ERROR ANALYSIS OF THE DISPERSION-COMPENSATED WIDE-BAND POLARIZATION SAGNAC INTERFEROMETER

Imaging polarimetry can obtain two-dimensional intensity distribution information and its corresponding states of polarization from the target simultaneously. Sagnac polarization imaging interferometer is one of the typical channeled polarimetry technologies. By splitting the incident light through the triangular optical structure, the polarization information of the target is modulated into the interference fringes and can be obtained by the demodulation algorithm. The non-ideal optical elements in the system will cause reconstruction errors. This article analyses several factors that affect the measurement accuracy, including the splitting ratio of polarization beam splitter and the diffraction efficiency of the blazed grating. We derive the modified intensity formula and obtain interference patterns through numerical simulations. By calculating the modulation degree of interference fringes and reconstruction error under different non-ideal parameters, we have come to the conclusion that to meet the requirement of modulation degree > 0.5 and reconstruction error < 10%, the beam splitting ratio of the PBS should be α < 1.22. The diffraction efficiency ratio of s-polarization to p-polarization of the blazed grating should be ηs/ηp > 0.83, and the first-order diffraction efficiency should be η1 > 79%.

Measurement of Circular Dichroism Spectra without Control of a Phase Modulator using Retardation Domain Analysis

This study investigated the measurement of circular dichroism (CD) spectra without controlling a phase modulator. In a conventional CD system, the peak retardation of the phase modulator must remain constant over the observed wavelength range. Thus, the phase modulator must be controlled to maintain an appropriate modulation degree at an observed wavelength. In contrast, CD obtained using retardation domain analysis is not affected by peak retardation. Consequently, CD spectra can be measured without control of the phase modulator, which was experimentally demonstrated in this study. Additionally, linear dichroism spectra were obtained using retardation domain analysis.

Bearingless PM synchronous machine with zero-sequence current driven star point-connected active magnetic thrust bearing

Common cylindrical bearingless drives require a separate thrust bearing, which is fed by a DC supply. Here, a technique is presented, which enables the feeding of the thrust bearing by an artificially generated zero-sequence current between the two star points of the two parallel windings in the bearingless PM synchronous machine. This way, no additional DC supply for an axial active magnetic bearing is needed. It is replaced by two three-phase inverters as stator winding supply, which are needed in any case to generate torque and lateral rotor force in the motor. This examination explains the technique of adapting the electric potential of the star points in two three-phase windings of the motor. The focus is on the determination of the operating area (maximum zero-sequence current and band width). It is constrained by the bearingless motor due to torque and lateral force ripple as well as additional eddy current losses. On the other hand, the DC link voltage and the modulation degree of the inverter for simultaneous motor operation as well as the bearing inductance limit the system dynamic. It is shown that the proposed technique is applicable for a modulation degree < 0.866, taking into account that other constraints by the bearingless machine and the inverter are mainly noncritical.

Characteristics of Local Modulation Beam Propagating through Spatial Filter System

As local defects may significantly harm beam quality and affect safe operation, a systematic analysis of the ability of a spatial filter to alleviate these adverse effects is required. Thus, the evolutional characteristics of a beam modulated by a local defect propagating through a spatial filter system at an image reply plane and a downstream plane are analyzed in detail. Modulation stripes appear at the image reply plane; these are caused by the pinhole cutoff effect. The modulation degree increases with increasing defect size. The maximum intensification factor can reach 3.2 under certain conditions. Thus, the defect size should be restricted to a reasonable size for safe operation with a specified pinhole size. Moreover, a maximal value appears at the downstream plane, and the intensity enhances with increasing defect size. To ensure beam quality, the maximum allowable defect size and angle of the spatial filter should meet special constraints. The maximum allowable defect size is calculated based on practical configuration parameters.

Numerical investigation of the effects of smoothing by spectral dispersion on stimulated rotational Raman scattering

The effect of smoothing by spectral dispersion (SSD) on stimulated rotational Raman scattering (SRRS) in air has been investigated both numerically and theoretically. The suppression effect of SSD on SRRS process is verified and it is demonstrated and proposed that the suppression effect is attributed to two aspects: the decreasing of the laser fluence modulation degree and the reducing of Stokes gain coefficient caused by the temporal and spatial variation of the phase of the incident laser pulse. The simulation results show that the SRRS threshold distance can be lengthened by choosing appropriate SSD parameters.