User`s manual

10
Pulse Picker
A pulse picker installed in the Wedge 50 femtosecond amplifier
system is used for one pulse selection from a train of stretched
pulses. As a result, seed pulses are formed for the amplification.
The pulse picker utilizes well known electrooptical Pockels
effect. Pulse train having horizontal polarization goes through
the Pockels cell. Without applied voltage pulses do not change
polarization and exit pulse picker with help of polarizers as
shown in the Figure 5. When half wave voltage is applied to the
Pockels cell, an input pulse changes its polarization from
horizontal to vertical, goes through polarizer and is used as a
seed pulse for the amplifier. Applied voltage is synchronized
with femtosecond pulse train and Nd:YLF pump pulses, and
seed pulses have pulse repetition rate equal to the repetition rate
of Nd:YLF pump pulses. Input polarizer is used to increase
polarization ratio for input pulses.
Synchronization Electronics
The unit is designed to trig high voltage window applied to the
Pockels cell and to synchronize this window with pump pulse
and femtosecond pulse train. The aim of synchronization is to
select one femtosecond pulse from train and to amplify it at the
maximum pump efficiency. The schematic diagram is shown in
the Figure 5 and the unit description is in the Section 5.