Evolution of blue laser diode spectral lines with applied current in the range 446-448 nm

High resolution spectral lines study is performed on the emissions of a blue laser diode as a function of applied current. The range of applied current used is between the threshold current of 20 mA and 100 mA with a 0.2 mA increment. With this range of current, the observed emission spectra are between 446 and 448 nm. Typically, 21 longitudinal modes are observed with a mode spacing of 0.05 nm. This mode spacing is found to be in good agreement with the predicted values calculated using the GaN index of refraction and the length of laser cavity. The peak location of each longitudinal mode is measured to shift uniformly with a rate of 0.0045 nm/mA. The intensity and wavelength of each longitudinal mode are observed to be stable over extended period of time. Selected longitudinal modes will be employed to detect traces of pollution gases.