Spacers

The spacer rings are used for the parallel mounting of the FPI plates in the interferometer assemblies. On each side they have three raised polished contact points spaced equidistant at 120° intervals. The parallelism error is less than λ/20 (λ = 550 nm) and can be completely adjusted in the interferometer assemblies. The etalons are supplied with a compensating ring in Vacodil 36 or in brass to fill out the remaining length of the holder.
Parallel adjustment of the interferometer plates (fine tuning) is achieved easily by means of adjustment screws in the interferometer assembly.
The thermal expansion coefficients of Vacodil and brass are 1,3*10^-6/K und 18*10^-6/K., respectively.

Fused Silica Thin Spacers

Three spacer plates with a diameter of 4 mm are used for plate separations from 0.2 to 0.9 mm. Their parallelism is approx. λ/100 (λ = 550 nm). The three spacers have identical thicknesses with an accuracy of  λ/20. After the Fabry-Perot plates have been coated, the spacers are optically contacted to a reflecting surface at equidistant 120° intervals, close to the edge of the plate.
The thermal expansion coefficient of fused silica is 0.5•10^-6/K.
When thin spacer plates are used alternatively with ring spacers, the contact points of the ring spacers must be raised to protect the thin spacer plates against damage. This is possible with ring spacers with a thickness of 3 mm or more.

• Price per set, including contacting → MET 3
• Compensating ring in Vacodil 36 to fill out the rest of the length of the holder → MET 36