An ultra-long optical needle field is created in the focal volume of high-NA lens utilizing the reversal of the radiation pattern from an electric dipole array. A depth of focus of 8λ can be obtained with this method. Within the depth of focus, the longitudinally polarized component is predominant and consists of higher than 86% of the total electric energy density. Nearly constant FWHM transverse spot size less than 0.414λ can be maintained throughout the depth of focus.
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