  Faraday isolators are usually limited to Faraday materials with strong Verdet
constants. We present a method to reach the 45{\deg} polarization rotation
angle needed for optical isolators with materials exhibiting a weak Faraday
effect. The Faraday effect is enhanced by passing the incident radiation
multiple times through the Faraday medium while the rotation angle accumulates
after each pass. Materials having excellent thermos-optical properties in the
ultraviolet and mid-infrared range become available for optical isolators.
Herriott-type multipass cells offer a simple and compact way to realize the
desired propagation length in usual optical materials of standard sizes. A
proof-of-principle experiment was carried out, demonstrating polarization
rotation of a 532 nm laser beam by an angle of 45{\deg} in
anti-reflection-coated fused silica surrounded by a standard neodymium ring
magnet.
