonator for
Pulsed EPR Spectroscopy

Pulsed EPR spectroscopy using high-power microwave pulses or arbitrary waveform generated (AWG) broadband pulses require a large resonator bandwidth (low resonator Q) to avoid distortion of the pulse shape. However, large resonator bandwidth often comes at the cost of a reduced microwave conversion factor. Loop-Gap Resonators (LGR) combine all these desired features together with an excellent field homogeneity across the sample. This is especially important 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 2 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.

For accurate temperature readings a temperature sensor is mounted right next to the sample space. The sensor is compatible with many commercially available temperature controllers. Instead of relying on the cryostat temperature, this will give more accurate readings of the actual sample temperature.

Large Bandwidth ...

Data courtesy of Dr. Alberto Collauto, PEPR Facility, Imperial College London, UK (Pmax = 300 W, 7 dB att., ~1 dB loss)

Large Bandwidth …

Using the micrometer screw on top of the resonator to adjust the iris position, the resonator can be completely overcoupled. Critically coupled, the B12TQLP has a loaded Q of ~ 400, corresponding to a bandwidth of 85 MHz. By changing the iris the resonator Q can be lowered to < 85, increasing the resonator bandwidth to > 400 MHz. The resonator coupling is designed with convenience in mind and the maximum bandwidth can be reliably achieved every time. Even at this low Q, the microwave conversion factor is > 5.1 G/sqrt(W).

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

Sample: BDPA/PS. Data courtesy of Prof. Song-I Han, UCSB, (Pmax = 300 W, tp(90) = 2 ns, 6 dB att., ~1 dB loss)

… and large B1e Fields

LGRs are known for their large microwave conversion factors. The Bridge12 QLP resonator can achieve B1e field strengths of > 125 MHz, even when the resonator is completely overcoupled (bandwidth > 400 MHz). This will allow for 1H ESEEM/HYSCORE measurements and any experiment that requires hard microwave pulses.

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 developed for dipolar pulsed EPR experiments (DEER/PELDOR, DQC …). The resonators large excitation bandwidth and microwave conversion factor guarantees high sensitivity and results in short acquisition times (data analyzed using the SVD method, Madhur Srivastava (Cornell University) as described here).

Ideal for DQC Experiments

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

Ideal for DQC Experiments

For DQC experiments, the entire EPR spectrum has to be excited. At Q-Band, the TEMPO spectrum has a widht of ~ 250 MHz. The Bridge12 QLP resonator is ideally suited for these type of experiments. With a bandwidth of > 400 MHz and a large microwave conversion factor the entire spectrum can be excited for DQC spectroscopy.

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): < 85
  • Bandwidth (low) Q): 400 MHz
  • Maximum Sample OD: 1.6 mm (e.g Wilmad-Labglass, WG-221T-RB)
  • Typical Sample Height: 4.0 mm (~5 uL)
  • Operating Temperature Range: < 2 K 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?