Mounting And Fixturing - HP 5501B Operating And Service Manual

2-33. Mounting and Fixturing

2-34. Heat Flow Considerations. The laser tuning technique of the HP5501B requires efficient heat
exchange with the ambient. Heat flow is primarily through the base of the laser head assembly to
the surrounding environment. An external heat sink is not required but free air circulation around
the laser head will ensure good performance.
2-35. In cases where vertical mounting of the HP5501B is desired, care should be taken to minimize
laser beam disturbances due to air turbulence caused by the HP5501B heat exchange. It is most
important to prevent differential effects which can occur due to turbulence in the beam path
between a polarizing beam splitter and a retroreflector or plane mirror. Differential turbulence
causes fluctuations in the optical path length difference that is being measured. Both differential
and common mode turbulence can cause fluctuations in alignment by bending the light beam.
Common mode turbulence is turbulence that is present in the beam path between the HP5501B
and a polarizing beam splitter. In either case some amount of noise can be present in the
interferometer measurement due to turbulence.
2-36. If interferometer components (optics) are mounted very close to the HP5501B such that the
operating temperature of the optics are affected, it is recommended that alignment and
operation of the interferometer be performed after the HP5501B has been running for a sufficient
period of time to allow thermal equilibrium to be established. In well ventilated installations, one
hour of running time should be sufficient. When enclosures are used and the ambient
temperature is changed by several degrees (centigrade) by the HP5501B, thermal equilibrium is
not established as quickly and the laser should be run for a longer period of time.
2-37. Mounting. Mount the laser head by means of the three slotted tabs that extend outward from the
bottom edges of the unit (refer to Figure 2-1 for exact locations and dimensions). The mounting
tabs may be secured to the work surface in any fashion that will not transmit stresses to the main
enclosure and, consequently, to the laser tube or printed-circuit assemblies. If necessary, the
tabs can be removed and the unit mounted on a flat surface with 4 mm machine screws; use the
same tapped holes that are used to secure the tabs, ensuring that the mounting method does
not stress the base casting and that the screws do not penetrate the base casting more than 7
mm.
2-38. Beam Alignment. Rotate the turret at the front of the laser head so that the beam exits through
the large aperture. DO NOT STARE DIRECTLY INTO THE BEAM APERTURE. Presence of the
red laser beam can be verified by placing a piece of paper in the beam path and observing the
beam reflection on the paper. The components of the laser transducer system must now be
aligned so that the laser beam strikes the photodetector of the receiver (HP10780A). Refer to the
HP10780A Receiver documentation and the Laser Transducer System Manual for further
alignment information.
2-39. Pointing Stability. The angle at which the laser beam exits the HP5501B can change from turn-
on through the time when the HP5501B and its surroundings reach thermal equilibrium.
2-40. The HP5501B should not be exposed to ambient temperature changes greater than ±5
Centigrade during operation to keep pointing stability variations to a minimum during
interferometer measurements.
HP5501B
Installation
2-9