Align an Off-Axis Parabolic (OAP) Mirror to Collimate a Beam (Viewer Inspired) | Thorlabs Insights

Off-Axis parabolic (OAP) mirrors are often used to collimate divergent beams, but aligning these mirrors can be a frustrating experience. This is because there are multiple variables that must be controlled during the alignment process. This demonstration divides the procedure into discrete steps and includes helpful tips for successfully positioning the mirror and light source. In addition, the dependence of the correct alignment on the mirror's geometry is discussed, and the typical effects of different misalignment geometries on the beam shape are shown on a viewing screen.

In this demonstration, the divergent output of an optical fiber and an OAP mirror are aligned so that the incident light and the collimated reflected beam travel in a plane parallel to the surface of the optical table. Because of this, an important initial step in the procedure is to set both the height of the source and the center of the mirror mount's bore at the height of the desired collimated beam. Then, an iterative approach is used in which the mirror is rotated to bring the plane of reflection parallel to the plane of the table, and the fiber's end face is moved to the mirror's focal point.

00:00 - Introduction
01:00 - Alignment and the Parent Parabola
02:12 - Attach the Adapter to the Mirror
02:55 -Mount and Coarsely Align the Mirror
04:58 - Set Mirror and Source Heights to be Equal
05:39 - Initial Positioning of Mirror and Source
07:20 - Fine Positioning of Mirror and Source
10:37 - Beam Quality, Options, and Having Patience

Key Components used in this Demonstration Include:

Other Components Include:

[blueberrydetective]

I really appreciate all of these tutorial videos. They are very informative and help a lot with learning about components I am unfamiliar with. Happy Holidays!

[TushhsuT]

Nice tutorial. Thank you! I believe I did such alignment once and it was a pain. Especially if one wants to refocus the beam, keeping nice gaussian shape in a focal spot..
As a suggestion - there are some parts which always need to be horizontal/vertical, being actually round and don't having any horizontal or vertical edge.. An example is just in the video. It would be much easier to align having a small reference face. For example - a part of long part of zylinder could be flattened (CNC, lathe/milling machine) during manufacture process, when one still exactly know where the axis is. It should not be big - 5x5 mm plane would be more than enough.
Same for wedges, periscopes, etc.
One could than simply take a screwdriver or hexkey, press it to this small reference plane with a finger and align element vertical/horizontal/aligned to holes on the table looking on some line (screwdriver) to orient. Would one want to be even more precise - some additional laser beam could be reflected from a piece of flat mirror attached to this surface and make a perfect horizontal alignment.
By this, the probability of an accident during wedge or periscope alignment could be strongly reduced. IMHO

[rachelanderson]

Great video! I assume these same techniques can be used to align spherical mirrors too?

[raoufkutaish]

Could you please tell me what should I order from Thorlabs to have the same LED that you used for alignment? The number of the fiber-coupled LED and the LED mount.

[rishabhsangal]

Hello, very helpful tutorial. I was also trying collimation/beam expansion with lenses(Achromats), i am using your SI254 to check the collimation and I am always getting curved fringes(aberrations) in shear. I was wondering is it my alignment fault or do we get better collimated beams with OAPs than lenses, any advise?

[lahuiss]

what is the source used ? it is ok to use a divergent lens with a USB PL201 laser ?

[moeswartz]

That's only half of the game. There is only a little chance that the fiber tip is perfectly placed into the focal plane of the oap. Ideally you want to focus the beam onto a small pixel detector for fine adjustment of the input w.r.t. the oap.

[odissey]

All work with optics should be performed whearing gloves.