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Old 16-05-2017, 12:31 PM
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luka
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Join Date: Apr 2007
Location: Perth, Australia
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Thank you all for your replies.

Bojan, thank you for the links. This made quite a few things clearer.

Ken, I have used AOTF in the past, hence the idea to try using it as a part of an astronomical spectrometer.

Robin, I never thought of actually recording a full image. That may be the next step if I ever get this working, see my ideas below.

Some physics:
In AOTF a single wavelength is separated from a broadband light source by applying an acoustic (vibrational) wave at radio frequencies (RF) to a crystal. By varying the frequency of the RF, the wavelength of the filtered light can be varied.

When an acoustic wave is passed through an optical medium, the crystal lattice is alternately compressed and relaxed, i.e. a refractive index wave is generated that behaves like a sinusoidal grating. However, unlike a classical diffraction grating, only one specific wavelength of light is diffracted as the diffraction takes place over an extended volume, not just at a surface or plane, and that the diffraction pattern is moving in real time. An incident light beam of the right wavelength passing through this grating diffracts into several orders, with first order having the highest efficiency. Its angular position is linearly proportional to the acoustic frequency.

In very simple words, a single wavelength is separated from the incoming light and passed out at a particular angle α (about 6 degrees for this particular AOTF). The remainder of the incoming light is passed straight through.


So, my idea was to mount a detector (a photodiode initially or even a camera as done in the paper Robin linked) at this angle α, with adequate separation from the AOTF to ensure the remainder of the light going straight through is separated and blocked.The selected wavelength can be scanned by a computer and the intensity detected by the photodiode recorded (or images stored).
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