In this article the properties of resonance cavity, operating condition, and radiation output of optical pumping laser are discussed. Factors affecting the operation and the resultant emission are analysed in detail. Evaluation standard for resonance cavity and active media are described. Cavity constructions for limiting the resonance to one or several modes are suggested, hence, photon degeneracy or brightness of light flux in unit frequency range may be increased by several orders of magnitude. Experimental results on the Ruby laser obtained in our laboratory are given. The interpretations of angular distrubution of light frequency, proposed by the auther, can be used to account for some experimental results published by recent investigertors.