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Registered Member #3215
Joined: Sun Sept 19 2010, 08:42PM
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Posts: 780
still 1 to 2 nanometers is achievable with such a setup
a standard michelson is way overkill to just view some lines with a width of 1 to 5 nanometer
what makes experimenting with interferometers cool is that you don't need much material
the most dificult part involves getting the emited spectrum to be collimated enough to make to the detector
I have all the parts necessary to construct one but I have no time for this yet... CaF2 beamsplitter, pin photodiode with biasing circuitry, piezzo, and even a dsp to perform real time FFT, but a job which take me too much energy
Registered Member #3792
Joined: Sun Mar 27 2011, 06:07PM
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Posts: 136
@Shrad: I know about "Sam's Laser Faq" and i've already read it many times (from there i learned about spectroscopes and the diffraction grating spectroscope). Fabri - Perot spectroscopes IS another solution to the problem, but as i see from prices at Ebay (45+$ for 1pc 535nm - no even at the wavelenght i want) the mirrors are definetely "do not touch" .
I managed to take apart (i mean, destroy) 2 LCD monitors and i got 2 sheets that behave like diffraction gratings (not sure if they are designed like this). If they are usable anyway, i'll use them to make my scanning spectroscope.
Registered Member #3215
Joined: Sun Sept 19 2010, 08:42PM
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Posts: 780
you might consider buying helium neon mirrors or even a dead tube with mirrors that you would cut off the tube, as they are 632.5nm and the range should extend +/- 10 nanometers away
that would be nice for a fabry-perot, as it has been done already to visualise a 650nm laser diode spectrum with nice precision (nanometer range)
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
If you look here you can see what's described as a large displacement piezo actuator. It has a range of about 60 microns. A typical piezo speaker gives something like a tenth of that. That means the optical path length difference you could get is roughly 15 microns The wavelength of visible light is of the order of half a micron so you would get a set of about 30 troughs and peaks if you used a normal piezo speaker to drive the mirror of a Michelson interferometer. The resolution would be about 1 in 30 or roughly 17 nm at 500 mn.
If you used a moving coil loudspeaker with a thorw of a milimeter or so you might be in business. As an exercise you might want to see how slowly you would need to scan the mirror in order to be able to capture the interferogram using an ordinary sound card.
Registered Member #3215
Joined: Sun Sept 19 2010, 08:42PM
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Posts: 780
hi BC
my first idea here was overdriving the usual piezzo speaker with a 100Vpp or so signal, in order to boost its displacement
this is in fact a crude setup which "could" work and is one of the best approaches in order to keep colinearity at its best for our means
a moving coil tweeter or so would tend to drift in the three dimensions and add noise to the measure
the ideal would be a linear motor moved by a sinusoidal signal, but it would be harder to maintain good electrode flatness than to find the good piezzo
Registered Member #3215
Joined: Sun Sept 19 2010, 08:42PM
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Posts: 780
probably not much, but it should still provide acceptable motion
the thorlabs piezzo I saw are not that different and are driven with 300V too
I know the material is certainly not the same, but piezzo layer thickness was approximately the same, and the only thing is it was a pierced piezzo to allow for an OC to be mounted on it
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Homebrew CD spectroscope?!?
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