Photon behavior in lasers

1. Mar 23, 2012

maxentropy

If a laser was shined at a device to measure the amount of photons striking it and then another laser was shined perpendicular to first laser, would the reading on the meter change?

2. Mar 23, 2012

Drakkith

Staff Emeritus
No, the photons will not interfere with each other.

3. Mar 23, 2012

euquila

I imagine it would because destructive interference at that point would result in a lower detection rate.

4. Mar 23, 2012

euquila

Sorry for double post but I just saw your post. Why would they not interfere with each other if the waves are 90° out of phase?

5. Mar 23, 2012

Drakkith

Staff Emeritus
Let's be clear. I thought the OP was talking about shining a beam THROUGH another beam. Is that what you were thinking?

6. Mar 23, 2012

Redbelly98

Staff Emeritus
You seem to have some misconceptions.

For starters, nobody said the two waves were 90° out of phase, only that the two beams were perpendicular to each other.
Secondly, two different & independent lasers would not maintain a constant phase difference.
Third, as I interpret the OP, the second laser beam is not shining on the detector, so the second laser has no effect on the detector reading.

7. Mar 23, 2012

maxentropy

That is correct Drakkit. And would the angle matter? What I was asking was would the beams interfere with each other? and the second laser was not shining on the detector

8. Mar 23, 2012

Redbelly98

Staff Emeritus
As long as the 2nd beam is not actually shining on the detector, then no the angle would not matter.

9. Mar 23, 2012

maxentropy

So the second laser would not affect the reading from the first, correct?

10. Mar 24, 2012

Drakkith

Staff Emeritus
Correct.

11. Mar 24, 2012

euquila

From what I understand, this is the situation (ignore the dots as I'm using them for spacing):
1......2
\....../
.\..../
..\../
...\/
----------------------- Detector

Beam 1 and 2 form and angle of 90° between each other and 45° to the detector.

Would there not be interference where the two beams meet at the detector?

Can you explain to me (never took optics) why would the phase difference between two lasers not be time invariant?

12. Mar 24, 2012

sophiecentaur

Why should it be? The two oscillators are not synchronous.

13. Mar 24, 2012

Redbelly98

Staff Emeritus

My understanding of the setup was more like this:
Code (Text):

1
|
|
2 ---+---->
|
|
|
V
---- detector

14. Mar 24, 2012

euquila

Right. There is no interaction with matter where they intersect. Thank you for clarifying!

15. Mar 24, 2012

sophiecentaur

Whatever the physical layout is, the two lasers would be independent of each other so you would not get any interference effects. Even if they were synchronised and the beams crossed each other at right angles, any interference would only occur where the beams cross and they would emerge from this overlap zone totally unaffected. The principle of superposition applies - field vectors add arithmetically in a linear medium.

Any interference pattern will only occur in regions where both beams are present.