To examine the wavelength of the laser and the mode spacing, the mirror in the LM setup should be blocked so there is no optical feedback. Here, the relationship between the wavelength of light and the angle of diffraction inside the spectrometer can be analyzed. This method can be used to find the laser wavelength, the laser mode spacing, or the tuning range (after feedback is present) by measuring the relevant angles. The diffraction spectrometer makes use of optical interference, with the angular location of the maxima for a reflective grating given by