Before And After Service Product Safety Checks; Laser Head Block Diagram Description - Agilent Technologies 5517B Operation And Service Manual

The WARNING signal denotes a hazard. It calls attention to a procedure or practice which could result in personal
injury if not adhered to or correctly performed.
The CAUTION signal denotes a hazard. It calls attention to an operating procedure or practice which could result in
damage or destruction to part of or all of the product if not adhered to or correctly performed.

8-18. Before and After Service Product Safety Checks

8-19. Visually inspect the interior of the serviced instrument for any signs of abnormal internally generated heat,
such as discolored printed circuit boards or components, damaged insulation, or evidence of electrical arcing.
Determine and remedy the cause of any such condition.

8-20. LASER HEAD BLOCK DIAGRAM DESCRIPTION

8-21. The major structures of the HP 5517B are shown on the HP 5517B Laser Head Block Diagram in Figure 8-2
and include the control electronics, laser assembly, sampler assembly, reference receiver, and the high voltage power
supply. All of the necessary control signals for the operation of the HP 5517B are generated internally. Power
requirements are ±15 Volts DC from external system power supplies.
8-22. Overall, the purpose of the laser head is to emit a collimated, dual frequency laser beam with a high degree of
stability. A portion of the emitted beam (about 10%) is directed to the sampler assembly to establish a reference
frequency while the main portion of the beam is directed to external optics and returned to an external
measurement receiver to develop a measurement frequency. The system electronics compare the reference and
measurement frequencies to calculate the relative displacement of the optics.
8-23. The control electronics determine the tuning of the laser assembly to ensure an accurate laser wavelength for
making measurements. Two phases of tuning are used, warmup mode and optical mode. When the desired
characteristics of the laser beam are obtained during the optical mode, the system is ready to make measurements.
8-24. The laser assembly optics ensure correct laser frequency polarizations and also collimate the laser beam.
Collimating minimizes variations in the diameter of the beam as it travels away from the laser head. Laser
frequency F2 (higher frequency) is polarized in a plane perpendicular to the base of the HP 5517B chassis. The other
laser frequency F] (lower frequency) is polarized perpendicular to Fj. The difference between the two laser
frequencies F| and F2 is small compared to their optical frequencies. The exit aperture shutter of the turret
assembly has three positions. The first blocks the laser beam entirely; the second allows a small diameter laser
beam to exit for optical alignment purposes; and the third passes the entire laser beam.
8-25. Before the laser light is emitted from the HP 5517B, a portion of it is sampled by the sampler assembly. Most
of this sample feeds into the reference receiver while the remainder is used to control laser tuning. The reference
receiver generates the reference frequency signal by mixing the two laser frequencies. The reference frequency is a
1.5 to 2.0 MHz, TTL level square wave. When the laser tuning stabilizes, the reference frequency is sent to the
system electronics.
8-26. During a measurement, the laser beam follows a path through external measurement optics and to the HP
10780 Receiver. If the optics remain stationary, the measurement frequency and the reference frequency are the
same. Relative motion between the measurement optics result in a change of the measurement frequency. The
electronics compare the measurement frequency to the reference frequency and calculate the displacement of the
optics. The measurement frequency output from the HP 10780 system receiver requires proper alignment of
measurement optics in addition to stable laser tuning.