Dear Prof. Zbigniew Motyka

I appreciate all of your help. Thank you for your presentation.

Your explanation is so good. However, there is another explanation of the Professor Qusay M Ali Hassan as follows:” A pump laser beam with Gaussian intensity distribution is able to stimulate a phase shift, ∆ϕ, in the shape of bell in a nonlinear medium in the transverse direction with respect to the direction of the beam as the one shown in Fig. 1.

On a Gaussian curve, for any point, ρ1, there exists another point, ρ2, having the same slope and wave-vector, their radiation can interfere. Destructive and constructive interferences occurs when the change in phase from the point ρ1, ∆ϕ(ρ1), and the one from the point ρ2, ∆ϕ(ρ2), when the relation ∆ϕ(ρ1)- ∆ϕ(ρ2)= mπ (where m is a constant being odd or even integer for destructive and constructive interferences respectively) is verified.”

https://www.researchgate.net/publication/319874037_EVOLUTION_OF_FAR-FIELD_DIFFRACTION_PATTERNS_AND_NONLINEAR_OPTICAL_PROPERTIES_OF_SAE_70_OIL?feedback/

I think the diffraction effect does not affect the radius measurement because diffraction only redistributes energy but does not result in energy loss.

Article EVOLUTION OF FAR-FIELD DIFFRACTION PATTERNS AND NONLINEAR OP...

Dear Prof. Zbigniew Motyka

I appreciate all of your help. Thank you for your presentation.

Your explanation is so good. However, there is another explanation of the Professor Qusay M Ali Hassan as follows:” A pump laser beam with Gaussian intensity distribution is able to stimulate a phase shift, ∆ϕ, in the shape of bell in a nonlinear medium in the transverse direction with respect to the direction of the beam as the one shown in Fig. 1.

On a Gaussian curve, for any point, ρ1, there exists another point, ρ2, having the same slope and wave-vector, their radiation can interfere. Destructive and constructive interferences occurs when the change in phase from the point ρ1, ∆ϕ(ρ1), and the one from the point ρ2, ∆ϕ(ρ2), when the relation ∆ϕ(ρ1)- ∆ϕ(ρ2)= mπ (where m is a constant being odd or even integer for destructive and constructive interferences respectively) is verified.”

https://www.researchgate.net/publication/319874037_EVOLUTION_OF_FAR-FIELD_DIFFRACTION_PATTERNS_AND_NONLINEAR_OPTICAL_PROPERTIES_OF_SAE_70_OIL?feedback/

I think the diffraction effect does not affect the radius measurement because diffraction only redistributes energy but does not result in energy loss.

Article EVOLUTION OF FAR-FIELD DIFFRACTION PATTERNS AND NONLINEAR OP...

Dear Lam Thanh Nguyen,

I'm not an expert on this. Probably the below article gives you some background info on this ring pattern occurence:

Li C., Zhou P. (1986) Ring Pattern of Laser-Induced Thermal Self-Defocusing. In: Gibbs H.M., Mandel P., Peyghambarian N., Smith S.D. (eds) Optical Bistability III. Springer Proceedings in Physics, vol 8. Springer, Berlin, Heidelberg

Hello

At first you could experimentally distinguish, is such effect linear or not? To do so, you could observe evolution of the ring structure if you will decrease incident laser intensity by a filter. If the size of the rings will changed, you really have some non-linear effect, otherwise it has nothing with non-linear optics.

As for me, this is possible that you have interference of scattered by your film light with its reflection by rear substrate surface. In such a case you can see, how ring structure will be changed if you rotate your film. For such mechanism ring structure should became elliptical one after rotation.

Dear Prof.Valeriy Sterligov,

Thank you for telling me how to distinguish the nonlinear optical and linear effects. How to explain your appearance of Rings is very good. But my film have a large thickness (greater than 0.3 mm) so the reflective interference effect may not contribute much.

Reminds me of Becke Lines/Halos . As you move the objective lens away from the focused image, do the lines move? If so, they probably move into the medium of higher Refractivity (n-1). That situation is central to my data-collection process when microscopically studying RIs (RI=n=c/v) of whole-rock-powder fragments in immersion liquids.

I hope this helps, Lam Thanh Nguyen.

-Steve- 

Thank you for your answer, Prof.Stephen Arthur Langford.

I agree with Dr. Zbigniew Motyka.

Thanks, this topic is out of my field .

Dear Lam Thanh Nguyen,

So, what are the results of experiments I have proposed? By the way, you could invert change of incident intensity: at first illminate sample by reduced by filter laser light, than remove filter and observe evolution of the rings.

What picture do you have with oblique light incidence?

If you have thermal mechanism, you could observe quick modification of the picture. For such observation you can without laser light put a photodetector into area where rings usually appear and observe its signal when you switch on laser, For thermal mechanism you should observe several light oscillations.

When you have such results, discussion about possible mechanism can be more productive

Thank you very much Prof. Valeriy Sterligov. In next week, I will do some experiments you have proposed.

The rings produced for the nonlinear media is a consequence of the self-phase modulation effect and the aberration caused by the photo-induced lens in the sample. The spot size at the end of the sample (or in the far field) depends on the instensity, and of course also the number of rings. You can read the following papers about it:

1. W. R. Callen, B. G. Huth, and R. H. Pantell, “Optical patterns of thermally self-defocused light,” Appl. Phys.Lett. 11(3), 103–105 (1967).

2. F. W. Dabby, T. K. Gustafson, J. R. Whinnery, and Y. Kohanzadeh, “Thermally self-induced phase modulationof laser beam,” Appl. Phys. Lett. 16(9), 362–365 (1970).

3. S. D. Durbin, S. M. Arakelian, and Y. R. Shen, “Laser-induced diffraction rings from a nematic-liquid-crystalfilm,” Opt. Lett. 6(9), 411–413 (1981).

4. E. Santamato, and Y. R. Shen, “Field-curvature effect on the diffraction ring pattern of a laser beam dressed by

spatial self-phase modulation in a nematic film,” Opt. Lett. 9(12), 564–566 (1984).

5. R. G. Harrison, L. Dambly, D. Yu, and W. Lu, “A new self-diffraction pattern formation in defocusing liquidmedia,” Opt. Commun. 139(1-3), 69–72 (1997).

Thank you very much, Prof. Derra Mourad and Prof. Isam Issa Omran !

That's a great answer, Dr.A. Balbuena Ortega.

Dear Lam Thanh Nguyen,

By this time, your main question have received many replies. I wish to call your attention to the fact that the number of rings induced in your media behaves linearly with the power of the excitation laser beam and, interestingly, from the slope of the straight line we have a facile method to measure the emission quantum efficiency of the studied material. If you wish to explore the quantum yield of your materials, you may give a look in the following references:

1. Pilla, V., Munin, E., & Gesualdi, M. R. (2009). Measurement of the thermo-optic coefficient in liquids by laser-induced conical diffraction and thermal lens techniques. Journal of Optics A: Pure and Applied Optics, 11(10), 105201

2. Iwazaki, A. N., Pilla, V., Dias, V. M., Munin, E., & Andrade, A. A. (2011). Self-induced phase modulation for thermo-optical characterization of annatto extracted using different solvents. Applied Spectroscopy, 65(12), 1393-1397.

Article Measurement of the thermo-optic coefficient in liquids by la...

I should have added:

Langford, S. A., and J. K. Nakagawa, 1978. A general equation for estimating refractive indices of Cargille liquids at various temperatures and wavelengths. The Microscope, v. 26, no. 4, pp. 167-170.

Sorry, no free digitized copy available; but:

1. http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2818.1991.tb03184.x/abstract

2. http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2818.1991.tb03184.x/pdf

For which, due to robber-baron outrages, I receive not one whit. :-(

-Steve-

Thank you very much for your answers, Prof.Egberto Munin and Prof.Stephen Arthur Langford.