Refractive index measurment apparatus and refractive index measurment method

摘要

A refractive index measurement apparatus includes a light source, a measurement cell including a sample as an object of refractive index measurement and diffracting light incident from the light source, a detector that detects the amount of diffracted light in at least one diffraction order other than zero order of diffracted light exiting from the measurement cell, and a control unit that determines refractive index of the sample based on the measured value of the amount of diffracted light by the detector. The measurement cell includes two substrates disposed so as to be opposed to each other and a diffraction grating disposed between the two substrates, and the diffraction grating has a plurality of members whose width decreases stepwise as approaching from one of the substrates to the other of the substrates, the sample being filled in the space between the substrates not occupied by the diffraction grating.

主权项

1. A refractive index measurement apparatus comprising:
a light source; a measurement cell including a sample as an object of refractive index measurement, and diffracting light incident from the light source; a detector that detects the amount of diffracted light exiting from the measurement cell in at least one diffraction order including a diffraction order other than zero order; and a control unit that determines refractive index of the sample corresponding to measured value of the amount of diffracted light in the diffraction order other than zero order among the at least one diffraction order detected by the detector using an equation expressing the relationship between diffraction efficiency in the diffraction order other than zero order among the at least one diffraction order and refractive index of the sample; wherein the measurement cell includes: a first transparent substrate and a second transparent substrate disposed so as to be opposed to each other so that a space in which the sample is filled is included between the first substrate and the second substrate; and a diffraction grating that is formed from transparent material having known refractive index, is disposed between the first substrate and the second substrate, and lies adjacent to the space, and diffracts light from the light source in accordance with difference between refractive index of the sample and refractive index of the transparent material; wherein the diffraction grating is a binary grating having a plurality of members formed from the transparent material whose width in a first direction parallel to a first surface of the first substrate opposed to the second substrate decreases stepwise as approaching from the first substrate to the second substrate, the plurality of members being periodically arranged at a prescribed pitch along the first direction; wherein the control unit obtains a first calculated value of diffraction efficiency in the diffraction order other than zero order among the at least one diffraction order based on measured value of the amount of diffracted light in the diffraction order other than zero order among the at least one diffraction order, and identifies, from among plural refractive indices presupposed as refractive index of the sample, refractive index which corresponds to a minimum value of error statistics between the first calculated value of diffraction efficiency and a second calculated value of diffraction efficiency obtained by inputting the presupposed refractive index into the equation expressing the relationship as refractive index of the sample.