A customized optical system composed of collimating and focusing lenses is proposed to achieve the beam focusing of high-brightness diode laser bars with high fill factor for optoacoustic applications. Through an optimized design, the beam of a 940-nm diode laser bar is first collimated and symmetrized between the fast and slow axes, and then is reduced in size into a square beam (~ 3.7 mm x 3.7 mm at 1/e2 of the peak) with intensity of ~ 3.2 kW/cm2. In an optoacoustic environment, the optical spot achieved can illuminate a small region of tissue at high intensity to achieve in-depth imaging with high resolution.