Crystalline Colloidal Array Optical Devices
Post on 04-Jun-2022
4 Views
Preview:
Transcript
Crystalline Colloidal Array Crystalline Colloidal Array Optical DevicesOptical Devices
Sanford A. AsherSanford A. AsherDept. of ChemistryDept. of Chemistry
University of PittsburghUniversity of PittsburghPittsburgh, PA 15260Pittsburgh, PA 15260
412412--624624--85708570asher@pitt.eduasher@pitt.edu
Sanford A. Asher, Department of Chemistry
CRYSTALLINE COLLOIDAL SELF-ASSEMBLY:
MOTIF
FOR
CREATING SUBMICRON
PERIODIC SMART MATERIALS
OutlineOutlineCCA and PCCA Photonic Crystal CCA and PCCA Photonic Crystal FabricationFabricationNanosecond Photonic Crystal SwitchesNanosecond Photonic Crystal SwitchesHydrogelHydrogel Volume Phase Transition Volume Phase Transition Refractive Index SwitchingRefractive Index Switching–– Thermally activatedThermally activated–– Chemically activatedChemically activated–– PhotochemicallyPhotochemically activatedactivated
Sanford A. Asher, Department of Chemistry
Holtz, Asher et al J. Am. Chem. Soc. 1994, 116, 4497
Crystalline Colloidal Arrays Self-Assemblyfabricated from monodisperse, highly charged colloidal particles
~ 1013 spheres/cm3
spacing dependent only upon particle number density and crystalline structure
-
Dialysis /Ion Exchange Resin
Self-assembly
Crystalline Colloidal Array
FCC--
----
- --
+
-
--
---
- --
+
--
---- -- -
--
--- ---
--
--- -
-
--
---
- --
-
--
---
- --
--
---- --
++
--
-
--
--
-
---
-----
--
---
- --
--
---
- --
--
---
- --
--
---
- --
--
-
-
-
--
++
+
++ + +
+
+
+
+
++ +
+
+
+
++
+
+
+
++
+
+
++
+
+
+
+
+
+
+ +
++
+
++
+
++
+ +
--
---- --
+
++
+
--
---- --
+ +
+
++
+
+
+
+
+
+
+
+ +
++
+
+
+
++ +
+
+
+
- ---
--
--
--
---- --+
+
--
--- --+
+
--
---- --+
+
+
+--
--- --+
---
-- -- ++
+
+
+
+
+
+
+
+
++
+
+-
-
--
-+
+
+
+
+
+
-
---
----
-+
+-
- -
Preparing ~ 100 nm Polystyrene Colloids
160 ml Water 60 ml Styrene (monomer) 2.00 g MA-80-1 (surfactant) 2.90 g COPS -1 (ionic co-monomer)2.00 g Divinyl Benzene (crosslinker)0.20 g Sodium Bicarbonate (buffer)0.70 g Ammonium Persulfate (initiator)
Polymerize at 70oC for 3 hrs.
Polystyrene Colloid Synthesis:EMULSION POLYMERIZATION
TEM of polystyrene spheres
Reese, Asher et al J. Colloid Interface Sci. 2000, 232, 76
Temperature ControllerN2
N2
H2O
-
Long polymer chain
Surfactant
Water
-
--
++
+
R•
R•
What Drives CCA Self-Assembly?
Medium Dielectric Constant
re
aeeZrU
ra κκ
κε
−
⎥⎦
⎤⎢⎣
⎡+
=222
1)(
Interaction Potential Energy
Sphere Radius
Ionic Impurities
( )ipB
nZnTk
e+=
επκ
22 4
Particle concentration
2ar
U
r
H+ SO3-
-O3SH+
+H H+
H+
-O3S-O3S
-O3S SO3-SO3
-
SO3-
+H
+H
+H
Shear boundary
Negatively charged particle
Debye layer thickness
nmwaterpurein 700~)(1κ
Sanford A. Asher, Department of Chemistry
Bragg Diffraction
Diff
ract
ed In
tens
ity, I
D
500 600 700 800Wavelength / nm
d ~ 200 nm
+
- - - - --------- -- - -
-
-
---
--
- - - - ------------ -
-
-
---
--+ + +
λ0
- - - - -------------
-
-
---
--- - - - ---
--------- -
-
-
---
--
- - - - ------------ -
-
-
---
--- - - - ---
--------- -
-
-
---
--
- - - - -------------
-
-
---
--
- - - - ------------ -
-
-
---
--
- - - - -------------
-
-
---
--
- - - - -------------
-
-
---
--
- - - - ------------ -
-
-
---
--- - - - ---
--------- -
-
-
---
--
- - - - -------------
-
-
---
--
- - - - ------------ -
-
-
---
--
+
+
++
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
dθB
mλo = 2ndsin θ
(111) FCC CCA
λ0 = wavelength of diffracted light n = refractive index of systemd = interplanar spacing in crystalθB = Bragg glancing angle
All Light Diffracted-Finite Widths-Top Hat Profiles
Diffraction Phenomena of Photonic Crystals
* Kinematic Diffractionx-rays: Atomic & Molecular Latticewimpy scatteringlittle attenuationeach layer contributes similarly
* Dynamical Diffractionstrong scatteringmust consider coupledincident and diffracted wave
* Theoretical Foundation Based on Work in1930-1940
W.H. Zachariasen, The Theory of X-ray Diffractionin Crystals, Wiley, 1945.
3-D Photonic Bandgap Crystals-for much larger modulations of refractive index
Dynamical Bragg Diffraction From Crystalline Colloidal Arrays, P. A. Rundquist, P. Photinos, S. Jagannathan, and S. A. Asher, J. Chem. Phys. 91, 4932-4941 (1989).
Ultra Efficient Diffraction
0 200 400 600 800 1000
0
2
4
6
8
10
-Log
T91 nm PS CCA
100 μm = 400 layers
Number of fcc (111) layers
A B
C
FCC: ABCABCABC…
FCC Twin: ABCABCBACBA…
Twin Planes
HCP: ABABABAB…
Stacking of closest-packed layers:
FCC Twin: ABCABCBACBACBABCABC…Lamellar
A B
C
FCC: ABCABCABC…
FCC Twin: ABCABCBACBA…
Twin Planes
HCP: ABABABAB…
Stacking of closest-packed layers:
FCC Twin: ABCABCBACBACBABCABC…Lamellar
FCC Crystal
0
.5
1
1.5
2
2.5
3
400 600 800 1000 1200 1400
L U
X
W
K
L
X
Wavelength (nm)
-log
10T
U
σ polarization
CCA in the middle: ABCABC layers. Reciprical lattice and unit cell.
Sanford A. Asher, Department of Chemistry
(-200)(0-20)
(-2-20)
Incident light
0 5 10 15 200
0.1
0.2
0.3
0.4
0.5
% stacking faults
Diff
ract
ed in
tens
ity ra
tio(200)/(111)(220)/(111)(311)/(111)
Dependence of Diffraction Efficiency on Number of Stacking Faults Along 111
Conclusions
• Diffraction from FCC 111 planes independent of stacking faults
• Diffraction from higher Miller index planes severely attenuated by stacking faults
• Stacking faults increase with particle spacing
• Stacking faults will be the major difficulty for fabricating 3-D photonic bandgapmaterials
Crystalline Colloidal Array Optical Crystalline Colloidal Array Optical DevicesDevices
••Passive Spectral Passive Spectral BandpassBandpass Reject FilterReject Filter
-log
T
λ-7
0 EXP: Raman Spectroscopy
rejecting Rayleighline, Δλ = 5 nm
First Photonic Crystal PatentSanford A. Asher, Department of Chemistry
Photonic CrystalsHave Revolutionary
Applications in Areas Such as Optics,
Optical Computing and Communications.
Crystalline Colloidal Array Crystalline Colloidal Array Tunable Optical DevicesTunable Optical Devices
•Refractive index thermal nonlinearities
•Hydrogel volume phase transitions
•Photochemically accuated lattice alterations
No Transmission
100% Transmission
Low Intensity
High Intensity
?
?
Optical Limiter and Switch
Sanford A. Asher, Department of Chemistry
Concept for Creating Nonlinear Optical Switch
Low intensity illumination :
High intensity illumination causes the sphere refractive indexto mismatch that of the medium - Bragg diffraction occurs.
no transmission
CCA
100% transmission
CCA
index matched (np = nm)
≠index mismatched (np nm)
Transmission Through CCA as a Function of the Refractive Index Between the
Spheres and the Medium
Nanosecond PhotothermalDynamics in Colloidal Suspension
R. Kesavamoorthy, M. S. Super, and S. A. Asher,
J. Appl. Phys. 71, 1116-1123 (1992).
Nanosecond Photothermal Dynamics in Colloidal SuspensionR. Kesavamoorthy, M. S. Super, and S. A. Asher, J. Appl. Phys. 71, 1116-1123 (1992).
Refractive Index Dependence on Temperature
Photothermal Effect: Δn = (dn/dT) · ΔT
Example: PMMA, dn/dT = -1.1 X 10-4 / 0° C×
Requirements:(1) To index match the particles to the aqueous medium (nH2O = 1.33), we need to use a low refractive index polymer to synthesize the particles.(2) We need to chemically bond a dye to the particles in order to prepare transparent, absorbing CCA.
OCH2CF2CF2CF3
OC
CH2 CHn( )
Wavele ngth / nm
Ext
inct
ion,
-log
(It/I
0)
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
500 550 600 650 700 750 800
medium refractive index, nm
Ext
inct
ion
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.34 1.36 1.38 1.40 1.42 1.44 1.46
np > nm = 1.333
np > nm = 1.437
Transmission Spec tra of PFB MA Pol ymerize d CCA at Di fferent Me dium Re frac ti ve Inde x
A ~ ( n p /n m )2 - 1
Dyed PFBMA CCA Hydrogel
0
0.2
0.4
0.6
0.8
1.0
400 450 500 550 600 650 700 750 800
Wavelength (nm)
Ext
inct
ion
dye absorption band
diffraction band
Covalently attached absorbing dye to the CCA in the hydrogel.
PCCA FabricationPCCA Fabrication
--
---- --
--
---- --
--
---- --
--
---- --
--
---- --
--
---- --
--
---- --
--
---- ---
----
- --
--
---- --
--
---- --
--
---- ---
----
- --
--
---- ---
----
- ----
---- --
--
---- --
--
---- --
--
---
- --
--
---
- --
--
---- --
--
---- --
--
---- --
--
---- --
--
---- -- -
----
- --
--
---- --
--
---- --
--
---- --
--
---
- --
+
+
++
+
++
+
+++
+
++
++
++
++
+
+
+
+
++
+
+
+
+
+
++
+
+
+
+
+
+
+
+ + ++
++
+ +
+
++
+
+ + --
---
- --
--
---
- --
--
---- --
--
---- --
--
---- --
--
---- --
--
---
- --
--
---
- ----
---- --
--
---- --
--
---- --
--
---- ---
----
- --
--
---
- ----
---
- ----
---- --
--
---
- --
--
---- --
--
---- --
--
---- --
--
---- --
--
---- --
--
---- --
--
---- --
--
---- -- -
----
- --
--
---
- --
--
---- --
--
---- --
--
---- --
+
+
++
+
++
+
+++
+
++
++
++
++
+
+
+
+
++
+
+
+
+
+
++
+
+
+
+
+
+
+
+ + ++
++
+ +
+
++
+
+ +AcrylamideBisacrylamide
Photopolymerize
Self Assembly Motif for Creating Submicron Periodic Materials. Polymerized Crystalline Colloidal Arrays,
S. A. Asher, J. Holtz, L. Liu, and Z. Wu, J. Am. Chem. Soc. 116, 4997-4998 (1994).
Experimental Set-up For Measuring Optical
Switching Nonlinearity
Pump beam
Probe beam
532 nm
594 nm D1
beam splitter
lens
cylinder with DMSO/water
CCA hydrogel sample
(reference signal)(diffraction signal)
shutter
D2
Medium indexn0E
xtin
ctio
n
Optical Switching of Dyed PCCA
nm (1.390) > np (1.386) , dyed PCCA
nm (1.382) < np , dyed PCCA
nm (1.388) > np , undyed PCCA
Incident Pump Beam Energy (mJ)
Ron
/ R
off
0.4
0.60.81.0
1.2
1.41.6
1.8
2.0
2.22.4
0 0.5 1.0 1.5 2.0 2.5 3.0
Tg = 62 0C
Nsec Switchable Polymerized Crystalline Colloidal Array Bragg Diffracting Materials
G. Pan, R. Kesavamoorthy, and S. A. Asher
J. Am. Chem. Soc. 120, 6525-6530 (1998).
1.0
1.5
2.0
2.5
3.0
-4 -2 0 2 4 6 8
Probe delay time / ns
Ron
/Rof
fat
Tg
Dependence of Nonlinear Effect on Probe Delay Time
Nsec Switchable Polymerized Crystalline Colloidal Array Bragg Diffracting Materials
G. Pan, R. Kesavamoorthy, and S. A. Asher
J. Am. Chem. Soc. 120, 6525-6530 (1998).
Conclusions
• Observed nsec photothermal switching• Problem low efficiency (<10%) !• Stay Tuned: Inefficiency results from
temperature dependence of diffraction λ• Switching should be 99 + %
Crystalline Colloidal Array Crystalline Colloidal Array Tunable Optical DevicesTunable Optical Devices
Refractive index thermal nonlinearities
•Hydrogel volume phase transitions
•Photochemically accuated lattice alterations
Poly(N-isopropylacrylamide) : T Dependent ΔGMIX
Chemical Structure of NIPAMPoly(N-isopropylacrylamide) (PNIPAM) undergoes a reversible phase transition when heated above 32.1 oC. This coil-globule transition is analogous to a liquid-vapor phase transition. The recipe and synthesis conditions determine the extent of volume changes and whether they are continuous or discontinuous.
ON
ON
Sanford A. Asher, Department of Chemistry
Thermally Switchable Periodicities from Novel Mesocopically Ordered Materials J. M. Weissman, H. B. Sunkara, A. S. Tse , and S. A. Asher
Science 274, 959-960 (1996).
Extin
ctio
n (-l
og I/
I o)
Optical switching from PNIPAM CCA
600
Wavelength (nm)
40 oC
10 oC
0
0.5
1
1.5
2
400 450 500 550
10 oC
40 oC
Sanford A. Asher, Department of Chemistry
Sanford A. Asher, Department of Chemistry
Unfortunately system does not switch quickly-
CCA disorders!
HydrogelMatrix
PNIPAM Colloid
MonomerCrosslinker
InitiatorUV
Polymerization
NIPAM CCA Lightly Polymerized into PCCA
“Nanogel Nanosecond Photonic Crystal Optical Switching,”
C. Reese, A. Mikhonin, M. Kamenjicki, A. Tikhonov and S.A. Asher
J. Am. Chem. Soc., 126, 1493-1496 (2004).
0
0.5
1
1.5
2
2.5
3
200 300 400 500 600 700 800 900 1000
Wavelength / nm
Abs
orba
nce
10 C15 C20 C25 C28 C30 C32 C34 C37 C40 C45 C
0.2
0.4
0.6
0.8
1
1.2
1.4
5 10 15 20 25 30 35 40 45 50
Temperature / C
Abs
orba
nce
at 7
16 n
m
40oC
20oC
PNIPAM Colloid
Wavelength / nm
0
.5
1
400 500 600 700
.5
1
400 500 600 700
.5
1
400 500 600 700
.5
1
1.5
400 500 600 700
−lo
g T
Wavelength / nm
4 ms
54 μs
9 μs
1.5 1
100 ns
0.48 ms0.3 ms
24 μs
1.5 μs1 μs
800 ns 600 ns 300 ns
0
.1
.2
.3
.4
56 0 600 64 0 680
.1
.2
.3
.4
56 0 600 64 0 680
−lo
g Δ
T
.1
.2
.3
.4
56 0 600 64 0 680
.1
.2
.3
.4
56 0 600 64 0 680 W avelen gth / nm
T
Wavelength / nm
0
.5
1
400 500 600 700
.5
1
400 500 600 700
.5
1
400 500 600 700
.5
1
1.5
400 500 600 700
−lo
g T
Wavelength / nm
4 ms
54 μs
9 μs
1.5 1
100 ns
0.48 ms0.3 ms
24 μs
1.5 μs1 μs
800 ns 600 ns 300 ns
0
.1
.2
.3
.4
56 0 600 64 0 680
.1
.2
.3
.4
56 0 600 64 0 680
−lo
g Δ
T
.1
.2
.3
.4
56 0 600 64 0 680
.1
.2
.3
.4
56 0 600 64 0 680 W avelen gth / nm
T
.1
.2
.3
.4
56 0 600 64 0 680
.1
.2
.3
.4
56 0 600 64 0 680
−lo
g Δ
T
.1
.2
.3
.4
56 0 600 64 0 680
.1
.2
.3
.4
56 0 600 64 0 680 W avelen gth / nm
T
Time Dependence of Diffraction Changes after 3 nsec T-jump
Kinetics
−Lo
g T
605 nm
0 40 80 1200.01
0.1
1
τ1 ≈ 870 ns (26%)
τ2 ≈ 19 μs (24%)
τ3 ≈ 130 μs (50%)
Delay time / μs
−Lo
g T
605 nm
0 40 80 1200.01
0.1
1
τ1 ≈ 870 ns (26%)
τ2 ≈ 19 μs (24%)
τ3 ≈ 130 μs (50%)
605 nm
0 40 80 1200.01
0.1
1
τ1 ≈ 870 ns (26%)
τ2 ≈ 19 μs (24%)
τ3 ≈ 130 μs (50%)
Delay time / μs
−Lo
g T
605 nm
0 40 80 1200.01
0.1
1
τ1 ≈ 870 ns (26%)
τ2 ≈ 19 μs (24%)
τ3 ≈ 130 μs (50%)
Delay time / μs
−Lo
g T
605 nm
0 40 80 1200.01
0.1
1
τ1 ≈ 870 ns (26%)
τ2 ≈ 19 μs (24%)
τ3 ≈ 130 μs (50%)
605 nm
0 40 80 1200.01
0.1
1
τ1 ≈ 870 ns (26%)
τ2 ≈ 19 μs (24%)
τ3 ≈ 130 μs (50%)
Delay time / μs
0 40 80 1200.01
0.1
1
−Lo
g T
Delay time / μs
375 nm
τ1 ≈ 1.2 μs (28%)
τ2 ≈ 21 μs (11%)
τ3 ≈ 147 μs (61%)
0 40 80 1200.01
0.1
1
0 40 80 1200.01
0.1
1
−Lo
g T
Delay time / μs
375 nm
τ1 ≈ 1.2 μs (28%)
τ2 ≈ 21 μs (11%)
τ3 ≈ 147 μs (61%)
0 40 80 1200.01
0.1
1
−Lo
g T
Delay time / μs
375 nm
τ1 ≈ 1.2 μs (28%)
τ2 ≈ 21 μs (11%)
τ3 ≈ 147 μs (61%)
0 40 80 1200.01
0.1
1
0 40 80 1200.01
0.1
1
−Lo
g T
Delay time / μs
375 nm
τ1 ≈ 1.2 μs (28%)
τ2 ≈ 21 μs (11%)
τ3 ≈ 147 μs (61%)
.05
.1
.15
400 450 500 550 600 650
.05
.1
.15
400 450 500 550 600 650
Wavelength / nm
ΔOD
0 μsec0.1 μsec0.2 μsec0.3 μsec0.4 μsec2.5 μsec20 μsec200 μsec1000 μsec1500 μsec
0 1 2
0.0 5
0.0 6
0.0 7
0.0 8
600 nm
τ ≈ 120 ns
Delay tim e / μs0 1 2
0.0 5
0.0 6
0.0 7
0.0 8
600 nm
τ ≈ 120 ns
Delay tim e / μs
.05
.1
.15
400 450 500 550 600 650
.05
.1
.15
400 450 500 550 600 650
Wavelength / nm
ΔOD
0 μsec0.1 μsec0.2 μsec0.3 μsec0.4 μsec2.5 μsec20 μsec200 μsec1000 μsec1500 μsec
.05
.1
.15
400 450 500 550 600 650
.05
.1
.15
400 450 500 550 600 650
Wavelength / nm
ΔOD
.05
.1
.15
400 450 500 550 600 650
.05
.1
.15
400 450 500 550 600 650
.05
.1
.15
400 450 500 550 600 650
.05
.1
.15
400 450 500 550 600 650
Wavelength / nm
ΔOD
0 μsec0.1 μsec0.2 μsec0.3 μsec0.4 μsec2.5 μsec20 μsec200 μsec1000 μsec1500 μsec
0 μsec0.1 μsec0.2 μsec0.3 μsec0.4 μsec2.5 μsec20 μsec200 μsec1000 μsec1500 μsec
0 1 2
0.0 5
0.0 6
0.0 7
0.0 8
600 nm
τ ≈ 120 ns
Delay tim e / μs0 1 2
0.0 5
0.0 6
0.0 7
0.0 8
600 nm
τ ≈ 120 ns
Delay tim e / μs
NSec Individual Sphere Volume Phase Transitions
Fast Kinetic Transmission Changes in
PNIPAM Photonic Crystals.
• Heating pulse: 3 ns duration, 1.9 μm, ~1.3
mJ/pulse
• T-jump ~ 23°C → 30°C ± 2°C, IR spot
diameter ~ 200 – 300 μm
• Transient absorption probed by temporally
delayed 120 ns “white-light” pulse
Crystalline Colloidal Array Crystalline Colloidal Array Tunable Optical DevicesTunable Optical Devices
•Refractive index thermal nonlinearities
•Hydrogel volume phase transitions
•Photochemically accuated lattice alterations
PHOTORESPONSIVEPOLYMERIZED CRYSTALLINE COLLOIDAL ARRAYS
AS A PHOTOSWITCHABLE DEVICE
Marta Kamenjicki, Igor K. Lednev, Sanford A. Asher
Department of ChemistryUniversity of Pittsburgh
Pittsburgh, PA 15260
N
N
N
N
Photochemically Controlled Photonic Crystals, M. Kamenjicki, I. Lednev, A. Mikhonin, R. Kesavamoorthy and S.A. Asher, Advanced Functional Materials, 13, 774-780 (2003).
λ1
O
O CHO
CH2CH2
λ1
UV
Vis, Δ
Trans -
N
HN
N O
OH
HO
λ2
Cis -
N N
HO
OHON
H
H2N-R
R=N O
OH
HO
N
PCCA PCPCCA PCPCCA
UV
AZOBENZENE PHOTOISOMERIZATION
VIS, VIS,
• reversible photochromism in fluids and solids
• isomerization results in changes of1) absorption spectrum2) dipole moment3) geometrical conformation
Trans-azobenzene Cis-azobenzene
60°
N
N
180°
9.0 Å
N N
5.3 Å
Azobenzene (water solution) Dynamics UnderUV and Vis Light
200 300 400 500 600 7000.0
0.5
1.0
Abs
orba
nce
Wavelength /nm
Dark
1 min 365 nm (12 mW)
20 sec. 488 nm (50 mW)
NH2N
N O
OH
OH
N
N
UV
Vis,
N N
200 300 400 500 600 7000.0
0.5
1.0
Abs
orba
nce
Wavelength /nm
Dark
1 min 365 nm (12 mW)
20 sec. 488 nm (50 mW)
NH2NH2N
N O
OHOH
OHOH
N
N
N
N
UV
Vis,
UV
Vis,
N NN N
1 cm quartz cell
Azobenzene Functionalized PCCA Dynamics Under UV and Vis Light
0
0.4
0.8
-log
T
350 450 550 650 750
Wavelength /nm
UV
Vis
Vis
UV
0.6
0.8
A (
340
nm)
Time
Peak
pos
ition
/a.u
.
Time
UVVisUV
a)
b)
0
.2
.4
.6
.8
360 400 440 480 520 t = 0.3 μs
0
.2
.4
.6
.8
360 400 440 480 520
t = 102.3 μs0
.2
.4
.6
.8
360 400 440 480 520
t = 302.3 μs
0
.2
.4
.6
.8
360 400 440 480 520
t = 2002.3 μs0
.2
.4
.6
.8
360 400 440 480 520 t = 6155.8 μs
0
.2
.4
.6
.8
360 400 440 480 520
t = 5.3 μs
Wavelength /nm
Wavelength /nm
Wavelength /nm
Wavelength /nm
Wavelength /nm
Wavelength /nm
0
.2
.4
.6
.8
360 380 400 420 440 460 480 500 520 540 Wavelength /nm
Fig. 11
0 s15 s36 s66 s120 s-lo
g T
Speed
Limit?
Optical Switching
• Use of Laser Heating to Drive HydrogelVolume Phase Transition
• Use of Photochemistry to Drive HydrogelVolume Phase Transition
• Use of Thermal Refractive Index Mismatch to Control Diffraction-Inefficiency due to dynamic diffraction wavelenght shift-stay tuned
FUTURE WORK
• Optimize these sensors to combine hydrogel volume phase transition with thermal heating by nsec pulses
• Available Δn > 0.15 !• Decrease characteristic size of switching
materials.
AcknowledgementsAcknowledgements
Asher Research Group Members
$: NIH, NCI, NASA and NSF
top related