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We discuss expectations for the absorption of high‐energy gamma‐rays by  γγ  pair production with intergalactic radiation fields (IRFs) at very high redshifts (  z ∼ 5–20 ), and the prospects thereof for probing the cosmic reionization era. For the evolving IRF, a semi‐analytical model incorporating both Population II and Population III stars is employed, which is consistent with a wide variety of existing high‐ z  observations including quasi‐stellar object spectral measurements,  Wilkinson Microwave Anisotropy Probe  Thomson depth constraints, near‐infrared source count limits, etc. We find that the ultraviolet IRF below the Lyman edge energy with intensities in the range of a few times  10 −19  erg cm −2  s −1  Hz −1  sr −1   can cause appreciable attenuation above ∼12 GeV at   z ∼ 5 , down to ∼6–8 GeV at   z ≳ 8–10 . This may be observable in the spectra of blazars or gamma‐ray bursts by the  Fermi  Gamma‐ray Space Telescope or next‐generation facilities such as the Cherenkov Telescope Array, Advanced Gamma‐ray Imaging System or 5@5, providing invaluable insight into early star formation and cosmic reionization.

Probing intergalactic radiation fields during cosmic reionization through gamma‐ray absorption