Re: Two Photon Microscope Low Signal Troubleshooting

Posted by Michael Giacomelli on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Two-Photon-Microscope-Low-Signal-Troubleshooting-tp7585738p7585746.html

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Hi Tim,

Those achromats are extremely dispersive.  That 30 mm is contributing 1100 fs^2 at 900 alone.  Are you really sure you need all of them?  Designing a low dispersion beam expander without using achromats is simple using only Thorlabs stock singles for example.  Usually dispersion is not a huge factor at 100 fs, but you still probably want to be very careful about using achromats except where absolutely necessary.  They're typically about 5-10x more dispersive then equivalent singlets, and its not too hard to find single parts in the Thor catalog that have more dispersion than typical objectives.

By the way, if you haven't checked it out, you can look up the dispersion of stock optical glasses here:

http://refractiveindex.info/?shelf=glass&book=SCHOTT-SF&page=N-SF6HT

Might be worth calculating how much pulse broadening you are getting from your optics.

Mike

On Thu, Sep 29, 2016 at 2:25 AM, Tim <[hidden email]> wrote:

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Thank you all for your responses.

@ Michael:

Our Ti-Sapphire has 100 fs pulses and is tuned to 900 nm. We use only protected silver mirrors and the following lenses from Thorlabs:

Initial Beam expansion with:

https://www.thorlabs.com/thorproduct.cfm?partnumber=AC254-030-B
https://www.thorlabs.com/thorproduct.cfm?partnumber=AC254-060-B

Scan lens: https://www.thorlabs.com/thorproduct.cfm?partnumber=LSM05-BB
Tube lens: https://www.thorlabs.com/thorproduct.cfm?partnumber=AC508-400-B

Do you think this would this constitute too many achromats?

@ Craig:

I am measuring power after objective using a power meter from Thorlabs (https://www.thorlabs.com/thorproduct.cfm?partnumber=S121C) held up against output end of the objective.

@ Andreas:

For the PS Speck beads on a slide, when you say that the image is not too far off the expected values do you mean the expected spatial resolution values of the system?