Comment on “A study of the longitudinal laser modes of a semiconductor laser using optical coherence tomography” [Am. J. Phys. 75, 569–571 (2006)]

Abstract

Although the longitudinal mode spacing and longitudinal mode widths of a typical laser diode can, in principle, be determined from an optical coherence tomography signal, the values presented by Poddar et al. [Am. J. Phys. 75, 569–571 (2006)] do not agree with the Fourier transform theory. Also, the mode spacing is inconsistent with the peak separation in the interference signal. Moreover, the laser cavity mirror reflectivity calculated from the laser spectrum is incorrect because it ignores the gain and the loss within the laser cavity. This Comment aims to help readers who may struggle to understand that paper or to reproduce its results.