A 520 nA external beam of 50 to 200 MeV is required for certain physics and medical experiments at the same time as 200 PA is being accelerated for meson production. A mode-locked laser, synchronizcd with the cyclotron rf, can produce a 20 nA parasit,ic JI' beam for continuous extraction. The best available Nd:YAG or Nd:YLF laser (Av l'.vr. 15 W) mode-locked at a harmonic of the cyclotron rf falls short of the required intensity by a factor of about 50. An optical delay liuc could trap the

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... ocked pulse train to achieve the reqliired intensity. The optical delay line is a near-concentric resonator irlst,allrd half above and half below the beam plane and in which al1 trapped pulses cross the midplane in synchronism with the cyclotron hcani bunches. An ana!ysis of the delay line is presented in terms of the transfer matrix for one round trip in the periodic focusing system formed by the end mirrors of the resonator. An enhancement factor 25.5 is possible with 80 trapped pulses if the mirror reflectivity 2 99%.