The plates of a Fabry-Perot interferometer have an intensity reflectance of R =
ID: 1377710 • Letter: T
Question
The plates of a Fabry-Perot interferometer have an intensity reflectance of R = 0.85 and the device is used to examine the Ha line of Hydrogen (656.28 1 nm). (i) Calculate the resolution R required to separate the components of the Ha line, which is a ?doublet? with a wavelength separation of delta lambda = 0.0136 nm. (ii) Assuming the incident angle is small, calculate the minimum spacing of the Fabry-Perot plates to achieve this resolution. (iii) Find the free spectral range for this interferometer.Explanation / Answer
i)
The resolution of an optical instrument is defined by the bandwidth of a spectral line, i. e. the broadening imposed on the line by the instrument. We have to calculate what spectral linewidth is equivalent to this instrumental linewidth. As hitherto, we assume normal incidence.
At the maxima, the phase difference