A technique based upon the measurement of light absorption upon irradiating a sample using a tunable laser source. This technique is generally used for quantitative measurements of the sample concentration or studying the spectral characteristics of the sample. Specific applications of this technique include saturation spectroscopy, heterodyne spectroscopy, opto-acoustic spectroscopy, and trace gas measurements in combustion, atmospheric, and kinetic studies. See Also diode laser, dye laser.