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An imaginary new HD video system (called Purple - Ray) has been launched and the laser it uses to read the disks has a wavelength of 400 nm (4 * 10 ^ -9 m). The lens used has a numerical appature of 1.5. What is the minimum size the markings on the disk (that represent the data) could have and still be resolved by the laser?

Note: numerical aperture is a dimensionless quantity, hence the lack of a unit.

Steven.

its not .002 meters is it?
sorry, I don't have much experience with optics..

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Hi Josh. In fact, I didn't even state the question right. 400 nm is of course 4 * 10 -7 m. Evsn so, the answer is still far smaller, being 600 nm (6 * 10 -7 m). The resolution is given by laser wavelength / numerical aperture. This is actually somthing that came up during my final year project at uni, 'cause I was building a two photon microscope. Anyway, do you have another question?

Steven.

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