ABSTRACT
In the two-wavelength method, when the interference fringes on the detector does not exceed its resolution, using the light which has a wavelength difference as detection light to detect the sample, and synthesising the results from different wavelengths, and the higher precision and resolution of the test results can be got. It can eliminate the disadvantages of a long-wavelength infrared transmission element method by using the twowavelength method. However, due to the need to work at different wavelengths, producing colour will greatly affect the test results.
