Reducing thermal lensing in diode-pumped laser rods

We present a diode-end-pumped Nd:YAG laser with multiple composite rods. Co mposite rods (rods with undoped endcaps) were used in order to remove the p art of thermal lens formed by the bending of the pump face of the rod. We g ive an analytical expression for determining the fraction of the thermal le ns contributed by the end effect in a homogeneously doped rod, such that th e improvement in a composite-doped rod can be determined. For the Nd:YAG ro ds used in this work this part of the thermal lens constituted approximatel y 47% of the total thermal lens in the homogeneously doped rod leading to t he maximum pump power being increased by almost 90%, on introduction of com posite rods. The laser was demonstrated, giving a maximum output power of o ver 16 W and an optical efficiency of over 42% in fundamental mode operatio n. (C) 2000 Elsevier Science B.V. All rights reserved.