Question on beamsplitter when light is backward-incident

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Discussion Overview

The discussion centers around the behavior of a beamsplitter when light is incident from the opposite side, specifically examining the effects of using a plate beamsplitter with different coatings on each side. Participants explore the implications of this configuration on light transmission and efficiency.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the behavior of a beamsplitter when light hits the anti-reflective (AR) coating first, questioning whether part of the light would transmit downwards while the rest passes through.
  • Another participant asserts that one-way transmission is impossible, citing the second law of thermodynamics and entropy considerations.
  • A different participant claims that the beamsplitter will function the same regardless of the direction of incidence, stating that there are no one-way mirrors.
  • One participant notes that using a dielectric beamsplitter in reverse may decrease efficiency, particularly if the angle of incidence is not optimal.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of one-way transmission, with some asserting it is impossible while others focus on the operational characteristics of the beamsplitter when used in reverse. The discussion remains unresolved regarding the specific outcomes of using the beamsplitter in this manner.

Contextual Notes

There are assumptions regarding the definitions of one-way transmission and the operational limits of the beamsplitter that are not fully explored. The implications of using the beamsplitter at non-nominal angles are also mentioned but not detailed.

swengzju
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Hi all,

I'm new to this forum and not sure if this is the right place to post this question.

I know that beamsplitters normally have dielectric coating on one side and AR coating on the other side. I'm looking at this plate beamsplitter specifically: https://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=4808

I want to know what would happen if light is incident inversely, eg, it hits AR coating first then the dielectric coating. Will I get part of the light going downwards and the rest going through the beamsplitter?

Basically I'm looking for a beamsplitter that only allows on-way transmission.

Any help is greatly appreciated!
 
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One-way transmission violates the second law of thermodynamics, it would allow to reduce entropy. I don't know how this beamsplitter would behave, but there is no one-way-transmission (neglecting exotic non-linear effects that are not relevant here).
 
It will work the same both ways around. There are no one-way mirrors.
 

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