Abstract: A new method for measuring refractive index, small angle, pressure or temperature is disclosed. The method of the present invention utilizes a heterodyne interferometry technique to measure the phase difference between s-(vertical) and p-(horizontal) polarizations, and then substitutes the difference into Fresnel's equations so as to obtain the physical values of the medium to be tested, such as refractive index, small angle, pressure or temperature.

Abstract: An incident ray is emitted into a vacuum probe manufactured by a transparent material inside a cavity and is totally reflected according to the invention. Based on Fresnel's equation, when an angle of incidence is fixed, the phase difference between a s-polarized light and p-polarized light is a function of two refractive indexes on the both sides of an interface. Therefore, when the refractive index of gas inside the cavity varies with pressure therein, the phase difference between the s-polarized light and p-polarized light can be measured by a total-internal-reflection heterodyne interfermetry. Next, the refractive index of the vacuum cavity can be estimated based on the variation of the phase difference. Then, the pressure inside the cavity is obtained from the measured refractive index of the vacuum cavity cooperating a known pressure contrast list, so that vacuum degree inside the cavity is known.