Apparatus for determining the thermal resistivity of electrically insulating crystalline materials

Apparatus for determining the thermal resistivity W s of an electrically insulating crystalline polycrystalline sample of host material, the host material containing a concentration of an impurity or of a combination of impurities, comprising

• (a) a first divider connected to receive both an input signal I.sub.0 representative of optical radiation directed on the sample and an input signal I representative of the optical radiation emerging from the sample, whereby the first divider can produce a first divider output that is representative of the ratio of I.sub.0 /I;
• (b) a logarithm converter connected to receive the first output and to multiply the first input by a factor .beta., whereby the logarithm converter can produce a logarithm converter output that is representative of the thickness t of the sample multiplied by the optical absorptivity .alpha..sub.s, of the sample;
• (c) a second divider connected to receive the logarithm converter output and to receive an input signal representative of the thickness t of the sample, whereby the second divider can produce a second output that is a representative of the optical absorptivity .alpha..sub.s of the sample;
• (d) a multiplier connected to receive both this second output and a constant output C from a first memory that stores the constant C, this value of C having been previously determined experimentally using at least a first body and a second body having the same host materials as that of the sample and the same impurity or combination of impurities as that of the sample for determining the value of the constant C, whereby the multiplier can produce a multiplier output that is a representative of C.alpha..sub.s ;
• and
• (e) an adder connected to receive the multiplier output and a constant output A from a second memory that stores the constant A, this value of A having been previously determined experimentally using said at least first and second bodies, the adder producing an adder output that is representative of A+C.alpha..sub.s, the adder output being representative of the thermal resistivity W.sub.s of the sample, where the experimentally determined constants A and C are determined by measuring the thermal resistivities W.sub.1, and W.sub.2 and the optical absorptivities .alpha..sub.1 and .alpha..sub.2 of said at least first and second bodies, respectively, using any well known or prior art apparatus and technique.