method and apparatus for performing spectroscopy , include the combining of first and second light beams to form a reference beam , focusing the first and second light beams and the reference beam onto a sample , receiving a reflected light beam from the sample at a monochromator , and viewing a predetermined wavelength band of the reflected light beam from the monochromator . portions of the first and second light beams , which may be visible and ir forms of electromagnetic energy , are heterodyned through a crystal . a monochromator receives a reflection of the reference beam from the sample , and fourier transformation is performed on the output of the monochromator . the first and second beams of electromagnetic energy can be split to form first and second component beams and the reference beam , all of which are propagated to the sample .