Measurement of the thermal lens of grazing-incidence diode-pumped Nd:YVO4 laser amplifier

The thermally induced lensing effects of a diode-pumped Nd:YVO4 laser amplifier in a grazing incidence bounce geometry are carefully measured experimentally. Measurements of the thermal effects are interpreted by considering the diode-pumped amplifier region as a thick lens. A more detailed modeling was made of a quadratic refractive index lens duct for the normal to the bounce plane distribution. Due to the asymmetric pumping the thermal lens shows significant astigmatism. The ratio between dioptric powers in the plane normal to bounce and in the bounce plane is measured to be approximately 20. A nonlinear component of the power dependence of the lens is observed and related to the nonlinear heating induced by energy transfer upconversion. Measurements made under non-lasing conditions are used to infer thermal lensing behavior under lasing conditions and this allows optimization of optical resonator design.