  Detailed polarization properties have been examined in laser-diode-pumped
(LD-pumped) micro-grained ceramic Nd:YAG lasers in different microchip cavity
configurations. Stable linearly-polarized single-frequency oscillations, whose
polarization direction coincide with that of an LD pump light, were observed in
an external cavity scheme. While, in the case of a thin-slice laser scheme with
coated reflective ends, elliptically-polarized single-frequency operations took
place in the low pump-power regime and dynamic instabilities appeared,
featuring self-induced antiphase modulations among counter-rotating
circularly-polarized components having slightly different lasing frequencies,
with increasing the pump power.
