Dear Shivaraj,

In my opinion it will be very hard to help without having the following information:

a) Which kind of sample (organic, inorganic or hybrid)?

b) The sample is liquid or solid?

c) Which are the laser characteristics?

d) Which average power was used to pump the sample?

Luis

Dear Luis M G Abegão,

Thank you for your answer, Its a organic sample, I have used the 0.01M concentrated solution for the experiment with the CW DPSS laser having 532 nm and 200 mW output power. Please let me know your answer.

Dear Shivaraj, how are you?

Maybe you could try CurveFit Expert 2.0[1]. It is easy to use with tons of options available. The trial is fully functional for 30 days and I was able to fit some really exotic curves with a nice statistical analysis at the end. The developer is, also, very kind and eager to help.

[1] - https://www.curveexpert.net/

What I would do in your situation:

> Repeat the measure decreasing the excitation power in about 20%, 40%, 60% and 80%, for example;

> Check if the Z-Scan signature will remain the same. If yes, probably it will be a real molecular/electronic behavior of the sample... Due to what? That's the question, I know... but to help you discussing that I will need more information...

Dear Luis M G Abegão,

I would really appreciate if you could give an equation to fit such curves, and if possible give an explanation for the origin of such signature, share whatever you are knowing with this regard. Thank you.   

Hello dear Henrique C. S. Junior,

I am doing great, nice to see you again, Hope you are doing well. Coming to your answer, Actually If I fit the curve with the equation it would directly give the 2 or 3 photon absorption coefficient from the Z-scan data using Origin or Matlab. Would it possible from the software you mentioned? If so Its a great one I can try. Thank you for your answer dear.

Hi, Shivaraj. It is great to see that you're busy with such interesting topics, my friend.

Give the software a try; even if the dozens of built-in functions are not exactly what you need you also have the option to create or tweak your functions (look at the advanced features).

Best of luck.

Dear Shivaraj,

It's not that i don't want to give you an equation to fit your data!

In my humble opinion, we use mathematical equations that will describe any real physical process... in the case of your Z-Scan signature, do you have any clue of which absorption process that is occurring? 

I'm sorry if my help was not enough.

Best regards,

Luis

Dear Luis M G Abegão, I am glad to see that we are working on the same field with similar molecules chalcones. We usually observe two photon absorption process for this type.

Cheers,

Indeed. But as you can see from your data, something happens when the sample is at the focus! 

At the focus the sample starts to decrease the absorption, that's why you see an increase of the transmittance!!! This is why from the beginning I recommended you to repeat the measure with a lower power, to check if this behavior is reproducible!

Is just a guess, but with the initial information that you gave me about the measurement parameters, i would bet that at the focus you have so much intensity that will cause the sample degradation, and this phenomenon it isn't a nonlinear optical effect. But like i told you, without any more information, is just a guess.

Dear Luis M G Abegão,

Thank you for sharing your thoughts on RG, I am still looking for the exact answers to my question.

You are very welcome! Good research!