For the Euclid mission a pre-development phase is implemented to prove feasibility of individual components of the
system. The optical system of EUCLID Near-Infrared Spectrometer & Photometer (NISP) is composed of 4 lenses,
bandpass filters and grisms. The lenses are made of different materials: the corrector lens (fused silica) directly behind
the dichroic and the lenses L1 (CaF2), L2 (LF5G15), and L3 (LF5G15) that are mounted in a separate lens barrel design.
Each lens has its separate mechanical interface to the lens barrel, the so called adaption ring.
The adaption ring shall provide the necessary elasticity caused by different CTEs of the lens and ring materials, as well
as shall allow the high position accuracy of the lenses relative to the lens barrel and the optical axis.
The design drivers for the adaption ring are high precision, cryogenic operation temperature (150 K) and the large
dimension of the lenses (150 - 170 mm). The design concept of the adaption ring is based on solid state springs, which
shall both provide sufficient protection against vibration loads at ambient temperature as well as high precision (<
±10 μm) and stability at cryogenic temperatures.
Criteria for the solid state spring design shall be low radial forces at cryogenic conditions to avoid any refractive index
and polarization variations. The design shall be compliant to the large temperature differences between assembly and
operation, the high precision and non-deformation requirements of the lenses as well as to the deviating CTEs of the
selected lens materials. The paper describes the selected development approach including justification, thermal and