In certain embodiments, a system for calibrating the focal point of a laser beam comprises a laser, focusing optics, detector optics, a two-photon absorption (TPA) detector, and a computer. The laser generates the laser beam. The focusing optics direct the focal point of the laser beam along a z-axis towards a zero-surface corresponding to a zero-plane, and receives a portion of the laser beam reflected by the zero-surface. The detector optics receive the reflected portion from the focusing optics, and directs the reflected portion towards a TPA detector. The TPA detector senses the peak intensity of the reflected portion, which indicates a proximity of the focal point to the zero-surface, and generates a signal representing the peak intensity of the reflected portion. The computer determines whether the focal point of the laser beam is calibrated in response to the signal representing the peak intensity.