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)

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

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)

How lasing can occur in a fully open structure ?

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 n
S in [1.05,2] in a matrix with n
0
=1
Anderson Localization
Reduced scattering (smaller n
S
)

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

Time evolution n
S
= 1.25
Max
Time
Emission spectrum
Frequency
Min
Laser Field Amplitude
Vanneste et al. PRL98 (2007)
Vanneste et al., PRL 98 , 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)

Rhodamine 6G
IN
PDMS
OUT
OUT
3 mm
Δn = 0.06
Weak scattering
Modes are extended
K. Bhaktha et al.
,
"An optofluidic random laser", APL 101 , 151101 (2012)

IN OUT
OUT
3 mm
K. Bhaktha et al.
,
"An optofluidic random laser", APL 101 , 151101 (2012)

256
128
0
0
2000
1500
1000
500
560
Position (mm)
2.8
565 570
Wavelength (nm)
575
256
128
0
0
2000
1500
1000
500
560
Position (mm)
2.8
565 570
Wavelength (nm)
575

All characteristics of classical lasers (threshold, narrow emission lines, Poissonian photon statistics)

+
Random emission spectrum

Non-directive laser emission

Complex structure of lasing modes

Strong dependence on pumping area

If design is greatly simplified, control over directionality and frequency emission is lost

Can control over random lasing emission be regained ?

Idea : spatial shaping of the optical pump

Inspired from spatial shaping methods recently employed for coherent light control

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 model valid only below threshold

Does not include




Spectrum to spectrum fluctuations
Gain saturation
Mode competition
Laser instabilities

IN
3 mm
OUT
OUT
Starting from uniform pumping

IN
3 mm
OUT
OUT

IN
3 mm
OUT
OUT

IN
3 mm
OUT
OUT


Singlemode operation at any desired mode

Optimal redistribution of the gain

Reduced threshold


Optimization of random laser directivity

Optimization of pulse duration

Extension to control of other type of lasers



Organic 2D lasers
Broad area lasers
…


For fundamental interest :

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 & Nonlinear phenomena
J. Andreasen et al., JOSAB28 (2011), PRA84 (2011)
…

For possible applications :
 where mirrors are not available



H. Cao, Optics & Photonics News (2005) in bio & chemical sensing
K. Bhaktha et al., ", APL 101 (2012) 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)
R. Kaiser, Cold atoms
Sapienza et al., Science 327 (2010)
Wiersma, PRL 93, 263901 (2004)