Abstract
Synthetic optical holography (SOH) provides efficient encoding of the complex optical signal, both amplitude and phase, for scanning imaging methods. Prior demonstrations have synthesized reference fields with a plane-wave-like linear variation of the phase with position. To record large images without probe-mirror synchronization, a long-travel, closed-loop reference mirror stage has been required. Here we present SOH with a synthetic reference wave with sinusoidal spatial variation of the phase. This allows the use of open loop, limited mirror travel range in SOH, and leads to a novel holographic inversion algorithm. We validate the theory with scans of graphene grain boundaries from a scanning near-field optical microscope, for which SOH has been shown to drastically increase scan speeds [Nat. Commun. 5, 3499 (2014)].
Highlights
In holography [1,2,3,4,5,6], an unknown complex signal is encoded as an intensity image such that information is distributed across the whole image through interference with a known reference field
In synthetic optical holography (SOH), the complex field scattered from a focus or a local probe interferes with a reference beam at a one-pixel detector
We demonstrate SOH with a sinusoidal-phase reference wave by s-SNOM imaging the same graphene grain boundary as in [18]. s-SNOM [29,30,31,32] is a scanning microscopy technique that circumvents the diffraction limit and provides nanoscale spatial resolution at visible, infrared and THz wavelengths by recording the light scattered at a scanning probe tip
Summary
In holography [1,2,3,4,5,6], an unknown complex signal is encoded as an intensity image such that information is distributed across the whole image through interference with a known reference field. As a specific example, we implement in this paper a reference in which the phase varies sinusoidally rather than linearly with position in the detector plane This reference field requires a modified inversion algorithm which might be seen to be a multidimensional generalization of pseudoheterodyne interferometry (PHI) [21,22,23,24]. The spatial variation of the signal manifests as broadband spatial frequency information, whereas the signal is usually taken to be monochromatic (that is sinusoidal) in PHI The latter difference requires a modified inversion process, and places constraints on the signal and reference fields.
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