Maser threshold characterization by resonator Q-factor tuning

Whereas the laser is nowadays an ubiquitous technology, applications for its microwave analog, the maser, remain highly specialized, despite the excellent low-noise microwave amplification properties. The widespread application of masers is typically limited by the need of cryogenic temperatures. The recent realization of a continuous-wave room-temperature maser, using NV− centers in diamond, is a first step towards establishing the maser as a potential platform for microwave research and development, yet its design is far from optimal. Here, we design and construct an optimized setup able to characterize the operating space of a maser using NV− centers. We focus on the interplay of two key parameters for emission of microwave photons: the quality factor of the microwave resonator and the degree of spin level-inversion. We characterize the performance of the maser as a function of these two parameters, identifying the parameter space of operation and highlighting the requirements for maximal continuous microwave emission

Kinetics of formation and dissociation of lanthanide(III) complexes with the 13-membered macrocyclic ligand TRITA

cited By 28International audienceThe tetraazamacrocyclic ligand TRITA4- is intermediate in size between the widely studied and medically used 12-membered DOTA4- and the 14-membered TETA4-. The kinetic inertness of GdTRITA- was characterized by the rates of exchange reactions with Zn2+ and Eu3+. In the Zn2+ exchange, a second order [H+] dependence was found for the pseudo-first-order rate constant (k0 = (4.2 ± 0.5) × 10-7 s-1; k′ = (3.5 ± 0.3) × 10-1 M-1S-1, k″ = (1.4 ±0.4) × 103 M-2s-1)- In the Eu3+ exchange, at pH <5 the rate decreases with increasing concentration of the exchanging ion, which can be accounted for by the transitional formation of dinuclear GdTRITAEu2+ species. At physiological pH, the kinetic inertness of GdTRITA- is considerably lower than that of GdDOTA- (t1/2 = 444 h (25°C) vs. 3.8 × 105 h (37°C), respectively). However, GdTRITA - is still kinetically more inert than GdDTPA2-, the most commonly used MRI contrast agent (t1/2 = 127 h). The formation reactions of LnTRITA- complexes (Ln = Ce, Gd and Yb) proceed via the rapid formation of a diprotonated intermediate and its subsequent deprotonation and rearrangement in a slow, OH- catalyzed process. The stability of the LnH2TRITA* intermediates (log KLnH2L* = 3.1-3.9) is lower than that of the DOTA-analogues. The rate constants of the OH- catalyzed step increase with decreasing lanthanide ion size, and are about twice as high as for DOTA-complexes. © The Royal Society of Chemistry 2005

Towards high performance dielectric microwave resonators for X-band EPR spectroscopy

Microwave (MW) resonators in Electron Paramagnetic Resonance (EPR) spectroscopy concentrate the MW magnetic field (B1) at the sample and separate the MW electric field from the sample. There are numerous experimental methods in EPR spectroscopy which all impose different requirements on MW resonators (e.g. high or low quality factor, MW conversion, and B1-field homogeneity). Although commercial spectrometers offer standardized MW resonators for a broad application range, newly emerging and highly-specialized research fields push these spectrometers to or beyond their sensitivity limits. Optimizing the MW resonator offers one direct approach to improve the sensitivity. Here we present three low-cost optimization approaches for a commercially available X-band (9–10 GHz) MW resonator for three experimental purposes (continuous-wave (CW), transient and pulse EPR). We obtain enhanced MW conversion factors for all three optimized resonators and higher quality factors for two optimized resonators. The latter is important for CW and transient EPR. Furthermore, we fabricated a resonator which features an extended area of homogeneous B1-field and, hence, improved pulse EPR performance. Our results demonstrate that small changes to a commercial MW resonator can enhance its performance in general or for specific applications