Uncovering phase maps from surface plasmon resonance images: Towards a sub-wavelength resolution

We present an original method for uncovering phase maps from surface plasmon resonance microscopy images. The phase images obtained from the recording of V(Z) maps with a scanning surface plasmon microscope are affected by zero-mean uncorrelated noise and mechanical drifts. We propose to replace standard phase unwrapping methods by the computation of the local derivative of the phase Δϕ/ΔZ from the V(Z) complex field. Phase unwrapping basically relies on a smoothness constraint of the phase field, which is severely hampered by the noise. Applications of the proposed derivation to interferometric plasmon phase images demonstrate a superior ability of restoring phase maps, preserving their discontinuities, together with an effective noise smoothing performance, irrespective of locally varying coherence characteristics.