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# Physics/Physics-refraction in index matching liquids

Question
QUESTION: Laser Light passing from air to glass tube,glass tube contains liquid with refractive index same as glass tube.How is the refraction  and reflection for different incident angle?

ANSWER: When light passes between two materials with no difference in their index of refraction, there is no reflection or refraction at that interface at all.  So I'm not sure what you're asking, are you asking about the air-glass interface?  Because there's nothing happening at the glass-liquid interface.

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Dynamic light Scatteri
QUESTION: As in the diagram attached below...laser light is passing from air-glass-liquid-sample-glass-liquid-glass-air ..the scattered light is collected by PMT at critical temperature of the sample...

sample:- Methyl Ethyl Ketone + secondary Butyl Alcohol +Water

sample cell and vat are in cylindrical geometry..

liquid inside vat , vat ,sample cell have same refractive index..

its difficulty for maintaining the incident angle exact 90 degree into the vat...

Is there any possibility for refraction and reflection in the path of laser beam?

Is there reflection and refraction at glass-sample-glass interface?

What you've drawn here seems to be a diagram for a quasi-elastic light scattering (QELS) experiment.  That's a very advanced experiment, so I'm surprised you're having trouble with Snell's law for refraction.  I assume that your PMT is actually observing the sample in a cylindrical geometry in the plane of the lab floor and not below the actual sample cell as you have it drawn.  IF everything is perfectly symmetrical in that case, then there should be no need to apply Snell's law to this experiment, it should be designed out of the experiment.  To make sure it is, you should repeat this experiment as many times as possible and check your results for consistency and statistical variation.  If it is a vertical angle to the tank, then you will have to simply apply Snell's law at the minimum (scattering at the start of the sample) and maximum (scattering at the end of the sample) angles to get the angle range of the outgoing scattered light into the PMT.  If you are following the diagram as drawn, perhaps you should consider attempting to draw an overhead view of the concentric cylindrical geometry and use the above technique to estimate your angle range observed by the PMT.  You will again have to apply Snell's law, and your exact sample cylinder size will determine your range of angles involved.

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#### Dr. Stephen O. Nelson

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