Gentec-EO Diffractive Optics (HBS) - Manual (Page 9)

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HBS Instruction Manual Revision 4.1 Feburary 2014
2 HBS SETUP AND ALIGNMENT
Normal Incidence Setup
The relation between the incidence angle upon the HBS and the angles where the secondary beams are
diffracted is determined by the properties associated with the general theory on gratings. In order to obtain
the specified secondary beams (angles, sampling ratio), it is recommended to place the HBS at normal
incidence with respect to the beam to be sampled.
Alignment
In order to avoid multiple parasitic diffracted orders between the HBS surfaces, the grating surface must
be placed as the output surface.
All beams are diffracted within the same plan. The plan's normal axis is parallel to the direction of the lines
engraved in the substrate. By turning the HBS around its perpendicular axis, the diffracted orders turn
accordingly and always within the same plan (see Fig. 2-1).
Because of the standard substrates' weak wedge, the zero order is slightly deviated with respect to the
incident axis. By turning the HBS in the above manner, the zero order should also slightly turn, especially
when observed at a great distance from the alignment point.