We report a giant thermal shift of 2.1 MHz/K related to the excited-state zero-field splitting in the silicon vacancy centers in 4H silicon carbide. It is obtained from the indirect observation of the optically detected magnetic resonance in the excited state using the ground state as an ancilla. Alternatively, relative variations of the zero-field splitting for small temperature differences can be detected without application of radiofrequency fields, by simply monitoring the photoluminescence intensity in the vicinity of the level anticrossing. This effect results in an all-optical thermometry technique with temperature sensitivity of 100 mK/Hz1/2 for a detection volume of approximately 10−6 mm3. In contrast, the zero-field splitting in the ground state does not reveal detectable temperature shift. Using these properties, an integrated magnetic field and temperature sensor can be implemented on the same center.

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Transitions inside the ground S = 10 multiplet of magnetic clusters Mn12-Ac have been observed in submillimeter transmission spectra measured by means of a quasi-optical backward-wave-oscillator technique in the frequency range ν = 3-33 cm −1 . The temperature dependence of the resonance frequencies, linewidths and mode contributions to the magnetic permeability in the range T = 3-35 K are consistent on the whole with a spin S = 10 ground state split by a tetragonal crystal field. However, some deviations between the calculated and observed mode contributions at high temperatures suggest the presence of other Mn12-Ac excited multiplets with S = 10.

Currently there is a great deal of interest in the investigation of substituted manganites R 1Ϫx A x MnO 3 , where R is a rare earth and A ϭCa,Sr, . . . This is due to the discovery of colossal magnetoresistance 1 as well as diverse magnetic and structural phase transformations 2,3 in these materials. These compounds all have the property that on doping with divalent Ca and Sr ions their magnetic structure changes from antiferromagnetic ͑with weak ferromagnetism͒ at xϭ0 to ferromagnetic at xϭ0.2±0.3, and their resistance decreases strongly. 2 Their crystal structure also undergoes a number of transformations. For example, as the Sr content in La 1Ϫx Sr x MnO 3 increases, the crystal symmetry changes from orthorhombic to rhombohedral, and in the intermediate Sr concentration range xϭ(0.1±0.15͒ an unusual polaron-ordered state is observed, which neutron diffraction data 4 show to be due to an ordered arrangement of heterovalent ions Mn 3ϩ /Mn 4ϩ in alternating ͑001͒ planes and to the formation of a corresponding superstructure.

We have developed a method of solid immersion THz imaging-a non-contact technique employing the THz beam focused into evanescent-field volume and allowing strong reduction in the dimensions of THz caustic. We have combined numerical simulations and experimental studies to demonstrate a sub-wavelength 0.35k 0-resolution of the solid immersion THz imaging system compared to 0.85k 0resolution of a standard imaging system, employing only an aspherical singlet. We have discussed the prospective of using the developed technique in various branches of THz science and technology, namely, for THz measurements of solid-state materials featuring sub-wavelength variations of physical properties, for highly accurate mapping of healthy and pathological tissues in THz medical diagnosis, for detection of sub-wavelength defects in THz non-destructive sensing, and for enhancement of THz nonlinear effects.