Photopolymerizable Nanoparticle-polymer Composite Materials

for Light and Neutron Beam Manipulations

Yasuo Tomita

1,†

, Kohta Nagaya

, Toshi Aoi

, Yuko Iso

, Akihisa Kageyama

, Naoya Nishimura

Keisuke Odoi

, Koichi Umemoto

, J¨urgen Klepp

, Christian Pruner

and Martin Fally

Department of Engineering Science, University of Electro-Communications, Chofu, Tokyo 182-8585, Japan

Materials Research Laboratories, Nissan Chemical Industries, LTD., Funabashi, Chiba 274-0052, Japan

Central Research Center, Daicel Corp., Himeji, Hyogo 671-1283, Japan

Faculty of Physics, University of Vienna, Vienna, Austria

Department of Materials Science and Physics, University of Salzburg, Salzburg, Austria

Keywords:

Nanocomposite Materials, Photonic Nanostructured Materials, Nanoparticles, Photopolymer, Volume Holo-

graphic Grating, Holographic Data Storage, Nonlinear Optics, Neutron Optics.

Abstract:

We report on a recent progress in a new class of photopolymerizable nanostructured materials, the so-called

photopolymerizable nanoparticle-polymer composites (NPCs). They consist of photoreactive monomer (pho-

topolymer) dispersed with inorganic or organic nanoparticles at high concentrations. The initially uniform

distribution of nanoparticles in a neat monomer host is spatially assembled under holographic exposure, pro-

viding the single step formation of large scale and multi-dimensional photonic lattice structures in NPC ﬁlms.

This property can be used for versatile applications in photonics and neutron optics such as holographic data

storage, holographic optical elements, nonlinear photonic crystals and slow-neutron beam control. Here we

describe applications of NPCs dispersed with new organic and inorganic nanoparticles to holographic data

storage and holographic diffractive elements for light and neutron beams.

1 INTRODUCTION

Photonic nanostructured materials having spatially

ordered arrangements such as photonic crystals and

metamaterials have been of considerable interest for

their tailored linear and nonlinear optical properties

that cannot be usually available by natural materi-

als (Lourtioz et al., 2005; Smith et al., 2004). An-

other type of nanostructured materials involves ei-

ther random arrangements of nanoscale materials,

i.e., nanoparticles (nanocrystals), embedded in a host

material or different materials ﬁnely interspersed

with/altered one another. Such nanocomposite ma-

terials exhibit the local-ﬁeld effect that can be also

used to control the linear and nonlinear optical prop-

erties by various types of spatial arrangements in-

cluding Maxwell-Garnett, Bruggeman and layered

composite geometries (Dolgaleva and Boyd, 2012).

However, these nanostructured materials are usually

photo-insensitive so that no light control of their ar-

rangement is possible.

As a novel photo-conﬁgurable nanostructured

material, in 2002 we demonstrated volume holo-

graphic recording in a new type of photopolymeriz-

able organic-inorganic nanocomposite material, the

so-called photopolymerizable nanoparticle-polymer

composite (NPC) (Tomita et al., 2016a), in which

inorganic TiO

nanoparticles were highly dispersed

in methacrylate photopolymer (Suzuki et al., 2002).

The idea of using inorganic nanoparticles possessing

a wide variety of refractive indices in the visible is to

employ them as transporting species under spatially

inhomogeneous illumination (holographic exposure),

so that nanoparticles and monomer species mutually

diffuse and phase-separate each other to form the spa-

tial density modulation of nanoparticles according to

the light-intensity distribution. It would induce large

refractive index modulation provided that refractive

indices between nanoparticles and the formed poly-

mer are large enough to form higher contrast pho-

tonic lattice structures (phase gratings) than those

formed in conventional all-organic photopolymer ma-

terials under holographic exposure. In addition, the

inclusion of inorganic nanoparticles contributes to

the improvement of mechanical and thermal stabil-

ity of the formed photonic lattice structure. Sub-

Tomita, Y., Nagaya, K., Aoi, T., Iso, Y., Kageyama, A., Nishimura, N., Odoi, K., Umemoto, K., Klepp, J., Pruner, C. and Fally, M.

Photopolymerizable Nanoparticle-polymer Composite Materials for Light and Neutron Beam Manipulations.

DOI: 10.5220/0006728803130322

In Proceedings of the 6th International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS 2018), pages 313-322

ISBN: 978-989-758-286-8

313

sequently, we reported volume holographic record-

ing in NPCs using other SiO

and ZrO

nanopar-

ticles dispersed in (meth)acrylate monomer capable

of the chain-growth polymerization. It was shown

that the saturated refractive index modulation am-

plitude (∆n

sat

) as large as 1 × 10

−2

was possible

in the blue and the green with reduced polymeriza-

tion shrinkage and high thermal stability (Suzuki and

Tomita, 2004; Suzuki et al., 2006; Tomita et al.,

2008; Omura and Tomita, 2010). In order to use inor-

ganic nanoparticle dispersed NPCs for optical record-

ing media in holographic data storage (HDS) (Co-

ufal et al., 2000; Curtis et al., 2010), we proposed

NPCs with thiol-ene/thiol-yne monomers capable of

the step-growth polymerization (Hata et al., 2011;

Mitsube et al., 2014; Kawana et al., 2015). It

was shown that a plane-wave holographic grating

recorded in such thiol-ene/thiol-yne based NPCs sat-

isﬁed all the requirements for HDS media, that is,

∆n

sat

≥ 5 × 10

−3

, the material recording sensitivity

higher than 500 cm/J and polymerization shrinkage

lower than 0.5 %. We then successfully demonstrated

shift-multiplexed holographic digital data page stor-

age in thiol-ene/thiol-yne based NPCs by using a two-

beam interference setup (Momose et al., 2012; Mit-

sube et al., 2014; Takayama et al., 2014).

High dispersion (>20vol.%) of inorganic

nanoparticles in host monomer always requires

careful surface treatment for their uniform dispersion

without any aggregation. In order to relax this severe

requirement, we proposed NPCs dispersed with

hyperbranched polymers (HBPs) (Gao and Yan,

2004), nanostructured polymer possessing highly

branched main chains, as organic nanoparticles.

Indeed, HBPs are preferable because of the ease

of their preparation and the controllability of the

size and refractive index. Until now we have re-

ported NPCs dispersed with various types of HBPs.

These include low refractive index hyperbranched

poly(ethyl methacrylate) (HPEMA) and high re-

fractive index hyperbranched polystyrene (HPS)

having their refractive indices of 1.51and 1.61 at a

wavelength of 589 nm, respectively (Tomita et al.,

2006b). They could be dispersed in multifunctional

(meth)acrylate monomer without any aggregation at

their concentrations up to 40 vol.%. They gave ∆n

sat

as large as 8 × 10

−3

and 7× 10

−3

, respectively, at a

recording intensity of 100 mW/cm

and at recording

and readout wavelengths of 532 nm. Recently, we

also introduced newly developed HBP having the

ultrahigh refractive index of 1.82 to increase ∆n

sat

further (Tomita et al., 2016b). An NPC grating

incorporated with such an HBP gave ∆n

sat

as large

as 2.2 × 10

−2

at 532 nm with good optical quality,

suggesting its application to a holographic diffractive

element for wearable eyeglasses to be used for

augmented and mixed reality by which the real-time

and ubiquitous access of virtual 2D/3D images is

possible in free space.

One can also utilize the composite nature of NPCs

for developing artiﬁcial nonlinear optical materials

when either guest or both guest and host have dis-

tinct optical nonlinearities. So far, optical nonlineari-

ties of metal-dielectric nanocomposites were reported

by many workers (Hache et al., 1988), where the sur-

face plasmon resonance (SPR) (Klar et al., 1998) tak-

ing place at the interface between metallic nanoparti-

cles and a dielectric host was used to induce the op-

tical nonlinearity due to the coherent oscillation of

free electrons occupying states near the Fermi level

in the conduction band. This SPR resulted in the

local-ﬁeld enhancement (Dolgaleva and Boyd, 2012),

leading to the enhancement of the optical nonlinear-

ities of metal-dielectric nanocomposites. We stud-

ied the nonlinear optical properties of holographically

recordable NPCs dispersed with HBP-metallic (Au or

Pt) nanoparticle complex (Liu et al., 2010). It was

shown that they exhibited the dielectric conﬁnement

effect near SPR and that the magnitude of their effec-

tive third-order nonlinear optical susceptibility was of

the order of 10

−10

esu at a wavelength of 532 nm. We

also investigated the optical nonlinearity in a semi-

conductorCdSe quantumdot dispersed NPC ﬁlm (Liu

et al., 2012). Because of the composite structure cas-

caded high order optical nonlinearitieswere observed.

Associated nonlinear Bragg diffraction from the1D

photonic lattice structure recorded in the NPC ﬁlm

were also observed.

Volume gratings recorded in NPCs can ﬁnd com-

pletely different applications from those in optics and

photonics. Namely, matter waves can be manipulated

by diffraction from gratings, where such an incoming

beam interacts with periodically assembled nuclei via

the strong (nuclear) force. Neutrons have been ex-

tensively used for scientiﬁc and engineering studies.

In particular, neutron optics and spectroscopy have

been deployed for nuclear physics, quantum physics,

condensed matter physics, biology, life and medical

sciences, materials science and engineering (Sears,

1989; Rauch and Werner, 2015; Klepp et al., 2014;

Willis and Carlile, 2013). For some of these purposes

efﬁcient neutron optical elements such as mirrors and

beam splitters are essential, for example, to construct

a neutron interferometer. A perfect silicon crystal is

employed to diffract a thermal neutron beam at neu-

tron wavelengths λ

neu

shorter than 0.4 nm. Because

the phase in neutron interferometer is proportional to

neu

(Rauch and Werner, 2015), as opposed to the in-

AOMatSens 2018 - Special Session in Advanced Optical Materials, Sensors and Devices

314

verse wavelength law in optics, slow neutrons (cold

and very cold neutrons) at longer wavelengths(0.4 nm

< λ

neu

< 10 nm) are advantageous. However, slow-

neutron optics requires other neutron optical elements

as Bragg’s law cannot be satisﬁed for slow neutron

beams with perfect silicon crystals. For this reason

Rupp et al. demonstrated the diffraction of a cold

neutron beam (λ

neu

= 1.5 nm) by a holographic vol-

ume grating optically recorded in PMMA-based pho-

topolymer with deuterium substitution (Rupp et al.,

1990). Despite their successful proof-of-principle

demonstration the diffraction efﬁciency was severely

limited by the Pendell¨osung oscillation (Klepp et al.,

2012a) that averaged out the diffraction efﬁciency due

to the very thick ﬁlm (∼2 mm) and the limited colli-

mation of an incident slow neutron beam. By taking

advantage of the composite nature of NPCs, we de-

veloped neutron optical elements by use of a volume

grating optically recorded in a 100-µm thick NPC ﬁlm

dispersed with SiO

nanoparticles that have substan-

tive interaction strength with slow neutrons. We suc-

cessfully demonstrated manipulation of slow neutron

beams such as beam splitting, triple beam division

and mirror operations (Fally et al., 2010; Klepp et al.,

2011; Klepp et al., 2012b; Klepp et al., 2012c).

In this paper we ﬁrst describe the grating forma-

tion mechanism in NPCs and discuss material’s de-

sign parameters governing ∆n

sat

. Then we describe

applications of NPCs dispersed with new organic and

inorganic nanoparticles to holographic data storage

and holographic diffractive elements for light and

neutron beams.

2 GRATING FORMATION

MECHANISM

Here we describe the grating formation in an NPC

ﬁlm where nanoparticles are uniformly dispersed in

host monomer capable of radical photopolymeriza-

tion, as shown in Fig.1(a). Photoinitiator species lo-

cally generate free radicals by their dissociation un-

der two-beam interfering exposure and the subsequent

reaction of free radicals with monomer leads to the

polymerization reaction between monomer radicals

and unreacted monomer in the bright regions. This

polymerization process lowers the chemical potential

of unreacted monomer in the bright regions, leading

to the diffusion of unreacted monomer from the dark

to the bright illuminated regions. Because nanopar-

ticles are photo-insensitive and their chemical poten-

tial increases as a result of the monomer consump-

tion in the bright illuminated regions, nanoparticles

counter-diffusefrom the bright to the dark illuminated

regions. In this way the mutual diffusion and the

phase separation of monomer and nanoparticles lead

to the spatial density modulation of nanoparticles dur-

ing holographic exposure [see Fig.1(b)]. Such holo-

graphic assembly of nanoparticles in the formed poly-

mer host (Tomita et al., 2005) results in the formation

of a refractive index grating due to the density and

compositional differences between the bright and the

dark illuminated regions. This model was conﬁrmed

experimentally as shown in Figs. 1(c) and 1(d) that

show electron-probe micro-analyzer (EPMA) images

of density distributions of Si and S atoms, respec-

tively (Tomita et al., 2006a), where Si and S atoms

correspond to constituents of nanoparticles and the

formed polymer.

monomer

nanoparticle

recording

beams

(a)

(b)

(c)

(d)

Figure 1: Holographic assembly of nanoparticles in an

NPC material (a) before and (b) after holographic expo-

sure. EPMA images of (c) Si (nanoparticles) and (d) S (the

formed polymer) atomic density distributions after holo-

graphic exposure.

It can be shown that ∆n

sat

for the 1st-order peri-

odic spatial modulation of the refractive index in an

NPC as a multi-component photopolymer system is

approximately given by (Tomita et al., 2016a)

∆n

sat

= a∆f (n

− n

), (1)

where a is a form factor depending on a waveform

of the density modulation of nanoparticles and ∆ f

is a difference in the volume fraction of dispersed

nanoparticles between the peak and the average vol-

ume fraction f of the nanoparticles. Also, n

) is

the refractive index of the nanoparticle (the formed

host polymer), respectively. The value for a is unity

for a sinusoidal waveform and is 2sin(rπ)/π for a

rectangular waveform with the duty ratio r. It can be

seen that ∆f and |n

− n

| are major material’s de-

sign parameters that determine ∆n

sat

. It is easy to ﬁnd

that ∆f takes values between 0 and f at 0 ≤ f ≤ 0.5

and between 0 and 1 − f at 0.5 ≤ f ≤ 1. Thus, ∆ f

is maximized to be 0.5 at f = 0.5 and the density

modulation index of nanoparticles deﬁned as ∆f/ f is

unity. In practice, however, an increase in f larger

than, say, 0.4 causes substantive holographic light

scattering (Suzuki and Tomita, 2007) during record-

ing when |n

− n

| is very large for a very thick NPC

Photopolymerizable Nanoparticle-polymer Composite Materials for Light and Neutron Beam Manipulations

315

ﬁlm dispersed with nanoparticles having ∼10 nm in

size. This situation would reduce ∆n

sat

. For this rea-

son ∆ f = f ∼ 0.4 would be a practical maximum

limit.

3 HOLOGRAPHIC DATA

STORAGE

As described in the introduction part, we developed

thoil-ene/thiol-yen based NPCs for HDS media and

employed them in shift-multiplexed holographic dig-

ital data page storage by using a two-beam interfer-

ence method (Momose et al., 2012; Mitsube et al.,

2014; Takayama et al., 2014). Here we describe their

use in coaxial holographic recording setup (Horimai

et al., 2005). Figure 2 illustrates our optical setup for

a holographic digital data page recording using the

coaxial holographic recording setup. The linearly po-

larized laser beam at a recording and readout wave-

length of 532 nm was expanded and collimated to

encode a circular and concentric input page pattern

for digital signal and reference data with the 9:16

symbol modulation coding format (Takayama et al.,

2014) [see Fig. 3(a)] via a transmission-type liquid

crystal spatial light modulator (HOLOEYE Photonics

LC2002) with 1024 768 pixels and a pixel pitch of

36 µm. The size of one data page [the circular por-

tion in Fig. 3(a)] had 12969 bits that corresponded to

14441 symbol data of information. No error correc-

tion coding (ECC) was made. The transmitted data-

bearing beam was loosely focused on an NPC ﬁlm

sample of 100-µm thickness via two relay lenses and

an objective lens. For thiol-ene based NPC ﬁlm sam-

ples we employed the stoichiometric thiol-ene for-

mulation of commercial secondary dithiol monomer,

1,4-bis(3-mercaptobutyryloxy)butane (Showa Denko

K.K.), and triene monomer, 1, 3, 5–triallyl–

triazine-2,4,6(1H,3H,5H)-trione (Sigma-Aldrich), to-

Figure 2: Setup for coaxial holographic digital data page

recording.

gether with the dispersion of 25 vol.% SiO

nanoparticles (the average size of 13 nm) and a

photoinitiator/green-sensitizer system consisting of

Irgacure 784 (Ciba) and BzO

(Sigma-Aldrich) at

1 and 1.25 wt.%, respectively, with respect to the

thiol-ene monomer blend. For thiol-yne based

NPC ﬁlm samples we employed the stoichiomet-

ric thiol-yne monomer blend consisting of com-

mercial trithiol monomer, trimethylolpropane tris(3-

mercaptopropionate) (Sigma-Aldrich), and diyne

monomer, 1, 7-octadiyne (Sigma-Aldrich). It was

mixed with a co-monomer at 15 wt.% with respect to

the thol-yne monomer blend, N-vinyl-2-pyrrolidone

(Sigma-Aldrich), acting as a plasticizer for the uni-

form dispersion of 25 vol.% SiO

nanoparticles. A

photoinitiator/green-sensitizer system consisting of

Irgacure 784 and BzO

at 1 and 1.25 wt.%, respec-

tively, with respect to the thiol-yne monomer blend

were also mixed. The reconstructed straight-through

image through a uniformly cured thiol-ene NPC ﬁlm

sample by an incoherent LED is shown in Fig. 3(b).

the symbol error rate (SER) and the signal-to-noise

ratio (SNR) are found to be 7.7×10

−5

and 14, respec-

tively. The reconstructed image from a recorded thiol-

ene based NPC ﬁlm sample is shown in Fig. 3(c) by

which SER and SNR are found to be 7.7×10

−5

and

12, respectively. Figure 3(d) shows the reconstructed

(a) (b)

Figure 3: (a) Digital data page pattern with the 9:16 sym-

bol modulation code. (b) Magniﬁed image of the straight-

through image via a uniformly cured thiol-ene based NPC

ﬁlm. (c) Magniﬁed image of the reconstructed digital data

page pattern from a recorded thiol-ene based NPC ﬁlm. (d)

Magniﬁed image of the reconstructed digital data page pat-

tern from a recorded thiol-yne based NPC ﬁlm.

AOMatSens 2018 - Special Session in Advanced Optical Materials, Sensors and Devices

316

image from a recorded thiol-yne NPC ﬁlm sample,

giving SER and SNR of 7.7×10

−5

and 11, respec-

tively. It is known that error-free retrieval of data

pages with an SER of lower than 1×10

−1

is possible

with ECC (Tanaka et al., 2007). Therefore, the mea-

sured performance suggests that error-free retrieval of

digital data pages is possible with our thiol-ene/thiol-

yne based NPCs.

4 HOLOGRAPHIC DIFFRACTIVE

ELEMENTS

4.1 Light Beams

Holographic diffractive elements usually require high

diffraction efﬁciencies near 100%. This is possible

when a volume phase grating is thick enough to meet

the conditions that the product of the coupling con-

stant κ(≡ π∆n

sat

/λcosθ

) and the grating thickness

L be near (2m− 1)π/2(m = 1, 2,···) for a transmis-

sion grating and be larger than, say, 2 for a reﬂec-

tion grating in light optics (Yeh, 1993). Here λ is a

readout wavelength in vacuum and θ

is the Bragg

angle in the volume grating. The latter is measured

from the optical axis for an incident readout beam.

There is often another requirement for wide angular

and/or wavelength selectivities (i.e., the angular aper-

ture and/or spectral bandwidth of the Bragg diffrac-

tion) for speciﬁc applications. In this case the selec-

tivity of a volume grating is inversely proportional to

L. For narrowband optical ﬁlters, holographic sen-

sors, and holographic data storage a thick volume

grating of the order of 100 µm is preferable. On

the other hand, a thin volume grating near 10 µm is

desired for applications such as wearable eyeglasses

used for augmented and mixed reality, which requires

high diffraction efﬁciencies at wide acceptable angles

(i.e., with a wide Bragg aperture). In such a case

the diffraction efﬁciency near 100% requires ∆n

sat

be larger than ∼ 2.5 × 10

−2

for transmission and re-

ﬂection volume gratings of 10 µm thickness at a vis-

ible wavelength. NPCs would be suitable for such

an application because of the ease of their coating on

curved eyeglass surfaces and the potentiality of in-

creasing ∆n

sat

by a suitable choice of nanoparticles

according to the material’s design strategy based on

Eq. (1).

Here we show our recent result of transmis-

sion NPC volume gratings dispersed with HBP or-

ganic nanoparticles with the ultrahigh refractive in-

dex. We synthesized HBP containing triazine and

aromatic ring units [see Fig. 4(a)] and the average

size was approximately 12 nm estimated by a small

angle X-ray scattering method. The refractive in-

dex was found to be 1.82 at a wavelength of 532

nm, which was much higher than those of HPEMA

and HPS used for NPCs in our past work (Tomita

et al., 2006b). Such an ultrahigh value can be at-

tributed to the incorporation of triazine and aromatic

ring units to the HBP structure. We mixed this HBP

with single functional monomers, tetrahydrofurfuryl

acrylate (THF-A, TCI) and N-vinyl-2-pyrrolidone

(NVP, Sigma-Aldrich), used as plasticizers. In this

work we employed multifunctional acrylate monomer

=1.48), di-pentaerythritol polyacrylate (A-DPH-

12E, Shin-Nakamura Chem. Co. Ltd) [see Fig.

4(b)], to the mixture to form the high cross-linked

structure after curing and increase the recording sen-

sitivity as compared to that of more viscous mul-

tifunctional monomer, dipentaerythritol penta-/hexa-

acrylate (DPHA, TOAGOSEI Co., Ltd.), used in our

previous work (Tomita et al., 2016b). The resultant

concentration ratio of THF-A: NVP: A-DPH-12E in

vol.% was 63:5:5 when the HBP concentration was

ﬁxed to be 27 vol.%, the maximum doping concen-

tration of HBP. A green photosensitizer Irgacure 784

(Ciba) was also added to the monomer blend of THF-

A, NVP, and A-DPH-12E. at 1.5 wt.% with respect

to A-DPH. The mixed syrup was cast on a glass plate

loaded with a 10-µm thick spacer and was ﬁnally cov-

ered with another glass plate for holographic record-

ing.

(a) (b)

Figure 4: Chemical structures of (a) HBP and (b) A-DPH-

12E.

We used a two-beam interference setup to write an

unslanted and plane-wave transmission volume grat-

ing at 1-µm grating spacing by two mutually coher-

ent beams of equal intensities at a wavelength of

532 nm. A low-intensity He-Ne laser beam operat-

ing at a photoinitiator-insensitive wavelength of 633

nm was employed as a readout beam to monitor the

buildup dynamics of the grating. All the beams were

s-polarized. Figure 5 shows photographs of a vol-

ume grating recorded in an NPC sample. Good uni-

formity and high transparency of the volume grating

are seen. Figure 6(a) shows the recording dynam-

ics of the diffraction efﬁciency, deﬁned as the ratio

Photopolymerizable Nanoparticle-polymer Composite Materials for Light and Neutron Beam Manipulations

317

(a) (b)

Figure 5: (a) Photograph of an NPC volume grating under

white light illumination from a ﬂuorescent lamp. (b) Photo-

graph of the same grating viewed from the top.

of the 1st-order diffracted signal power to the sum

of the transmitted and the 1st-order diffracted beam

powers, at a readout wavelength of 633 nm and at

a recording intensity of 75 mW/cm

. The inset is

a Bragg-angle detuning dependence of the saturated

diffraction efﬁciency probed at 633 nm. The solid

curve denotes the least-squares curve ﬁt of the data

to Kogelnik’s formula (Kogelnik, 1969). A good ﬁt

of the data to the formula with the correlation coefﬁ-

cient higher than 0.99 indicates the uniformity of the

recorded NPC volume grating along the thickness di-

(a)

(b)

Figure 6: (a) Recording dynamics of the diffraction efﬁ-

ciency probed by a 633-nm laser beam at a recording inten-

sity of 75 mW/cm

. The curve in green is the extrapolated

recording dynamics of the diffraction efﬁciency at 532 nm

as described in the text. The inset is a Bragg-angle detun-

ing dependence of the diffraction efﬁciency probed at 633

nm. (b) Buildup dynamics of ∆n at wavelengths of 532 nm

(green) and 633 nm (red).

rection. It was determined that the effective thick-

ness ℓ

eff

of the recorded NPC volume grating was

10.8 µm. The extrapolated recording dynamics of the

diffraction efﬁciency at 532 nm (the curve in green)

was also plotted in Fig. 6(a) by measuring the sat-

urated diffraction efﬁciency at 532 nm together with

∆n

sat

at 532 nm and ℓ

eff

as described below. It can be

seen that the diffraction efﬁciency at 532 nm ﬁnally

saturates below 100% due to the overmodulation ef-

fect. Figure 6(b) shows the corresponding buildup dy-

namics of the refractive index modulation amplitude

∆n that was extracted from measured diffraction ef-

ﬁciency data by ℓ

eff

and Kogelnik’s formula. In this

extraction procedure estimated values for ∆n at 633

nm were converted to those at 532 nm by multiplying

the former by a factor being the ratio of ∆n

sat

mea-

sured at 532 nm to that measured at 633 nm. We

found that ∆n

sat

at 532 nm was 2.7×10

−2

, larger than

2.2×10

−2

obtained by our previous NPC composition

with DPHA (Tomita et al., 2016b). Furthermore, the

recording intensity (75 mW/cm

) was lower than a

half of that with the previous one (200 mW/cm

) due

to the use of A-DPH having higher photochemical re-

activity and lower viscosity than those of DPHA. Us-

ing Eq. (1), we could estimate ∆f to be 0.09 at a=1

(the sinusoidal modulation) and 0.14 at a = π/2 (the

rectangular modulation at r = 0.5). Therefore, further

increase in ∆n

sat

would be possible.

4.2 Neutron Beams

Until now we have successfully demonstrated various

manipulation schemes for slow-neutron beams (e.g.,

beam splitting, triple beam division and total beam

deﬂection) via transmission volume gratings recorded

in NPCs dispersed with SiO

and ZrO

nanoparti-

cles (Fally et al., 2010; Klepp et al., 2012b; Klepp

et al., 2012c). As shown in Fig. 7, however, it was

necessary to effectively increase the interaction length

of an NPC transmission grating by tilting it at a large

angle ζ (∼ 70

◦

) so that the diffraction efﬁciency can

approach near 100% due to the Pendell¨osung inter-

ference effect [see, for example, (Sears, 1989) and for

the particular method see (Somenkov et al., 1978)].

Note that the tilt at ∼ 70

◦

corresponds to an effective

increase in L by a factor of 1/cos70

◦

∼ 2.9. Such a

large increase in thickness by the grating tilt is detri-

mental in device applications owing to a substantive

increase in incoherent scattering and absorption loss

for a slow-neutron beam propagating in supporting

glass substrates and an NPC material.

In order to avoid such a grating tilt, we need to

increase ∆n

sat

for neutrons. In neutron optics n

and

in Eq. (1) must be given at slow-neutron wave-

AOMatSens 2018 - Special Session in Advanced Optical Materials, Sensors and Devices

318

(a)

(b)

Figure 7: (a) Recording dynamics of the diffraction efﬁ-

ciency probed by a 633-nm laser beam at a recording in-

tensity of 75 mW/cm

. (a) Schematic of the slow-neutron

beam diffraction via an NPC transmission grating. (b) Peak

(Bragg-matched) diffraction efﬁciencies η

as a function of

NPC grating’s tilt angle ζ for an incident very cold neutron

beam at a neutron wavelength of 3.76 nm, while the solid

curve is a theoretical plot (Klepp et al., 2011).

lengths. The neutron refractive index n

neu

of a non-

magnetic material is approximately given by (Klepp

et al., 2012a)

neu

= 1−

neu

2π

, (2)

where b

is the average mean coherent scattering

length for a particular isotope and ρ is the atomic

number density of the material. Therefore, the fac-

tor n

− n

in Eq. (1) is determined by a differ-

ence in b

ρ between dispersed nanoparticles and host

monomer. For the core SiO

material of nanoparticles

used in our measurement [see Fig. 7(b)] b

ρ is given

by 3.64 × 10

−6

. It is well known that diamond

possesses very high coherent and very low incoherent

scattering cross sections with low absorption for neu-

trons as compared with other materials. Diamond has

ρ of 1.17× 10

−5

, which is approximately three

times larger than that of SiO

. It implies that ∆n

sat

NPC gratings dispersed with nanodiamonds is three

times larger than that of NPC gratings dispersed with

SiO

nanoparticles. It follows immediately that no

grating tilt is necessary to obtain high diffraction efﬁ-

ciency.

Recently, we have investigated the possibility of

using nanodiamond for NPC volume gratings. Here

we describe our proof-of-principle result below. Nan-

odiamonds were prepared by the explosion method

and then were made some surface treatment on the

core of a nanodiamond (4 nm in diameter) for good

dispersion in host monomer. We could successfully

disperse nanodiamonds at the concentration of 19

vol.% in an acrylate monomer blend. A green pho-

tosensitizer Irgacure 784 (Ciba) was also added at the

concentration of 4.3 wt.%. Figure 8(a) illustrates a

photograph of an NPC transmission plane-wave grat-

ing at grating spacing of 1 µm recorded by two 532-

nm lasers at the total intensity of 100 mW/cm

. The

deﬁnite diffraction from an area (∼ 1 cm in diame-

ter) can be seen. Figure 8(b) shows a transmission-

electron microscope image of the cross section of the

grating. The dark (bright) banded areas correspond

to high concentration portions of nanodiamonds (the

formed polymer), showing holographic assembly of

nanodiamonds in the formed polymer.

(a) (b)

Figure 8: (a) A photograph of an NPC transmission plane-

wave grating at grating spacing of 1 µm under white light

illumination from a ﬂuorescent lamp. (b) A transmission-

electron microscope image of the cross section of the grat-

ing.

Figure 9(a) shows the Bragg-angle detuning curve

probed at 633 nm for the saturated NPC grating.

The solid curve denotes the least-squares curve ﬁt

of the data to Kogelnik’s formula, giving ℓ

eff

to be

33 µm. Figure 9(b) shows the buildup dynamics of

∆n at 532 nm, which was extracted as similar to

the way described above. We found that ∆n

sat

was

2.7×10

−3

. We estimated the density modulation of

nanodiamonds by using the measured value for ∆n

sat

and the refractive indices of nanodiamonds and the

formed monomer blends. We found ∆f to be 0.006

at a = 1 and 0.010 at a = π/2 and r = 0.5, approx-

imately one order smaller than that of the HBP dis-

persed NPC grating shown in Fig. 6. This result

suggests that the mutual diffusion of nanodiamonds

and monomer needs to be facilitated much more for

an increase of ∆ f. Our investigation is underway to

increase ∆f in nanodiamond-dispersed NPC gratings

and apply them to neutron diffraction experiments. It

would also be expected that nanodiamonds dispersed

NPC gratings are useful for holographic applications

Photopolymerizable Nanoparticle-polymer Composite Materials for Light and Neutron Beam Manipulations

319

(a)

(b)

Figure 9: (a) Bragg-angle detuning dependence of the

diffraction efﬁciency at 633 nm. (b) Buildup dynamics of

∆n at wavelengths of 532 nm.

in light optics because of very high refractive index

=2.417) of bulk diamond in the visible spectral re-

gion.

Finally, it should be noted that we have recently

succeeded volume holographic recording in NPCs

dispersed with superparamagnetic Fe

nanoparti-

cles. Such magnetic nanoparticle dispersed NPC grat-

ings have potential applications such as slow-neutron

beam’s spin control (Klepp et al., 2012a; Tomita et al.,

2016a; Li˘cen et al., 2017) as well as magneto-optic

devices in light optics (Tomita et al., 2005).

5 CONCLUSIONS

We have described the mechanism of the holographic

grating formation in NPCs and our recent results for

holographic applications to holographic data storage

and to holographic diffractive elements in light and

neutron optics. It has been shown that thiol-ene/thiol-

yne based NPCs provide excellent performance with

satisfactorily low SERs and high SNRs in a coaxial

holographic digital data page recording system. It has

also been shown that transmission gratings recorded

in NPCs dispersed ultrahigh refractive index HBP

give ∆n

sat

close to 3× 10

−2

at moderate grating spac-

ing, promising for holographic diffractive elements in

light optics. In addition, we have successfully demon-

strated volume holographic recording in NPCs dis-

persed with nanodiamonds that possess very high co-

herent and very low incoherent scattering cross sec-

tions with low absorption for neutrons. It can be ex-

pected that nanodiamondsdispersed NPC grating pro-

vide a new possibility of slow-neutron beam control.

ACKNOWLEDGEMENTS

The authors would like to thank a number of col-

laborators, including E. Hata, K. Mitsube, K. Mo-

mose, S. Takayama, K. Chikama, P. Geltenbort (ILL,

Grenoble, France), and J. Kohlbrecher (PSI, Villigen,

Switzerland) for their contribution to this work. This

work was supported by the Ministry of Education,

Culture, Sports, Science and Technology of Japan un-

der the grant numbers 15H03576 and 17K19072.

REFERENCES

Coufal, H. J., Psaltis, D., and Sincerbox, G. T., editors

(2000). Holographic Data Storage. Springer, Berlin.

Curtis, K., Dhar, L., Hill, A. J., Wilson, W. L., and Ayres,

M. R., editors (2010). Holographic Data Storage

From Theory to Practical Systems. Wiley, West Sus-

sex.

Dolgaleva, K. and Boyd, R. W. (2012). Local-ﬁeld effects

in nanostructured photonic materials. Advances in Op-

tics and Photonics, 4:1–77.

Fally, M., Klepp, J., Tomita, Y., Nakamura, T., Pruner,

C., Ellabban, M. A., Rupp, R. A., Bichler, M.,

Drevenˇsek-Olenik, I., Kohlbrecher, J., Eckerlebe, H.,

Lemmel, H., and Rauch, H. (2010). Neutron op-

tical beam splitter from holographically structured

nanoparticle-polymer composites. Physical Review

Letters, 105:123904–1–123904–4.

Gao, C. and Yan, D. (2004). Hyperbranched polymers:

from synthesis to applications. Progress in Polymer

Science, 29:183–275.

Hache, F., Ricard, D., Flytzanis, C., and Kreibig, U. (1988).

The optical kerr effect in small metal particles and

metal colloids: The case of gold. Applied Physics A,

47:347–357.

Hata, E., Mitsube, K., Momose, K., and Tomita, Y. (2011).

Holographic nanoparticle-polymer composites based

on step-growth thiol-ene photopolymerization. Opti-

cal Materials Express, 1:207–222.

Horimai, H., Tan, X., and Li, J. (2005). Collinear hologra-

phy. Applied Optics, 24:16196–16209.

Kawana, M., Takahashi, J., Yasui, S., and Tomita, Y. (2015).

Characterization of volume holographic recording in

photopolymerizable nanoparticle-(thiol-ene) polymer

composites at 404 nm. Journal of Applied Physics,

117:053105–1–053105–6.

AOMatSens 2018 - Special Session in Advanced Optical Materials, Sensors and Devices

320

Klar, T., Perner, M., Grosse, S., von Plessen, G., Spirkl, W.,

and Feldmann, J. (1998). Surface-plasmon resonances

in single metallic nanoparticles. Physical Review Let-

ters, 80:4249–4252.

Klepp, J., Pruner, C., Tomita, Y., Geltenbort, P., Drevenˇsek-

Olenik, I., Gyergyek, S., Kohlbrecher, J., and Fally,

M. (2012a). Holographic gratings for slow-neutron

optics. Materials, 2012:2788–2815.

Klepp, J., Pruner, C., Tomita, Y., Mitsube, K., Geltenbort,

P., and Fally, M. (2012b). Mirrors for slow neutrons

from holographic nanoparticle-polymer free-standing

ﬁlm-gratings. Applied Physics Letters, 100:214104–

1–214104–3.

Klepp, J., Pruner, C., Tomita, Y., Plonka-Spehr, C.,

Ivanov, S., Geltenbort, P., Kohlbrecher, J., Ellabban,

M. A., and Fally, M. (2011). Neutron diffraction by

holographic gratings recorded in SiO

nanoparticle-

polymer composites. Physical Review A, 84:013621–

1–013621–7.

Klepp, J., Sponar, S., and Hasegawa, Y. (2014). Fundamen-

tal phenomena of quantum mechanics explored with

neutron interferometers. Progress of Theoretical and

Experimental Physics, 2014:082A01–1–082A01–61.

Klepp, J., Tomita, Y., Pruner, C., Kohlbrecher, J., and Fally,

M. (2012c). Three-port beam splitter for cold neu-

trons using holographic nanoparticle-polymer com-

posite diffraction gratings. Applied Physics Letters,

101:154104–1–154104–3.

Kogelnik, H. (1969). Coupled wave theory for thick holo-

gram gratings. The Bell System Technical Journal,

48:2909–2947.

Liu, X., Adachi, Y., Tomita, Y., Oshima, J., Nakashima,

T., and Kawai, T. (2012). High-order nonlinear opti-

cal response of a polymer nanocomposite ﬁlm incor-

porating semiconducotor CdSe quantum dots. Optics

Express, 20:13457–13469.

Liu, X., Matsumura, K., Tomita, Y., Yasui, K., Kojima, K.,

and Chikama, K. (2010). Nonlinear optical responses

of nanoparticle-polymer composites incorporating or-

ganic (hyperbranched polymer)-metallic nanoparticle

complex. Journal of Applied Physics, 108:073102–1–

073102–9.

Li˘cen, M., D.-Olenik, I.,

Coga, L., Gyergyek, S., Kralj, S.,

Fally, M., C.Pruner, P.Geltenbort, Gasser, U., Nagy,

G., and Klepp, J. (2017). Neutron diffraction from su-

perparamagnetic colloidal crystals. Journal of Physics

and Chemistry of Solids, 110:234–240.

Lourtioz, J.-M., Benisty, H., Berger, V., G´erard, J.-M., and

Mystre, D. (2005). Photonic Crystals. Springer,

Berlin.

Mitsube, K., Nishimura, Y., Nagaya, K., Takayama, S.,

and Tomita, Y. (2014). Holographic nanoparticle-

polymer composites based on radical-mediated thiol-

yne photopolymerizations: Characterization and shift-

multiplexed holographic digital data page storage.

Optical Materials Express, 4:982–996.

Momose, K., Takayama, S., Hata, E., and Tomita, Y. (2012).

Shift-multiplexed holographic digital data page stor-

age in a nanoparticle-(thiol-ene) polymer composite

ﬁlm. Optics Letters, 37:2250–2252.

Omura, K. and Tomita, Y. (2010). Photopolymerization

kinetics and volume holographic recording in ZrO

nanoparticle-polymer composites at 404 nm. Journal

of Applied Physics, 107:023107–1–023107–6.

Rauch, H. and Werner, S. A. (2015). Neutron Interferome-

try. Oxford University Press, Oxford, 2nd edition.

Rupp, R. A., Hehmann, J., Matull, R., and Ibel, K. (1990).

Neutron diffraction from photoinduced gratings in a

PMMA matrix. Physical Review Letters, 64:301–302.

Sears, V. F. (1989). Neutron Optics. Oxford University

Press, Oxford.

Smith, D. R., Pendry, J. B., and Wiltshire, M. C. K. (2004).

Metamaterials and negative refractive index. Science,

305:788–792.

Somenkov, V. A., Shilstein, S. S., Belova, N. E., and

Utemisov, K. (1978). Observation of dynamical os-

cillations for neutron scattering by Ge crystals using

the inclination method. Solid State Communications,

25:593–595.

Suzuki, N. and Tomita, Y. (2004). Silica nanoparticles-

dispersed methacrylate photopolymer with net diffrac-

tion efﬁciency near 100%. Applied Optics, 43:2125–

2129.

Suzuki, N. and Tomita, Y. (2007). Holographic scattering

in SiO

nanoparticles-dispersed photopolymer ﬁlms.

Applied Optics, 46:6809–6814.

Suzuki, N., Tomita, Y., and Kojima, T. (2002). Holographic

recording in TiO

nanoparticle-dispersed methacry-

late photopolymer ﬁlms. Applied Physics Letters,

81:4142–4123.

Suzuki, N., Tomita, Y., Ohmori, K., Hidaka, M., and

Chikama, K. (2006). Highly transparent ZrO

nanoparticle-dispersed acrylate photopolymers for

volume holographic recording. Optics Express,

14:12712–12719.

Takayama, S., Nagaya, K., Momose, K., and Tomita,

Y. (2014). Effects of symbol modulation coding

on readout ﬁdelity of shift-multiplexed holographic

digital data page storage in a photopolymerizable

nanoparticle-(thiol-ene)polymer composite ﬁlm. Ap-

plied Optics, 53:B53–B59.

Tanaka, K., Hara, M., Tokuyama, K., Hirooka, K., Ish-

ioka, K., Fukumoto, A., and Watanabe, K. (2007).

Improved performance in coaxial holographic data

recording. Optics Express, 15:16196–16209.

Tomita, Y., Chikama, K., Nohara, Y., Suzuki, N., Fu-

rushima, K., and Endoh, Y. (2006a). Two-dimensional

imaging of atomic distribution morphology cre-

ated by holographically induced mass transfer of

monomer molecules and nanoparticles in a silica-

nanoparticle-dispersed photopolymer ﬁlm. Optics

Letters, 31:1402–1404.

Tomita, Y., Furushima, K., Ochi, K., Ishizu, K.,

Tanaka, A., Ozawa, M., Hidaka, M., and Chikama,

K. (2006b). Organic nanoparticle (hyperbranched

polymer)-dispersed photopolymers for volume holo-

graphic storage. Applied Physics Letters, 88:071103–

1– 071103–3.

Tomita, Y., Hata, E., Momose, K., Takayama, S., Liu,

X., Chikama, K., Klepp, J., Pruner, C., and Fally,

Photopolymerizable Nanoparticle-polymer Composite Materials for Light and Neutron Beam Manipulations

321

M. (2016a). Photopolymerizable nanocomposite pho-

tonic materials and their holographic applications in

light and neutron optics. Journal of Modern Optics,

63:S1–S31.

Tomita, Y., Nakamura, T., and Tago, A. (2008). Improved

thermal stability of volume holograms recorded in

nanoparticle-polymer composite ﬁlms. Optics Letters,

33:1750–1752.

Tomita, Y., Suzuki, N., and Chikama, K. (2005). Holo-

graphic manipulation of nanoparticle-distribution

morphology in nanoparticle-dispersed photopoly-

mers. Optics Letters, 30:839–841.

Tomita, Y., Urano, H., Fukamizu, T., Kametani, Y.,

Nishimura, N., and Odoi, K. (2016b). Nanoparticle-

polymer composite volume holographic gratings dis-

persed with ultrahigh-refractive-index hyperbranched

polymer as organic nanoparticles. Optics Letters,

41:1281–12884.

Willis, B. T. M. and Carlile, C. J. (2013). Experimental

Neutron Scattering. Oxford University Press, Oxford.

Yeh, P. (1993). Introduction to Photorefractive Nonlinear

Optics. Wiley, New York.

AOMatSens 2018 - Special Session in Advanced Optical Materials, Sensors and Devices

322