  We present two distinct ultra-low frequency noise lasers at 729 nm with a
fast frequency noise of 30 Hz^2/Hz, corresponding to a Lorentzian linewidth of
0.1 kHz. The characteristics of both lasers, which are based on different types
of laser diodes, are investigated using experimental and theoretical analysis
with a focus on identifying the advantages and disadvantages of each type of
system. Specifically, we study the differences and similarities in mode
behaviour while tuning frequency noise and linewidth reduction. Furthermore, we
demonstrate the locking capability of these systems on medium-finesse cavities.
The results provide insights into the unique operational characteristics of
these ultra-low noise lasers and their potential applications in quantum
technology that require high levels of control fidelity.
