While neuron stimulation through modulated ultrasound has already been demonstrated in various animal models, there is yet no consensus on the detailed work principle of this modality. This paper presents therefore the design, fabrication and characterization of an acoustic collimator dedicated to improving the spatial resolution of an ultrasound neuron modulation system. We designed a family of acoustic collimators to modify the focal length of a large commercial ultrasound transducer to target various focal distances and accommodate transducer and animal model (mouse)sizes. We 3D-printed the acoustic collimators and characterized their new focal distances. We achieved focal depth modification from 1mm to 5mm by simply switching different collimators. Moreover, measurement results closely matched design performances. Finally, a multi-index ultrasound neuron stimulation setup was built using these collimators.