Operation improvement of side-pumped Er:Yb:glass lasers through optical compensation techniques

Abstract

In this paper we report the results of the research on a double side-pumped Er:Yb:glass slab laser. Due to the nonsymmetric power distribution inside the slab a displacement of the laser beam is observed thus leading to cavity misalignment and consequently to extraction efficiency loss. At repetition rates of about 5Hz this allows just a burst operation with an increased thermal load inside the slab. Numerical-theoretical studies about time-dependent temperature distribution in the laser material with appropriate boundary conditions concerning the considered asymmetric geometry lead to a model for mode axis thermal shift and allow to evaluate the amount of cavity misalignment in order to restore the maximal extraction efficiency. By turning or shifting the cavity mirrors is possible to improve the burst operation but the maximal overlap between the mode axis and the inverted region cannot be recovered. Then, an alternative optical configuration able to intrinsically account for the cavity misalignment has to be designed. The matrix formalism was effectively employed to calculate the specifics of one or more optical compensators to be inserted in the cavity to realign the laser resonator. Several configurations were analyzed and the beneficial effects on both thermal lensing and bending were predicted. Experimental measurements validated the model. In particular, an uninterrupted pulsed operation at the highest repetition rates was effectively recovered thus reducing the thermal load inside the laser slab and making such a laser system more effective in free-space laser applications.