Surface plasmon microscopic sensing with beam profile modulation

Abstract

Surface Plasmon microscopy enables measurement of local refractive index on a far finer scale than prism based systems. An interferometric or confocal system gives the so-called V(z) curve when the sample is scanned axially, which gives a measure of the surface plasmon propagation velocity. We show how a phase spatial light modulator (i) performs the necessary pupil function apodization (ii) imposes an angular varying phase shift that effectively changes sample defocus without any mechanical movement and (iii) changes the relative phase of the surface plasmon and reference beam to provide signal enhancement not possible with previous configurations.

Ultrastable embedded surface plasmon confocal interferometry

“…In the work reported here and previously, 8,9 the interference occurs between different parts of the illumination beam, so that one portion of the illumination beam acts as a reference. This approach facilitates our aim to obtain fine phase measurements between different paths within the same beam.…”

“…This confocal arrangement therefore ensures that the path of the SPs is well defined by the optical configuration rather than their propagation length. We have shown in subsequent publications 8,9 how a spatial light modulator conjugate with the back focal plane is effective in allowing for different processing methods that overcome mechanical scanning or allow the amplitude and phase of the SP to be extracted directly, thus providing an exceptionally robust means of processing the signal. For instance, the spatial light modulator (SLM) can be used to change the phase of P1 relative to P2 so that phase stepping may be performed which allows the phase associated with SP to be extracted directly.…”

“…In our previous publications, we have used linear input polarization in the back focal plane which gives a continuous variation between ppolarization and s-polarization as the azimuthal angle changes 6,8,9 ( Figure 2a). The use of radial polarization incident in the back focal plane has often been advocated in SP microscopy which means the light incident on the sample is p-polarized for all azimuthal angles, so that more energy is coupled in SPs and the focus is tight and circularly symmetrical.…”

“…Alternatively, the optical element can be placed in the path of the incident beam, as shown in Figure 1b, so that its path follows P19 and hits the sample at point 'b' so that on reflection it also appears to come from focus thus also forming an arm of the interferometer. 6,8,9 In our experimental arrangement, the optical element (a spatial light modulator) was applied on the incident beam; thus corresponding to the scheme associated with Figure 1b. Figure 2 shows a schematic of the pattern on the back focal plane used to effect the beam deflection.…”

Confocal surface plasmon microscopy with vortex beam illumination for biosensing application: Label free biosensing application of confocal surface plasmon microscope

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We have developed surface plasmon interferometric microscope and demonstrated that by integrating a phase spatial light modulator (SLM) on conjugate back focal plane of confocal microscope objective lens, this enables us to perform surface plasmon phase imaging and phase sensing using phase stepping interferometry over well confined region [1][2][3][4][5][6]. In this paper, we address one of the key limitations of the system, which is data acquisition time.

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