Experimental and theoretical investigations on the modulation capabilities of a sample of vertical cavity surface emitting laser diodes for atomic vapour applications

This paper discusses various frequency modulation and intensity modulation capabilities within a sample of direct laser current modulated identical vertical cavity surface emitting laser diodes. The presented analysis is based on measurements of the spectral amplitudes as a function of the applied modulation power at a constant modulation frequency of 3.517 GHz. Their evaluation by Bessel function fits produces the three modulation parameters: frequency modulation index, intensity modulation index (via the α parameter) and the side band asymmetry of the first order side bands. The variation of the laser diode’s modulation capability is discussed. It is found that the individual laser diodes show a significant variations in their modulation capabilities. Thus an experimental preselection of the laser diode is required to find laser diodes which are suitable as a light source for atomic vapour applications, with special emphasis on a coherent population trapping-based scalar magnetometers.