User:Andy Maloney/Notebook/Lab Notebook of Andy Maloney/2009/03/31/Optical tweezers

Collimation

After many failed attempts, I have finally figured out the best way to collimate the laser diode. The first thing to do is to map the diode element away from it's cooling element so that you have space to put other optics in the path. Of course this is obvious and I thank Dr. Koch for pointing it out. Anthony and I used 2 25.4 mm focal length lenses to map the element out of the cooling housing. These lenses add lots of aberrations due to their f/# being 1. Of course, companies sell matched pairs that are aspheres and I think we may want to get one if the beam quality is important to us. But maybe not if we use a spatial filter upstream.

So, after moving the diode element (imaging it out of the cooling housing) I tried very hard to use the cylindrical lenses to collimate the beam. There are many factors that prevented me from collimating today, one of which was figuring out space issues. The mounts for the cylindrical lenses are quite large and I had to find a way to mount them on separate translation stages and at the same time, position them close enough to each other to collimate the beam. The good news is that we do have a set of lenses that will let us use the anamorphic prisms and I will have the beam collimated tomorrow. Collimation is a must. Especially since Larry got the isolator in today and I look forward to using that as well.