Localization measure calculations for different microscope configurations. Panel a shows the variation of the 2D localization measure of *x*_{0}/*y*_{0} coordinate as a function of the expected number of detected photons for dMUM (×,○) and for a standard microscope (*). Here, the photon detection rate for the standard microscope is set to 10,000 photons/s. For dMUM we consider two scenarios, one where we have the same photon detection rate of 10000 photons/s for the top and bottom scopes (×) and the other where we have different photon detection rates of 20000 photons/s and 10000 photon/s for the top and bottom scopes, respectively (○). The latter scenario of unequal photon detection rates occurs in our experimental data (). The following are the numerical values of the other parameters that are used to generate the plots in this panel: *n*_{a} = 1.2, M = 63, λ = 555 nm, the pixel array size is 11 × 11, the pixel size is 12.9 μ*m* × 12.9 μ*m*, the background component is 300 photons/pixel/s, the mean and standard deviation of the readout noise of the imaging detector are 0 *e*^{-}/pixel and 8 e^{-}/pixel, respectively, the X-Y coordinate of the nanoprobe is assumed to coincide with the center of the pixel array, and the noise statistics is assumed to be the same for all pixels. The x-axis range denotes the expected number of detected photons in the bottom scope which corresponds to an acquisition time range of 0.01 s to 1 s.

Panel b shows the variation of the 3D localization measure of *z*_{0} as a function of the z-position for dMUM (○), for two plane MUM (×) and for a standard microscope (*). The vertical dotted lines indicate the position of the two × focal planes (0 μ*m* and 1.2 μ*m*) that are simultaneously imaged in dMUM/MUM. The photon detection rate and background component for the standard microscope are set to 10000 photons/s and 600 photons/pixel/s, respectively. In MUM, the photons collected by the objective are split by a 50:50 beam splitter. Hence for the two plane MUM setup, the photon detection rate and background component are set to 5000 photon/s per plane and 300 photons/pixel/s per plane, respectively. In dMUM, the photon detection rate and the background component are set to 10000 photons/s and 600 photons/pixel/s, respectively for both the top and bottom scopes. For all the microscope configurations, the exposure time is set to 0.5 s and all other numerical values are identical to those used in panel a.

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