1. LCLS Drive Laser Stabilization using Feed-Forward Techniques Axel Brachmann, SLAC November 20, 2003
Electro-Optical Modulation
Nonlinear Optics Techniques
Self Focussing
Two Photon Absorption
LCLS Drive Laser Review, November 20, 2003
Axel Brachmann, SLAC

2. Electro-Optical Modulation
Principle of operation
Pockels cell / polarizer cube as intensity modulator
Modulation of Pockels cell retardation based on laser intensity monitor
Adjustable delay line using fast pockels cells to compensate for propagation delay of HV pulser
LCLS Drive Laser Review, November 20, 2003
Axel Brachmann, SLAC

3. Electro-Optical Modulation Layout
Input beam
Photodiode
Pulse stretcher
Faraday Isolator
Wedged window
(Pick off)
/2
Switch out Pockels cell
Switch in Pockels cell
PBS
Adjustable Delay Line
/4 (optical bias)
Modulating
Pockels cell
HV Amplifier
PBS
LCLS Drive Laser Review, November 20, 2003
Axel Brachmann, SLAC

4. Modulating Pockels Cell and Driver
SLAC built device
Propagation delay: 50 to 100 ns
SLAC built HV amplifier
Uses commercial Pockels cell
Previous use for E158 temporal laser pulse shaping
LCLS Drive Laser Review, November 20, 2003
Axel Brachmann, SLAC

5. EO Feed-Forward Simulation (I)
Pockels cell transmitted intensity:
Pockels cell phase shift:
: phase shift
b: Phase shift introduced by optical bias
n0: refractive index
63: electro-optical constant
Vz: applied voltage pulse
LCLS Drive Laser Review, November 20, 2003
Axel Brachmann, SLAC

6. EO Feed-Forward Simulation (II)
LCLS Drive Laser Review, November 20, 2003
Axel Brachmann, SLAC

7. Feed forward cost estimate
Item
Qty.
Unit cost
Ext. Cost
Manufacturer
Faraday isolator 1
5,000
OFR
IO VHP
window
190
CVI Lasers
ELW UV
telescope lenses for beam diameter adjustment 2
220
440
BICX-25.4-XXX-C-532(1)
half wave plate to maximize transmission
480
QWPO R15
clean up polarizer
270
PBS
delay line polarizer
540
delay line Pockels cells and pulser
9,300
18,600
Laser Metrics
5046E (Pulser)
Q1059P SG (Pockels cell)
delay line end mirrors
195
390
Y CC
delay line folding mirrors
130
260
Y S
optical bias quarter wave plate
QWPO R15
modulating PC and pulser (SLAC build)
10,000
SLAC
N/A
polarizer past modulating PC
Total:
36920
LCLS Drive Laser Review, November 20, 2003
Axel Brachmann, SLAC

8. Fast forward experimental timeline
Activity
Month 1
Month 2
Month 3
Month 4
Month 5
Test Amplification of photodiode signal
Photodiode Signal conditioning (level/timing)
Setup of delay line
Setup of modulation system
Experimental evaluation of system
LCLS Drive Laser Review, November 20, 2003
Axel Brachmann, SLAC