  Volume-phase holographic gratings (VPHGs) are widely used in astronomical
spectrographs due to their adaptability and high diffraction efficiency. Most
VPHGs in operation use dichromated gelatin as a recording material, whose
performance is sensitive to the coating and development process, especially in
the near-UV. In this letter, we present the characterization of two UV-blue
VPHG prototypes for the BlueMUSE integral field spectrograph on the VLT, based
on dichromated gelatin and the Bayfol$\circledR$HX photopolymer film as
recording materials. Our measurements show that both prototypes meet the
required diffraction efficiency and exhibit similar performance with a
wavelength-average exceeding 70% in the 350-580 nm range. Deviations from
theoretical models increase towards 350 nm, consistently with previous studies
on similar gratings. We also report similar performances in terms spatial
uniformity and grating-to-grating consistency. Likewise, no significant
differences in wavefront error or scattered light are observed between the
prototypes.
