Thermo-optic refractometry

A method of determining a refractive index of a material sample, comprising:

• removably mounting the material sample into a sample holder having a thermal control mechanism, a thermal expansion compensation mechanism, and a rotation mechanism;
• projecting a laser beam into the material sample, wherein the material sample has a predetermined orientation and temperature, wherein the material sample has parallel sides defining parallel planes for entry and exit of the laser beam into and out of the material sample;
• collecting a refracted laser beam from the material sample;
• and
• determining the refractive index for the material sample at the predetermined temperature, wherein the rotation mechanism comprises a rotation shaft,
• wherein the thermal expansion compensation mechanism comprises
• a support base supported on the rotation shaft for controllable rotation about a rotation axis;
• a pair of support brackets attached to the support base;
• a hollow center guide including a flange on each end for flexibly securing the center guide to the support brackets, wherein the flanges are flexibly attached to the support brackets with a plurality of threaded fasteners and springs;
• a left stabilizer having a flange on its outer end, the left stabilizer extending into the center guide and secured to the fasteners with complementary fasteners and springs;
• a right stabilizer having a flange on its outer end, the right stabilizer extending into the center guide and secured to the fasteners with complementary fasteners and springs in a manner identical to that of the left stabilizer, the left stabilizer and right stabilizer extending into a cavity in the center guide toward each other in a manner to trap and support the material sample.