The relation between the internal reflectivity of output end face of a laser rod and the energy output under usual excitation is investigated. By analytical calculations, the following are deduced.
(1) For a given pumping energy, there is an optimum value of end face reflectivity to maximize the energy output.
(2) This optimum value decreases as the pumping energy increases.
(3) The maximum value of output energy is proportional to the square of logarithm of this optimum value of reflectivity.
(4) As is known, the energy output varies linearly with the pumping energy for a given value of reflectivity and depends largely upon the losses in the rod.
Changing of reflectivity of the end face is equivalent to varying of the degree of coupling with the rod, for which two methods are tried, one is to increase gradually the number of small holes made by removing the dielectric multilayer that covers the end face to make it a mirror, the other is to vacuum-evaporate a silver film onto the end face and to vary its thickness. The value of energy output obtained by measurement is in reasonable agreement with the value obtained by calculation.
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