What is Collimation? What is Laser Collimator?

The concept of collimation is a very unique concept and is a perspective used to make corrections in laboratories. It also plays a vital role in astronomy. Today’s standard 8-inch telescopes can see distant quasars and galaxies, how these ordinary telescopes clarify these distant objects. The answer is that today’s telescopes mostly come with laser or optical collimators. Before looking at what a laser collimator is, it is first necessary to know what a beam means.

What is Collimation?

When light passes through any refractive object, it undergoes a certain amount of diffraction. The light beams are scattered and do not reach the observers; they also have diffuse angles, not parallel rays of light. On the other hand, a collective light beam is a light beam with extremely parallel light rays. Thus, collimation is defined as the process of converting scattered light into a beam of light with a large number of parallel rays.

A collective light beam is a low beam divergence beam (typically a laser beam) so that the beam radius does not undergo significant changes at medium radius distances. It means that in the case of simple and frequently encountered Gaussian beams, the Rayleigh length must be long compared to the projected span. A collimator is a device with a light beam narrowing. The narrowing of a light beam can have two meanings. First, it means arranging the light beam in a certain direction, and the second means shrinking the spatial cross-section of a beam.

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How to Collect Laser Beam?

The laser can be defined as a device that produces a coherent beam of high-intensity monochromatic light. Most normal lasers used by civilians are laser diodes. Unlike gas or crystalline laser counterparts found in laboratories, laser diodes have a significant level of divergence. A diode laser beam has low wave front quality, severe astigmatism, and elliptical problems. Astigmatism in a laser diode generally refers to the level of deviation faced by the laser beam from the laser diode. Elliptical beams can also allow the laser to leak a little from the edges; instead of forming a perfect point, they form a small ellipse. Both of these problems can be corrected using a few optical corrections.

The simplest and most popular way to collect laser diode beams is to use a single aspherical lens. The larger the focal length of this lens, the greater the post-irradiation beam diameter. Also, for example, if a particular beam adjustment is required to expand the beam radius of a collective beam, usually two lens systems are used and this is called a telescope. A lens with a negative focal length and a lens with a positive focal length form a setup for collecting the beam and expanding or narrowing it. To correct the elliptical problem, an elliptical beam collected by expanding in the direction of the slow axis in the form of an ellipse or by compressing it in the fast axis direction can be circularized.

Laser Collimator in the Telescope

A laser collimator allows to properly align the optics of the reflecting telescope. First, the laser collimator is used to determine whether the secondary mirror points directly to the center of the primary mirror. The first thing to do is to polish the laser collimator through the telescope’s tube. Make sure that the laser collimator is securely in place without any movement. This ensures that the laser collimator is correctly aligned without any bending or slipping. The laser beam will reflect the secondary mirror and reach the primary mirror. The primary mirror usually has a small marking tape on it. The laser is aligned to hit this pointer, and the secondary mirror is then directed and focused accordingly. The collision of the laser is done for a very good reason.

Theoretically, it helps to align the focus of the image at infinity, and this helps to increase the clarity of distant celestial bodies. Consider a theoretical example that might explain why a laser is used to collide in telescopes. The aggregation problem arises when remote objects appear as point sources. Unfortunately, nothing is a true spot source and if the spot source has radius y1 and a maximum angle beam θ1, the size of the weld should be included in any calculation. If we sum the output from this source using a lens with a focal length, the result will be a beam with a radius y2 = θ1f and a radius angle2 = y1 / f. Whichever lens is used, it should be noted that the beam radius and beam divergence have a mutual relationship. Hence, if the focal point is to be infinite, it causes the beam angle to be zero and thus sumps the light beam.

Laser Collimation in Laboratories

Beamed laser beams are very useful in laboratory setups because the beam radius remains approximately constant, so the distances between optical components can be easily changed without applying extra optics and excessive beam radii are avoided. Most solid-state lasers emit naturally collected rays; A straight output coupler forces straight wavefronts (i.e. a beam waist) at the output, and the beam waist is usually large enough to avoid excessive deflection. However, edge-emitting laser diodes emit strongly deflecting beams and are therefore often equipped with collimation optics. At least one fast axis collimator greatly reduces the strong deflection in the fast direction. For fibers, a simple optical lens can usually be sufficient for collimation, but beam quality can be better preserved with an aspherical lens.

Reference: https://link.springer.com/chapter/10.1007%2F1-84628-071-0_10