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for whatever reason your link gets me a 404 error.. They're probably talking about longitudinal modes instead of transverse modes. While these diodes are likely single-transverse mode, all commercially available laser diodes are multi-longitudinal mode. Longitudinal modes are not usually manifested visually. A laser that is multi-longitudinal mode simply has more than one frequency of standing waves present in the cavity instead of just one. A theoretically perfect laser beam is one with only one frequency (single-longitudinal mode) one transverse mode (TEM00), a small beam diameter and no divergence (0mrad), resulting in an m^2 of 1. Such a beam is impossible in the real world, but lasers that are single-longitudinal mode (SLM) and single transverse with very low divergence are the most highly sought after and most costly. The extremely short cavity length of a laser diode makes SLM operation all but impossible, although I am aware of some research into SLM diodes producing good results.
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