Continuous wave electron paramagnetic resonance L-band spectrometer with direct digitalization using time-locked...

Area of Science:

• Spectroscopy
• Physical Chemistry
• Instrumentation

Background:

• Conventional Continuous Wave (CW) Electron Paramagnetic Resonance (EPR) spectrometers often rely on analog components and magnetic field modulation.
• Direct digital detection offers potential advantages in terms of signal processing and sensitivity.

Purpose of the Study:

• To describe a novel digital L-band EPR spectrometer employing direct digital detection with time-locked subsampling (TLSS).
• To evaluate the performance of this new spectrometer, particularly its phase noise characteristics and signal-to-noise (S/N) ratio.

Main Methods:

• Development of a microwave source using direct digital synthesis (DDS) with an ultra-low noise master clock.
• Implementation of a digital receiver with a high-speed Analog-to-Digital Converter (A/D) for direct signal digitalization.
• Time-locking of the generator and receiver using a common reference source for simultaneous absorption and dispersion signal detection.

Main Results:

• Achieved exceptionally low phase noise (-140 dBc/Hz at 30.5 kHz from 1.15 GHz carrier).
• Demonstrated simultaneous detection of absorption and dispersion signals.
• Obtained a S/N ratio greater than 160 for an 11 µm aqueous TEMPOL solution within 69 seconds.

Conclusions:

• The developed digital L-band EPR spectrometer represents a significant advancement in EPR instrumentation.
• The direct digital detection technique, as implemented, shows promise for replacing conventional analog CW spectrometers.
• The spectrometer's performance, particularly its low phase noise and high S/N ratio, validates the employed methodology.