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We used 3D phase images obtained by laser interference microscopy (LIM) for ex vivo evaluation of changes in the structure of myelin during repetitive stimulation. In this work we propose a simple model of myelinated nerve fiber (mNF), which describes phase images as a result of different geometry and membrane-to-cytoplasm ratio in various regions, particularly, the internode and paranodal–nodal–paranodal region, including the node of Ranvier. Application of this model provides clear interpretation of the phase images and also demonstrates that repetitive action potentials are accompanied by structural changes in myelin in the internode and cytoplasmic modification in the node of Ranvier. The first 20 min of stimulation did not induce significant changes in the measured parameters, but then the optical path difference at the periphery of mNF and at the node of Ranvier declined reversibly. We believe that our model is also applicable to other modifications of interference and non-interference imaging.

An experimental investigation was made of a Raman laser emitting picosecond optical pulses from an LiIO3 crystal (λl = 1.143 μm), pumped synchronously by a train of pulses from a phosphate neodymium glass laser with mode self-locking (λp = 1.054 μm). The time characteristics of the Raman laser radiation were determined as a function of the mismatch of the resonator lengths. When the resonator lengths were matched, the duration of the output pulses was shortened by a factor of 7 or 8 compared with the pump pulses. In this case, the duration of the output pulses was ~ 1 ps and the energy conversion efficiency was ~ 30%.

An investigation is made of the feasibility of using various uniaxial and biaxial nonlinear crystals to measure the autocorrelation function of a single picosecond optical pulse using the second-harmonic beam method. General requirements are formulated for the wave interaction geometry in a crystal in order to maximize the temporal resolution and sensitivity of the autocorrelator. An analysis is made of LiIO3, KDP, KB5O84H2O and LiCHOOH2O crystals. The optimum interaction geometry is determined and the scanning duration and upper measurement limit are calculated for each crystal. Measurements of these quantities are reported for an LiIO3 crystal autocorrelator.