Rutherford Appleton Laboratory

Vulcan Front End OPCPA System

Stage 1 - BBO

Stage 2 - BBOStage 3 - LBO

Pump Laser

Rutherford Appleton Laboratory

0

200

400

600

800

1000

1200

1400

1020 1030 1040 1050 1060 1070 1080 1090Wavelength [nm]

Output Spectrum

Bandwidth ~ 50 nm @ 1053 nm

Spectrum of Amplified seed

0.E+00

1.E+03

1040 1050 1060 1070

Wavelength (nm)

Inte

nsit

y (

a u

)

•Theoretical bandwidth for this system is > 250 nm (@ 1053 nm

• In previous tests (limited by bandwidth of optics) we demonstrated ~ 50 nm

•Actually require just 16 nm

•So far first 2 stages tested (unsaturated gain of 106)

•Need the 3rd stage for saturation and stability

OPCPA Test Bandwidth

PW Scheme

Rutherford Appleton Laboratory

Focusing on target

(F3.2 OAP)

Compression to 500fs(1480 l/mm)

Existing Building New Target Area

Stretch2 x 2 pass ;

4.8 ns; 16 nm

Expansion to 600 mm(19 m VSF)

Pre-amp. pump

200 mJ 10 Hz

X 3.107

Amplification in Vulcan

(85J ; 150 mm P & Si)

X 450

Oscillator5 nJ 100fs TiSa

3 ex NOVA 208 amplifiers(650J ; 208 mm)

X 8

Adaptive mirror

3 - stage OPCPA

2 x BBO + LBO

Rutherford Appleton Laboratory

Rutherford Appleton Laboratory

Energy on target 500JPulse duration 500 fsec

Intensity on target 1021 Wcm-2

The Vulcan PW Facility

Computer Schematic - 2000

Vulcan PW Facility - 2002

Rutherford Appleton Laboratory

E

B

k

Single electron motion

A single electron in the laser field exhibits a figure of eight motion due to the vxB term in the Lorentz force

F = -e(E+vxB)

Twice every laser cycle, electrons are accelerated in the direction of k

The kinetic energy the electron acquires is roughly proportional to the ponderomotive potential

kT~E ( )mc I / . keVosc Wcm

1 511 1 137 12

10

12

18 2

At 1021 Wcm-2, kT 10 MeV.

Rutherford Appleton Laboratory

Rutherford Appleton Laboratory

•Wave breaking of self-modulated laser wakefield demonstrated using 100 TW Vulcan facility - large energy spread.

• Improved electron beam quality expected with conventional laser wakefield - long focal length optics.

•CPA beatwave schemes also possible and will be investigated on the PW facility

Self-modulated wakefield, classical wakefield and beatwave accelerators studies on the

VULCAN PW facility

Rutherford Appleton Laboratory

Rutherford Appleton Laboratory

Accelerated electrons observed at energies up to 120 MeV

MIK Santala et al. Phys. Rev. Lett, 86, 1227 (2001)

• In the self modulated wakefield, stimulated Raman scatter arises from noise - generating an electron plasma wave and a down-shifted electromagnetic wave. This em wave ‘beats’ with the incident laser pulse, and the increased intensity in the beat-wave pattern enhances the plasma wave. Gradients of 1 GeV/cm have been measured. Eventually, the plasma wave breaks, generating a wide energy spread shown here.

• In the classical wakefield, the laser intensity and plasma density are reduced below the threshold for stimulated Raman scatter. In this case, the ponderomotive force expels electrons from the focus, but space charge requires that they return after the laser pulse has passed. This sets up a large amplitude (GeV/cm) oscillating longitudinal electric field that can accelerate low emittance electron bunches - provided the plasma wakefield is quasi - 1 dimensional - requires PW -class lasers with long focal lengths optics.

Rutherford Appleton Laboratory

Beat-wave accelerators

• Beatwave accelerators were the first to be studied in the 1980’s

• Two laser pulses of different frequencies are focused into a plasma gas. At a resonant density, the ponderomotive force of the induced beat pattern amplifies small density fluctuations arising from noise - and a large amplitude longitudinal electric field is set up.

• Nd glass operating at 1m is better than CO2 (10.6m) as higher plasma densities are required - hence larger electric fields.

• However, if the laser pulse duration is too long, the modulation instability limits the amplitude of the plasma waves that can be generated.

• With chirped pulse, picosecond laser pulses, a beat-wave pattern can be induced by spectral shaping the laser pulse. The pulse duration is sufficiently short to amplify the plasma waves before the modulational instability can grow to disrupt the process.

• The VULCAN PW laser will be used to study this beat-wave accelerator process.

Astra is extremely compact, driving

physics at up to 1019Wcm-2 at 10Hz with

“table top” scale

The final amplifier will be upgraded next

year to enable full energy to be delivered

to TA2

Beam expander

Pulse pickerTiSa rod,

16mm aperture

The “engine” for Astra’s high energy

output is the 5J frequency doubled

Nd:YAG pump laser

Astra laser hall

Rutherford Appleton Laboratory

Target chamber

Vacuum pulse

compressor

Astra high intensity target area

Rutherford Appleton Laboratory