The most difficult aspects in manufacturing a reflective slit substrate are achieving a precisely fabricated slit
surrounded by an optically flat surface. A commonly used technique is to polish a metal substrate that has a slit cut by
electric discharge machine (EDM) methods. This process can produce 'optically flat' surfaces; however, the EDM can
produce a slit with edge roughness on the order of 10 microns and a RMS field roughness of ~1 micron. Here, we
present a departure from these traditional methods and employ the advantages inherent in integrated circuit fabrication.
By starting with a silicon wafer, we begin with a nearly atomically flat surface. In addition, the fabrication tools and
methodologies employed are traditionally used for high precision applications: this allows for the placement and
definition of the slit with high accuracy. If greater accuracy in slit definition is required, additional tools, such as a
focused ion beam, are used to define the slit edge down to tens of nanometers. The deposition of gold, after that of a
suitable bonding layer, in an ultra-high vacuum chamber creates a final surface without the need of polishing. Typical
results yield a surface RMS-roughness of approximately 2nm. Most of the techniques and tools required for this process
are commonly available at research universities and the cost to manufacture said mirrors is a small fraction of the
purchase price of the traditional ones.