External cavity diode lasers (ECDL) are presently experiencing a surge in popularity, as laser light-sources for advanced
optical measurement systems. While these devices normally require external optical-output controls, we simplified the
setup, a bit, by adding a second external cavity. This technique boasts the added advantage of having a narrower
oscillation-linewidth than would be achievable, using a single optical feedback. Because drive-current and atmospheric
temperature directly impact the ECDL systems' oscillation frequency, during frequency stability checks, it was
necessary, in this instance, to construct a slightly smaller ECDL system, which we mounted on a Super-Invar board, to
minimize the influence of thermal expansion. Taking these and other aggressive and timely measures to prevent
atmospheric temperature-related changes allowed us to achieve an improvement in oscillation-frequency stability, i.e.,
to obtain the square root of Allan variance σ =2×10<sup>-10</sup>, at averaging time τ =10<sup>-1</sup>.
We introduced a vertical-cavity surface-emitting laser (VCSEL) to the setup, for the simple reason that its frequency is
far less susceptible to changes in temperature, than other lasers of its type. And, because VCSELs are widely available,
and the ECDL systems that use them improve frequency stability, we replaced the Fabry-Perot semiconductor laser with
External cavity diode laser (ECDL) systems are presently experiencing a surge in popularity as laser light-sources, in
advanced optical communications- and measurement-systems. Because such systems require that their external
reflectors be precisely controlled, to eliminate low frequency fluctuations (LFF) in optical output, we conducted
experiments with a two-cavity version, which easily eliminated LFFs, as expected. The technique has the added
advantage of a narrower oscillation-linewidth than would be achievable, using a single optical feedback. However, the
ECDL's oscillation frequency is susceptible to the influences of the drive-current, as well as changes, both in the
refractive index, and the overall length of the external reflector that results from fluctuations in atmospheric temperature.
We made every effort to maintain the length of the ECDL cavity, while evaluating oscillation-frequency stability. We
used a Super-Invar board as the platform for our compact ECDL system to minimize the influence of thermal expansion,
because of its low expansion coefficient. We then compared the effect of atmospheric temperature variations between
two experimental conditions, with the Super-invar board and without it, and finally took note of the improvement in
performance, using the board.