CW-EPR spectra of P1 centers in HPHT diamond in the vicinity of Rabi resonance: possible standard for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si35.svg"><mml:msub><mml:mi>B</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math> evaluation in EPR and DNP enhanced NMR spectroscopies

Synthetic commercial type-IIa diamond crystal containing low concentration of P1 (Ns0) centers ([Ns0] <1ppm) was examined as a possible calibration standard for evaluating microwave magnetic field intensity (B1) in the spectrometer cavity. The reliability this experimentally and theoretically tested by employing two different types cavities with distributions B1 values. procedure relies on ordinary continuous wave electron paramagnetic resonance (CW-EPR) modulation (ωrf/2π=100 kHz) applied under regime power (PMW) saturation out-of-phase first harmonic signal. PMW∼B11/2 analyzed respect to change spectral lineshape when Rabi frequency (ω1=γB1, γis gyromagnetic ratio) approaches ωrf. phenomenon inversion sideband lines while passing condition (ω1=ωrf) analyzed. In specific, from simulation experimental lineshapes close vicinity (ω1≈ωrf) correspondingB1 can be assigned. For chosen value B1≈3.6µT at determined what makes it convenient DNP enhanced NMR spectroscopy which requires relatively small B1.