In most analyzers the necessary interaction length between the light beam and the sample is obtained in a multipass Herriott cell. The group has the right expertise and tecnical capabilities to realize multipass cells up to 100 m pathlength. An example is given in the photo, showing in foreground the back of one mirror, and in background, across the hole, the opposite mirror. The sequence of the spots of a HeNe alignment laser is well visible. Entrance and exit occurr across two peripheral holes in the background mirror. This is the reason for which a spot is missing in the low-right side of the foreground mirror. In case of entrance and exit across the same hole, this spot would be present. In case of mirrors with one peripheral hole each, the beam would leave the cell across the missing spot.
We realized open and closed cells, with different materials: BK7, fused silica and stainless steel for the mirrors; glass, aluminum, stainless steel and carbon fibers for the structure, according to specific requirements.
In the above cell, the mirrors are kept by a carbon fiber pipe, inserted across the holes, and fixed by using glue.