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Question Video: Identifying Light Beams Used in Creating a Hologram Physics

The diagram shows some apparatus used in holography, including a cylindrical object. Which of the following is the term used to describe the beam that follows the path 𝐡𝐢 and 𝐡𝐷? [A] Virtual beam [B] Image beam [C] Object beam [D] Illumination beam [E] Reference beam. Which of the following is the term used to describe the beam that follows the path 𝑏𝑐𝐢 and 𝑏𝑑𝐷? [A] Object beam [B] Reference beam [C] Virtual beam [D] Image beam [E] Illumination beam

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Video Transcript

The diagram shows some apparatus used in holography, including a cylindrical object. Which of the following is the term used to describe the beam that follows the path capital 𝐡, capital 𝐢 and capital 𝐡, capital 𝐷? (A) Virtual beam, (B) image beam, (C) object beam, (D) illumination beam, (E) reference beam.

Let’s begin by identifying this beam on our diagram. We see that point 𝐡 on our diagram is here and the beam that goes from capital 𝐡 to capital 𝐢 and capital 𝐷 is this one here. This is all the same beam. The light that is reflected off of this mirror passes through a prism so it spreads out. We see that this beam comes from point 𝐴 on our diagram and ultimately comes from our laser light source. It never interacts then with the object that we’re looking to make a hologram of. Despite that fact, this beam is vital to creating a hologram because it provides a standard or a reference for the beam that does indeed interact with our object.

In making a hologram, the idea is that a beam that interacts with the object of interest and a beam that doesn’t interfere with one another. When they do, a three-dimensional image, a hologram, is created of the object. As we’ve seen, the beam from capital 𝐡 to capital 𝐢 and capital 𝐷 is a reference. We could think of it as a standard or a baseline against which to compare the light that does interact with our object. The term used to describe this beam is reference beam. We choose answer option (E).

Let’s look now at part two of our question.

Which of the following is the term used to describe the beam that follows the path lowercase 𝑏, lowercase 𝑐, capital 𝐢 and lowercase 𝑏, lowercase 𝑑, capital 𝐷? (A) Object beam, (B) reference beam, (C) virtual beam, (D) image beam, (E) Illumination beam.

Whereas before we were talking about the beam of light that doesn’t interact with our object, now we’re talking about the beam that does. This beam is identified as the one that goes from lowercase 𝑏 to lowercase 𝑐 to uppercase 𝐢 and from lowercase 𝑏 to lowercase 𝑑 to uppercase 𝐷. This is one beam. And as we see, it bounces off of the object and then reaches this last component in our diagram. The fact that this beam does interact with the object is what gives it its name. It’s called the object beam.

Interestingly, the object beam by itself is not enough to create a hologram of our object of interest. The object beam and the reference beam must interfere with one another to make the hologram. In any case, for our answer, we choose option (A). The term used to describe the beam that follows the path lowercase 𝑏, lowercase 𝑐, uppercase 𝐢 and lowercase 𝑏, lowercase 𝑑, uppercase 𝐷 is object beam.

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