We report the first observation of terahertz (THz) radiation from an undoped (111) InAs surface excited by 1.55 µm femtosecond laser pulses. The surface illuminated by an unfocused beam at an incidence angle of 45 degrees measured with respect to the surface normal emits THz radiation with weak dependence of the amplitude on the azimuthal angle. The results indicate that the radiation excited by the unfocused beam at a power density less than ∼1 W/cm2 is mainly explained by the surge current effect accompanied by a small component associated with the optical rectification effect.

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Hypermedia/hypertext-based resources for learning generally provide learners with hyperspace, which consists of pages and links among the pages. In the hyperspace, they can navigate the pages in a self-directed way to learn the domain concepts/knowledge. The navigation often involves constructing knowledge, in which they would make semantic relationships among the contents learned in the navigated pages. Such self-directed learning in hyperspace requires learners to reflect on their knowledge construction process, which they have carried out so far, since what and how they have learned becomes hazy as the navigation progresses. However, it is hard for them to keep reflection during navigating hyperspace. The main issue addressed in this paper is how to facilitate learners' reflection to promote their self-directed learning. Our approach to this issue is to provide learners with a learning tool, which allows learners to annotate their navigation history representation with their knowledge construction process. The annotated navigation history enables them to reflect on their knowledge construction process. This paper also demonstrates an interactive history, which generates the annotated navigation history from learners' annotation. It also generates a knowledge map that visualizes the semantic relationships among the pages learners have learned in hyperspace. This paper also describes a case study with the interactive history. The results indicate that it facilitates reflection on knowledge construction process carried out in hyperspace.