• Question: How do you align the laser?

    Asked by kushy103 to Mike, Pip, Tianfu, Tim, Tom on 22 Jun 2012.
    • Photo: Tom Lister

      Tom Lister answered on 22 Jun 2012:

      I do a quick check each day a laser is being used to make sure the output energy is what we expect it to be. If it’s ok, then the optics must be aligned.

      I don’t take the laser apart and play with it, that’s generally the job of the service technician.

    • Photo: Tim Stephens

      Tim Stephens answered on 23 Jun 2012:

      If the laser beam is visible (many are not) and is safe to look at, you can see where it’s going. If it’s not safe to look at, the people adjusting it must wear laser safety glasses which mean that they cannot see the beam at all. In this situation, you can use special ‘visualiser’ cards that glow a different colour when the laser hits them and let you see the beam whilst wearing safety glasses.

      There are two different types of alignment that we would carry out on a laser.
      The first is aligning the insides: most lasers contain two mirrors inside the laser head and they need to be perfectly parallel to one-another for the laser to work. Normally, you wouldn’t do this, and would get a service technician to do this job for you (unless your job is as a service technician!). It’s a fiddly job and one that takes a bit of practice to get right.
      The second type of alignment is to align the laser with your experiment. Laser beams travel in a straight line in air, so you either need to point the laser directly at your experiment, or use adjustable mirrors to bounce the beam into the right place. These mirrors are on a special mount that lets you adjust the angle of the mirror very accurately, so it’s a case of carefully adjusting the mirrors until the beam is where you need it.

    • Photo: Tianfu Yao

      Tianfu Yao answered on 25 Jun 2012:

      The laser light in an fibre laser cavity is not so easy to align. Since most of the light is invisible, so you first need a IR card or viewer to display the laser beam. Then you should launch the collimated laser beam into the small core (like 10 micronmeter) by the coupling lens. The fibre is fixed on the translation stage. There is some output power emitting from the fibre output end. After that, you can adjust the fibre input end by the output power of the fibre.

    • Photo: Philippa Bird

      Philippa Bird answered on 25 Jun 2012:

      It takes a long time and a lot of iterations of moving mirrors and checking things with the viewing card. You can also see invisible IR lasers on a camera, so I actually have a webcam like you would use on skype! We also have something called an “Iris” which is basically a hole that you can adjust the size of to see how straight the laser is going through it.
      It’s good fun, but you need to have the radio on at the same time to not get too bored!!

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