Shake it, baby

At the 2.5m Nordic Optical Telescope on La Palma, Canary Islands, Spain, efforts had been ongoing to improve the performance of the FIES spectrograph so that improved radial velocity measurements could be made.  This would hopefully lead to a higher success rate in the detection of exoplanets, as well as other areas of astronomy, requiring accurate measurements of the motions of stars.

One way to improve the accuracy is to ensure that the light entering the spectrograph, and hits the spectrograph grating, is as uniform as possible. If you have a spectrograph that is fed by an optical fiber, like FIES, it will usually suffer from modal noise which creates a speckle-pattern of the light hitting the grating. This pattern depends both on how the light enters the fiber and on the wavelength on the light itself. So, in other words, you do not have a uniform light. There are many ways of getting rid of this speckle pattern, most of which are referred to as “scrambling”. One way of achieving scrambling is to shake the fiber while you are observing your star. This will mean that the speckle pattern moves around and is effectively “smeared out”, resulting in a more uniform illumination of the instrument.

Always striving to make the most of their instrument, it was decided to implement a fiber shaker, with the expectation that this would be an efficient way to improve FIES. However, fiber shakers are not exactly off-the-shelf items,  so as the true entrepreneurs they are, the staff decided to build their own fiber shaker. After all, building something that shakes back and forth is not exactly rocket science.

The first fiber shaker prototype at the Nordic Optical Telescope.

The first fiber shaker prototype at the Nordic Optical Telescope. Photo Credit: Nordic Optical Telescope

Since the Nordic Optical Telescope is run by the Scandinavian countries, there was very little choice, really, as to what materials should be used to build the fiber shaker prototype. Staying true to the favourite building blocks of any sensible person from the Nordic countries, a shaking mechanism was quickly constructed out of LEGO, and set to work at the telescope. LEGO being as awesome as it is, this fiber shaker actually improved the performance, but unfortunately the shaker had to be decommissioned after a few weeks, as the person in charge (aka the instrument scientist’s son) demanded his toys back. It also turned out that although LEGO is great, it isn’t quite sturdy enough for prolonged use as a fiber shaking mechanism.

It was naturally disappointing that the shaker had to be taken out of use after such a short period of time, but these kind of setbacks are not something that kills the spirit of an instrument scientist. It merely represent a challenge to come up with a better solution. So once again, the staff was off hunting a shaking, vibrating contraption, to replace the LEGO scrambler. This did not take long, since people apparently have all sorts of things stashed away in attics and basements.

The fiber shaker upgrade at the Nordic Optical Telescope. Much more potent than the first version.

The fiber shaker upgrade at the Nordic Optical Telescope. Much more potent than the first version. Note the essential duct tape, holding the optical fiber in place. Photo credit: Nordic Optical Telescope.

Meet the fiber shaker prototype 2: Bigger, better, sturdier. An item more commonly known as a foot massager, but now enjoying a life as an integral part of  a modern-day telescope. That gotta be more exciting than retirement, or massaging people’s smelly feet! At the time of writing, the foot massager is still sitting comfortably in the dome of the Nordic Optical Telescope.

In related news, the staff at the Wendelstein Observatory outside of Munich, Germany, implemented a low-frequency fiber shaker, built from the car-wipe engine from an old car belonging to one of the observatory staff members. When the fiber optics specialists at one point asked in horror; “But aren’t you worried that you will damage the optical fiber with all this shaking?” the instrument scientist replied; “Well… a while back, someone forgot to turn the wiper engine off, so we had it running continuously for more than a month, and the fiber was just fine. So no, we’re not overly concerned about that.”

Due to the ingenuity of engineers and scientists such as these, functional solutions are made with whatever equipment they have in hand. Best part? It often works! And after all, being able to claim that a foot massager is an important part of an astronomical instrument, is rather cool, really.


2 thoughts on “Shake it, baby

  1. So please explain how shaking something makes it more stable? That’s kind of an important concept to explain that is missing in this article.


    • Right, “stable” was probably a poor choice of words. Good comment! 🙂 “Uniform” would be more appropriate. By mechanically shaking the fiber you can “smear out” the speckle pattern in the light coming from the fiber, arising from modal noise.
      I have added a little additional text, and a link to a more in-depth explanation.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s