ABSTRACT
The local plane-interface approximation (LPIA) is a method for propagating electromagnetic fields through the inhomogeneous regions (e.g., elements) of an optical system. The LPIA is the superclass of all approximations that replace the usually curved optical interfaces with local tangential planes. Therefore the LPIA is restricted to smooth optical surfaces. A maximum radius of curvature of the optical interface of the order of a few wavelengths is a rough estimate for the validity of the LPIA. Two important approximation levels of the LPIA are the thin-element approximation (TEA) and a geometric-optical version of the LPIA (LPIA(ray)). The latter combines the wave-optical propagation of an electromagnetic field in the homogeneous region of an optical system with a ray-tracing step in the inhomogeneous region. We discuss the regions of validity of the LPIA in general and the approximation levels LPIA(ray) and TEA in detail.
ABSTRACT
The spatial shaping of laser beams is a subject of research in modern optics. Recently the introduction of diffractive elements in laser resonators has offered an alternative to external beam-shaping optics by mode shaping within the resonator. We describe the specification of the laser resonator mirrors to obtain by means of internal mode shaping a desired beam outside the resonator. Modal discrimination of the modified resonator and the mirror alignment sensitivity is discussed. Basic features of resonator-originated and external beam shaping are compared.
ABSTRACT
Present and estimated future use of personal computers (PCs) in clinical cancer research was assessed after the distribution of 24 personal computers to clinicians and scientists engaged in clinical cancer research. Two questionnaires were sent to the clinicians with an interval of six months. The clinicians were divided into two main groups, 'Experts' and 'Non-experts', based on their background knowledge of and previous experience with computers. Word processing and recording of patient details were the main application fields for the PC. Requested tasks for future were the performance of statistical analyses and graphics. The clinicians, especially the Non-experts, met the following problems upon the reception of the PC: Lack of time and help to become acquainted with the PC, as well as lack of appropriate software. Half of the clinicians were reluctant to admit any usefulness of artificial intelligence for clinical cancer care. It is concluded that the introduction of personal computers will probably improve the facilities for clinical cancer research. However, clinicians need sufficient time and help to get started, and appropriate software must also be provided.
