The Laser as a Light Source for Ultramicroscopy and Light Scattering by Imperfections in Crystals. Investigation of Imperfections in LiF, MgO, and Ruby

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Abstract
A cw 1‐mW He–Ne laser was used for the study of 90° light scattering in crystals in the arrangement of an ultramicroscope. Motorized translation of the illuminating objective allowed us to take photographs of extended sections through the crystal. When the laser was compared with light‐scattering performance of an unfiltered unpolarized 100‐W mercury arc lamp it appeared to be appreciably more intense. On calibration, 880‐Å latex particles suspended in water were easily visible by eye, and 3570‐Å particles were photographed at 1 32 ‐sec exposure. It is estimated that 1‐h exposures would make visible particles of some 300 Å e.l.d. (equivalent latex diameter) and with more powerful lasers, particles of about 100 Å e.l.d. could be theoretically reached. Lithium fluoride crystals of high purity show scattering defects concentrated at small‐angle boundaries. Magnesium oxide crystals of lesser purity show many imperfections. Ruby laser crystals show imperfections at small‐angle boundaries and also along lines perpendicular to the boundaries.