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# NSDD parameter definition

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Hi,
I'd like to use the NSDD to do the optimization in NSC mode.
But I am confuse about the parameters of NSDD for the Data definition.
What are the definition of flux (Data 0), flux/area (Data 1), and normalized flux (Data 3) in NSDD?
Is the flux unit definition (Data 0) same as the power(Lumens) of the light source?
What is the pixel value relation between the Detector and NSDD?
I tried to find the relation of pixel value between the Detector and NSDD.
But they are always different.
So is the same definition of pixel value between Detector and NSDD?

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Best answer by David.Nguyen 19 March 2024, 15:41

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Userlevel 7
+2

@Cheng-Mu Tsai

You can uses a Source Ray to aim at a Detector Rectangle with a single pixel to help you understand your issue. If I assign a Power(Watts) of 1.234W to a Source Ray and direct a single ray onto a single pixel of a Detector Rectangle, I can read the different NSDD Data values.

As you can see, for Data = 0, we get the flux and since all the power is transferred to the pixel we retrieve the 1.234W. For Data = 1, we divide the flux by the area of the pixel. In my case, the pixel is 0.2x0.2mm^2 or 0.04mm^2 or 0.0004cm^2. If you divide our power by this area we get 1.234 / 0.0004 = 3 085W/cm^2. For Data = 2, we divide the flux by the solid angle. In my case, there’s a single pixel to cover the -90 to 90 degree (default) of the detector, the solid angle is a half sphere. Since the whole sphere subtend 4pi radians, a half sphere is 2pi radians. If you divide our power b y this solid angle we get 1.234 / (2pi) = 0.196W/sr.

If you change the size of the pixels, either by changing the size of the whole detector, or by changing the pixel density, Data = 1 and 2 will change accordingly. Note that for Data = 2 the solid angle is deduced from the X/Y Angle Min/Max columns of the Detector (which are -90 to 90 deg by default, hence the half sphere).

Regarding Data = 3, this is an excerpt from the Help File:

A value of 3 is only supported when Pix# is a positiveinteger; in this case the returned flux for the pixel is normalized to the peak flux for all consecutive NSDD operands in the Merit Function Editor which refer to the same surface and detector. A value of 3 should generally be used only as a part of the NSC Bitmap Merit Function (see "NSC Bitmap Merit Function Tool").

For this one, I’m not exactly sure what it means and it seems to be specific to the Bitmap optimization.

Note also that the units used in the non-sequential component editor and in the Merit Function editor are specified in the Setup..System Explorer..Units..Source Unit and Analysis Unit.

Take care,

David

Hi, David,
I have another question about how to obtain the Merit Function (MF) value.
Could the MF get the value without using Analyze-->Ray Trace?
Does the MF have its ray tracing?
Is there any difference in the ray tracing between Analyze-->Ray Trace and MF?

Userlevel 7
+2

@Cheng-Mu Tsai

I’m not sure what you mean. In non-sequential mode, the Merit function needs a ray trace, however it doesn’t use Analyze..Ray Trace. Instead, it uses a special Merit function operand called NSTR for non-sequential ray trace. If you navigate the Help File to The Optimize Tab (non-sequential ui mode) » Automatic Optimization Group (optimize tab, non-sequential) » Merit Function Editor (optimize tab, non-sequential) » NSC Operands, you can find a more thorough description of how the non-sequential Merit function should be setup. This is an excerpt from this section of the Help File:

First, NSDD operands would be used to clear the data in the current detectors. Use NSDD with the detector number set to zero to clear all energy in all detectors. Usually a single NSDD at the top of the merit function is all that is needed. NSDD returns a value of zero and has no effect on the merit function value when used to clear detectors.

Second, NSTR operands are used to trace rays from NSC sources. NSTR i traces analysis rays from source i; NSTR 0 traces all analysis rays from all sources. Note the number of analysis rays on the NSC editor determines how many rays are traced and how long the evaluation of the NSTR operand will take. NSTR always returns a value of zero and has no effect on the merit function value. The NSTR operand supports options to split, scatter, and use polarization.

Third, a new group of NSDC, NSDD, NSDE, or NSDP operands are used to read out the detector data.

The parameters of the NSTR operands can be adjusted to mimic the Analyze..Ray Trace settings.