A review is given on the status and basic properties of lasers and nonlinear optical sources in the wavelength region of ultraviolet and vacuum-ultraviolet. In the ultraviolet (200nm<λ<400nm), a wide range of developments is described concerning ionized gas lasers, nitrogen molecular lasers, dye lasers as well as alternative nonlinear optical techniques such as harmonic and sum-frequency generation. In the vacuum-ultraviolet region (λ<200nm), recent advances in molecular bound-bound and bound-free lasers are presented with particular emphasis on the alternative method of vuv optical mixing using third-order nonlinearity in atomic vapors. A wide range of their new applications and future developments in expanding to the soft X-ray region are also discussed briefly.
The method for obtaining information of the normal and abnormal state of biological tissue by the use of ultrasonics in the mega hertz range is called as ultrasonic diagnostics in medicine. In the ultrasonic diagnosis currently used for clinical examination in routine, the ultrasonic beam radiating from an ultrasonic transceiver, called a probe, travels through the biological tissue which form the sound medium for the beam. Diagnostic information is obtained from the reflection and attenuation of the ultrasound peculiar to the tissue under examination. A special merit of this method is that it is possible to detect the characteristic beam of soft tissue in the form of acoustic tissue structure. In the present report; firstly, the application of ultrasonic diagnostics for clinical examination in various branches of medicine is reported. Secondly, a survey of ultrasonic technique used in ultrasonic diagnostics is given. In particular, the status of the ultrasonic pulse reflection method and the ultrasonic Doppler method which are mainly used at present are described. Lastly, as, future aspects, the development of a new field which might be termed ultrasonic biology, the improvement of the ultrasonic transceiver as being a particularly important equipment for ultrasonic diagnostics, the development of the scanning system for ultrasonic beams, and the information processing of the biological information obtained by the present method, are dealt -with as important problems to be solved in the future.
Distributed Bragg-reflector lasers with optical loss in corrugated waveguide are analyzed in the scheme of coupled-mode theory. Threshold solution for the laser gain is calculated for various values of the coupling coefficient, the pumped length, and the optical loss coefficient. It is shown that the distributed Bragg-reflector laser considered here has a minimum value of the threshold gain, if the pumped length is chosen appropriately. As the optical loss of the corrugated waveguide is increased, the optimum pumped length ratio increases under the condition that the normalized coupling coefficient kL has a constant value. If the pumped length is adjusted to operate under optimum condition, the optical loss does not affect the threshold gain to any appreciable extent.
The excitation mechanism of Ar-Kr ion laser has been investigated by observing the time sequence of spontaneous emission from upper laser levels in the discharge with a square current pulse. It is shown that the dominant excitation process of laser levels of argon is the energy transfer from some metastable states of ionized krypton in Kr-rich Ar-Kr mixtures, whereas krypton is excited by electron collision as in the case of pure Kr ion laser. A detailed account is proposed of the possible processes for the energy transfer mechanism of Ar-Kr ion laser.