Fundamental Noises in Diode Laser Spectroscopy

The influence of fundamental noises of a diode laser and a photodetector on the registration of absorption spectra by diode laser spectroscopy (DLS) has been studied. It is shown that the diode laser noise is maximal at pump currents close to the threshold value. At currents significantly exceeding the threshold values, the signal-to-noise ratio tends to a constant. When the recorded radiation flux increases, the relative noise of the photodiodes decreases and at sufficiently high values becomes negligible compared to the diode laser noise. Thus, it is experimentally shown that the minimum achievable limits of detection of various substances in diode laser spectroscopy are determined by the noise of the diode laser itself. The obtained results have an important application value; they can be used to design analytical equipment for measuring low concentrations of gaseous substances.