We have been developing a combined technique of using ultra-fast laser in conjunction with fiber-probe delivery to ablate substrate surface in near-field region. Often it is found too difficult to do an in-situ nanometer machining on a pre-formed nanometer structure using traditional optical microscope due to resolution limited by fundamental diffraction limit. Therefore a processing method with nanometer metrology that can be applied in air is advantageous for precision machining on pre-formed nanometer structures. Fundamentally, diffraction limit also restricts the laser spot size to larger than half of the wavelength in free space optics. We will illustrate our technique of sub-diffraction limit drilling by using NSOM (near-field scanning optical microscope) delivered femto-second pulses with nanometer precision. Nanometer-scale surface topology modification has been demonstrated. The ablation characteristics are studied. A precision process control is also developed to reduce the influence of recoil force and debris buildup.

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