The razor blades were wrapped individually, and the discarded wrappings is the big mess in the background.
It’s not 100% black, the reflection of the laser is still visible:
but it’s still a lot better than the next best thing; a piece of black anodized aluminium:
The razors are placed in a 3D-printed structure, where a clever combination of geometry and absorbing filters takes good care of any excess photons.¹ And here it is:
The filters are the cheapest red colour correction filters I could find, and while they exhibit an optical density >3 at 532 nm, they are quite unusable.
The reddish dot next to the razors is fluorescence inside the red filter. It will likely cause severe interference with the Raman signal.
I will exchange them with Hoya B-390 or Schott BG12 bandpass filters, whichever I stumble upon first.
¹ A simple, high-performance Thomson-scattering diagnostic for high-temperature plasma research
D J Den Hartog and M Cekic 1994 Meas. Sci. Technol. 5 1115