The spin—lattice relaxation time T1 of 19F was measured over a temperature range of 77° to 1300°K in natural and synthetic CaF2 crystals and in CaF2 crystals doped with 0.05% Sm, 0.16% Sm, and 1.20% Sm. Most of the data was taken with the magnetic field along the [100] and [111] directions using the magnetic recovery method. For annealed samples T1 at room temperature and below is found to be inversely proportional to the concentration of samarium. Measurements show that in the high-temperature regions T1 is primarily governed by translational diffusion. Activation energies in the extrinsic and intrinsic regions were found to be 0.36 and 2.3 eV, respectively, for the pure sample and 0.53 and 2.4 eV for the doped samples. These are in good agreement with the activation energies obtained from conductivity measurements. The knee separating the extrinsic and intrinsic regions occurred at higher temperatures as the amount of dopant was increased. The T1-vs−1/T curves had a minimum at 1120°K for all the samples. Below 400°K T1 was found to be directly proportional to temperature for the doped samples. The low-temperature data indicate that the correlation time of samarium at room temperature is of the order of 10−14 sec.

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A magneto-optical method has been developed to determine the spin-lattice relaxation times of paramagnetic ions from the maximum rate at which paramagnetism can follow an ac magnetic field modulating a dc magnetic field of 0–6000 G. The spin-lattice relaxation time τ of the paramagnetic ion determines the maximum rate at which the Faraday rotation of plane polarized light traversing the material may be modulated at low temperatures. By measuring the phase angle between the light modulated by the Faraday rotation and the perturbing magnetic field for both the pure host material and the host material doped with paramagnetic ions, one is able to determine the relationship between τ and the applied static magnetic field at low temperatures. The apparatus and the method employed for this measurement are described.

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Visible light from a helium-neon laser was directed onto a white-card surface capable of rotation, and the granularity characteristics of the scattered light were observed. Photographs are given showing the degree of granularity observed under various rotational speeds. It is indicated that the visible granularity, due to the extremely high degree of coherence of the laser light, disappears from view as a consequence of persistence of vision when the light is scattered by a moving surface. Additional observations relating to the phenomenon of granularity are also presented and discussed.