The study of the properties of modes in high Fresnelnumber cavities was carried out in conjunction with experiments to test the practicability of locking a large number of high-order transverse modes to produce a scanning beam. To satisfy requirements that the laser exhibit stable, high, optical quality and a large frequency bandwidth, an argon-ion laser was constructed. To facilitate achievement of large Fresnel numbers in the cavity, the laser was constructed from a short length of beryllium oxide tubing with a 1.0 cm bore diameter.Such a laser may be excited by use of a solenoidal rf field. 8 Although such an excitation technique does not seem well suited for long, narrow-bore lasers it is quite appropriate in the case under study. 9 The active length of the discharge was approximately 25 cm; the over-all length between the Brewster-angle windows was approximately 40 cm.