  Harmoni is the ELT's first light visible and near-infrared integral field
spectrograph. It will provide four different spatial scales, ranging from
coarse spaxels of 60 x 30 mas best suited for seeing limited observations, to 4
mas spaxels that Nyquist sample the diffraction limited point spread function
of the ELT at near-infrared wavelengths. Each spaxel scale may be combined with
eleven spectral settings, that provide a range of spectral resolving powers
from R 3500 to R 20000 and instantaneous wavelength coverage spanning the 0.47
- 2.45 {\mu}m wavelength range of the instrument. The consortium consists of
several institutes in Europe under leadership of Oxford University. Harmoni is
starting its Final Design Phase after a Preliminary Design Phase in November,
2017. The CRAL has the responsibility of the Integral Field Unit design linking
the Preoptics to the 4 Spectrographs. It is composed of a field splitter
associated with a relay system and an image slicer that create from a
rectangular Field of View a very long (540mm) output slit for each
spectrograph. In this paper, the preliminary design and performances of Harmoni
Image Slicer will be presented including image quality, pupil distortion and
slit geometry. It has been designed by CRAL for Harmoni PDR in November, 2017.
Special emphases will be put on straylight analysis and slice diffraction. The
optimisation of the manufacturing and slit geometry will also be reported.
