Transcript Taming random lasers - Weizmann Institute of Science

Patrick Sebbah
Nicolas Bachelard, Sylvain Gigan
Institut Langevin, ESPCI ParisTech CNRS UMR 7587, Paris
A.
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)
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
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)
H. Cao et al., Appl. Phys. Lett. 76, 2997 (2000)
Spectrum
Emission
H. Cao et al., Appl. Phys. Lett. 76, 2997 (2000)
Spectrum
Emission
H. Cao et al., Appl. Phys. Lett. 76, 2997 (2000)
Spectrum
Emission
H. Cao et al., Appl. Phys. Lett. 76, 2997 (2000)
Feedback for lasing is phase sensitive (coherent) and
therefore frequency dependent (resonant). (not ASE)
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How lasing can occur in a fully open structure ?
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How is coherent feedback possible in a random structure
where phases are randomized ?
J. Andreasen et al., “Modes of Random Lasers”,
Advances in Optics and Photonics, Vol. 3 Issue 1, pp.88-127 (2011).
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)
Intensity
Time evolution
FDTD Method to simulate
Maxwell equations
coupled to the population
equations of of a four-level
atomic structure
nS = 2
Max
Time
Intensity
Emission spectrum
Min
Frequency
Laser Field Amplitude
Vanneste et al. PRL87 (2001) , Sebbah et al. PRB66 (2002)
Intensity
Time evolution
nS = 1.25
Max
Time
Intensity
Emission spectrum
Min
Frequency
Laser Field Amplitude
Vanneste et al. PRL98 (2007)
Vanneste et al., PRL98, 143902 (2007)
 Random
lasing occurs even in the diffusive
regime (extended modes – no confinement).
Threshold depends on mode confinement
 Lasing
modes are built on the
resonances/quasinormal modes of the
passive cavity
These resonances 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)
K. Bhaktha et al.,
"An optofluidic random laser", APL 101, 151101 (2012)
PDMS
Rhodamine 6G
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Δn = 0.06
Weak scattering
Modes are extended
K. Bhaktha et al.,
"An optofluidic random laser", APL 101, 151101 (2012)
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3 mm
K. Bhaktha et al.,
"An optofluidic random laser", APL 101, 151101 (2012)
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Position (mm)
2.8
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Power Spectrum a.u.
Power Spectrum a.u.
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Wavelength (nm)
575
Position (mm)
2.8
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Wavelength (nm)
575
All characteristics of classical lasers (threshold, narrow
emission lines, Poissonian photon statistics)
+
 Random emission spectrum
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Non-directive laser emission
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Complex structure of lasing modes
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Strong dependence on pumping area
If design is greatly simplified, control over
directionality and frequency emission is lost
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Can control over random lasing emission be
regained ?
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Idea : spatial shaping of the optical pump

Inspired from spatial shaping methods recently
employed for coherent light control
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Iterative method without prior knowlegde of the
lasing modes.
N. Bachelard et al., "Taming random lasers", PRL 109, 033903 (2012)
N. Bachelard et al., "Taming random lasers", PRL 109, 033903 (2012)
N. Bachelard et al., "Active control of random laser emission", in preparation
 Numerical
 Does
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model valid only below threshold
not include
Spectrum to spectrum fluctuations
Gain saturation
Mode competition
Laser instabilities
Starting from uniform pumping
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 Singlemode
operation at any desired mode
 Optimal redistribution of the gain
 Reduced threshold
Optimization of random laser directivity
 Optimization of pulse duration
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 Extension

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to control of other type of lasers
Organic 2D lasers
Broad area lasers
…
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For fundamental interest :

Nature of the lasing modes
J. Andreasen et al., AOP 3 (2011)
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Revisiting laser equation in absence of a cavity
H. Tureci et al., Science 320 (2008)
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Multimode regime & Nonlinear phenomena
J. Andreasen et al., JOSAB28 (2011), PRA84 (2011)
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…
For possible applications :
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where mirrors are not available
H. Cao, Optics & Photonics News (2005)
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in bio & chemical sensing
K. Bhaktha et al., ", APL 101 (2012)
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as intense, spatially incoherent light sources
B. Redding et al., Optics Lett. 36 (2011)

…
C. López, Photonic Glass RL
J. Fallert et al.
Nature Photonics, 279 (2009)
Garcia et al., PRB 82 (2010)
Sapienza et al., Science 327 (2010)
R. Kaiser, Cold atoms
Wiersma, PRL 93, 263901 (2004)