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)

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

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  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