Variator allows you to study how the design spectral characteristics change with variations of layer thicknesses and layer refractive indices. Variator adjusts the parameters of the reverseengineering model, and modified parameters are immediately shown in all other OptiRE windows. Using sliders, [] and [+] buttons, or numerical controls you can adjust the parameters of the design, substrate and incident medium and almost instantly see the effect of such a change. The changes are applied to all other OptiRE windows, therefore you can study multiple effects at once. In the case of dispersive materials the variations are considered as offsets of the refractive index or extinction coefficient. In other words, a constant value controlled by the Variator is added to the refractive index spectral dependence. Revert Back button allows you to restore the initial parameters. 

Example. Comparison of the experimental and nominal transmittance data related to a 43layer quarterwave mirror reveal errors in layer thicknesses and/or inaccuracies in refractive indices: Discrepancy function value (bottom left) \(DF=26.36\). 
After application of the "Systematic errors" model, fitting of experimental data by model data is improved:
Discrepancy function value is significantly reduced \(DF=13.20\). There are still deviations 
Varying refractive indices it is possible to find that the discrepancy function can be reduced by decreasing low refractive index: 
Decreasing low refractive index leads to better fitting between experimental and model data: Discrepancy function value is now 11.43. 
The most likely, you have a problem with USB bus controller at your computer. It may suspend communications with the hardware key in some quite rare cases. For example, we had issues with USB3 controllers at some modern computers. If it is your case, it is quite easy to fix: just try other USB ports! It is better to use not USB3, but classical USB2 ports. In cases if your computer has only USB3 connections, you can use any cheap USB hub that will automatically downgrade USB3 to USB2.
Please, try the following:
1) If you are using USB3 port for the dongle, try to switch to USB2. If you do not have USB2 port at your computer, you can use any nonexpensive USB2 hub attached to USB3 port.
2) In some cases the installation of latest USB3 drivers from the USB3 controller manufacturer helped.
3) It is also worthwhile to install all Windows updates at your computer, since OptiLayer programs use the standard Windows HIDinterface to communicate with the dongle.
4) If above steps do not help, we can reprogram the key to a different mode, in which it will not rely on HID problematic interfaces. We can reprogram the key remotely.
New evolutionary postproduction characterization algorithm significantly improves the search for the best fit in the case of multiscan data. The new option is available in OptiRE through: Solve > Random Errors Solve > QuasiRandom Errors Solve > QuasiRandom Inhomogeneities Solve > Random Errors (scientific mode) Solve > QuasiRandom Errors (scientific mode) 

In comparison with the previous versions, there is a choice between two algorithms in "Method" field: Simple Refinement and Triangular algorithm. In the case of "Simple Refinement", discrepancy function \(DF\) is minimized with respect to all "Active" layer thicknesses: \[ DF^2=\frac{1}{m}\sum\limits_{k=1}^m\frac 1L\sum\limits_{j=1}^L\left[\frac{T(d_1,...,d_m;\lambda_j)\hat{T}^{(k)}(\lambda_j)}{\Delta T_j}\right]^2, \] where \(m\) is the number of design layers, \(\{\lambda_j\}, \; j=1,...,L\) is the wavelength grid, \(\hat{T}^{(k)}(\lambda_j)\) transmittance scan recorded after the deposition of \(k\)th layer, \(\Delta T_j\) are measurement tolerances. 

In the case of "Triangular algorithm", partial discrepancy functions \(DF(i)\) are minimized with respect to all "Active" layer thicknesses among \(d_1,...,d_i\): \[ DF^2(i)=\frac{1}{i}\sum\limits_{k=1}^i\frac 1L\sum\limits_{j=1}^L\left[\frac{T(d_1,...,d_i;\lambda_j)\hat{T}^{(k)}(\lambda_j)}{\Delta T_j}\right]^2,\] where \(m\) is the number of design layers, \(\{\lambda_j\}, \; j=1,...,L\) is the wavelength grid, \(\hat{T}^{(k)}(\lambda_j)\) transmittance scan recorded after the deposition of \(k\)th layer, \(\Delta T_j\) are measurement tolerances. Important: At each \(i\)step, starting approximations of actual layer thicknesses are taken from the result of the \((i1)\)step. This reduces the instability in determination of actual layer thicknesses significantly.


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