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The photon spectrometer TAPS is a versatile instrument to measure nuclear bremsstrahlung and neutral mesons via their γ decay. The formation and evolution of compressed nuclear matter is studied in heavy ion collisions at relativistic energies by analyzing the yield and spectral distribution of neutral meson (π0, η). Pion absorption through the Δ capture process is derived from the pion energy spectrum. The nuclear bremsstrahlung is exploited to study the evolution of the equilibrating collision zone and to infer the strength of dissipation mechanisms. Off-shell effects and subnucleonic degrees of freedom in the NN interaction are being studied with polarized protons on protons and nuclear targets.