Superresolution effect on a microstep phase image in a laser heterodyne microscope

Abstract

The possibility of achieving superresolution on a microstep phase image in a laser scanning differential heterodyne microscope is studied both heoretically and experimentally. The superresolution is estimated as the width ratio for the amplitude and phase components of the microscope response measured at half the height of the corresponding parts of the response. It is shown theoretically that superresolution greatly exceeding unity can be achieved for an object in the form of a phase microstep introducing a phase shift equal to π. Superresolution of ∼2 is experimentally obtained for certified test micro-objects. A possibility of tuning a test sample into the superresolution regime by shifting a point photodetector in the microscope’s Fourier plane is demonstrated.

Superresolution in phase image of π-phase step on plasmonic metasurface using differential heterodyne microscope

“…The above-mentioned possibility of controlling the phase response width was shown in Ref. 30 only theoretically, which determined one of the goals of this work—to obtain experimental confirmation of this possibility. This is very important from the practical point of view, since it is the width of the phase response that determines the edge detection accuracy, while the width of the amplitude response is determined by the diffraction limit.…”

“…The properties of phase response to the phase step object were considered in Ref. 30 using scalar theory. It was shown that the SDHM response to a rectangular step object with the phase increment φ = π can be written as D(x)=[1–2 H(x)][1–2 H(x−ε)],where H(x)=12+1π∫0kxNAsinttdt.…”

“…Therefore, it is possible to decrease the width of the phase response Arg[D(x)] to an arbitrarily small value without reducing its peak amplitude merely by lowering the interval ε by decreasing the heterodyne frequency. To quantify superresolution, we introduced the superresolution coefficient, 30 which is equal to the ratio of the width of the amplitude response wa to that of the phase response wφ SR=wawφ.…”

“…In Ref. 30, we theoretically and experimentally investigated an alternative scheme for achieving superresolution in the edge detection problem using a scanning differential heterodyne microscope. In this scheme, a He–Ne laser with one transverse spatial mode is used; an acoustooptic modulator is used to form two spatially separated probing beams with different frequencies.…”

Characterization of gap-plasmon based metasurfaces using scanning differential heterodyne microscopy

“…The measurements were carried out on SDHM experimental setup (Fig. 1 ) based on a well-known common path scheme of Mach–Zehnder interferometer with a He–Ne laser at wavelength λ = 633 nm as a light source 13 . Two diffraction probe beams are formed by a Bragg acousto-optic modulator with a centre frequency f 0 = 160 MHz.…”