Effect of a thermal lens in a crystal of yttrium aluminum garnet on the stability of the emission of a continuous laser

It is shown that the relative fluctuations in the focal length of the thermal lens induced in the YAG:$Nd^{3+}$ crystal of a continuous laser with a common cooling flow of the pumping lamp and the crystal, have a value of the order of 20%. A theoretical calculation, confirmed by experimental measurements, shows that these fluctuations are due to relative variations in the emission power of not less than 10%, and also have a considerable effect on the spectral composition of the emission.