Abstract
Mueller microscopes enable imaging of the optical anisotropic properties of biological or non-biological samples, in phase and amplitude, at sub-micrometre scale. However, the development of Mueller microscopes poses an instrumental challenge: the production of polarimetric parameters must be sufficiently quick to ensure fast imaging, so that the evolution of these parameters can be visualised in real-time, allowing the operator to adjust the microscope while constantly monitoring them. In this report, a full Mueller scanning microscope based on spectral encoding of polarization is presented. The spectrum, collected every 10 μs for each position of the optical beam on the specimen, incorporates all the information needed to produce the full Mueller matrix, which allows simultaneous display of all the polarimetric parameters, at the unequalled rate of 1.5 Hz (for an image of 256 × 256 pixels). The design of the optical blocks allows for the real-time display of linear birefringent images which serve as guidance for the operator. In addition, the instrument has the capability to easily switch its functionality from a Mueller to a Second Harmonic Generation (SHG) microscope, providing a pixel-to-pixel matching of the images produced by the two modalities. The device performance is illustrated by imaging various unstained biological specimens.
Highlights
The microscope is based on a standard upright confocal microscope with these polarized state generator (PSG) and PSA blocks respectively at the input and the output of the microscope in such a way that polarization states are generated and analysed for each wavelength delivered in time by the swept-source laser
We have developed a multi-modal optical scanning microscope able to (i) display in real-time birefringent images coded in HSV space where hue is generated for any specimen orientation, (ii) measure the full Mueller matrix at each point on the specimen at the typical frame rate of optical scanning microscopes, (iii) produce Second Harmonic Generation (SHG) images with the same pixel-to-pixel matching as Mueller images
Optical Coherent Tomography46 (OCT) and our Mueller microscope are both optical scanning methods and all the relevant information is contained in the modulations of the channelled spectra
Summary
RL RCX4, 1.7 × 1.7 mm 138.4° ± (0.1°, 1°) 4° ± (0.2°, 3°)X20, 90 × 90 μm 139.1° ± (0.1°, 0.3°) 0.13° ± (0.1°, 0.1°)DL(×10−3) 14 ± (2, 4) 6 ± (2, 3)DC(×10−3) 13 ± (2, 4) 4 ± (2, 3)Δ (×10−3) 45 ± (2, 7) 78 ± (2, 4). The mean values of the linear diattenuation DL are close to the theoretical value (maximum relative error of 1.1%) with a standard deviation equal to 0.005 at the centre of the image. NA has an impact on the depolarization parameter Δ (Δ = 0.021 for NA = 0.16 and Δ = 0.048 for NA = 0.75) the bias is less important due to the high acceptance angle of the linear polarizer used for the assessment of the Mueller microscope
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