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How to Model Thermal Effects using ZEMAX
- By Nam-Hyong Kim
- Published 21 July 2006
- Thermal Analysis
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Athermalizing a Design
The thermal modeling capability also allows athermalization of a design. In this cemented doublet design, we will minimize the RMS wavefront error difference between two temperatures; 20 and 100 degrees C.
Open the attached sample file "athermalization.zmx".
The first configuration is the system at reference temperature of 20 degrees C and the second at 100 degrees C. The Make Thermal tool was used to insert all the operands and thermal pickups in the Multi-Configuration Editor (MCE).
The OPD is clearly different between the two configurations.
We will athermalize this design using the glass substitution with Hammer optimization. For the resulting design, we want to keep the difference between the two glass TCEs to be less than 1 ppm, in order to limit the amount of mechanical stress at the cemented joint during thermal expansion and contraction. The effective focal length will be kept same as the original design; 100 mm.
Inspect the Merit Function Editor carefully.
The EFFL operand in line #2 of the Merit Function Editor maintains the effective focal length of 100 mm.
Lines 3 to 7 are used to constrain the TCE difference between glasses. We are not constraining the TCEs directly but rather the difference between the TCEs to be less than 1 ppm.
The rest of the Merit Function, below the DMSF operand, was constructed using the RMS wavefront error Default Merit Function tool.
The two glasses have "substitution" status in the MCE, indicated by the letter S next to them, so that when Hammered the glass type can change. The glasses are picked from the specified system glass catalogs.
Hammer optimization will be used to search for solutions that have similar form as the starting design. Remember that glass substitution requires Global Search or Hammer optimization.
Click Hammer optimization under Tools > Optimization > Hammer Optimization
Run the optimization for few minutes and then stop.
The optimized design will show almost identical OPD between the two configurations/temperatures.
You can also verify that the TCE difference between the two glasses is less than 1 ppm, by opening the glass catalog.
For frequently asked questions about thermal modeling, refer to the following knowledge base article.
Open the attached sample file "athermalization.zmx".
The first configuration is the system at reference temperature of 20 degrees C and the second at 100 degrees C. The Make Thermal tool was used to insert all the operands and thermal pickups in the Multi-Configuration Editor (MCE).
The OPD is clearly different between the two configurations.
We will athermalize this design using the glass substitution with Hammer optimization. For the resulting design, we want to keep the difference between the two glass TCEs to be less than 1 ppm, in order to limit the amount of mechanical stress at the cemented joint during thermal expansion and contraction. The effective focal length will be kept same as the original design; 100 mm.
Inspect the Merit Function Editor carefully.
The EFFL operand in line #2 of the Merit Function Editor maintains the effective focal length of 100 mm.
Lines 3 to 7 are used to constrain the TCE difference between glasses. We are not constraining the TCEs directly but rather the difference between the TCEs to be less than 1 ppm.
The rest of the Merit Function, below the DMSF operand, was constructed using the RMS wavefront error Default Merit Function tool.
The two glasses have "substitution" status in the MCE, indicated by the letter S next to them, so that when Hammered the glass type can change. The glasses are picked from the specified system glass catalogs.
Hammer optimization will be used to search for solutions that have similar form as the starting design. Remember that glass substitution requires Global Search or Hammer optimization.
Click Hammer optimization under Tools > Optimization > Hammer Optimization
Run the optimization for few minutes and then stop.
The optimized design will show almost identical OPD between the two configurations/temperatures.
You can also verify that the TCE difference between the two glasses is less than 1 ppm, by opening the glass catalog.
For frequently asked questions about thermal modeling, refer to the following knowledge base article.