Near-Field Imaging

Near-field imaging involves using a mask to project a pattern of laser light onto a part. The features contained in the pattern are etched into the target material at a magnification determined by the optical element relative positioning. This technique is the basis for excimer laser micromachining in many materials processing systems.

With near-field imaging, fluence and spatial distribution are controlled by optical magnification. Image quality is independent of beam divergence, diffraction, and incoherence.

Advantages of Near-Field Imaging

The advantages of using near-field imaging include:

• Near-field imaging is very flexible, which allows for a wide range of shapes.
• Setting up the optics for near-field imaging is fairly simple.
• High tolerances can be met.
• You have a choice of different masks for different applications (metal, chrome on quartz, dielectric).
• A very wide range of demagnification is possible.

Disadvantages of Near-Field Imaging

The disadvantages of using near-field imaging include:

• The mask must fit into the usable portion of the beam.
• Focus is critical to feature quality.
• Spherical aberration can distort image shape.
• Energy density non-uniformity across the mask is duplicated on the part.
• The work area on the process material is limited by demagnification.

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