The optical set-up used in the experiments is shown in finaloptsetup.
The two plano-convex lenses have focal lengths of respectively 
and 
. The diameter of the lenses are 
.
The two lenses were already available in the laboratory, and other lenses would
have been just as good.
The distance between the lenses and the size of
the pin-hole was adjusted to optimize the homogeneity of the sheet.
(We wanted a sheet with thickness around 
for reasons
discussed in chapter 
). The size of the pin-hole
was chosen to 
. This size corresponds to about one half of the diameter
of the beam from the laser. The hole is large enough for most of the laser light
to pass through, and the irradiance of the light passing through is approximately
constant. For this beam diameter the distance between the lenses was adjusted
to minimize variations of the thickness. The distance between the two lenses was
adjusted while using the video camera system to monitor the variations.
The laser sheet was measured to be 
wide over a range
of 
around the center of the thin region. The distance between
the two lenses then was 
. Using this value together with a desired
length of 
for the thin region and a wavelength of 
in equation
and gives 
and 
.
In our experimental set-up the center of the thin region was located
behind the last lens. Using this value in equation
the limiting thickness is 
, while the thickness was measured to .
We conclude that the theoretical estimates seem fairly good.