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Fig. 7.4 Dielectric constants
e 2 (a) and its electric field-
induced change De 2 (b). Solid
line is the experimental
results and the dotted line is
the fitting result using a
discrete-level model. Adapted
from [ 10 ]
most typical reference is a plate of SiO 2 . The details of the measurements
procedures of the Z -scan were reported in [ 13 , 14 ].
7.3 Third-Order Optical Nonlinearity in Ni-X Chain
Compounds
7.3.1 Electroreflectance Spectroscopy
Linear optical constants of Ni-X chain compounds were evaluated by the
measurements of polarized reflectivity ( R ) spectra. Figure 7.4a shows the spectrum
of the imaginary part of the dielectric constants,
e 2 , in [Ni(chxn) 2 Br]Br 2 , which was
obtained from the R spectrum by the KK transformation. A sharp peak is observed
at around 1.3 eV, which is assigned to the CT transition from Br to Ni mentioned
above [ 8 , 9 ].
Electroreflectance (ER) spectra of three Ni-X chain compounds, [Ni(chxn) 2 Br]
Br 2 (abbreviated as Ni-Br-Br, hereafter), [Ni(chxn) 2 Cl]Cl 2 (Ni-Cl-Cl), and [Ni
(chxn) 2 Cl](NO 3 ) 2 (Ni-Cl-NO 3 ), were reported first by Kishida et al. [ 3 ]. The
electric field change
De 2 of
e 2 obtained from the ER spectrum was shown in
Fig. 7.4b . Around the
e 2 are observed. The
positive and negative signals indicate the increase and the decrease of
e 2 peak, oscillation-type changes of
e 2 , respec-
w ð 3 Þ as mentioned in Sect. 7.3.1 ,
which is scaled by the right axis in Fig. 7.4b . The max
tively.
De 2 is converted to the imaginary part of
w ð 3 Þ ðo;
j
Im
0
;
0
; oÞj
10 5 esu in Ni-Br-Br. The
ER spectroscopy was performed in other Ni-X compounds. The max
w ð 3 Þ j
(hereafter, abbreviated as max
j
Im
) reaches 9
w ð 3 Þ j
values of Ni-X compounds are plotted in Fig. 7.5 [ 3 , 10 ], together with those of
j
Im
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