A method and apparatus for spectroscopic material analysis are provided. Two coherent beams of monochromatic radiation are directed through a sample of material. A tuning mechanism adjusts the frequency difference between the radiation beams to equal substantially the rotational frequency of a preselected constituent of the material. Molecular energy of a preselected constituent of the material is increased, thereby producing a detectable signal in the form of a pressure wave. The signal is received by a detecting mechanism which indicates the magnitude thereof.