High-field/high-frequency EPR spectrometer operating in pulsed and continuous-wave mode at 180 GHz

Abstract

A novel electron paramagnetic resonance (EPR) spectrometer is reported, which has been developed to allow pulsed EPR experiments with high sensitivity and time resolution at a microwave (MW) frequency of 180 GHz (G-band) and wavelengths of approximately 1.6 mm. This corresponds to a magnetic field of about 6.4 T for g -2 signals. The "hybrid" system architecture combines components of quasioptical as well as conventional MW techniques, making it possible to achieve excellent spectrometer performance with respect to sensitivity and time resolution. Quasioptical MW components have been used to design an MW circulator allowing high sensitivity and low bias operation in the reflection mode. A miniaturized, closed-type cylindrical cavity provides a high sample filling factor and an adequate MW field strength (B,) enhancement and thus permits reasonably short MW pulses (60 ns for a it/2 pulse) even with a moderate MW input power (15 mW at the cavity). Commercial quartz capillaries (up to 0.5 mm internal diameter) can be used as sample holders for a broad range of applications.

High-Frequency EPR Instrumentation

“…The ease of operation and the possibility to integrate these devices in heterodyne as well as homodyne configurations lead to the expectation that these may be the sources of the future. Several groups already have integrated these designs in their HF-EPR spectrometers [38,41,42,56].…”

“…At 95 GHz, an incident power of approximately 100 mW is necessary for a p/2 pulse of 50 ns (cavity Q = 2000) [28]. At 180 GHz, this is 20 mW (Q = 1500) [38]. For 360 GHz, only 4 mW would be needed for a 50 ns p/2 pulse (Q = 1500) [39].…”

“…Steinhoff et al [100] used the same design in their 95-GHz instrument. Prisner et al [38] used this principle in their 180-GHz pulse EPR spectrometer. The W-and D-band bridges developed by Vladimir Krymov (Donetsk Physical-Technical Institute, Ukraine), however, used scheme in Fig.…”

“…To control these high powers and maintain a very short system dead-time, advanced quasioptical techniques have proven to be essential [36,37]. Also pulsed EPR at frequencies higher than 150 GHz (using quasi-optical spectrometers) is being pursued in an increasing number of laboratories [38][39][40][41][42].…”

A field-sweep/field-lock system for superconducting magnets—Application to high-field EPR

“…As a consequence, commercial spectrometers are available up to 95 GHz and custom designed highfield EPR spectrometers are currently operating from 95 up to 360 GHz [1][2][3][4][5][6] and the applications of high-field EPR are manifold and expanding rapidly [7,8].…”