User:Andy Maloney/Notebook/Lab Notebook of Andy Maloney/2009/07/07/1064 laser tweezers

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New stuff

Today at around 10 am I received the 2 inch diameter 1064 laser line mirrors and the corresponding mounts from Thorlabs. I put them on the periscope with the same irritation as before for alignment. I believe I've gotten much better at it from having to build this guy 3 different times. Some things of merit for aligning a laser with the periscope are:

  • Set the bottom mirror so that the beam goes somewhat straight up. It doesn't really matter too much if you don't get it spot on because that's what the mirror mount is for.
  • Put the top mirror in and roughly adjust it so that the mount is straight. Ideally you want the beam going through the center of both mirrors but it okay to get it there roughly. Fine tuning comes later.
  • Once the mirrors are in place, set two points in your optical path that you can measure where the beam is with respect to your two points. Remember, 2 points uniquely describe a line.
  • Fuss with the bottom mirror until the beam goes through your first point.
  • Fuss with the top mirror until the beam goes through your second point.
  • If you notice that you keep going through the same motions with both mirrors to get the beam through both points, then that means your top mirror is not in the proper spot vertically. No worries, if this happens you want to position the top mirror such that the beam goes below (or above depending on how you introduced tilt to the system) the first point. Use the bottom mirror tip/tilt knobs to realign and repeat with the top mirror tip/tilt knobs. Eventually, you will get it.

Total time for me to get this thing working again was 2 hours. Way too long in my opinion.

Realignment

Now that I have the optical path going straight into the microscope, I need to reposition the mirrors such that it goes straight through the microscope. To do this, I never never never mess with the tip/tilt knobs on the mirror mounts. Those were used to position the beam straight down an optical path. What I use are the 2 translation stages the mirrors are mounted on. Using these and not the tip/tilt knobs will allow my beam to continue to go straight down an optical path, however, it will offset the beam by however amount I move the stages. This is the beauty of a periscope. Once you get an optical path defined with the tip/tilt knobs for your mirror mount, you can offset the beam using the relative positions of the mirrors without changing your straight optical path.

Make a how to for using a periscope.

So, realigning the beam through the microscope is exactly like anything else, 2 points make a straight line. Approximate time to align this, 10 minutes.

Tweezing & QPD

Koch and I got the tweezers to tweeze close to the coverslip. The next thing to do is setup the QPD and the associated optics for it.

After some time fussing with things, I've realized that I cannot complete what I wanted to get done today. So, I'll update tomorrow and try and get the cube setup properly. I think I may have to disassemble it and align the cube with a HeNe before putting it on the microscope because right now, it's way too cumbersome to get it to work.

Steve Koch 23:02, 7 July 2009 (EDT): Reading this is tempting me to think about putting in the HeNe for detection altogether (co-aligning with 1064). This is probably a good idea long term. But since we only have 7 days-ish left for our ridiculous goal of getting preliminary data, it's definitely not a good idea to delay more. But let's keep it in mind.
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