# Mirrors/prisms - optics

1. Feb 24, 2006

### itzela

I'm trying to find a mirror or a prism which would always reflect any incident light ray parallel to the a fixed axis (drawing attatched), no matter what the angle. I've found that right angle prisms reflect light parallel to the an axis, but I don't think works for rays coming at different angles. I would really appreciate any help =)

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2. Feb 24, 2006

### Staff: Mentor

I'm not sure I understand what you are asking, but if I do, I'm pretty sure the answer is that there is no such prism/mirror. You're looking for something where the light out is always horizontal (in your sketch) regardless of what angle the light comes in at? Not possible: the angle of incidence always equals the angle of reflection.

3. Feb 24, 2006

### DaveC426913

"Not possible: the angle of incidence always equals the angle of reflection."

In a simple mirror, yes. But some combination of shapes or combination of mirrors and prisms might yield what she's looking for.

Itzela, I can't help you either, but try considering it from the other end. If you stepped into that beam of light emanating from your device what would you see?

4. Feb 26, 2006

### pallidin

Perhaps using mirrors or prisms could not achieve what you are looking for, but THERE IS a way to do it if image clarity is of little concern!
The method involves using fiber optics.
If you had enough fiber optic strands, one could construct a shape with them that would be similar to the shape of a mushroom(cap and stem).
From this arrangement, any incident light on the fiber optic "cap" would be directed out the "stem"
With enough fiber optic strands, one could advance the working principle and create a "sphere" as the cap, with the stem coming out of the sphere.

5. Feb 26, 2006

### Cliff_J

6. Feb 26, 2006

### 0rthodontist

A Fresnel lens only works on light coming from one particular point.

Light coming out of fiber optic cables does not come straight out, it bounces around on the interior of the fiber and usually exits at an angle.

7. Feb 27, 2006

### itzela

I just thought about using a concave mirror and adjust the light source to always pass through the focal point of the mirror. That way all the reflected rays would come out parallel to the principal axis. Do you guys think it'll work?

8. Feb 27, 2006

### Staff: Mentor

How do you always get the incident light to pass through the focal point?

9. Mar 2, 2006

### itzela

Maybe by placing the light source directly on the focal point and varying the incident angle.... or by manually simply changing the location of the light source (laser) so it passes through the focal point. Any better ideas?

10. Mar 2, 2006

### Integral

Staff Emeritus
A point source located at the focus of a parabola will create a beam parallel to the symmetry axis of the parabola.

11. Mar 8, 2006

### itzela

I was thinking of mounting a laser to a rotatable tripod and placing the tip of the laser on the focal point and rotating the tripod in order to produce parallel beams at different heights. But I'm not sure if the reflected beams will always come out parallel to the symmetry axis of the parabola since they're being shifted from the focal point as the laser rotates. Is there any setup which would allow for the rays to always reflect parallel to the axis?

12. Mar 8, 2006

### Michael_E

As long as the center of rotation of the laser is at the focus of the parabola ,then you're in business. Regardless of where the laser is located, if a line along the axis of the laser continues to go through the focus of the parabola then the output will be parallel. If you've got a large angular range, then the tough part is to pick the correct shape and then build it accurately enough to satisfy your needs.