Wide band free space transmission link utilizing a modulated infrared laser

For years, Fermilab has utilized wide bandwidth transmission links for stochastic cooling feedback systems. Stochastic cooling requires the feedback signal to arrive at the kicker in time synchrony with the beam on the same turn. While coaxial cables suffice at lower microwave frequencies, their high loss and dispersion make them unsuitable at higher frequencies. Coaxial cables up to 125 meters in length have been utilized in the Antiproton Source. With the advent of the Recycler ring, (600-900 meters in diameter) coaxial cables have unacceptable losses. Stochastic cooling will be utilized in the Recycler to maintain a small beam emittance and momentum spread. A new means of transmitting the signal across the ring is necessary. While optical fibers have very low loss and excellent bandwidth characteristics, their propagation velocity is too slow to meet the beam on the other side of the ring. A modulated infrared laser is expanded from single mode fiber (utilizing telescopes) and transmitted in an evacuated pipe across the ring. The system will be described with preliminary results presented