336
T. N. Smirnova et al.
of 35 cm. The diameter of the beam in the focus was 58 μm; aperture transmittance
was 0.36. The intensity of the laser beam in the focus was I 0 = 0.14 GW/cm 2 .
The real (Re) and imaginary (Im) parts of the complex third-order susceptibility
χ (3) , the nonlinear absorption coefficient β, and the nonlinear refractive index n 2
were calculated by the method proposed by Sheik-Bahae et al. [40].
The mentioned laser radiation parameters were chosen to avoid the influence
of thermal accumulative effect on experimental results. The measurements were
repeated several times to ensure the reproducibility of the results. In our experiments, there were no irreversible changes in the transmission. The repetition of
measurements for a pure matrix showed an absence of nonlinear response under the
same conditions.
21.3 Results and Discussion
21.3.1 Production and Characterization of the Samples
Previously, we proposed so-called in situ method for the formation of periodic
polymer–metal NP structures [41]. The initial composite for holographic patterning
is a homogeneous mixture containing monomers, photoinitiator of polymerization,
and metal precursor solution. During the first step – photopolymerization in the
interference pattern – a stable volume grating polymer–metal precursor is formed.
Reduction of the precursor and formation of metal NPs occur mainly during the
second stage of photo- or thermo-processing. The optimal proposed composition
includes two copolymerized monomers, which form a cross-linked polymer network
and solution of AgNO 3 in acetonitrile as an Ag NP precursor. Michler’s ketone
and camphorquinone were used as the components of the photoiniating system for
photo-induced radical polymerization of monomers. Camphorquinone provides the
sensitivity of the composition in the range of 440–500 nm. A standard two-beam
interference scheme based on the Ar–ion laser, operating at λ rec = 488 nm, was used
for the holographic recording.
The reactive samples for the holographic patterning were prepared by sandwiching a drop of the initially liquid composites between two glass slides separated by
spacers with a thickness of about 10 μm. Then a half the sample surface was exposed
to an interference pattern. UV flood exposure of the sample after holographic
illumination was carried out to provide curing of residual monomers and formation
of a random structure in the film area outside the grating (Fig. 21.2).
The mechanism of the grating formation was discussed in [41]. It was established
that during photopolymerization in the periodic light pattern, both main components, the monomer and the metal precursor solution, take part in the irreversible
photo-induced mass transfer, providing the stability of the resulting structure. The
T. N. Smirnova et al.
of 35 cm. The diameter of the beam in the focus was 58 μm; aperture transmittance
was 0.36. The intensity of the laser beam in the focus was I 0 = 0.14 GW/cm 2 .
The real (Re) and imaginary (Im) parts of the complex third-order susceptibility
χ (3) , the nonlinear absorption coefficient β, and the nonlinear refractive index n 2
were calculated by the method proposed by Sheik-Bahae et al. [40].
The mentioned laser radiation parameters were chosen to avoid the influence
of thermal accumulative effect on experimental results. The measurements were
repeated several times to ensure the reproducibility of the results. In our experiments, there were no irreversible changes in the transmission. The repetition of
measurements for a pure matrix showed an absence of nonlinear response under the
same conditions.
21.3 Results and Discussion
21.3.1 Production and Characterization of the Samples
Previously, we proposed so-called in situ method for the formation of periodic
polymer–metal NP structures [41]. The initial composite for holographic patterning
is a homogeneous mixture containing monomers, photoinitiator of polymerization,
and metal precursor solution. During the first step – photopolymerization in the
interference pattern – a stable volume grating polymer–metal precursor is formed.
Reduction of the precursor and formation of metal NPs occur mainly during the
second stage of photo- or thermo-processing. The optimal proposed composition
includes two copolymerized monomers, which form a cross-linked polymer network
and solution of AgNO 3 in acetonitrile as an Ag NP precursor. Michler’s ketone
and camphorquinone were used as the components of the photoiniating system for
photo-induced radical polymerization of monomers. Camphorquinone provides the
sensitivity of the composition in the range of 440–500 nm. A standard two-beam
interference scheme based on the Ar–ion laser, operating at λ rec = 488 nm, was used
for the holographic recording.
The reactive samples for the holographic patterning were prepared by sandwiching a drop of the initially liquid composites between two glass slides separated by
spacers with a thickness of about 10 μm. Then a half the sample surface was exposed
to an interference pattern. UV flood exposure of the sample after holographic
illumination was carried out to provide curing of residual monomers and formation
of a random structure in the film area outside the grating (Fig. 21.2).
The mechanism of the grating formation was discussed in [41]. It was established
that during photopolymerization in the periodic light pattern, both main components, the monomer and the metal precursor solution, take part in the irreversible
photo-induced mass transfer, providing the stability of the resulting structure. The