This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

Precision Diagnostics for the Advanced Radiographic Capability on the National Ignition Facility

3rd International Conference on Ultrahigh Intensity Lasers (ICUIL)Development, Science and Emerging Applications,

Shanghai-Tongli, China

Constantin HaefnerPhoton Science and Applications Program

NIF and Photon Science Principle Directorate

October 31, 2008

LLNL-PRES-408199

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 2

Outline

1. Introduction to ARC and its split-beam architecture

2. Requirements and limitations for laser diagnostics

3. ARC diagnostic development and performance

4. Dispersion Management in the ARC laser beamlines:• Overview and need for precision dispersion balancing• Group delay diagnostics• First results

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 3

ARC-Diagnostics Team (present and past)

• G. Appel • C.P.J. Barty• J. Crane • R. Hackel• C. Haefner• J. Halpin• M. Henesian• J.E. Hernandez• C. W. Siders• R. Sigurdsson• M. Taranowksi• G. Tietbohl• N. Wong

• I. Jovanovic*• B. Shaw**• N. Troy**• K. Williams

* Purdue University** UC Davis

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 4

The split-beam architecture of enables multi-shot radiographic imaging

J. Crane, ICUIL session 1J. Crane, ICUIL session 1

Full NIF beam aperture is square

First aperture(uses one grating)

Second aperture(uses one grating)

Gives 8 Petawatt beams with adjustable delay control

4x 2 ARC sub-apertures will be focused on target with variable time delay, enabling hard x-ray, multi-frame radiography of imploding NIF capsules

4x 2 ARC sub-apertures will be focused on target with variable time delay, enabling hard x-ray, multi-frame radiography of imploding NIF capsules

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 5

Single-Shot characterization is required for a kJ-class split-beam short pulse laser system

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 6

Diagnostics system is placed behind target bay wall to shield against neutrons and EMP

ARCDiagnostic

Radiation shielding

Diagnostic beamline

Compressors

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 7

To avoid pulse distortions in the diagnostic beamline, we keep ΣB-Integral below ~ 1 rad

MainBeam to Target

Calorimeter

Diagnostics

DM1NIF-ARC Amplifier

~0.2% leak

Compressor 1-8 VRT1

VRT2 R~1%

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 8

B-Integral limits maximum energy available for laser diagnostics

Energy to employ all diagnostic instruments is limited to ~20 mJ for 3 ps pulses and ~55 mJ for 10 ps pulses to not exceed B>1 rad in diagnostic beamline

Title of GraphTitle of GraphSpatial beam profile at ARC diagnostic relay plane, B=0.4 rad, E=20 mJ

Title of GraphTitle of GraphSpatial beam profile at ARC compressor output for 1 kJ, 3 ps pulse

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 9

The diagnostic package is developed and calibrated offline utilizing our Short-Pulse OPCPA system

The diagnostic package is developed and calibrated offline utilizing our Short-Pulse OPCPA system

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 10

Spatial diagnostics have been installed and calibrated and meet specifications

λ

x

Spectrometer measuring gain narrowing and spatial chirp. Resolution <0.08 nm.

y

x

16 bit Far Field camera in TCC conjugated plane.

Res.<0.01μrad/px

Near-Field Camera: intensity profile, alignment, clipping: Res. < 0.5 mm/px

Testing in progress

FF split beam A

FF split beam B

Pointing-Camera: beam parallelism, alignment :

Res. <0.54 μrad/px

Phasix Shearing Interferometer: FF-

redundancy, adaptive mirror

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 11

Temporal diagnostics cover a window of 40 ns seamlessly with high dynamic range

Scanning pJ-Cross-Correlator: Intra-beam

timing and pulse duration

λ

τ -200 -150 -100 -50 00.00.20.40.60.81.0

Sign

alam

plitu

de(n

orm

)

TOCC

PD

PM

mask

A

B

Large temporal window third order Cross-Correlator with Tweaker

20 ps – Single Shot FROG detects pulsefront-tilt and

spatial chirp

D1

D2

D3

Cascaded Photodetectors: detect temporal pulse

shape from 40 ns – 35 pswith 90 dB

Time (ps)

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 12

Outline

1. Introduction to ARC and its split-beam architecture

2. Requirements and limitations for laser diagnostics

3. ARC diagnostic development and performance

4. Dispersion Management in the ARC laser beamlines:• Overview and need for precision dispersion balancing• Group delay diagnostics• First results

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 13

To produce high intensity, short-pulses dispersion must be carefully balanced

ϕ1(ω)

750 fs

10 ps

50 ps

Amplification & partial compression

Mode-locked Fiber oscillator

Chirped Fiber Bragg Grating

StretcherDispersion Tweakers

Dispersion Tweaker

Diagnostics

ϕ2(ω)x4

Multiplexing

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 14

Data acquisition

We are using the phase-shift technique* to measure group delay better than +/- 0.6 ps

λLaser

S(λ)

λLaser

S(λ)

Scanning SLM-Laser

Receiver (Photodiode)

System under test: ϕ(λL)

AM-Modulator

wavemeter

RF-Generator

Network analyzer

( ) ( )RF

G fT

πλϕλ

2=

Phase-reference

ϕ(λC)

( ) ( ) ( )[ ]{ }LRFLmCosS νϕννϕπνλ −++= 2

Reference.:

1. S. Ryu, Y. Horiuchi, K. Mochizuki, “Novel Chromatic Dispersion Measurement Method Over Continuous Gigahertz Tuning Range”, IEEE J. Lightwave Tech. 7, 1177 (1989)

2. J. K. Crane, R. H. Page, M. Y. Shverdin, M. J. Messerly, J. D. Nissen, V. K. Kanz, J. W. Dawson, B. H. Shaw, C. Haefner, G. Shih, C. W. Siders and C.P.J. Barty: “Group Delay Measurement for Balancing Dispersion in Complex Stretcher-Compressor Systems”, Conference on Lasers and Electrooptics, San Jose, 2008

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 15

We measure group delay as a function of wavelength or radial frequency

Grating

GratingFiber circulator

Signal detector

Laser in

Reference detector

Retro mirror

Modulator

Slant distanceAOI

Group delay measurement of a double-passed Treacy Compressor

σ for this data is ±0.6 ps. Systematic error in the residuals is attributed to distortion in the modulation sine wave.

1500.0

1000.0

500.0

0.0

-500.0

-1000.0

-1500.0-8 -6 -4 -2 0 2 4 6 8

4

3

2

1

0

-1

-2

-3

-4

Radial freq. (rad/ps)

Gro

up d

elay

(ps)

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 16

Polynomial and Treacy fits to the group delay data agree with the compressor layout

Residual Errors

Residual error decreases with modulation frequency and sample size

• GDD repeatability: >99.9 %• TOD repeatability: >99.3 %• Treacy fit repeatability: >99.6 %

This data taken with 2 GHz modulation

Comparison of physically measured parameters

Comparison of resultant GDD and TOD values

-16.615±0.074-16.630TOD/GDD [fs]

2.871±0.0122.874TOD [ps3]

-172.793±0.050-172.821GDD [ps2]

Treacy model fit for GD

Error from polynomial

fit

3rd order polynomial fit

2499.52497±3Slant distance [mm]

76.5776.60 ± 0.05 Included angle [deg]

GD DiagnosticsTreacy fitMeasured values

1.0

0.8

0.6

0.4

0.2

0.010 100 1000 10000

Phase sampling rate

Stan

dard

dev

iatio

n (p

s)

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 17

We recently applied the GD diagnostic to a full system for dispersion balance

Amplifier

Stretcher Compressor

1482 l/mm 1486 l/mm

Dispersion balancing

-4000

-3000

-2000

-1000

0

1000

2000

3000

4000

-8 -4 0 4 8

Spec

tral

Pha

se [r

ad]

-60

-40

-20

0

20

40

60

Res

idua

l pha

se [r

ad]

• Using the dispersion diagnostics we optimized angle of incidence and slant distance of the compressor to flatten the spectral phase.

• We discovered the residual group delay was caused by a bad coating on one optic.

We measured stretcher and compressor separately, and as a combined system

Compressor

Stretcher

Residual afteroptimization

(data)

Residual φstr + φcomp

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 18

• Measure the group delay of the chirped-fiber Bragg grating in a separate measurement

• Use model for compressors and measured group delay from front end to design two tweakers(A & B) that give 1-50 ps pulse width adjustment

• Use group delay diagnostic to set up each of the 8 ARC compressors. Match the group delay in all A compressors and all B compressors.

Mode-locked oscillator:ΦMO(ωL)

stretcher3 ns

ΦCFBG(ωL)

A

B

A B

δTAB

Pulse tweakers:ΦA ; ΦB; δTAB

Shaper

ΔT1

ΔT2

ΔT3

ΔT4

4-way split;timing adjust;

Injection, amplification

8 compressors;2 vessels:

Φ1A , Φ1B, …. Φ4A , Φ4B

δTAB

ΔT34

We will measure each dispersive element separately to balance net total dispersion

LLNL-PRES-408199 Haefner, ICUIL October 31, 2008 19

Summary

• The split beam geometry of ARC provides a versatile short pulse laser system for multi-frame X-ray radiography supporting fusion ignition and high-energy density experiments

• The radiation environment around the target chamber is challenging for the development of short pulse laser diagnostics

• High-dynamic range diagnostics have been developed to meet requirements for measuring the temporal pulse shape and pulse contrast

• Aligning 4 compressors with a total of 32- large gratings willbe a challenge

• We have demonstrated a specialized technique for balancing the dispersion in the ARC Quad

• The Group-Delay diagnostic is capable of measuring GD downto +/- 0.6 ps