FIG. 2.

Experiment demonstration of the increased depth of focus by using the designed grating pattern consisting of two different spatial frequencies compared with the result by using the normal grating pattern. (a)–(c) The measured 2D intensity profile (perpendicular to the optical axis) of the focused beam showing that the Bessel-like beam with increased DOF is generated near the focal plane of the objective along the beam path (Z axis). Z = 0 represents the focal plane. (d)–(f) The normalized intensity curves corresponding to the center lines of (a)–(c), respectively. The coordinate values correspond to the pixel numbers of the CCD camera with the pixel size of 3.6 μm.