Agilent Technologies 5517B, Руководство пользователя

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28 Agilent 5517B/BL/C/D/DL/FL User’s Guide
3
Installation
Heat flow considerations
The laser tuning technique of the laser head requires efficient heat
exchange with the ambient. For lasers without vented covers, 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. For lasers with
vented covers, the majority of heat is removed with proper air flow.
In cases where vertical mounting of the laser head is desired, care should
be taken to minimize laser beam disturbances due to air turbulence caused
by the laser head 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 laser head and a polarizing beam splitter. In either case some
amount of noise can be present in the interferometer measurement due to
turbulence.
If interferometer components (optics) are mounted very close to the laser
head such that the operating temperature of the optics are affected, it is
recommended that alignment and operation of the interferometer be
performed after the laser head 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 (Celsius) by the laser head, thermal equilibrium is not established
as quickly and the laser should be run for a longer period of time.
Vibration isolation
Since the system measures only the relative motion between the
interferometer and reflector, measurements are not affected by vibration
along the beam axis of the laser source or the receiver. When vibration of
the laser head causes displacement of the beam (perpendicular to beam
axis) at an interferometer or receiver, the beam signal power can fluctuate.
If this fluctuation is too great, insufficient beam signal will arrive at the
receiver, causing a “measurement signal error.”
Magnetic shielding
Agilent laser heads contain a permanent magnet. When installing an
Agilent laser measurement system in an application sensitive to magnetic
fields, shielding around the laser head may be required.