Experiments on transverse mode locking of circular cylindrical optical beams and certain flat beams

Transverse mode locking of the Laguerre forms with proper magnitudes and phases in an optical beam with circular cylindrical symmetry can produce a beam with time-varying spot size and intensity. The effect is demonstrated by locking two modes of the cylindrically symmetric set, TEM00qand TEM10qof an He-Ne 6328-Å laser with relative amplitudes 1 and 0.6, respectively. Verification of the time-varying spot was by sampling of the beam with an iris moved about the beam at constant radius. The shape and phase of the detected pulses agreed with predictions for the mode-locked beam. For a flat strip beam, the rectangular TEM00q, TEM20q, and TEM40qmodes were locked with relative amplitudes 1, 0.5, and 0.3, respectively. A beam with time-varying width resulted and was sampled with a slit.