Thermal effects in transparent laser crystals and ceramics are generally undesired consequence of the pumping process. In particular temperature gradients determine a non uniform distribution of the refractive index variation and a distortion of the optical surfaces crossed by the laser beam so that the entire medium acts as a lens (thermal lens). Thermal lensing effect when not properly compensated, can seriously hamper the laser performances especially in high power devices. Layered structures with a tailored modulation of the doping level can be used to reduce the peak level of the thermo-mechanical stress as well as the thermally induced deformation of the laser material, thus mitigating the overall thermal lens effect. In this work we present the characterization of the thermal lens occurring in Yb3+ activated ceramics, either with uniform doping or with composite structure of variously doped and undoped layers (doping levels in the range of 1-7% at.). The design of the composite structures aimed to optimize the thermal behaviour was carried out by a computer modelling (finite element analysis). Experimental investigation was performed on samples featuring different doping distributions set in a longitudinally diode pumped laser cavity. The laser efficiency under high thermal load conditions has been compared to that obtained from samples with uniform doping, operating under the same experimental conditions. The thermal lensing effect was detected by means of a wave-front sensor (Shack-Hartmann) whereas its overall effect on the produced laser beam was characterized, measuring the M2 beam quality factor. A detailed comparison of the numerical simulation with the experimental results is carried out to test the reliability of the modelling. This tool can result useful to improve the design of the layered structures aimed to enhance the laser beam quality and the overall efficiency. This research program is supported by a bilateral joined project CNRS-France, CNR-Italy.
Characterization of thermal lensing in layered YAG - Yb: YAG laser ceramic structures
Guido Toci;Angela Pirri;Matteo Vannini;Marco Ciofini;Antonio Lapucci;Laura Esposito;Andreana Piancastelli
2013
Abstract
Thermal effects in transparent laser crystals and ceramics are generally undesired consequence of the pumping process. In particular temperature gradients determine a non uniform distribution of the refractive index variation and a distortion of the optical surfaces crossed by the laser beam so that the entire medium acts as a lens (thermal lens). Thermal lensing effect when not properly compensated, can seriously hamper the laser performances especially in high power devices. Layered structures with a tailored modulation of the doping level can be used to reduce the peak level of the thermo-mechanical stress as well as the thermally induced deformation of the laser material, thus mitigating the overall thermal lens effect. In this work we present the characterization of the thermal lens occurring in Yb3+ activated ceramics, either with uniform doping or with composite structure of variously doped and undoped layers (doping levels in the range of 1-7% at.). The design of the composite structures aimed to optimize the thermal behaviour was carried out by a computer modelling (finite element analysis). Experimental investigation was performed on samples featuring different doping distributions set in a longitudinally diode pumped laser cavity. The laser efficiency under high thermal load conditions has been compared to that obtained from samples with uniform doping, operating under the same experimental conditions. The thermal lensing effect was detected by means of a wave-front sensor (Shack-Hartmann) whereas its overall effect on the produced laser beam was characterized, measuring the M2 beam quality factor. A detailed comparison of the numerical simulation with the experimental results is carried out to test the reliability of the modelling. This tool can result useful to improve the design of the layered structures aimed to enhance the laser beam quality and the overall efficiency. This research program is supported by a bilateral joined project CNRS-France, CNR-Italy.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
