  Objective: In the framework of the Cometary Physics Laboratory (CoPhyLab) and
its sublimation experiments of cometary surface analogues under simulated space
conditions, we characterize the properties of intimate mixtures of juniper
charcoal and SiO$_2$ chosen as a dust analogue \citep{Lethuillier_2022}. We
present the details of these investigations for the spectrophotometric
properties of the samples.
  Methods: We measured these properties using a hyperspectral imager and a
radio-goniometer. From the samples' spectra, we evaluated reflectance ratios
and spectral slopes. From the measured phase curves, we inverted a photometric
model for all samples. Complementary characterizations were obtained using a
pycnometer, a scanning electron microscope and an organic elemental analyser.
  Results: We report the first values for the apparent porosity, elemental
composition, and VIS-NIR spectrophotometric properties for juniper charcoal, as
well as for intimate mixtures of this charcoal with the SiO$_2$. We find that
the juniper charcoal drives the spectrophotometric properties of the intimate
mixtures and that its strong absorbance is consistent with its elemental
composition. We find that SiO$_2$ particles form large and compact agglomerates
in every mixture imaged with the electron microscope, and its
spectrophotometric properties are affected by such features and their
particle-size distribution. We compare our results to the current literature on
comets and other small Solar System bodies and find that most of the
characterized properties of the dust analogue are comparable to some extent
with the spacecraft-visited cometary nucleii, as well as to Centaurs, Trojans
and the bluest TNOs.
