Nonlinear optical response of a Co:ZnO epitaxial thin film for large spectral range pulse modulation

We demonstrate the large spectral range nonlinear optical response of a Co:ZnO epitaxial thin film (with single crystal structure) with the absorption range from 1.0 μm to 2.0 μm, for the first time to our knowledge. The third-order nonlinear optical properties and saturable absorption of Co0.15Zn0.85O (Co:ZnO) were studied with the modulation depth of 0.68% and saturation fluence of 1.532 μJ/cm2. Passive Q-switched lasers at the wavelengths of a 1.4 μm Nd:YGG laser and a 1.9 μm Tm:LuVO4 laser were realized with the Co:ZnO epitaxial thin film as the saturable absorber. In the case where the wavelength is 1.4 μm, we obtained the shortest pulse width, the largest pulse energy and the highest peak power, which were recorded at 89 ns, 2.3 μJ and 25.8 W, respectively. Moreover, when the laser output wavelength is 1.9 μm, we got the smallest pulse width of 274 ns. This work provides a promising saturable absorber with a large spectral range response.