Kompakte, grün emittierende Laser auf Basis von Pr:YLF

Abstract

Solid-state lasers have become an established tool in the sectors of production and metrology. The processing conditions common in these sectors determine requirements upon the energetic, spatial, temporal and spectral characteristics of the laser in question. While material processing requires high power output at short pulse durations, applications such as those in medicine, metrology and entertainment need continuous power below one watt at an adapted wavelength in the visual spectrum. These requirements strongly limit the choice of active laser media and designs, and have only been examined in the last few years. Lasers based on Pr:YLF, can emit in the visible spectral ranges of cyan via green, orange and red. When InGaN diodes emitting blue are used as a pump source, lasers can be built with a high efficiency and a compact set up. These lasers exhibit, thus, a high potential for applications in diverse fields of medicine, metrology and entertainment, where a mobile use or the integration in a treatment, measurement or entertainment devise is required. Currently, laser-based digital projectors for mobile use provide a clear example for the use of beam sources of moderate output power in the visible spectral range in large lot sizes. The use of laser-based projectors would increase the efficiency in a much smaller space, but has, however, failed to date because the lack of a compact and efficient laser source with an adequate output power in the green spectral range. The demands upon a high degree of integration of the source creates a challenge which had not been examined for the sources based on Pr:YLF. In this work, a systematic comparison has been made of the potential of highly compact free-space and waveguide lasers on the basis of this active medium. For this purpose laser-beam sources are examined with an emission in the green spectrum, which aim for a high degree of compactness and efficiency. The concrete requirements result from the application as a beam source for digital projectors; the use of the sources examined, however, is not limited to this application. As a pump source, an InGaN laser diode emitting blue is used, whose emission wavelength suits an absorption line of Pr:YLF. Configurations of free-space lasers as well as waveguide lasers were investigated analytically, numerically and experimentally. A very compact demonstrator model of a free-space laser fulfills all the requirements placed on the beam source regarding output power, beam quality, efficiency and volume. For the first time, a compact Pr:YLF laser with a power density of 200 mW / cm^3 has been demonstrated to be feasible. In addition, the design and the construction strategy allow automation and enable a cost-effective mass production. Moreover this study compares under which conditions regarding dimension and losses waveguide laser have advantages over the design presented here of a free-space laser. For this, waveguide structures are generated by means of fs-laser irradiation and, through experimental investigations of a waveguide laser, its losses are determined. Furthermore, this paper examines the potential, for the first time, that microscopically manufactured waveguides made out of Pr:YLF exhibit