Accelerator Test Facility

Laser Systems


Marcus Babzien, BNL





      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



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


1 mJ / pulse


200 mJ



Repetition rate

1.5, 3 Hz



Pulse duration (FWHM):


Oscillator IR

7 ps

Amplified IR

14 ps


10 ps


8 ps



Beam on cathode (FWHM)

0.2 - 3 mm



Profile Uniformity (P-P)




Shot-to-shot stability (rms):



<0.2 ps


2 %

Pointing (fraction of beam )




Drift (8 hour P-P)



<2 ps


<20 %

Pointing (fraction of beam )





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






Pulse duration (FWHM)

20 ps

7 ps

CW power

~65 mW (currently)

500 mW

Amplitude stability

<0.3% (10kHZ-10 mHz)


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*


*-has operated 36,000 hours



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



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)

Text Box:  TimeText Box: 720 ps Full Scale
Text Box: 360 ps Full Scale
Text Box: 3.6 ns Full Scale
Text Box: 1.8 ns Full Scale

Oscillator Upgrade

GE-100 Phase Stability



       CW phasemeter (DC-10 Hz bandwidth) shown over 4 minutes


Pulse Durations

IR after amplification


Pulse duration 142 ps FWHM


Green before quadrupler


Pulse duration 102 ps FWHM


Streak Camera Results

UV in laser room


Pulse duration 82 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



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  GWTW 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


isotopes 10 ATM vessel

I  Compression to shortest possible pulse duration