Abstract: A laser apparatus and a polycrystalline material are described. The apparatus includes the polycrystalline material which is configured to receive pumping light at a pump wavelength and to produce an optical gain for laser oscillation at a laser wavelength different from the pump wavelength. The polycrystalline material includes a ceramic material with a predetermined grain size. The polycrystalline material further includes a rare earth dopant with a predetermined concentration, wherein the predetermined grain size and the predetermined concentration cause the polycrystalline material to exhibit the optical gain at the laser wavelength.

Abstract: A power amplifier is disclosed which reliably amplifies an input signal and decreases power consumption. A pre-driving circuit pre-drives a driving circuit of a power amplifying circuit in response to an input signal. The driving circuit drives an output circuit in the power amplifying circuit. A detecting circuit detects the level of the output of the driving circuit. The pre-driving circuit receives the output of the detecting circuit and supplies the pre-driving circuit with a pre-driving current varying in response to the output of the detecting circuit. Consequently, the pre-driving current can be designed to change in response to demand, i.e., the pre-driving current can be low when demand is low and increase as the occasion demands.

Abstract: The muting circuit of the present invention comprises a first and second differential amplifier. The first differential amplifier comprises first and second transistors. The base electrode of the first transistor receives an input signal. The second differential amplifier comprises third and fourth transistors. The collector electrode of the third transistor is connected to the collector electrode of the second transistor, while the collector electrode of the fourth transistor is connected to the collector electrode of the first transistor. A switching circuit, receiving an intercepting signal, is coupled to the first and second differential amplifier. In the absence of an intercepting signal, the switching circuit causes the conduction of the first differential amplifier, and while cutting off the second differential amplifier. Upon receiving an intercepting signal, the switching circuit cuts off the first differential amplifier while it causes the conduction of second differential amplifier.