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Measurement of Temperature
Coefficients of Refractive Indices

Refractive index of materials changes per the change of the temperature.
Temperature coefficients of refractive index show the changes of refractive indices of the material when the temperature of the material raises by 1 degree C.
Usually the coefficient is achieved by averaging the change of the refractive indices of 20 degree C temperature range. We have various measuring methods depending on the type of the materials :		  

Chart 6
Test materials Solid Liquid
Optical Glasses/Optical crystals Plastic
Wavelengths
or
spectrum lines		 1153nm,
C',
633nm,
D,e,F',g,i,
254nm		 t,795nm,
780nm,
C,C',
633nm,
d,e,
F,F',g		 Spectral lines
measurable
between
185nm~2325nm		 t,795nm,
780nm,
C,C',
633nm,
d,e,
F,F',g		 t,795nm,
780nm,
C,C',
633nm,
d,e,
F,F',g
Range of
temperature for
measurement		 -40°C~100°C -18°C~40°C 20°C,25°C -18°C~40°C -18°C~40°C
Measuring
method		 Ohara original
equipment
(Interferometri
cmethod)		 Refractometer
(V-Block
method)		 Spectrometer
(Minimum
deviation
method)		 Refractometer
(V- Block
method)		 Refractometer
(V- Block
method)
Size of
samples		 30×30×10
(mm)		 20×20×10
(mm)		 40×40×40
(mm)		 20×20×10
(mm)		 Approx. 10cc

Typically, the temperature coefficients of refractive index are measured by our original measuring equipment which measures the amount of the variation of refractive indices per the change of the temperature. The other way the coefficients are derived is by using refractive indices measured at 2 different temperatures using a refractometer or spectrometer.