Abstract: A ZnO thin film is fabricated on the c-surface of a sapphire substrate through use of a laser molecular beam epitaxy (MBE) method-which is effective for epitaxial growth of an oxide thin film through control at an atomic level. The thus-formed ZnO thin film has a considerably high crystallinity; the half width of an X-ray rocking curve was 0.06.degree.. The thin film is of an n-type and has a carrier density of 4.times.10.sup.17 /cm.sup.3. The thin film fabricated in a state in which oxygen partial pressure is held constant at 10.sup.-6 Torr has a structure in which hexagon-shaped nanocrystals of uniform size are close-packed, reflecting the crystal behavior of a wurtzite type. Since in each nanocrystal there is observed a spiral structure formed by steps of a unit cell height (0.5 nm), the nanocrystals are considered to grow in a thermodynamically equilibrated state. The lateral size of the nanocrystal can be controlled within the range of approximately 50 to 250 nm.

Abstract: A target is irradiated with a laser beam having an energy of h.nu./n, where n is an integer, instead of the photon energy h.nu. required for a reaction to proceed using a conventional single-photon excitation method. A desired reaction is selectively induced by the absorption of multiple photons instead of single photons. It is thus possible to induce a photoreaction in which an absorption is carried out in accordance with a selection theory different from that of single-photon absorption, and which is quite different from a photoreaction induced by a single-photon excitation. Namely, a target or reactant is irradiated with a photon energy h.nu..sub.2 having a wavelength integral times longer than that of the photon energy h.nu..sub.1 necessary for a photoreaction to proceed. Photon energy h.nu..sub.2 is either used in place of the photon energy h.nu..sub.1 necessary for a photoreaction, or together with the photon energy h.nu..sub.

Abstract: A chrysoberyl solid state laser comprising:(a) a rod-like laser medium composed of a chrysoberyl single crystal containing trivalent titanium ions as luminescent ions, the direction of c-axis of said crystal being made approximately the same as the longitudinal direction of the rod.(b) a means for generating excitation light for exciting said luminescent ions to emit light therefrom.(c) a means for focussing excitation light, generated by said means for generating excitation light, in said laser medium, and(d) a light resonator for generating oscillated laser light by resonating the light emitted from said luminescent ions with said focussed excitation light.