Nicolas Bachelard, Institut Langevin (Paris), Supervisor...

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Active control of random lasers Nicolas Bachelard, Institut Langevin (Paris), Supervisor Patrick Sebbah

Transcript of Nicolas Bachelard, Institut Langevin (Paris), Supervisor...

Page 1: Nicolas Bachelard, Institut Langevin (Paris), Supervisor ...mesoimage.grenoble.cnrs.fr/IMG/pdf/cargese2014/bachelard.pdf · Active control of random lasers Nicolas Bachelard, Institut

Active control of random lasersNicolas Bachelard, Institut Langevin (Paris),Supervisor Patrick Sebbah

Page 2: Nicolas Bachelard, Institut Langevin (Paris), Supervisor ...mesoimage.grenoble.cnrs.fr/IMG/pdf/cargese2014/bachelard.pdf · Active control of random lasers Nicolas Bachelard, Institut

Introduction: Random Laser?

Page 3: Nicolas Bachelard, Institut Langevin (Paris), Supervisor ...mesoimage.grenoble.cnrs.fr/IMG/pdf/cargese2014/bachelard.pdf · Active control of random lasers Nicolas Bachelard, Institut

Classical Laser

Pump

Emission

Components

Gain medium

Optical cavity

Feedback = Mirrors

Properties

Regular spectrum

Directional emission

Amplification fixed by cavity

Page 4: Nicolas Bachelard, Institut Langevin (Paris), Supervisor ...mesoimage.grenoble.cnrs.fr/IMG/pdf/cargese2014/bachelard.pdf · Active control of random lasers Nicolas Bachelard, Institut

Classical laser:

Pump

Emission

Ψ1

Ψ2

⇒ Maxwell-Bloch along passive modes (Ωk ,Ψk ):

⇒ Lasing modes solution of

ω2 =

Ω21 . . . 0.... . .

.

.

.

0 . . . Ω2n

+

V11 . . . 0...

. . ....

0 . . . Vnn

+ ǫNL(E)×

no coupling

⇒ Non linearities ≈ 0 (near threshold)

Lasing Modes ≈ passive + No coupling

Page 5: Nicolas Bachelard, Institut Langevin (Paris), Supervisor ...mesoimage.grenoble.cnrs.fr/IMG/pdf/cargese2014/bachelard.pdf · Active control of random lasers Nicolas Bachelard, Institut

Random Laser

1D

2D

ǫ1ǫ0

Pump

Emission

b

bb

b

bb

b

b

b

b

bb

bb

b

b

b

b

b

b

b

b

bb

b

b

bb

b

b

b

b

b

bb

b

bb

b

bb

b

bb

b

b

b

bb

b

b

b

b

b

bb

b

b

b

b

b

b b

b

bIout

Iout

Iout

Iout

Components

Gain medium

Scatterers

Feedback = Scattering

Properties

Random spectrum

Random emission

Gain unconstrained

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Random laser:

ǫ1ǫ0

Pump

Emission

Ψ1

Ψ2

⇒ Local gain fe(x)

⇒ Maxwell-Bloch along passive modes (Ωk ,Ψk )

ω2 =

Ω21 . . . 0.... . .

.

.

.

0 . . . Ω2n

+

V11 . . . V1n

.

.

.. . .

.

.

.

Vn1 . . . Vnn

+ ǫNL (E)×

coupling

⇒ Non linearities ≈ 0 (near threshold)

Lasing Modes , passive + Coupling available

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Condition of mode coupling:

Coupling term:

Vpq =

Ψp(x)Ψq(x)fe(x)dx

Passive system Local gain

⇒ ΨpΨq , 0 if modes overlap

⇒ Non uniform gain influences mode coupling

⇒ Question: Gain = degree of freedom?

Page 8: Nicolas Bachelard, Institut Langevin (Paris), Supervisor ...mesoimage.grenoble.cnrs.fr/IMG/pdf/cargese2014/bachelard.pdf · Active control of random lasers Nicolas Bachelard, Institut

Control of random laser with non-uniform pump profile

Page 9: Nicolas Bachelard, Institut Langevin (Paris), Supervisor ...mesoimage.grenoble.cnrs.fr/IMG/pdf/cargese2014/bachelard.pdf · Active control of random lasers Nicolas Bachelard, Institut

Method

Uniform fe(x) λ

II(λ0)

Optimized fe(x) λ

I

N. Bachelard, J. Andreasen, S. Gigan and P. Sebbah (PRL), 2012

Idea

Input = Pump Profile fe(x)

Output = Spectrum

Control

fe(x)→ SLM

Criterion =I(λ0)

max(I(λi,0))

Optimization Algorithm

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Spectral optimization

Optimized pump profile

0

7000

I(λ)

Uniform high−pump profile

557 559 561 563 565 5670

7000

I(λ)

561.77

Wavelength λ (nm)

N. Bachelard, S. Gigan, X. Noblin and P. Sebbah (Nat. Phy.), 2014

B. N. Shivakiran Bhaktha, N. Bachelard, X. Noblin and P. Sebbah (APL), 2012

Sample

1D microfluidic→ Dielectric = PDMS→ Gain = Rhodamine 6G

Hadamard basis 32 elements

Optimization

Spectrum acquisition

≈ 250 iterations

≥ 10 dB sideband rejection

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Performances

Spectral Selectivity down to 0.06 nm

0 1.40

128

256

Position (mm)

Pump profile

560.5 561 561.50

3000

Nor

mal

ized

Inte

nsity

(a.

u.)

Wavelength (nm)

0 1.40

128

256

Position (mm)

Pump profile

560.5 561 561.50

3000

Wavelength (nm)

N. Bachelard, S. Gigan, X. Noblin and P. Sebbah (Nat. Phy.), 2014

Single-mode over the whole dye

Bandwidth

560 561 562 563 564 565

−15

−10

−5

0

5

10

15

Wavelength λ (nm)

10×l

og10

R(λ

0) (d

B)

optimized pumpinguniform pumping

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Control the emission directivity of 2D random lasers

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Method

θ0

∆θ0

∆θback

Sample

2D microfluidic→ Dielectric = resin→ Gain = Rhodamine 6G

Zernike basis 100 elements

Optimization

CCD acquisition

Criterion =I∆θ0I2π−

I2πI∆θback

200 iterations

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Uniform pumping

Below threshold

Above threshold

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Optimized pumping

θ0 = 135 and ∆θ0 = 45 θ0 = −135 and ∆θ0 = 45

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Conclusion

Page 17: Nicolas Bachelard, Institut Langevin (Paris), Supervisor ...mesoimage.grenoble.cnrs.fr/IMG/pdf/cargese2014/bachelard.pdf · Active control of random lasers Nicolas Bachelard, Institut

Conclusion:

Achievements:

Control of spectral emission

Control of emission directivity

Perspectives:

Temporal control

Different lasers

Non-hermitian problems

Page 18: Nicolas Bachelard, Institut Langevin (Paris), Supervisor ...mesoimage.grenoble.cnrs.fr/IMG/pdf/cargese2014/bachelard.pdf · Active control of random lasers Nicolas Bachelard, Institut

Thank you for your attention!!!