To further understand the effect of optical feedback, the
wavelength of the laser can be correlated to the angle of
the mirror inside the Littman-Metcalf configuration. As the
angle of this mirror is changed, the wavelength that is fed
back into the diode changes, and so the output wavelength
changes. With this mirror mounted to allow precision adjustment
of the angle (Thorlabs P/N KM100), the changing of
the laser wavelength can be observed in the spectrometer
while changing the angle of this reflecting mirror. The mirror
angle can be adjusted to be perpendicular to beams diffracting
at a smaller angle from the normal. If hm is negative,
smaller wavelengths would diffract at smaller angles from
the normal. This can be verified by observing the beam location
at the image plane moving in the direction of a lower
wavelength when the reflecting mirror is adjusted to smaller
angles hm. A detailed study of the change in wavelength with
change in mirror angle is discussed in Sec.