I am trying to measure index of refraction of ZnO film using metricon prism coupler. It shows two reference peak while table referencing. But during measurement it says no mode found. Can anybody explain how to get coupling so that it can detect different modes. I also tried different silicon wafer to get coupling but couldn't get. Do you have any solution to this problem?
Hello, I used this prism coupler. To get coupling, you need to ensure that you selected the right prism (with higher refractive index than your film). Then you need to make sure that the contact between the prism and your thin film is correct (if your film is really rough, it may not couple nicely. you can adjust the pressure applied to your sample for instance to optimize the coupling. you also need to make sure that the laser spot is indeed in the coupling spot (where sample and prism are in contact), you can adjust the position with the two micrometer screws. To finish, you need to make sure your thickness is big enough to support coupling of a few modes. I hope this helps,
Sebastien
Sebastien is exactly right. ZnO should work well for you, as I had good luck with similar measurements in graduate school using this tool and similar films. I'll add a couple of comments with regards to proper operation of the tool:
1. Make sure the surfaces are all clean. Dirt and dust can prevent the necessary intimate contact between the prism and sample.
2. You may be having trouble with the Si samples since the standard Metricon configuration uses a red HeNe laser. Your Si wafers will absorb this wavelength strongly. That said, you can get very good coupling into the SiO2 layer on Si provided it is thick enough. I would recommend using something like this as a standard sample to verify operation.
Correction: you won't get good waveguiding effect with the SiO2/Si sample I mentioned here due to the refractive index requirements John posted below.
3. If you are having trouble using the tool at all, contact Metricon. They are very helpful and can provide guidance with alignment and tool operation.
I agree with the above.
First make sure your prism has high enough. It should be a rutile (TiO2) prism. Index is around 2.4.
You don't say what the ZnO is on. If it is on silicon you won't form a waveguide. if it is on sapphire you should form a nice waveguide if the film is thick enough. Even if the film is thin it is likely you will form one mode (unless it is really really thin.).
The instrument is sensitive to alignment. If you have a reference sample that you know has several nice modes, verify that you can see them first, then your instrument will be close to alignment.
Adjusting the pressure of the plunger can help too, Different materials have different optimum pressures.
When making adjustments you have to watch the signal very closely very minor adjustments can make big changes in the mode coupling.
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