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Natural Science Forum / Physics / Optics / July 2008Need help with wavefront distortions on filter surfaces
Hello, I have a question and I thought someone in this group might have some experience with this. I am trying to setup a confocal fluorescence microscope and would like to use a dichroic mirror to separate the collected fluorescent signal into two arms. The transmission arm works OK, however, I don't get a good focusing on the reflection arm. It turned out that the dichroic is distorting the wavefronts in reflection so much that I can't efficiently focus it through the pinhole. The filter company says the coating on the filter puts stress on the filter and causes it to bend slightly. I just have the bare filter without any mount.It's 1mm thick.I tried mounting on metal fixtures and using rings, gluing the filter to aluminum filter holders, but my every attempt failed and did not improve focusing. Do you have any suggestions for mounting the filter so that I make sure that the filter surface if flat? Should I purchase a thicker dichroic? Thanks, Mehmet Hi Mehmet, who is the manufacturer of this filter? normal dichroics are always thick like that and they are held with springs in position. So, are you sure your problem is related to the dichroic? Btw, do you want to use lasers or optical grids? yours, heini Thanks Heini, The company I got the filter from is Semrock.(Part #: FF560- Di01-25x36) Actually it's not really thick, only 1.1 mm.(dimensions: 25X36X1.1 mm) I'm sure that the problem is related to the dichroic, because when I have a flat mirror instead of a dichroic, I get the expected focusing and transmission through a pinhole. I'd like to use it in a fluorescence collection scheme. Mehmet On Jul 10, 11:00 am, heini <buerg...@physiologie.uni-heidelberg.de> wrote: > Hi Mehmet, > who is the manufacturer of this filter? [quoted text clipped - 4 lines] > > yours, heini Hi Mehmet, Did you mount the right side of the dichroic towards the light source? You might get double reflections from the surface and the coating, if it is on the distant side. Maybe you also reduce the angle of reflection, so that only absolute reflection from the coating becomes likely. This dichroic is not listed as suitable for lasers, so this could be your broblem also.... yours, heini Hi Heini, I'm mounting the correct side. Actually, I talked to the company and they say that the hard coating is introducing stress and bending the filter slightly.So, it turned out that this filter is not suitable for my application.I'm looking for a different filter with "soft" coating. Thanks for your suggestions Mehmet On Jul 13, 1:47 pm, heini <buerg...@physiologie.uni-heidelberg.de> wrote: > Hi Mehmet, > [quoted text clipped - 8 lines] > > yours, heini snip snip snip Where exactly is your filter? How thick is it? What's the NA of your objective? Hello, The filter is after a 50/50 beam splitter cube which is after a 1.4 NA objective. The excitation comes through the beam splitter to the objective and the fluorescence is collected by the objective, passes through the cube, then a notch filter for laser rejection and to the dichroic. It's 1 mm thick. So, it turned out that due to the hard coating putting stress on the filter, this filter is not suitable for my application. Thanks for your suggestions > snip snip snip > > Where exactly is your filter? > How thick is it? > What's the NA of your objective? |
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