Interference window holders
In the interference system, two narrow parallel beams are emitted from the light
source through a slit mask. One beam passes the sample sector, the other the
reference sector. Afterwards, both beams are brought to converge onto the plane
of projection, producing an interference phenomenon.
The interferogram is actually much larger than the image seen on a standard analytical ultracentrifuge, showing only the inner and brightest fringes. Complete interferograms, recorded with the AIDA system, show not only the zeroth, but also the first order of diffraction. The influence of stray light can be observed in the transition from the zeroth to the first order.
For such interferograms, interference window holders have proven to provide much clearer images, as shown on the right image of Fig. 2. Consequently, Fourier transforms of such images are less noisy and more stable. It may be questionable whether interference window holders provide an enhancement on classical interference systems as well. In any case, they force the user to adjust the laser delay very precisely towards the center of the sectors – the slits will allow only 0.1 degrees tolerance before the interferogram diminishes. This guarantees that detection occurs well in the sectors' center and not towards one of the walls.
Only the window holder directed towards the light source is replaced; the other has a standard