Continuum Surelite EX 10, Operation And Maintenance Manual

Page: 63 / 114

Section 4: Subassembly and Module Descriptions
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Laser bench electronics
Active Q-switch
The combination of a polarizer, Pockels cell and
λ
/4 plate within the oscillator is known as a Q-
switch. A Q-switch prevents lasing in the resonator until the laser gain reaches its peak and then
opens the cavity to allow oscillation. This then produces ultra-fast, high peak power laser pulses.
Principle of operation
The Q-switch consists of the following:
•
Optical
−
Pockels cell
−
Plate polarizing element
−
Quarter-wave plate
•
Electrical
−
Timed pulse generated by the PCU unit
−
Marx bank (750 V)
−
750 volt power board
P
OCKELS CELL
The Pockels cell has a longitudinal field KD*P crystal with a 15 mm clear aperture
mounted at 43 mm beam height. A voltage of ~3600 V results in a quarter wave of
rotation for photons at 1,064 nm passing in either direction. A voltage of 0 volts results
in no rotation.
P
LATE POLARIZER
The thin film multilayer dielectric polarizer has an angle of incidence of 57°. In its
standard orientation, the polarizer is highly transparent (>95%) to horizontally polarized
light while being highly reflective (>99%) to vertically polarized light. The
contrast/extinction ratio is >500:1.