michael j. williams - national space grant foundationmichael j. williams photonics imaging...

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