I am looking for a cheap source of low power single transverse mode laser diode in order to focus them to a very small point. I thought I would get that from a DVD drive but the pattern I see at the focus point isn't a single point at all (2 or more points). I find that strange. Could you confirm that the DVD diodes aren't single transverse mode? (suggestions and reference of suitable diode are welcomed)
Diode lasers consist of many tiny emitters that are stacked together for power scaling, which has negative effects on beam quality. For the same reason, the laser beam also behaves different in both axes in respect to divergence and beam quality. That might be the reason why you see multiple focal points.
Reaching an actual single transverse mode for a laser is usually done with a special optical resonator (pun with my username not intended lol), containing elements to increase losses for higher modes. There is no room for that in a DVD drive.
According to wikipedia, you can also achieve single transverse mode by using a special structure in the semiconductor, for example a DBR (distributed bragg reflector).
However, the laser diodes in a DVD player are cheap mass produced diodes, so I don't expect such sophisticated structures to be used in them when they are not needed.