  Observations of the phase curves and secondary eclipses of extrasolar planets
provide a window on the composition and thermal structure of the planetary
atmospheres. For example, the photometric observations of secondary eclipses
lead to the measurement of the planetary geometric albedo $A_g$, which is an
indicator of the presence of clouds in the atmosphere. In this work we aim to
measure the $A_g$ in the optical domain of WASP-43b, a moderately irradiated
giant planet with an equilibrium temperature of $\sim$1400~K. To this purpose,
we analyze the secondary eclipse light curves collected by CHEOPS, together
with TESS observations of the system and the publicly available photometry
obtained with HST WFC3/UVIS. We also analyze the archival infrared observations
of the eclipses and retrieve the thermal emission spectrum of the planet. By
extrapolating the thermal spectrum to the optical bands, we correct the optical
eclipses for thermal emission and derive the optical $A_g$. The fit of the
optical data leads to a marginal detection of the phase curve signal,
characterized by an amplitude of $160\pm60$~ppm and 80$^{+60}_{-50}$~ppm in the
CHEOPS and TESS passband respectively, with an eastward phase shift of
$\sim50^\circ$ (1.5$\sigma$ detection). The analysis of the infrared data
suggests a non-inverted thermal profile and solar-like metallicity. The
combination of optical and infrared analysis allows us to derive an upper limit
for the optical albedo of $A_g<0.087$ with a confidence of 99.9\%. Our analysis
of the atmosphere of WASP-43b places this planet in the sample of irradiated
hot Jupiters, with monotonic temperature-pressure profile and no indication of
condensation of reflective clouds on the planetary dayside.
