A three-module SLD (Broadlighter, T840-HP, Superlumdiodes Limited, Moscow, Russia) with a center wavelength of 840 nm and a full width at half maximum (FWHM) bandwidth of 100 nm was used. The configuration of the OCT system is the same as in our previous publications, 9 except that we did not use an optical scanner in the sample arm for the experiments. However, the effect of polarization mismatch on the resolution of a fiber-based OCT has not been reported. Polarization controllers are usually used in a fiber-based OCT to optimize an OCT image by changing the amplitude and orientation of birefringence in the sample or reference fiber. 2, 4, 5 In biological tissues, scattering and birefringence can modify the polarization states of the incident sample light 6 – 8 in addition to the polarization modification by the single mode optical fibers in the sample and reference arms. 1 – 3 We all know that the depth resolution of an OCT system depends on the bandwidth and the center wavelength of the light source if the spectra and dispersion of the reference and sample arms in the interferometer are well balanced. By using either superluminescent diode (SLD) or femtosecond laser-based light sources, depth resolution better than 3 µm in the tissue has been achieved. Ultrahigh resolution OCT has been demonstrated in both TD and SD systems. As in all imaging modalities, resolution is an important parameter that describes the spatial resolving capability of a system. Both time domain (TD) and spectral domain (SD) detection techniques have been applied in OCT with great success. Optical coherence tomography (OCT) is an interferometer-based optical imaging modality that can reveal the microscopic structures of biological samples. When DOP=1, uniform resolution along the depth of a sample can be achieved. Adjusting polarization controllers can only improve the depth resolution at a certain depth in a sample if the polarization state of light changes along the depth. With DOP<1, the depth resolution can be quickly degraded by either birefringence or scattering in the sample. This discovery has fundamental importance for high-resolution OCT imaging of biological tissues. ![]() When we polarize the source light with a polarizer, then the degree of polarization (DOP) is unity, and the depth resolution becomes independent of the polarization mismatch. When their polarization states are mismatched, the PSF can be so distorted that the depth resolution is degraded to several times the theoretical value. When the polarization states of the two arms are matched, the measured point spread function (PSF) is almost identical to the theoretical prediction. This overview covers room-temperature investigations of the Verdet constant of several materials, which could be used for the ultraviolet, visible, near-infrared and mid-infrared wavelengths.We find for the first time that polarization mismatch of the sample and reference arms in optical-fiber-based optical coherence tomography (OCT) has critical effect on its depth resolution when the light source is partially polarized. In the final part of this review, we present a brief overview of several magneto-active materials, which have been to-date reported as promising candidates for utilization in the Faraday devices. A general model for describing the measured Verdet constant data as a function of wavelength and temperature is given. The experimental setup used for the characterization is a flexible and robust tool for evaluating the Faraday rotation angle induced in the magneto-active material, from which the Verdet constant is calculated based on the knowledge of the magnetic field and the material sample parameters. ![]() A practical methodology for advanced characterization of the Verdet constant of these materials is presented, providing a useful tool for benchmarking the new materials. We review the progress in the investigation of the Verdet constant of new magneto-active materials for the Faraday-effect-based devices used in high-power laser systems.
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