Technical Issues - FilmStar News 2017

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January 16    Photopic Response Curves

A user requested an automatic way to plot photopic transmittance as a function of wavelength. This is readily accomplished manually in Excel, but tedious. Our solution combines the FilmStar Workbook, FilmStar BASIC and the FSPlot Module. It works as well for photopic reflectance.

Download, unzip and copy (assuming default directories)

PhotopicPlot.bas  >>>  C:\Winfilm\Basic32
Photopic.vts  >>>  C:\Winfilm\Workbook
Highpass_CIE_1nm.faw  >>>  C:\Winfilm\Designs

Referring to Setup...Parameters, we utilize Transmittance vs. Wavelength Range. This allows us to set graph range 350-800 even though CIE calculations are 380-780. The example uses CIE 1931 values (1 nm interval) and is easily modified. Users requiring help with FilmStar BASIC or Workbook should contact FTG Software.

January 17    Auto-Optimize in Workbook

The Workbook is useful for designs that cannot be defined by usual targets. Examples: beamsplitter, color with and without ITO layer.

A user asked about automating Workbook optimization. This raises issues as BASIC can be embedded in the Workbook (BasRun, BasExec, BasChain) and Workbook functions can also be triggered from Main Menu BASIC <F6>.

BASIC functions WbOptimize and WbExecute do not allow BASIC embedded in Workbook macros. Attempting to do so triggers the BASIC Conflict error message.

In this particular case the user was hoping to utilize BASIC GetCieData. Our suggested workaround is simply to perform CIE calculations in the Workbook itself. This is slower and a bit of work, but quite straightforward.

Here's a simple illustrative example. Download; unzip and copy as follows (assuming default directories).

AutoWbOpti.bas  >>>  C:\Winfilm\Basic32
BBAR_AutoOpti.vts  >>>  C:\Winfilm\Workbook
BBAR*.faw  >>>  C:\Winfilm\Designs

You should get a similar graph after clicking <Ctrl+Z> for Zoom Mode. Changing the Workbook Macro from CALCULATE; ($D$1) to something like BasExec x=5; gives the BASIC Conflict message. The Workbook may be the most challenging module in FilmStar; users are invited to contact FTG Software for an online run-through via Glance Networks.

January 20    Zero Layers

An Overflow error can occur in DESIGN when thick absorbing films are evaluated at short wavelengths. These conditions force calculations beyond numeric limits.

DESIGN's Set Zero Layers effectively 'removes' layers without affecting the film design. This capability has been updated.

The algorithm relies on the fact that light does not penetrate the entire absorbing stack. Users should verify that removal of layers below a given wavelength has no effect on the reflectance spectrum.

As illustrated for an IR reflector evaluated from 200 nm to 20 Ám, we compare Zero Layers with Ignore Layers. (Ignore Layers is effectively the same as actual deletion, but more convenient). Designs containing parentheses are not supported. Click here to download the design example.

As shown above, there is a great difference in the spectra when 14 layers (including a massive 1 mm Si substrate) are deleted. But as Zoom Mode shows below, the spectrum at short wavelengths is not affected by the removal, thus verifying the algorithm.

Note how spectra overlap at short wavelengths, verifying
that UV/Vis/NIR light does not penetrate the structure.

Previous versions failed when Side 2 Compensation <> FWD ignore Side 2. That is still the case, but now Zero Layers automatically changes Side 2 Compensation if necessary, thereby eliminating error messages. Substrates should be treated as massive layers; designs with parentheses are not supported. Most users will never require Zero Layers, but those that do consider it to be a very important capability.

February 17    MONITOR Turning Point Adjustment

In some cases it is useful for MONITOR to approximate a near-exact QWOT by a full QWOT. This is accomplished with new BASIC Sub TurnPtAdjust. By default only the last layer on a chip is modified, but that option can be changed as shown below. The magenta color indicates modified layers.


TurnPtAdjust can be assigned to a macro button or automated by specifying it as a Calculation Macro (new) in Tools.. Macro Commands. The simplest macro is BasExec TurnPtAdjust. New BASIC Sub WsSetNum and Sub WsSetText offer further customization. The new functions are described in an updated help file.

By default, near-exact (depends on Cutoff Precision) QWOTs (Cutoff Ratio 0) no longer utilize turning points from previous layers. This can be changed, restoring original behavior, by checking Include previous TPs in near-QWOT swings in Setup.. Parameters. This capability is independent of BASIC Sub TurnPtAdjust.

February 23    MEASURE (Scantraq) Saving Two File Types

A user requested the ability to automatically save spectra in two formats. Click here to download BASIC code that does the job. Copy to your C:\Winfilm\Basic32 directory. In order to automatically save scans, enter the following in the Setup.. Scan Macros editor. Substitute Scantraq for Winfilm as required.

When there is no Scan Macros editor, as is the case for instruments such as Ocean Optics or FTIR, the code is specified at the end of the Sample Scan macro in the Control Macros dialog (part of the Setup.. Scan Method sequence).

Sub Main
    BasChain "C:\Winfilm\Basic32\Save_CSV&SPC.bas"
End Sub

You can also enter the following in Tools.. Macro Commands, in this case assigning to Macro Button 4.

March 6    Identifying bad data

Measuring %R/%T for a fused silica substrate seems easy, but maybe not! A user, intending to deduce n&k vs. wavelength, sent us data collected with a PerkinElmer Lambda 1050 with a goniometer accessory and UV Winlab software. As this is a well-known material, expected values are easy to  calculate. Comparing theory (SiO2 Sopra.itw) and measurements in FSPlot's View.. Zoom Mode <Ctrl+Z>, we note problems from 300-400 and 800-900 nm. There is no better way to identify bad data. Such comparison will be difficult (impossible??) in UV Winlab.


Transmittance results were disappointedly similar. Was integration time (scan speed) optimal? Was the tungsten lamp aligned properly, stabilized, and not approaching burnout? Operator error? 0% baseline compensation? Would FilmStar smoothing help? This includes the ability to smooth before normalization, thereby minimizing noise. That would not, however, improve 300-400 and 800-900 nm regions. Reasonable n&k results from 400-800 nm were deduced with INDEX Calculate n,k Algorithm #4.

Failure to examine data before hitting <Calculate> often leads to wasted hours, frustration, and possible crashes. If in doubt, send us your data (in one Excel file please). We note, however, that the accuracy required for n&k analysis typically exceeds that required for QA pass/fail specifications. When plotted on a 0-100% scale the above spectra give a different impression.

March 20    Preserving design format

A user wants to enter designs in a structured format, as in...

(1H 1L)2 6H (1L 1H)2 1L
(1H 1L)2 4H (1L 1H)2 1L
(1H 1L)2 6H (1L 1H)2 1L

His problem is that the Groups editor modifies the format, resulting in something like this...

(1H 1L)2 6H (1L 1H)2 1L (1H 1L)2 4H (1L 1H)2
1L (1H 1L)2 6H(1L 1H)2 1L 

Observe how the Interactor supports QWOT designs as shown at the right. Most importantly, set Layer Change = QWOT. This is our recommended approach for evaluating QWOT-based designs.

Returning to the original issue, there are several possibilities: 1. Type a design in Notepad, copy and paste into the editor. The same can be accomplished with Microsoft Word or Excel via DDE (dynamic data exchange). Enable DDE by checking Show Import / Export commands in File.. Configuration.. Misc. A new feature is the addition of hotkey <F6> to DDE Import.

A single Word or Excel file can contain many designs, distinguished by Bookmark (Word) or Name (Excel). Refer to updated (<F1>) Help instructions: Design Menu.. Groups Design Editor.. Edit...Import. DESIGN 2.61.3980 adds Import hotkey <F6>. Please contact FTG Software if instructions are not clear.

Interactor QWOT editor

Since solutions based on Notepad or Word/Excel may be inconvenient, 2.61.3980 adds a new option to the Groups editor: Edit...Lock Design. In this mode designs can be edited and evaluated but are locked against reprocessing, thus appearing as originally typed when saved and reopened. Optimization and other features are disabled in this mode. The status bar adds  Design Lock  when activated.

May 8    Scan or Calculate with the Collector

Content moved to Saving Multiple Spectra

June 28   Triangle Graph, etc.

A FilmStar user attending Ron Willey's optical coating course indicated that he found RTA Triangle graphs useful. Ron then generously supplied his Excel triangle chart code and asked whether we could embed it within FilmStar DESIGN, thereby simplifying calculations. Note: triangle graphs are described in Practical Design of Optical Thin Films.

This has been accomplished as shown below. Since the graph is implemented in the Interactor, it's very easy to manipulate layers and visualize changes. In addition, all Interactor graphs plotted as a function of layer thickness newly utilize line colors assigned to materials and display designs in colors as shown in the Layer column Clicking Line Colors opens the following:

As shown at the bottom, color-coded lines are useful in polar diagrams (Admittance and Reflectance Amplitude). Previously, even and odd layers were in different colors, thus confusing when more than two materials.

As the black background does not print well, the Color Mode pull-down offers white background options.

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