  We report the first determination of the in-plane complex optical
conductivity of 1111 high-Tc superconducting iron oxypnictide single crystals
PrFeAsO0.6F0.35 and thin films SmFeAsO1-xFx by means of bulk-sensitive
conventional and micro-focused infrared spectroscopy, ellipsometry, and
time-domain THz transmission spectroscopy. A strong itinerant contribution is
found to exhibit a dramatic difference in coherence between the crystal and the
film. Using extensive temperature-dependent measurements of THz transmission we
identify a previously undetected 2.5-meV collective mode in the optical
conductivity of SmFeAs(O,F), which is strongly suppressed at Tc and experiences
an anomalous T-linear softening and narrowing below T*=110K>>Tc. The
suppression of the infrared absorption in the superconducting state reveals a
large optical superconducting gap with a similar gap ratio 2D=kBTc=7 in both
materials, indicating strong pairing.
