Fast frequency control of microchip lasers

We present the heterodyne of microchip Nd:YAG (and Nd:YVO/sub 4/) lasers with the phase locked loops. The first one, slow, established large thermal drift by thermoelectric element. The second one used electrooptic LiNbO/sub 3/ phase internal modulator to control fast frequency fluctuation. The both PLL´s were optimised. The frequency stability was improved up to seven orders (compare to free running system) and for example offset frequency deviation was about 1 Hz at 10 s averaging time. The criteria of optimisation of optical phase loop will be presented.