I am looking for a summary of practical methods of focusing and collimating laser light, which I guess are contradictory objectives, or are they?
For example, when I use typical small diode lasers, even with the as-shipped collimating lens I find the beam tends to be around 1mm to 2mm in diameter, and often very irregular or speckly. I would much rather have a beam that is uniform and more like 0.1 mm, but do not know how to achieve that.
Obviously it is possible to tightly focus a laser because DVD players make a tiny spot microns in size, but this I assume is only at one particular focal length, not along the length of a beam. For my application (machining metrology) I need to have a beam that does not need to be focused, yet is as narrow as possible.
Note that this type of application operates on a table top scale, all of the illuminated areas will be between 1 inch and 3 feet or so.
What are the best practical methods of shaping a laser beam according to this need?