michael j. williams - national space grant foundationmichael j. williams photonics imaging...
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Michael J. Williams
Photonics Imaging LaboratoryDepartment of Physics & Engineering
Delaware State UniversityDover, DE
Investigation of Third-Order Nonlinear Optical Properties of
Diamond Nanoparticles
Outline
•Significance of Diamond Nanoparticles•Third-order nonlinear susceptibility
•Z-scan technique
•Experiment• Closed aperture• Open aperture
•Data/Results
•Conclusion
Significance of Diamond Nanoparticles
• Biophotonics
• Quantum optics
• Raman lasers
• Our focus: nonlinear optical properties
Source: www.laserfocusworld.com
Third-order Nonlinear Optical Susceptibility χ(3)
• χ(3) is responsible for wide-range of nonlinear
optical effects
• i.e., third-harmonic generation, self-phase modulation,
and intensity-dependent nonlinear refractive index 𝑛2 :
𝑛 = 𝑛0 +𝑛22𝐼
• 𝑛2 ∝ 𝑅𝑒 𝝌(𝟑) , nonlinear refractive index
• 𝛽 ∝ 𝐼𝑚[𝝌(𝟑)], nonlinear absorption coefficient
Detector
ApertureZ-scan
Lens
Z-scan (mm)
tran
smit
ted
sig
nal
(mV
)
The Z−scan technique
Detecto
rZ-scan direction
Pump beam
𝑛2 measurement: closed aperture z-scan
Z-scan distance (mm)
Tra
nsm
itta
nce
(T
)
Aperture
Use transmission data to determine n2
n2 = k ∗ 𝐼0 ∗ 𝐿𝑒𝑓𝑓 ∗ (0.406
∆𝑇𝑝−𝑣)
𝑇𝑝
𝑇𝑣
Self-lensing effect
𝑛2 < 0, 𝑛𝑒𝑔𝑎𝑡𝑖𝑣𝑒 𝑛2 > 0, 𝑝𝑜𝑠𝑖𝑡𝑖𝑣𝑒
Z-scan distance (cm)
Tran
smit
tan
ce (
mV
)
Tran
smit
tan
ce (
mV
)
Z-scan distance (cm)
Tra
nsm
itta
nce
(m
V)
𝛽 measurement: open aperture z-scan
Z-scan distance (mm)
Z-scan directionD
etector
Pump beam
Use transmission data to determine β
β measured from fitting :
T = (𝑒−𝛼0∆𝑧/𝛽𝐼0𝐿𝑒𝑓𝑓) ∗ (1 + 𝑧2
𝑧𝑅2) ∗
ln(1 +𝛽𝐼0𝐿𝑒𝑓𝑓
1+ 𝑧2
𝑧𝑅2
)
Experimental Setup(532 cw laser)
Detector
Nd
:YA
Gcw
53
2n
m
Aperture
Motorized Stage
oscillo
scop
e
Nanodiamond sample
Closed aperture (532 cw laser)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
5 10 15 20 25 30 35 40
No
rmal
ized
Tra
nsm
itta
nce
z-scan distance (mm)
25nm ND sample @ .025wt%
161 MW/m^2
339 MW/m^2
532 MW/m^2
729 MW/m^2
929 MW/m^2
1127 MW/m^2
Intensity at Focus 𝒏𝟐 (cm2/W)
161 MW/m2 -1.2526e-15
339 MW/m2 -8.7148e-16
532 MW/m2 -5.6736e-16
729 MW/m2 -3.5000e-16
929 MW/m2 -2.5138e-16
1127 MW/m2 -1.2832e-16
Nonlinear Refraction Index Measurement of 25nm ND, 0.015wt% (cw laser)
Open aperture (532 cw laser)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-15 -10 -5 0 5 10 15
No
rmal
ized
Tra
nsm
itta
nce
Total Distance (mm)
25nm ND sample @ 0.015 wt%
339 MW/m^2
532 MW/m^2
729 MW/m^2
929 MW/m^2
1127 MW/m^2
Intensity at Focus 𝜷 (cm/W)
161 MW/m2 3.3899e-09
339 MW/m2 1.5443e-09
532 MW/m2 1.1670e-09
729 MW/m2 8.4867e-10
929 MW/m2 6.6002e-10
1127 MW/m2 5.7881e-10
Nonlinear Absorption Measurement of 25nm ND, 0.015wt% (cw laser)
Experimental Setup (1064nm pulsed laser)
Q-switched pulselaser @ 1064nm
Aperture
Motorized Stage
Detector
oscilloscope
Nanodiamond sample
Z-scan closed aperture
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
7 12 17 22 27 32
No
rmal
ized
Tra
nsm
itta
nce
z-scan distance (mm)
.035wt% NDs using 1064nm pulse laser @ 35% pulse power
500 Hz rep rate
100 Hz rep rate
Conclusion
• Measured n2 and β using single beam Z-scan for nanodiamonds in aqueous solution using cw laser
• Continue investigation using pulsed laser
Acknowledgements
• Delaware Space Grant Consortium
• National Science Foundation CREST
• Optical Science Center for Applied Research