Patrick Sebbah

Nicolas Bachelard, Sylvain GiganInstitut Langevin, ESPCI ParisTech CNRS UMR 7587, Paris

A.Christian Vanneste, Xavier NoblinLPMC – Université de Nice– CNRS UMR 6622, Nice, France

Jonathan AndreasenUniversity of Arizona, Optical Sciences, Tucson (AZ)

Kiran BhakthaIndian Institute of Technology Kharagpur, India

Supported by the Agence Nationale de la Recherche (ANR GLAD)

In a conventional laser light scattering introduces additional loss, thus increases lasing threshold

Gain Medium : Light amplification

Optical Cavity : Feedback

Pour la Science n°396, Oct 2010

Multiple scattering : dwell time increasesenhanced light amplification

Lethokov, Sov. Phys. JETP 26, 835 (1968).Review: Wiersma, Nature Physics, 4, 359(2008)

Wiersma, Nature, 406, 132(2000)

Mirrorless laser : ASE or lasing with resonant feedback ?

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

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

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).

Reduced scattering (smaller nS)

Anderson Localization

2D random collection of scatterers with refractive index nS in [1.05,2] in a matrix with n0=1

FDTD Method to simulate Maxwell equationscoupled to the population equations of of a four-level atomic structure

Laser Field Amplitude

Min

Max

Time evolution

Time

Inte

nsi

ty

Emission spectrum

Frequency

Inte

nsi

ty

Vanneste et al. PRL87 (2001) , Sebbah et al. PRB66 (2002)

nS = 2

Time evolution

Time

Inte

nsi

ty

Emission spectrum

Frequency

Inte

nsi

ty

Vanneste et al. PRL98 (2007)

Laser Field AmplitudeMin

Max

Vanneste et al., PRL98, 143902 (2007)

nS = 1.25

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 regimeVanneste 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)

IN OUT

OUT

3 mm

Rhodamine 6G

Δn = 0.06Weak scattering

Modes are extended

PDMS

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)

0 2.80

128

256

Position (mm)

560 565 570 575500

1000

1500

2000

Wavelength (nm)

Pow

er S

pect

rum

a.u

.

0 2.80

128

256

Position (mm)

560 565 570 575500

1000

1500

2000

Wavelength (nm)

Pow

er S

pect

rum

a.u

.

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 includeSpectrum to spectrum fluctuationsGain saturationMode competitionLaser instabilities

Starting from uniform pumping

IN OUT

OUT

3 mm

IN OUT

OUT

3 mm

IN OUT

OUT

3 mm

IN OUT

OUT

3 mm

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 lasersOrganic 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 cavityH. Tureci et al., Science 320 (2008)

Multimode regime & Nonlinear phenomenaJ. 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 sourcesB. Redding et al., Optics Lett. 36 (2011)

…

R. Kaiser, Cold atoms

J. Fallert et al.Nature Photonics, 279 (2009)

C. López, Photonic Glass RL

Garcia et al., PRB 82 (2010)Sapienza et al., Science 327 (2010)

Wiersma, PRL 93, 263901 (2004)