This invention relates to optically pumped lasers, and more particularly to such lasers as laser diode pumped Nd:YAG lasers.
Many applications require an efficient reliable laser source having a high peak to average power capability, and capable of emitting a stable radiation pattern. Optical communication over the deep space is such an application. Nd:YAG lasers pumped by semiconductor laser diodes have figured prominently among potential sources for such applications. In this arrangement many GaAlAs/GaAs laser diodes can be combined to optically pump the Nd:YAG laser. Recent work reported by the inventor in Appl, Phys, Lett. 47(2), July 15, 1985, pp 74-76, has indicated that by utilizing the proper pump geometry, nearly half of the output of the GaAlAs/GaAs diode laser can be converted to Nd:YAG laser light.
The Nd:YAG laser can be thought of as a means for converting incoherent light from laser diodes to coherent light. In that manner, many laser diodes with poor spatial and spectral qualities may be converted into a single coherent source with vastly improved spatial and spectral properties. Thus, as compared to simply combining incoherent laser diode sources, a powerful, extremely bright, coherent laser source can be realized with such a converter while sacrificing little in size or efficiency. Moreover, the increased power allow the system designer of a deep space communication system the added freedom to trade for increased data rate or decreased aperture or pointing requirements, thus reducing size mass and complexity of the communications system.
In prior-art devices, the geometry conventionally used to accomplish this conversion of incoherent light from laser diodes into a coherent light is the side-pumped geometry in which the diodes are placed along the length of the laser medium, such as a crystal rod (e.g., Nd:YAG) or liquid column (e.g., dye laser). The medium is thus pumped perpendicular to the direction of propagation of the laser resonator mode. As more power is required, more diodes can be added along and around the laser medium. However, this prior-art arrangement is relatively inefficient, and thus requires large numbers of pump diodes to achieve a respectable output power level.