Tsunami - Beckman Institute Laser Resource Center

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Lok-to-Clock Electronics
Functional Overview
The optional Model 3930 Lok-to-Clock (LTC) electronics module provides
phase-locked loop (PLL) stabilization of output pulses and allows
you to precisely synchronize those output pulses to either the internal 80
MHz reference source or to an external one, such as an rf synthesizer or
another mode-locked laser. The LTC system is capable of reducing timing
jitter to < 3 ps rms (100 Hz to 10 kHz).
The phase (timing) of the output pulse train (as monitored on a photodiode)
is compared to the phase of a stable reference oscillator. Any phase
difference (where a phase difference of 360" or 2n corresponds to a
timing error of about 12 ns) is converted to an error voltage. This error
signal is filtered, amplified, and used to drive a piezo-electric transducer
(PZT) mounted on an intracavity mirror (M4). The mirror movement
changes the cavity length of the Tsunami laser and modifies the pulse
repetition rate to minimize the phase difference. When the pulses are
perfectly overlapped, there is no phase error and the cavity length and
pulse repetition rate are held constant. Figure 8-1 illustrates the phaselocked
loop (PLL) control circuit.
PZT
Laser
I t
-
Phase
Detector
- Servo
Filter1 -
Electronics Amplifier
Source
Internal Reference
Source
Figure 8-1: The Lok-to-Clock Phase-locked Loop.
8-1