Thank you very much for your answer. With a help, I found the code, so I share the code who can give me a curve like the curve on Excel, maybe you can understand me better :
# y ~ (-k*x+To)+x^-0.5
mod <- glm(y ~ pupil_timestamp_secondes + sqrt(pupil_timestamp_secondes), df, family="gaussian")
summary(mod)
plot(y~pupil_timestamp_secondes, df, type="l")
lines(df$pupil_timestamp_secondes, predict(mod), col = 'blue')
And you can see the result on the picture
Now, I would like do the same for this curve just below with this formula, but it's very more difficult 
Formula : A1*(1-exp(-t/To1))+A2*(1-exp(-t/To2))+D0
Picture :
Someone can help me ?
Yours sincerely,
GIOVANNANGELI Cyril