Sensitivity improvement of non- linearities measurements using binary diffractive optics

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. Outline • Nonlinearities measurements : the Z-scan technique • A diffractive optical element (DOE) as a divergence amplifier • Theoretical sensitivity improvement • Experimental setup • Experimental multiplying factor • Conclusion

3. Non-linearities measurements : the “Z-scan” technique M. Sheik-Bahae et al. , IEEE J. Quantum Electron. 26, 760 (1990) Intensity in the sample Transmission PT/P0 • Optical Kerr effect measurements : • n = n0 + n2I (typically n2≈ 10-12 cm2.W-1) • Population lensing effect measurements • …

4. Non-linearities measurements : the “Z-scan” technique Z-scan technique sensitivity : λ/ 300 Divergence diagnostic Divergence amplification Eclipsing Z-scan technique sensitivity : λ/ 104 (x30) T. Xia et al., Opt. Lett. 19, 317 (1994) Normalized peak-valley transmission contrast increasing Sensitivity improvement Need to find a way to increase the divergence of the beam…

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

6. 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 (T1) and with (T2) the phase aperture (simulation) t

7. Theoretical sensitivity improvement Multiplying factor : A huge enhancement of η is noticed (almost 800) when YPI is close to 0.83 Variation of η the multiplying factor as a function of the parameter YPI R. de Saint Denis et al., Applied Physics B, 90, 513 (2008)

8. Laser beam Reference arm D1 L4 L1 PD1 PA1 L3 D2 L2 sample PD2 Z PA2 Main arm 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

9. Experimental multiplying factor ηexp,max ≈ 370 Sensitivityenhancement ΔTPV→ thickness, n2 The maximum of ηexp occurs for YPI ≈ 0.91 Better accuracy on the measurement of n2 T. Godin et al., Applied Physics B, 95, 579 (2009)

10. Conclusion • Theoretically : 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 enhancement • A factor close to 400 has been reached …

11. Thank you for your attention !