Laser scanner

  • 11 February 2021
  • 4 replies
  • 155 views
R

Hello,


I am doing some trials with a laser scanning setup. These are just preliminary, I still need to insert the right collimating lens, focusing lens and beam expander later. But is was trying to position the 'moving lens' to get the smalles spot size (image at focus), but from the lay outs, it seems the focus is a bit in front of the image plane. Is there another way to do this optimization? Or is this the right result?


Edit: My bad, this is probably just the spherical abberation that is out of whack.


Also, how can I best model the input laser beam? It will be a singlemode fiber with a 25µm core. Now I did it via object space NA number.

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S
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Hi Rick


Your merit function seems properly set up. You are targeting the smallest RMS spot radius. You actually don't need all the boundary operands as only the thickness of 7 is targeted so you could just clear this a bit.


What you could do to make a 1st step is click on Optimize...Quick Adjust:



About the single mode fiber, I think this is correct to use the NA number. I would change the apodization. Usually the NA is given for a gaussian apodization of 1. What does the term apodization mean?. We usually set a higher NA so that the marginal ray contains less energy.


You might also have a look at that article: Should I use POP or Single Mode Coupling for my single-mode fiber coupling system?


Let us know if you have any further questions.


Sandrine

Sandrine Auriol
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In your syste, an Object Space NA of 0.27 with an Apodization Factor of 4 is equal to an Object Space NA of 0.14 with an Apodization Factor of 1.


An Apodization Factor of 4 means that the intensity of the marginal ray is 1/e^2G = 0.03%.

Sandrine Auriol
R

Sandrine,


Thank you for the helpful information.


I do have another question on the topic of the laser scanner. I want to optimize the position of the moving lens, so the spot is in focus over a broad field. At the moment, I added in my file some configurations via the multi-configuration editor. I don't want to optimize for all, but for each configuration on it's own. How can I do that?

S
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Userlevel 6
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Hi Rick


I have only one configuration in the file you sent. But I probably don't need the file.


When you build your merit function in a multi-configuration system, the default merit function will contain CONF operands. It means that all the operands below a CONF operand will only calculate for a specific configuration. 


For example, if you open the sample file '\Zemax\Samples\Sequential\Zoom systems\Scanning mirror.zmx', I can create a default merit function:



The Merit Function will contain CONF operands. Each spot of each configuration will be optimized separately:



If the variables are in the editor, then the software will try to find a compromise between each configuration. 


If the variables are in the multi-configuration editor, then the software will find the best value in each configuration.


Let me know if that helps and do not hesitate if you have other questions.


Sandrine

Sandrine Auriol

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