Figure 4. Experimental geometry for the fluorescent microscopy based on multimode fibre image transfer.

The appropriate selection of lenses L1 and L2 and a lenslet array LA provides expansion and collimation of the laser beam on the SLM. During calibration, the AOD deflects the initial laser beam onto a central segment of the lenslet array and these settings are kept unchanged during the calibration measurement. Similarly as in the case of bright-/dark-field geometry, using a polarization beam splitter PBS and a half-wave plate λ/2 the light is coupled into the fibre (by microscope objective MO1) in both polarization states to achieve maximal efficiency. The signal leaving the fibre is imaged onto the CCD by a telescope (MO2 and TL). Once the calibration is accomplished, we reset the system for imaging. In this case, the AOD periodically alternates the alignment of the beam onto different segments of the LA that changes the angle of the incidence onto the SLM. The imaging hologram applied to the SLM acts in such a way that for every angle of incidence of the laser beam the light behind the fibre forms an optimally focussed beam at different locations across the sample plane. This provides a rapid scanning of the focused excitation beam. Fluorescence emission light from illuminated objects is collected by the fibre, separated from the excitation pathway using a dichroic mirror DM1 and detected by photomultiplier PMT.