  The Far-UV Off Rowland-circle Telescope for Imaging and Spectroscopy (FORTIS)
has been successful in maturing technologies for carrying out multi-object
spectroscopy in the far-UV, including: the successful implementation of the
Next Generation of Microshutter Arrays; large-area microchannel plate
detectors; and an aspheric "dual-order" holographically ruled diffraction
grating with curved, variably-spaced grooves with a laminar (rectangular)
profile. These optical elements were used to construct an efficient and
minimalist "two-bounce" spectro-telescope in a Gregorian configuration.
However, the susceptibility to Lyman alpha (Ly$\alpha$) scatter inherent to the
dual order design has been found to be intractably problematic, motivating our
move to an "Off-Axis" design. OAxFORTIS will mitigate its susceptibility to
Ly$\alpha$ by enclosing the optical path, so the detector only receives light
from the grating. The new design reduces the collecting area by a factor of 2,
but the overall effective area can be regained and improved through the use of
new high efficiency reflective coatings, and with the use of a blazed
diffraction grating. This latter key technology has been enabled by recent
advancements in creating very high efficiency blazed gratings with impressive
smoothness using electron beam lithography and chemical etching to create
grooves in crystalline silicon. Here we discuss the derivation for the
OAxFORTIS grating solution as well as methods used to transform the FORTIS
holographic grating recording parameters (following the formalism of Noda et
al.1974a,b), into curved and variably-spaced rulings required to drive the
electron beam lithography write-head in three dimensions. We will also discuss
the process for selecting silicon wafers with the proper orientation of the
crystalline planes and give an update on our fabrication preparations.
