They are available cheaply. You can purchase a blu ray reader and hack it. The reason a ready packaged sensor is not available cheaply is simply because of economics and market size.

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amelius 3 days ago | parent [-]

I'm not convinced by the market/economics argument. Cheap and small ToF sensors exist, even though the market initially was also small.

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rowanG077 3 days ago | parent [-]

ToF sensors have huge applications. Initially ToF sensors also cost thousands of dollars. What huge applications do you see that should have driven the prices of over the counter integrable interferometers down? As I stated blu ray (and DVD, CD and laser disc before it) readers are tiny purpose build inferometers. And they are cheap.

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namibj 3 days ago | parent [-]

Since when are CD reader optics interferometers? The linked video shows a CW homodyne LIDAR used for measuring vibration frequency and counting vibration amplitude in fringes.

Last I looked CD readers used a 4-detector sensor's differential low-pass signals for closed-loop track-following so the rotation need not be optically centered. I also see no reason why optical disc readouts would need homodyne let alone heterodyne readout.

	▲	rowanG077 3 days ago \| parent [-]
		The pits and valleys are spaced λ/4 apart. The reason there is such a stark difference in intensity is because this λ/4 spacing causes interference at pit->valley and valley->pit transition points. Of course this not a standard interferometer but rather a purpose build one. Wikipedia says: > Interferometry is a technique which uses the interference of superimposed waves to extract information. And a blu ray player directly uses interference of superimposed waves to extract information. It squarely fits in the homodyne category.