Open-aperture Z-scan study for absorption saturation: accurate measurement of saturation intensity in YLF:Yb for optical refrigeration.

Knowledge of saturation intensity of gain or absorption plays a fundamental role in a variety of applications ranging from lasers to many nonlinear optical processes. Here, we present an analytical expression for open-aperture Z-scan transmission for accurately measuring the saturation intensity in the low absorbance samples but at arbitrary pump intensities. We exploit this formalism to investigate the absorption saturation of : (YLF:Yb) in the anti-Stokes excitation region for optical refrigeration at high pump intensities. An absorption saturation intensity of 14.5±1/ was measured in YLF:Yb at 1020 nm (||) at room temperature.