Abstract Single frequency laser has the advantages of high stability in frequency and low noise. Therefore, single frequency laser is now widely used in applications, such as high precision measurement, holography and data storage. Attempts to generate second harmonic radiation using a linear cavity have typically resulted in significant amplitude fluctuations due to longitudinal mode coupling. Various techniques have been proposed for solving the so called ¡§green problem¡¨ to achieve single longitudinal mode operation, such as inserting optical component in the conventional linear cavity or use ring cavity instead of linear cavity. Uni-directional ring cavity has shown to be the most robust method for producing single frequency laser. The purpose of this study is to develop compact and low-cost single frequency IR and green lasers. A novel symmetrical two-mirror figure ¡§8¡¨ ring cavity is developed. Instead of using several laser mirrors for beam deflection, this ring laser system employs only two spherical mirrors to form the laser cavity for traveling wave oscillation and eliminates ¡§spatial hole burning¡¨ caused by the standing wave operation. In this thesis, we use two-mirror figure ¡§8¡¨ ring cavity for the generation of single frequency IR and green lasers. The polarization status is crucial for high efficient intracavity frequency doubling. The polarization evaluation in a nonplanar and reentrant ring cavity is characterized by measuring the thermally induced linear and circular birefringence and analyzing the polarization rotation due to cavity configuration. We have demonstrated a 2-mirror figure ¡§8¡¨ ring cavity which is compact and has few optical elements. The stable single frequency laser output of our ring cavity promises to make the design widely applicable to solid-state lasers.