Electron spin dynamics during microwave pulses studied by 94 GHz chirp and phase-modulated EPR experiments

Area of Science:

• Physical Chemistry
• Spectroscopy
• Quantum Dynamics

Background:

• Electron spin dynamics under microwave irradiation are crucial for electron paramagnetic resonance (EPR) and dynamic nuclear polarization (DNP).
• Locking electron spins into a 'dressed' state has significant applications in these fields.
• Modern pulsed EPR techniques utilizing arbitrary waveform generators enable precise control over spin dynamics.

Purpose of the Study:

• To investigate electron spin dynamics during microwave irradiation using shaped microwave pulses in pulsed EPR.
• To probe Rabi nutations, echoes, and echo decays during spin locking of a BDPA radical at 94 GHz.
• To analyze coherence transfer pathways and measure decoherence times in the spin lock frame.

Main Methods:

• Employed phase-modulated microwave pulses in pulsed EPR experiments.
• Studied spin dynamics of a BDPA radical at 94 GHz EPR frequency.
• Utilized chirped Fourier transform EPR and a density matrix model for analysis.

Main Results:

• Observed distinct echo types dependent on the initial magnetization state.
• Measured a decoherence time $T_{2\rho }$ that is 2-3 times longer than $T_m$.
• Experimental results were accurately reproduced by a density matrix model incorporating $T_{2\rho }$ relaxation.

Conclusions:

• Shaped microwave pulses effectively probe electron spin dynamics in the dressed state.
• The measured longer decoherence time $T_{2\rho }$ is beneficial for EPR and DNP experiments.
• This work provides a foundation for optimizing hole-burning EPR techniques like ELDOR-detected NMR.