@ Fikret Kuş

p-polarized light is necessary for SPR to take place

Thank you for your answers Arya .K and Farooq Abdulghafoor Khaleel

BTW Farooq Abdulghafoor Khaleel

Dear Fikret Kuş

You must apply polarization TE polarized light, and you will get a good SPR.

you can note these too:

Article Two-prism setup for surface plasmon resonance studies

Article Tuning and sensitivity enhancement of surface plasmon resonance sensor

https://nano-optics.physik.uni-siegen.de/education/teaching/lab_courses/spr-exp-manual.pdf

https://chihyulai.com/surface-plasmon-resonance-platform/

Dear Saad Zahraw Sekhi I am using polarized sun glasses as a polarizer. Is this a good choice?

I think you should review previous works and base your results on them.

Fikret Kuş , to verify your polarization source you can use simple Brewster angle layout: if your polarizer oriented correctly you will have minimum of usual, common reflection from plane glass surface: you direct incident beam on glass and changing angle of incidence, observing reflected beam on some paper screen. With correct polarization you will see pronounced minimum when angle of incidence will be ~55°. For such layout your polarization is ready to observe SPR effect. As reflecting glass you can use one of the external surfaces of your prism.

Next stage is to verify relations of indices of refraction of your prism and chip substrate.

I don't remember exactly, but it seems that n=1.61 of chip supposing water-like media on top of the chip. You could check this by drop of water on top of chip and cover by flat glass to have sufficiently big area.

More precisely answer this question you could by calculation of your system properties with free SPR software Winspall:

http://res-tec.de/downloads.html

Report your results, good luck!

Valeriy Sterligov thanks for your suggestions. Your instructions are very helpfull. I managed to see the SPR pattern. I have added figure1 as the image of the spr image on paper screen.

But now I have another problem. When I direct the SPR laser to a cmos sensor without an objevtive I see the pattern at figure2. As clearly could be seen some interference patterns added to the image at figure1.

How to fix this problem and where does it comes from?

Fikret Kuş , you are welcome.

>As clearly could be seen some interference patterns added to the image at figure1.

At first, your CMOS sensor is definitely saturated. You can't have correct light distribution measurements from such an image. You need either decrease laser intensity by some absorbing filters either decrease your sensor sensitivity by decreasing exposition time or its gain if you have such possibility.

Second, the interferential structure that you are observing is a famous speckle structure, which is produced due to the coherence of the laser light and its interaction with a rough surface structure, probably in your case with a paper screen.

>How to fix this problem and where does it comes from?

There are several ways how to decrease speckle structure influence on such light distribution. The size of speckles, light intensity grains of your image is determined by the relationship between the size of your beam and the typical sizes of your rough surface structure. For bigger beams and smaller roughness speckle sizes will be smaller.

Another possibility to suppress speckle structure is using averaging. If you will register several images a little bit changing your paper screen position and then averaging all images, speckle structure will be significantly suppressed.

A similar result could be obtained if your speckle source (paper screen in your case) will be vibrating in such a way that during exposition time it will change his position. Vibration has to be performed mainly on a paper plane. Such a method is very similar to the previous ones, but you will have averaged results into one image.

The alternative way is destroying laser coherence by passing an incident laser beam through quickly rotated transparent non-plane film, like polyethylene or transparent plastic wrap. Like in the previous case during CMOS exposition time position of such film should be significantly changed.

Valeriy Sterligov thanks again. Let me clarfy the situation. Figure1 taken from the paper screen. The objective lens mounted on the camera. I am totaly ok with this image.

Then I removed the objective lens and direct the laser to the cmos sensor. There is no screen paper. The interference problem began with this situation. This can be seen at figure2.

I noticed that interference pattern affected by the cleanliness of the SPR chip. But not too much.

I know about speckle structures. But after reading hundreds of paper about SPR I couldn't find anything about this problem. How is this possible? This should be a common problem.

Rotated transparent non-plane film is looks like a solution. I will try it. But is there any solid state solution. I mean without any moving part.

>I noticed that interference pattern affected by the cleanliness of the SPR chip. But not too much.

Each speckle spot is formed as the result of interference of many coherent light beams from different source's points which are reaching given place of screen or CMOS sensor place.

So even a small position change of the source will produce a change of this interference sum, so a speckle peak can be exchanged by a valley. This is the reason why the tiny mechanical movement of the layout will produce change of the speckle structure and enable suppress it by averaging

>I know about speckle structures. But after reading hundreds of paper about SPR I couldn't find anything about this problem. How is this possible? This should be a common problem.

So if all of your SPR components are clean, free from any contaminations or defects you will not have a pronounced speckle structure. This is the one reason why such kind of issue is not discussed in publications.

Another reason can be related to the typical for SPR experiments measurements of reflected beams, which have rather strong intensity. For such beams intensity modulation due to speckle processes is not important. But if you will measure the scattered beam, which is several orders weaker, the situation is changed. By the way, you observe pronounced speckle structure into a peripherical zone of your reflected beam in Figure 2, for which the scattered component is significant.

>Rotated transparent non-plane film is looks like a solution. I will try it. But is there any solid state solution. I mean without any moving part.

All methods of speckle suppression, which I know are related to some movement of optical layout to introduce interfering components phase change.

If you strictly like to avoid such movements, you could try to pass the incident laser beam through some transparent liquid crystal under an electric field, which a little bit scatter this beam, so changing of field value will change the phase of the transmitted beam and probably in such a way you could reach speckles averaging without moving details. But for such a method, you have to fix the correct polarization of the transmitted beam to keep SPR conditions. I don't know about the experimental realization of this idea, hope it will work.

https://www.osapublishing.org/ao/fulltext.cfm?uri=ao-60-25-G64&id=453161&utm_medium=Email&utm_source=TopDownloads&utm_campaign=AOTopDownloads&utm_term=2020&utm_content=OCTOBER

This and following articles exactly related to answer on your question; I try to give it in very concise form, but there you can find complete one

Are you sure your chip is right? because I had the same problem and was related to the sensor chip.

Habibeh Pourhassan can you clarify your situation please? How was it related to the chip? How did you solve the problem? My sensor is IMX179 from sony.

@Fikret Kus

My problem was related to gold layer that is coated on the chip. I had to coat new gold layer and after I did it, I measured spr dip in reflection beam.

My step is the same your and I did all things you mentioned, but I couldn't see any thing. Therefore, I think if it is possible you test your chip. Is it new or used before?

Habibeh Pourhassan, is it correct that you significantly change gold layer thickness, increasing it probably twice relatively initial thickness? In such case conditions of SPR will be dramatically dropping; this could be the reason that you don't observe reflectivity dip. For optimal SPR observation thickness of the gold layer must be very close to an optimal value.

Valeriy Sterligov, No my layer was damaged, and I coated it again with optimum thickness.