Sensitivity improvement of non- linearities measurements using binary diffractive optics Thomas Godin M. Fromager, E. Cagniot, B. Païvänranta, N. Passilly,

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1 Sensitivity improvement of non- linearities measurements using binary diffractive optics Thomas Godin M. Fromager, E. Cagniot, B. Païvänranta, N. Passilly, G. Boudebs and K. Aït-Ameur University of Caen Basse-Normandie / CIMAP (Research Center on Ions, Materials and Photonics)

2 Centre de Recherche sur les Ions, les Matériaux et la Photonique nom dateréunion Outline Nonlinearities measurements : the Z-scan techniqueNonlinearities measurements : the Z-scan technique A diffractive optical element (DOE) as a divergence amplifierA diffractive optical element (DOE) as a divergence amplifier Theoretical sensitivity improvementTheoretical sensitivity improvement Experimental setupExperimental setup Experimental multiplying factorExperimental multiplying factor ConclusionConclusion

3 Centre de Recherche sur les Ions, les Matériaux et la Photonique nom dateréunion Non-linearities measurements : the “Z-scan” technique Transmission P T /P 0 Intensity in the sample M. Sheik-Bahae et al., IEEE J. Quantum Electron. 26, 760 (1990) - Optical Kerr effect measurements : n = n 0 + n 2 I (typically n 2 ≈ 10 -12 cm 2.W -1 ) - Population lensing effect measurements - …

4 Centre de Recherche sur les Ions, les Matériaux et la Photonique nom dateréunion Non-linearities measurements : the “Z-scan” technique Divergence diagnostic Need to find a way to increase the divergence of the beam… Z-scan technique sensitivity : λ/ 300 Eclipsing Z-scan technique sensitivity : λ/ 10 4 (x30) Sensitivity improvement Divergence amplification Normalized peak-valley transmission contrast increasing T. Xia et al., Opt. Lett. 19, 317 (1994)

5 Centre de Recherche sur les Ions, les Matériaux et la Photonique nom dateréunion The π-plate: a DOE as a divergence amplifier The π-plate : a DOE as a divergence amplifier Introducing a π phase shift in the central region of an incident beam PP Gaussian Beam ? Normalized phase aperture radius R. de Saint Denis et al., Applied Optics, 45, 31 (2006)

6 Centre de Recherche sur les Ions, les Matériaux et la Photonique nom dateréunion The π-plate: a DOE as a divergence amplifier The π-plate : a DOE as a divergence amplifier Beam divergence after the π-plate Beam divergence before the π-plate Variation of diaphragm normalized transmittance without (T 1 ) and with (T 2 ) the phase aperture (simulation) t

7 Centre de Recherche sur les Ions, les Matériaux et la Photonique nom dateréunion Theoretical sensitivity improvement Variation of η the multiplying factor as a function of the parameter Y PI Multiplying factor : A huge enhancement of η is noticed (almost 800) when Y PI is close to 0.83 R. de Saint Denis et al., Applied Physics B, 90, 513 (2008)

8 Centre de Recherche sur les Ions, les Matériaux et la Photonique nom dateréunion Experimental setup Deformable mirror (silicon with gold coating) to simulate the increasing and decreasing of the angular divergence π-phase shift phase aperture M² < 1.1 Pure lensing effect verified using a wave-front sensor Phase aperture : radius varying from 150µm to 256µm Laser beam Z L1L1 L2L2 D1D1 L3L3 PD 2 D2D2 PA 2 sample L4L4 PD 1 PA 1 Reference arm Main arm

9 Centre de Recherche sur les Ions, les Matériaux et la Photonique nom dateréunion Experimental multiplying factor η exp,max ≈ 370 The maximum of η exp occurs for Y PI ≈ 0.91 Sensitivity enhancement T. Godin et al., Applied Physics B, 95, 579 (2009) Better accuracy on the measurement of n 2 ΔT PV → thickness, n 2

10 Centre de Recherche sur les Ions, les Matériaux et la Photonique nom dateréunion Conclusion Theoretically : a simple DOE leads to a significant improvement of the Z-scan sensitivity, up to a factor 800Theoretically : a simple DOE leads to a significant improvement of the Z-scan sensitivity, up to a factor 800 Experimentally : adjusting the balance between global transmission and sensitivity enhancementExperimentally : adjusting the balance between global transmission and sensitivity enhancement A factor close to 400 has been reachedA factor close to 400 has been reached …

11 Centre de Recherche sur les Ions, les Matériaux et la Photonique nom dateréunion Thank you for your attention !