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## curvefit of the reflectivity with Lev-Mar

Hello,

I am a beginner with Labview and I need your help, I recuper the data of the reflectivity from the spectrometer (3648 points) and I am going to make the fitting to extract information about the thickness and refractive indices n and k (k in the general case it will be zero because the materials used are oxides and I work in the visible range.

I want to use the model of Lev-Mar but I have the problem with the model, i have used the formula node to write the eqaution of the reflectivity, and currently I am block.

Data.txt
column1 = Lambda
column 2 : Reflectivity

the substrate is Pyrex  ; n= 1,47
the thin film is Ti-Nb, the index is like that of the titane(Antase) : ñ = 2,561 + i2,488

Thank you very much.

Nb: i know my english is so bad 🙂

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## Re: curvefit of the reflectivity with Lev-Mar

It is difficult to be sure from an image of a block diagram but it looks like your model VI multiplies X by an empty array. The result will be an empty array which then means that the For loop executes zero times and the output f(X,a) will also be an empty array.

Fix: The array constant should have thesame number of elements as X. If all the elements will be 1E-9, just use a scalar constant. The Multiply function will accept an array on one input and a scalar on the other and produce an output array with each element of the input array multiplied by the scalar.

Depending on how many iterations it may take to do the fitting, you may find that replacing the  formula node with standard LabVIEW functions is faster.

Lynn

Message 2 of 4
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## Re: curvefit of the reflectivity with Lev-Mar

Thank you very much Lynn,

I did what you told me to do and it works a better,

I would like to know if you can help me, I have the values of the reflectivity R as a function of the wavelength (lambda) but the indices " nand " k " are also a function of lambda.
R = (n,k,d,lambda )   and  the dispersion equation n(lambda) and k(lambda)

With the curvefit Lev-Mar is possible to define these parameter ? if you have ideas that will be cool

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## Re: curvefit of the reflectivity with Lev-Mar

You may need to transform the equations.  Please post your VI with some typical data saved as default. Also, please provide the equations.

Lynn

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