Optical depth Atomic hydrogen 1 Bacteriophages 1 Clouds 1 Column density 1 Depth measurements 1 Device design 1 ISM : clouds 1 ISM: atoms 1 ISM: clouds 1 MHD 1 Method: numerical 1 Molecular clouds 1 Numerical methods 1 Optical properties 1 Optical telecommunication bands 1 Optical- 1 Property 1 Quantum efficiency 1 Quantum memory 1 Radio lines: ISM 1 Self absorption 1 Silicon 1 Solar neighbourhood 1 Solar power generation 1 Spin/photon interfaces 1 T centers 1 Telecommunication bands 1 methods: numerical 1 radiative transfer 1