Taming Random lasers

1. Taming Random lasers Patrick Sebbah Nicolas Bachelard, Sylvain Gigan Institut Langevin, ESPCI ParisTech CNRS UMR 7587, Paris Christian Vanneste, Xavier Noblin LPMC – Université de Nice– CNRS UMR 6622, Nice, France Jonathan Andreasen University of Arizona, Optical Sciences, Tucson (AZ) Kiran Bhaktha Indian Institute of Technology Kharagpur, India Supported by the Agence Nationale de la Recherche (ANR GLAD)

2. Random lasers

3. Conventional laser Gain Medium : Light amplification Optical Cavity : Feedback Pour la Science n°396, Oct 2010 In a conventional laser light scattering introduces additional loss, thus increases lasing threshold

4. Random Laser • Multiple scattering : • dwell time increases • enhanced light amplification Mirrorless laser : ASE or lasing with resonant feedback ? Wiersma, Nature, 406, 132(2000) Lethokov, Sov. Phys. JETP 26, 835 (1968). Review: Wiersma, Nature Physics, 4, 359(2008)

5. ZnOnanoparticles H. Cao et al., Appl. Phys. Lett. 76, 2997 (2000)

6. Spontaneousemission Emission Spectrum H. Cao et al., Appl. Phys. Lett. 76, 2997 (2000)

7. Singlemode lasing Emission Spectrum H. Cao et al., Appl. Phys. Lett. 76, 2997 (2000)

8. Multimode lasing Emission Spectrum H. Cao et al., Appl. Phys. Lett. 76, 2997 (2000)

9. RandomLasingwithresonantFeedback Feedback for lasing is phase sensitive (coherent) and therefore frequency dependent (resonant). (not ASE) • How lasingcanoccur in a fully open structure ? • How iscoherent feedback possible in a random structure where phases are randomized ?

10. Nature of Randomlasing modes J. Andreasen et al., “Modes of Random Lasers”, Advances in Optics and Photonics, Vol. 3 Issue 1, pp.88-127 (2011).

11. Modes of a scattering medium 2D random collection of scatterers with refractive index nS in [1.05,2] in a matrix with n0=1 Anderson Localization Reduced scattering (smaller nS)

12. Max Min Laser Field Amplitude Laser action FDTD Method to simulate Maxwell equations coupled to the population equations of of a four-level atomic structure Time evolution Intensity nS = 2 Time Emission spectrum Intensity Frequency Vanneste et al. PRL87 (2001) , Sebbah et al. PRB66 (2002)

13. Vanneste et al., PRL98, 143902 (2007) Max Min Laser Field Amplitude Laser action Time evolution Intensity nS = 1.25 Time Emission spectrum Intensity Frequency Vanneste et al. PRL98 (2007)

14. Nature of the modes • Randomlasingoccurseven in the diffusive regime (extended modes – no confinement). Thresholddepends on mode confinement • Lasing modes are built on the resonances/quasinormal modes of the passive cavity Theseresonances are selected by the gain True in the singlemode regime Vanneste et al. PRL87 (2001) , Sebbah et al. PRB66 (2002), Vanneste et al. PRL98 (2007)

15. An optofluidic Random laser K. Bhaktha et al., "An optofluidic random laser",APL101, 151101(2012)

16. IN OUT OUT 3 mm A 1D optofluidic random laser PDMS Rhodamine 6G Δn = 0.06 Weak scattering Modes are extended K. Bhaktha et al., "An optofluidic random laser",APL101, 151101(2012)

17. IN OUT OUT 3 mm A 1D optofluidic random laser K. Bhaktha et al., "An optofluidic random laser",APL101, 151101(2012)

18. Uniform vs partial pumping

19. Uniform vs partial pumping

20. Signatures of a random laser All characteristics of classical lasers (threshold, narrowemissionlines, Poissonian photon statistics) + • Randomemissionspectrum • Non-directive laser emission • Complex structure of lasing modes • Strongdependence on pumping area

21. Active control of aRandom laser

22. Controlingrandom laser emission If design isgreatlysimplified, control over directionality and frequencyemissionislost • Can control over randomlasingemissionberegained ? • Idea : spatial shaping of the opticalpump • Inspiredfrom spatial shapingmethodsrecentlyemployed for coherent light control • Iterativemethodwithoutpriorknowlegde of the lasing modes.

23. Principle

24. Principle

25. Active control of aRandom laser:Numericaldemonstration N. Bachelard et al., "Taming random lasers", PRL 109, 033903(2012)

26. Numericaldemonstration N. Bachelard et al., "Taming random lasers", PRL 109, 033903(2012)

27. Active control of aRandom laser:Experimentaldemonstration N. Bachelard et al., "Active control of random laser emission", in preparation

28. Experimental challenge • Numerical model valid only below threshold • Does not include • Spectrum to spectrum fluctuations • Gain saturation • Mode competition • Laser instabilities

29. IN OUT OUT 3 mm Experimentaldemonstration Starting from uniform pumping

30. IN OUT OUT 3 mm Experimentaldemonstration

31. IN OUT OUT 3 mm Experimentaldemonstration

32. IN OUT OUT 3 mm Experimentaldemonstration

33. conclusion • Singlemode operation at any desired mode • Optimal redistribution of the gain • Reduced threshold

34. Perspectives • Optimization of random laser directivity • Optimization of pulse duration • Extension to control of other type of lasers • Organic 2D lasers • Broad area lasers • …

35. Thankyou for your attention

36. Whyrandom lasers ? • For fundamentalinterest : • Nature of the lasing modes J. Andreasen et al., AOP 3 (2011) • Revisiting laser equation in absence of a cavity H. Tureci et al., Science 320 (2008) • Multimode regime & Nonlinearphenomena J. Andreasen et al., JOSAB28 (2011), PRA84 (2011) • … • For possible applications : • wheremirrors are not available H. Cao, Optics & Photonics News (2005) • in bio & chemicalsensing K. Bhaktha et al., ", APL 101(2012) • as intense, spatially incoherent light sources B. Redding et al., OpticsLett. 36 (2011) • …

37. J. Fallert et al. Nature Photonics, 279 (2009) R. Kaiser, Cold atoms Otherexamples C. López, Photonic Glass RL Garcia et al., PRB 82 (2010) Sapienza et al., Science 327 (2010) Wiersma, PRL 93, 263901 (2004)