Accelerator Test Facility
Laser Systems
Marcus Babzien,
BNL
Outline
·
Nd:YAG system: history,
current performance, upgrades
·
Future goals
·
GW CO2
performance
·
TW CO2 project:
history, status
Nd:YAG Improvements
Past
Activity
· New class 10,000 clean room adjacent to gun with dedicated lab space
· Replaced Nd:YAG oscillator with newer Nd:YVO4 oscillator
· New SHG crystals and Pockels cell for smoother beam profile
· Improved thermal monitoring and regulation on table
· Identified and corrected alignment instability before preamp
· Improved diagnostics for harmonic generation and gun hutch
Current Status
Capabilities
I Photocathode and CO2 slicing fully available on-demand
I Electron
beam-synchronized optical pulses available for users:
5 mJ, 14 ps @ 1064 nm in laser lab (exclusive of slicing)
50 mJ, 10 ps @ 532 nm in laser lab or
FEL room (not implemented)
50 mJ, 8 ps @ 266 nm in gun hutch and
laser lab
I Delivered light on 112 of 130 days since October 1, 1999 (~86% of available time), for a total of 1300 running hours.
I System typically ready for gun operation within 15 minutes, including data collection.
Demonstrated YAG Laser Performance
Energy (dual
pulse mode) |
|
UV on cathode |
0-30 mJ |
IR at CO2 table |
7 mJ |
Laser output: total IR |
30 mJ |
IR into 2w |
5 mJ / pulse |
Green |
1 mJ / pulse |
UV |
200 mJ |
|
|
Repetition
rate |
1.5, 3 Hz |
|
|
Pulse
duration (FWHM): |
|
Oscillator IR |
7 ps |
Amplified IR |
14 ps |
Green |
10 ps |
UV |
8 ps |
|
|
Beam on cathode
(FWHM) |
0.2 - 3 mm |
|
|
Profile Uniformity (P-P) |
<20% |
|
|
Shot-to-shot
stability (rms): |
|
Timing |
<0.2 ps |
Energy |
2 % |
Pointing (fraction of beam ) |
<1% |
|
|
Drift (8 hour P-P) |
|
Timing |
<2 ps |
Energy |
<20 % |
Pointing (fraction of beam ) |
<5% |
|
|
New Nd:YVO4 Oscillator
Improved stability in both energy, phase, and pointing
High reliability reduces maintenance - realignment should be unnecessary
Old oscillator provides emergency backup in case of failure
|
LWE-131 |
GE-100 |
Pulse duration (FWHM) |
20 ps |
7 ps |
CW power |
~65 mW (currently) |
500 mW |
Amplitude stability |
<0.3% (10kHZ-10 mHz) |
<0.2% |
Pointing stability |
< 50 microradian |
<30 microradian |
Phase stability |
<1 ps p-p (minutes) < 1ps/hour drift |
<0.3 ps p-p (minutes) < 0.5ps/hour drift |
Estimated laserdiode lifetime |
> 30,000 hours* |
>10,000 |
*-has operated 36,000 hours
Diagnostics
Continuously on-line:
I Scanning autocorrelator for oscillator monitoring
I 14 CCD cameras for transverse mode and position measurement with beam profile analyzer*
I 5 pyroelectric energy measuring probes with pickoffs and calibrated readout*
I High speed silicon photodiodes
I Laser-RF Phasemeter*
I 16-channel thermocouple temperature monitoring
Additional:
I 2 ps resolution streak camera (Instrumentation Div.)
I CW laser power meter
I 2 GHz digital sampling oscilloscope
* - output available facility-wide
Performance Tests
Pulse Contrast After Cathode (March 99)
Oscillator Upgrade
GE-100 Phase Stability
· CW phasemeter (DC-10 Hz bandwidth) shown over 4 minutes
Pulse Durations
IR after amplification Pulse
duration 14±2 ps FWHM Green
before quadrupler Pulse duration 10±2
ps FWHM
Streak Camera Results
UV
in laser room Pulse
duration 8±2 ps FWHM
Future Prospects
Short Term
I Complete transition to Nd:YVO4
oscillator
I Complete projects for transverse beam
shaping
I Improve temporal diagnostics for all
wavelengths
I Implement pulse shortening
I Improve passive stability or implement
active feedback where required
I Improve imaging in gun hutch
Future Prospects
Long Term
Significant
changes to laser system must not result in significant facilty-wide shutdown ®
develop second drive laser in parallel
Optical
synchronization between electrons and laser offers increased advantage as CO2
pulse duration decreases ® retain "single-laser"
philosophy
Reliable
oscillators now available in bulk and fiber with phase feedback ®
freedom to choose gain medium for amplification
Arbitrary
longitudinal shaping of photocathode pulse requires gain medium with larger
bandwidth (~100 fs) for "pulse stacking" ®
Nd:YAG not optimum
Direct
diode-pumping should be used for passive stability, reliability ®
Ti:Al2O3 not optimum
Saturation
mechanisms, active feedback should be planned from start
Beam Quality
Cathode Monument
266 nm
Radial Beam
Shaping
Gaussian Reflector
Radial Beam Shaping
Gaussian Reflector
Radial Beam
Shaping
Variable Intensity Filter
f=155, q=45
f=145, q=35
f=115, q=115
f=15, q=5
SHG Crystal Distortion
Imaged at Photocathode
Conjugate Plane
Temporal Shaping
Saturable Absorption
Saturable Absorber
Testing with ATF laser
Temperature Control
On-table Monitoring
TW CO2 Status
Progress
I System accepted after on-site work by vendor
I Pressure vessel modified, safety reviewed again to ensure
compliance
I Discharge at 8 ATM optimized, gain demonstrated
I Pulse chopping to 30 ps tested, measured with GW seed
I GWÛTW transport line completed
I Safety improvements: exhaust, sheilding, plumbing
I Simulations completed
CO2 Pulse Shape
From Compton Experiment
TW CO2 Future Work
Towards Commissioning
I Complete final safety documentation
I Reassembly of amplifier pressure vessel, optics, plumbing
I Re-establish discharge conditions (Optoel)
I Provide seed pulse
I Test output, optimize
I Deliver 30J!!!
CO2 System Upgrades
I Oscillator replacement: parametric generation from YAG
I Increase gain bandwidth of GW preamplifier
ß
ß
isotopes
10 ATM vessel
I Compression to shortest possible pulse duration