Nicolas Bachelard, Institut Langevin (Paris), Supervisor...
Transcript of Nicolas Bachelard, Institut Langevin (Paris), Supervisor...
Active control of random lasersNicolas Bachelard, Institut Langevin (Paris),Supervisor Patrick Sebbah
Introduction: Random Laser?
Classical Laser
Pump
Emission
Components
Gain medium
Optical cavity
Feedback = Mirrors
Properties
Regular spectrum
Directional emission
Amplification fixed by cavity
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
Random Laser
1D
2D
ǫ1ǫ0
Pump
Emission
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b b
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bIout
Iout
Iout
Iout
Components
Gain medium
Scatterers
Feedback = Scattering
Properties
Random spectrum
Random emission
Gain unconstrained
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
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?
Control of random laser with non-uniform pump profile
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
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
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
Control the emission directivity of 2D random lasers
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
Uniform pumping
Below threshold
Above threshold
Optimized pumping
θ0 = 135 and ∆θ0 = 45 θ0 = −135 and ∆θ0 = 45
Conclusion
Conclusion:
Achievements:
Control of spectral emission
Control of emission directivity
Perspectives:
Temporal control
Different lasers
Non-hermitian problems
Thank you for your attention!!!