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SECTION 4: MAINTENANCE
The following sections discuss seeder and host laser service which can be performed in the
field if the system is not performing properly.
4.1 HOST LASER MAINTENANCE
The injection seeder assembly is factory aligned and adjusted. There are no parts within the
injection seeder requiring routine maintenance. When used in conjunction with the injection seeder,
however, the host laser requires special attention beyond that required for non-seeded operation.
Specifically, the following items should be monitored periodically and attended to if necessary.
1. It is important to monitor the power rejected off the host polarizer which is incident on the
injection seeder. This is especially true if the ambient temperature around the seeder/host laser
system changes significantly (>10°C) from the temperature during installation. Power is
rejected off the host polarizer for two reasons:
a. The Pockels cell does not give a perfect, uniform, quarter-wave phase retardation across the
entire beam diameter at the exact time that the pulse is being emitted from the host. A
typical reason for this is the Pockels cell quarter-wave voltage is a function of
temperature, changing by approximately 50 V/°C.
As a result, if the ambient operating temperature changes significantly from the initial
installation temperature, the Pockels cell voltage must be adjusted to prevent an
excessive amount of energy from being directed back towards the injection seeder. The
procedure for making this adjustment is in Section 2.2.3.
The Pockels cell also can give a non-quarter-wave phase retardation due to the inherent
difficulties in applying a uniform high voltage across the entire aperture of the crystal
within the Pockels cell. This, however, should not change over time provided the
Pockels cell is properly aligned and in good working condition.
b. The host laser's polarizer angle has shifted. This may occur due to changes in temperature
and/or humidity. If the shift in angle causes the polarizer to reject a significant amount
of "p" (vertical) polarization, then a certain fraction of the circulating power within the
host resonator will be rejected off the host polarizer in the direction of the injection
seeder. If such a shift in angle occurs, it should be corrected.
2. The water reservoir should be kept at least >75% full. The water in the reservoir acts as a large
thermal mass, damping any rapid changes in the circulating water temperature. This improves
the temperature control of the circulating water and thus improves seeding stability.
3. A strong holdoff condition must be maintained in the host laser. The stability of seeding is
greatly impaired by inadequate holdoff. Operating the laser system with insufficient holdoff
can lead to damage in both the injection seeder and the host laser. A periodic check of the
holdoff condition can help prevent this from becoming a problem.
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