Applications for Collimated Light in Astronomy

Applications for Collimated Light in Astronomy

What is Collimated Light?

The rays of a collimated beam of light are parallel to each other. This means that there is minimal spread in the light beam as it travels. Non collimated light travels more in the shape of a cone, because its rays are not parallel to each other causing it to spread as it travels. Collimated light travels more like a cylinder. 

Examples of Collimated Light

Examples of Collimated Light
  • Lasers – Light from a laser is collimated because it is formed in an optical cavity between two parallel mirrors and is coherent. For high quality laser beams the divergence of the light beam is less than 1 milliradian. 
  • Synchrotron Light – When you bend relativistic electrons around a circular track you can create highly collimated light call synchrotron light. 
  • Distant Sources – For almost any purpose the light from distant stars can be considered collimated. This is because the source is so far away that is has almost no angular size. 
  • Lenses and Mirrors – If you focus a small point source through a parabolic mirror it will result in a collimated light beam. Spherical mirrors can produce approximately collimated light. 

Uses for Collimated Light in Astronomy

Spectroscopy – One of the most important methods in astronomy. Spectroscopy is splitting a beam of light into its individual wavelengths, or its spectra. Think shining a white light through a prism and seeing a rainbow on the other side. Astronomers study spectra from stars and galaxies to study their chemical composition. There are three laws that govern spectroscopy. 

  1. A blackbody will emits a continuous spectra, free of any spectral lines. 
Uses for Collimated Light in Astronomy
  1. A hot transparent gass will emit emission lines. Bright lines against a dark background. 
Uses for Collimated Light in Astronomy (2)
  1. Absorption lines (opposite of emission lines, black lines on a spectra), will be produced by a cool transparent gas in front of a black body. 
Uses for Collimated Light in Astronomy (3)

The dark lines in the spectra appear in the space place as the emission lines would if the cloud of gas was hot and made of the same material. 

Astronomers study the light from galaxies and stars based on these laws to determine their chemical composition. However, a prism is not used to separate the light, but a diffraction grating is used to separate the light in a spectrometer. There are three main components to a spectrometer. 

  1. The Slit – where the light enters the spectrometer
  2. The collimator and diffraction grating – the collimator focuses the light onto the diffraction grating that splits the light into its fundamental colors. A diffraction grating is a special cut glass with small lines etched into it. 
  3. Camera Lens or CDC detector – this is where the reflected spectra is captured. 
components of a spectrometer

Collimating Telescopes

In astronomy collimating is often used in a different way, it is the process of aligning the optics of a telescope. Adjusting the mirrors and/or lenses to get the best image possible. In 2018, Michael Coughlin et al. published a paper entitled “A Collimated Beam Projector for Precise Telescope Calibration”. Though all “projection” of light is still on a relatively small scale for telescopes. 

Writers note:

While I do not see any major application for your technology for astronomy at a high level, I can see great uses for it in an educational setting. I taught physics and optics labs and often when we worked with spectroscopy the spectrums were all very small and hard to find emission or absorption lines. You could look into using your technology for optics demos at the high school and University level. For that I would suggest reach out to professors who are in charge of running physics labs at their given universities. 

References:

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Cassie Hatcher

Cassie Hatcher

Cassie is a lifelong learner with a passion for communicating high level science in a conversational matter. She holds a B.S. and M.S. in physics and has written two astronomy theses, one of which is published. She earned an internship at NASA’s Goddard Space Flight Center in 2016 and got the chance to see the James Webb Space Telescope while it was being built.

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