Random phase noise effect on the contrast of an ultra-high intensity laser Y.Mashiba 1, 2, H.Sasao 3, H.Kiriyama 1, M.R.Asakawa 2, K.Kondo 1, and P. R.

Random phase noise effect on the contrastof an ultra-high intensity laser

Y.Mashiba1, 2, H.Sasao3, H.Kiriyama1,M.R.Asakawa2, K.Kondo1, and P. R. Bolton1

1Kansai photon Science Institute, Japan Atomic Energy Agency, 8-1-7 Umemidai, Kizugawa, Kyoto 619-0216, Japan

2Faculty of Science and Engineering, Kansai University, 3-3-35 Yamate-cho, Suita, Osaka 564-8680, Japan

3Naka Fusion Institute, Japan Atomic Energy Agency, 801-1 Mukoyama, Naka, Ibaraki 311-0193, Japan

Poster Session II Ultra-intense Laser Design And PerformanceThe International Committee on Ultra-High Intensity Lasers (ICUIL 2014)

October 14, 2014Hotel Cidade De Goa, Goa, India

Outline

• Objective

• Origin of spectral random phase noise (SRPN)

• Numerical analysis

• Calculation results on temporal contrast with SRPN

• Conclusion

In the application of a high-intensity laser to solid-target experiments, a pedestal can generate unwanted plasmas before the main pulse arrive on the target.

Solid-target

Main pulse

Pedestal

The unwanted plasmas modify the experimental condition.

A part of pedestal goes ahead of main pulse

The pedestal intensities have reached up to W/cm .1110 2

Limiting factors in temporal contrast

We have evaluated the spectral random phase noise (SRPN).

High order spectral phase dispersion

1

-500 -400 -300 -200 -100 0 10010-12

10-10

10-8

10-6

10-4

10-2

Amplified spontaneous emission

Spectral random phase noise

Ref. H.Kiriyama et al.Opt. Lett. 37, 3363-3365 (2012)

Nor

mal

ized

inte

nsity

Time [ps]

Origin of spectral random phase noise (SRPN)

Noise of the surface flatness is directly converted tospectral random phase noise (SRPN).

Chirped-pulse from the amplifier

Grating 2

Grating 1

Grating 3

Grating 4

Large gratings “2,3” have the surface roughness.

Compressor

Compressed pulse

Our large grating (W:420 mm, H:210 mm) have the surface roughness of 9-12 nm (peak to valley; P-V) along the center.

50 10 15 20 25Distance [cm]

0

4

8

12

Hei

ght [

nm] 12 nm

Photo of our large grating

420 mm

210 mm 25.9 cm

Measured surface roughness

The roughness is measured to be 9-12 nm (P-V).

0

3

6

9

9 nm

Laser beam

Grating 2

Grating 3

md )sin(sin

1.0

1.2

1.4

1.6

1.8

750 790770 810 830 850Wave length ( ) [nm]

Spec

trum

rand

om

phas

e no

ise

(δ) [

rad]

2

)21( ZZ

Spectrum random phase noise

d: lattice constantα: angle of incidence at grating 1β: angle of emergence at grating 1m: degree

Numerical analysis (1/2)

Spectral random phase noiseLaser having wavelength

ΔZ1 ΔZ2

Grating 2 Grating 3

Dispersed laser from the grating 1 to grating “2,3”

Optical path difference due to the roughnessΔZ1 and ΔZ2 are from the measured surface roughness.

dkekItf ckti )()()(

I(k): Spectral intensityc: speed of lightk: wave number

0

0.4

0.8

1.2

1.6

0.0750 790770 810 830 850

Wave length ( ) [nm]Sp

ectr

al in

tens

ity( I

(k) )

[arb

.u.]

Contrast analysis based on Fourier inverse transformation

Equation

• We have taken account of grating “2,3” for calculation of the spectral random phase noise (Grating “1,4” have flat surface) .

• We have considered the temporal contrast in one dimensional analysis.

Assumption

Numerical analysis (2/2)

This SRPN generates a pedestal in ±100 ps range, which is in fairly good agreement with the experimental observation.

The SRPN can be a good explanation for the pedestal observed in our contrast measurement.

0-500 -400 -300 -200 -100 100

1e-12

1e-10

1e-8

1e-6

1e-4

1e-2

1

Nor

mal

ized

inte

nsity

Time [ps]

Measured contrastCalculated contrast

Conclusion

• Our large gratings (W:420 mm, H:210 mm) have the

surface roughness of 9-12 nm (P-V) along the center.

• The spectral random phase noise generated

in the grating in a compressor is the most probable

factor causing the pedestal.

• Two dimensional analysis

• Larger gratings (W:565 mm, H:360 mm) evaluation……

Next step