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. Bolton 1 1 Kansai photon Science Institute, Japan Atomic Energy Agency, Umemidai, Kizugawa, Kyoto , Japan 2 Faculty of Science and Engineering, Kansai University, Yamate-cho, Suita, Osaka , Japan 3 Naka Fusion Institute, Japan Atomic Energy Agency, Mukoyama, Naka, Ibaraki , Japan Poster Session II Ultra-intense Laser Design And Performance The International Committee on Ultra-High Intensity Lasers (ICUIL 2014) October 14, 2014 Hotel 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. 2

Limiting factors in temporal contrast We have evaluated the spectral random phase noise (SRPN). High order spectral phase dispersion Amplified spontaneous emission Spectral random phase noise Ref. H.Kiriyama et al. Opt. Lett. 37, (2012) Normalized intensity Time [ps]

Origin of spectral random phase noise (SRPN) Noise of the surface flatness is directly converted to spectral 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 Distance [cm] Height [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) nm Laser beam Grating 2 Grating 3

Wave length ( ) [nm] Spectrum random phase noise (δ) [rad] Spectrum random phase noise d: lattice constant α: angle of incidence at grating 1 β: angle of emergence at grating 1 m: degree Numerical analysis (1/2) Spectral random phase noise Laser having wavelength ΔZ1 ΔZ2 Grating 2 Grating 3 Dispersed laser from the grating 1 to grating “2,3” Optical path difference due to the roughness ΔZ1 and ΔZ2 are from the measured surface roughness.

I(k): Spectral intensity c: speed of light k: wave number Wave length ( ) [nm] Spectral intensity ( 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 e-12 1e-10 1e-8 1e-6 1e-4 1e-2 1 Normalized intensity Time [ps] Measured contrast Calculated 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