Spectral density contrast in DPSS and ECD lasers for quantum and other narrow-linewidth applications

With increasing demand for narrow-linewidth lasers for applications such as atom cooling, metrology and sensing, the research community has centered its focus around locking and referencing the lasing wavelength with the highest stability achievable. The two main platforms emerging to accommodate for such specific needs are diode pumped solid-state (DPSS) and external cavity diode lasers (ECDL). Being in the early stages of their product life cycles, both platforms are seeking ways to provide users with reasonably high and stable output powers. Our paper looks into the details of the performance differences between the two platforms. Primarily it shows that whilst similar output powers can be achieved using both platforms within Sub-GHz bandwidths, due to additional spontaneous emission noise terms, encountered in ECDLs, there exists a difference in the spectral density contrast. In fact, these noise terms, being detectable by power meters for output power specifications, compromise on the spectral density contrast within the linewidth of interest, which can be critical for narrow- linewidth applications. We have compared some of the most recently reported ECDL spectra to a standard Nd:YAG DPSS laser to show that in case of both platforms specified for the same output power, a DPSS laser can provide at least 3-times more useful output power, within the specified narrow spectral linewidth, than an ECDL, which puts the feasibility of these platforms into a new perspective.