Mirror Rotation Research Articles

Endoscopes for observation of plasma-wall interactions in the divertor of Wendelstein 7-X

The stellarator Wendelstein 7-X is being prepared for long pulse operation. This includes diagnostics for investigation of plasma wall interaction processes. A versatile optical observation system has been developed for local characterization of the divertor plasma and the divertor target surface. The optical systems consist of two endoscopes each with perpendicular fields of view and the opportunity of tomographic reconstruction. Mirror based optics has been chosen in order to assure good optical properties independent of the wavelength. A narrow field of view allows for high spatial resolution while rotation of the first mirror covers the full poloidal divertor sections. An integrated shutter mechanism and a vacuum window far back minimize coating of optical components. For assessment of change of light transmission, a relative calibration function is implemented. The output light is split into wavelength ranges. Both, cameras equipped with narrow band filters as well as spectrometers are connected. The first endoscope was mounted at W7-X after successfully passing mechanical, optical and functional tests.

Strength reliability of rotating mirrors for ultra-high-speed cameras

This study aims to identify numerical analysis methods for the reliability prediction of rotating mirror(RM) strength at the early-stage design. A mathematical model for the strength reliability analysis of RM is established based on the Monte Carlo method, small-sample theory, and reliability principle. Numerical analysis on the strength reliability of RM is conducted, and the results are experimentally verified according to small-sample theory. The spearman rank order correlation coefficients between structure parameters and the maximum stress is the circumradius of mirror body, and that of the material variable is the elastic modulus of high-strength aluminum alloy(Al). The skewness and kurtosis values of maximum stress and strain are all positive. Calculated statistical results obey normal distribution and are right skewed. At 95% confidence level, the strength reliability of the RM with a design speed of 70,000 rpm is 0.999. This finding shows that the strength reliability of the RM meets the required design in ideal state. No failure of RMs occurs among strength reliability experiment, proving the validity of the numerical model. This model provides an economic, feasible, and effective method for estimating the strength reliability of RM.

Общность и различие схем поверки главного условия нивелира

The causes of the violating horizontal positioning of the vision axis as the main geometric leveling condition were studied. The importance of this condition at leveling forward performed as the main method of altitude measurements for topographic and geodetic engineering works was particularly emphasized. When analyzing the ways of calibrating the main position, the authors highlighted the general regulations for different methods of determining the calibration base and mirror rotation of the tested level to the differences in visualization the visual scale readings depending on the length of shoulders of the upcoming leveling process. The obligatory required return of testing to initial altitude of calibration base creates a closed loop of heights that enables to define the correction of horizontal sight axis and the difference between the inequality sums of rear and front shoulders. For performing field works, a new scheme of calibration the main position of level with its offset from alignment calibration base is offered.

Development of a tomographic Mueller-matrix scatterometer for nanostructure metrology.

In this paper, we describe the development of a novel instrument, tentatively called tomographic Mueller-matrix scatterometer (TMS), which enables illuminating sequentially a sample by a plane wave with varying illumination directions and recording, for each illumination, the polarized scattered field along various directions of observation in the form of scattering Mueller matrices. The incidence angle is varied from 0° to 65.6° with the rotation of a flat mirror that changes the position of the focal point of a light beam on the back focal plane of a high numerical aperture objective lens. The scattering Mueller matrices are collected over a wide range of scattering angles (0°-67°) and azimuthal angles (0°-360°). The developed instrument was then applied for the measurement of nanostructures in combination with an inverse scattering problem solving technique. The experiment performed on a periodic nanostructure preliminarily demonstrates the performance of TMS as well as its potential in nanostructure metrology. It is expected that the TMS would be a powerful tool for characterizing the polarized scattered-field distributions and measuring nanostructures in nanomanufacturing.

Mirror rearrangement optimization for uniform flux distribution on the cavity receiver of solar parabolic dish concentrator system

The nonuniform and high-gradient solar radiation flux on the absorber surface of solar dish concentrator/cavity receiver (SDCR) system will affect its operational reliability and service lifetime. Therefore, homogenization of the flux distribution is critical and important. In this paper, 2 mirror rearrangement strategies and its optimization method by combining a novel ray tracing method and the genetic algorithm are proposed to optimize the parabolic dish concentrator (PDC) so as to realize the uniform flux distribution on the absorber surface inside the cavity receiver of SDCR system. The mirror rearrangement strategy includes a mirror rotation strategy and mirror translation strategy, which rotate and translate (along the focal axis) each mirror unit of the PDC to achieve multipoint aiming, respectively. Firstly, a correlation model between the focus spot radius and mirror rearrangement parameters is derived as constraint model to optimize the PDC. Secondly, a novel method named motion accumulation ray-tracing method is proposed to reduce the optical simulation time. The optical model by motion accumulation ray-tracing method and optimization model of SDCR system are established in detailed, and then, an optimization program by combining a ray-tracing code and genetic algorithm code in C++ is developed and verified. Finally, 3 typical cavity receivers, namely, cylindrical, conical, and spherical, are taken as examples to fully verify the effectiveness of these proposed methods. The results show that the optimized PDC by mirror rearrangement strategies can not only greatly improve the flux uniformity (ie, reduce the nonuniformity factor) and reduce the peak local concentration ratio of the absorber surface but also obtain excellent optical efficiency and direct useful energy ratio. A better optimization results when the PDC is optimized by mirror rotation strategy at aperture radius of 7.0 m, focal length of 6.00 m, and ring number of 6; the nonuniform factor of the cylindrical, conical, and spherical cavity receivers is greatly reduced from 0.63, 0.67, and 0.45 to 0.18, 0.17, and 0.26, respectively; the peak local concentration ratio is reduced from 1140.00, 1399.00, and 633.30 to 709.10, 794.00, and 505.90, respectively; and the optical efficiency of SDCR system is as high as 92.01%, 92.13%, and 92.71%, respectively. These results also show that the dish concentrator with same focal length can match different cavity receivers by mirror rearrangement and it can obtain excellent flux uniformity.

Vibration-resistant Er-doped superfluorescent fiber source incorporating a Faraday rotator mirror

Improvement in the mean wavelength vibration stability is crucial to the realization of a high-precision fiber-optic gyroscope. We design a vibration-resistant Er-doped superfluorescent fiber source (VR-EDSFS) incorporated with a Faraday rotator mirror and compare it with the conventional Er-doped superfluorescent fiber source (ED-SFS) under different vibration conditions. As shown by experimental results, the mean wavelength vibration stability of the VR-EDSFS is much better than that of the conventional ED-SFS. Under the 1000 to 2000 Hz vibration condition, the former is just 3.4 ppm, which is about 7 ppm less than the latter over 2 h.

Ultra-short pulse generation in a linear femtosecond fiber laser using a Faraday rotator mirror and semiconductor saturable absorber mirror

An innovative method for obtaining ultra-short and perfectly stable femtosecond pulses in a linear erbium-doped fiber laser is proposed. A commercial semiconductor saturable absorber mirror and a standard Faraday rotator are used in both sides of the linear fiber optic laser configuration to shorten the pulse duration and suppress undesirable effects on the polarization state. The laser operation is investigated theoretically using a physical model and it is verified using experimental results. The main idea of this research is to apply a Faraday rotator mirror for pulse shortening purposes. For this reason, two types of Er-doped fiber optics with different group velocity dispersion parameters are used to achieve the optimum net group velocity dispersion in the cavity. Output results demonstrate good consistency between theory and experimental results. The output power of the linear oscillator is approximately 45 mW with 135 fs pulses at the 23.5 MHz repetition rate without any pulse compression.

Optics of beam emission spectroscopy diagnostic on EAST tokamak

128-channel Beam Emission Spectroscopy (BES) diagnostic basing on neutral beam injection (NBI) has recently been developed on EAST tokamak. It can diagnose plasma density fluctuation with a sample rate of 1 MHz and a spatial resolution of 1–3 cm, according to the diagnosing spatial positions. The Doppler-shifted beam emission line is led through prisms, lens groups and mirrors, and finally divided into two detection branches. By means of rotating the rotation mirror in the optical path, the viewing area, which is a 20 cm × 10 cm rectangle, can be moved from plasma core to edge. Three-cavity-interference filter with a center frequency of 659 nm and a bandwidth of 1.59 nm is used to eliminate the interference background Dα signal and carbon radiation. First experimental results show high performance of this diagnostic.

Needles of light produced with a quasi-parabolic mirror.

We propose a quasi-parabolic mirror that can produce a long needle of light by focusing a radially polarized annular beam. The quasi-parabolic mirror can be acquired by moving the axis of rotation of a parabolic mirror. Using the extended Richards-Wolf theory for axisymmetric surfaces, we calculated that the needle obtained can have a longitudinal FWHM over hundreds to thousands of wavelengths by keeping the transverse FWHM under 0.36λ. The consistent expression of the approximate relationship between the angular thickness of the incident beam and the longitudinal FWHM based on both geometrical optics and wave optics is presented.

A fiber-optic sensor based on no-core fiber and Faraday rotator mirror structure

An optical fiber sensor based on the single-mode/no-core/single-mode (SNS) core-offset technology along with a Faraday rotator mirror structure has been proposed and experimentally demonstrated. A transverse optical field distribution of self-imaging has been simulated and experimental parameters have been selected under theoretical guidance. Results of the experiments demonstrate that the temperature sensitivity of the sensor is 0.0551 nm/°C for temperatures between 25 and 80 °C, and the correlation coefficient is 0.99582. The concentration sensitivity of the device for sucrose and glucose solutions was found to be as high as 12.5416 and 6.02248 nm/(g/ml), respectively. Curves demonstrating a linear fit between wavelength shift and solution concentration for three different heavy metal solutions have also been derived on the basis of experimental results. The proposed fiber-optic sensor design provides valuable guidance for the measurement of concentration and temperature.

Development and characterization of a handheld hyperspectral Raman imaging probe system for molecular characterization of tissue on mesoscopic scales

Raman spectroscopy is a promising cancer detection technique for surgical guidance applications. It can provide quantitative information relating to global tissue properties associated with structural, metabolic, immunological, and genetic biochemical phenomena in terms of molecular species including amino acids, lipids, proteins, and nucleic acid (DNA). To date in vivo Raman spectroscopy systems mostly included probes and biopsy needles typically limited to single-point tissue interrogation over a scale between 100 and 500 microns. The development of wider field handheld systems could improve tumor localization for a range of open surgery applications including brain, ovarian, and skin cancers. Here we present a novel Raman spectroscopy implementation using a coherent imaging bundle of fibers to create a probe capable of reconstructing molecular images over mesoscopic fields of view. Detection is performed using linear scanning with a rotation mirror and an imaging spectrometer. Different slits widths were tested at the entrance of the spectrometer to optimize spatial and spectral resolution while preserving sufficient signal-to-noise ratios to detect the principal Raman tissue features. The nonbiological samples, calcite and polytetrafluoroethylene (PTFE), were used to characterize the performance of the system. The new wide-field probe was tested on ex vivo samples of calf brain and swine tissue. Raman spectral content of both tissue types were validated with data from the literature and compared with data acquired with a single-point Raman spectroscopy probe. The single-point probe was used as the gold standard against which the new instrument was benchmarked as it has already been thoroughly validated for biological tissue characterization. We have developed and characterized a practical noncontact handheld Raman imager providing tissue information at a spatial resolution of 115 microns over a field of view >14 mm2 and a spectral resolution of 6 cm-1 over the whole fingerprint region. Typical integration time to acquire an entire Raman image over swine tissue was set to approximately 100 s. Spectra acquired with both probes (single-point and wide-field) showed good agreement, with a Pearson correlation factor >0.85 over different tissue categories. Protein and lipid content of imaged tissue were manifested into the measured spectra which correlated well with previous findings in the literature. An example of quantitative molecular map is presented for swine tissue and calf brain based on the ratio of protein-to-lipid content showing clear delineations between white and gray matter as well as between adipose and muscle tissue. We presented the development of a Raman imaging probe with a field of view of a few millimeters and a spatial resolution consistent with standard surgical imaging methods using an imaging bundle. Spectra acquired with the newly developed system on swine tissue and calf brain correlated well with an establish single-point probe and observed spectral features agreed with previous finding in the literature. The imaging probe has demonstrated its ability to reconstruct molecular images of soft tissues. The approach presented here has a lot of potential for the development of surgical Raman imaging probe to guide the surgeon during cancer surgery.

Classification of accidental band crossings and emergent semimetals in two-dimensional noncentrosymmetric systems

We classify all possible gap-closing procedures which can be achieved in two-dimensional time-reversal invariant noncentrosymmetric systems. For exhaustive classification, we examine the space-group symmetries of all 49 layer groups lacking inversion, taking into account spin-orbit coupling. Although a direct transition between two insulators is generally predicted to occur when a band crossing happens at a general point in the Brillouin zone, we find that a variety of stable semimetal phases with point or line nodes can also arise due to the band crossing in the presence of additional crystalline symmetries. Through our theoretical study, we provide the complete list of nodal semimetals created by a band inversion in two-dimensional noncentrosymmetric systems with time-reversal invariance. The transition from an insulator to a nodal semimetal can be grouped into three classes depending on the crystalline symmetry. First, in systems with a twofold rotation about the $z$ axis (normal to the system), a band inversion at a generic point generates a two-dimensional Weyl semimetal with point nodes. Second, when the band crossing happens on the line invariant under a twofold rotation (mirror) symmetry with the rotation (normal) axis lying in the two-dimensional plane, a Weyl semimetal with point nodes can also be obtained. Finally, when the system has a mirror symmetry about the plane embracing the whole system, a semimetal with nodal lines can be created. Applying our theoretical framework, we identify various two-dimensional materials as candidate systems in which stable nodal semimetal phases can be induced via doping, applying electric field, or strain engineering, etc.

Novel dual-loop optoelectronic oscillator based on self-polarization-stabilization technique.

A novel dual-loop optoelectronic oscillator (OEO) based on self-polarization-stabilization technique has been experimentally demonstrated. The input light in each loop will retrace its path through a 45° Faraday rotator and single mode fiber with different length after reflecting off a 45° Faraday rotator mirror. By this way, the polarization state of the output signal is always rotated by 180° from the polarization state of the input signal in each loop even if the round-trip fiber is perturbed by the mechanical vibration or temperature. Moreover, the required fiber length is cut in half due to the round-trip transmission in each path, resulting in higher system stability and more compacter structure. The experimental results show that in an intensity modulator (IM)-based OEO system, this scheme has better phase noise performance than the traditional polarization multiplexing method. Furthermore, to avoid the DC bias drifting problem of IM, a simple phase modulation to intensity modulation convertor by using a polarization-dependent phase modulator and a polarizer is proposed without the need of expensive optical filters or dispersive devices. Based on this scheme, a novel dual-loop OEO using phase modulator and self-polarization-stabilization technique has been experimentally demonstrated. The phase noise of -114.1 dBc/Hz at 10 kHz away from the carrier (10 GHz) is achieved and the side mode suppression ratio is improved to 63 dB.

Development of beam emission spectroscopy diagnostic on EAST.

Beam Emission Spectroscopy (BES) diagnostic based on Neutron Beam Injection (NBI) on the Experimental Advanced Superconducting Tokamak has been developed. This system consists of 16 × 8 channels which can diagnose the density fluctuation in a rectangular area of about 20 × 10 cm2 in the cross section, whose radial position is adjustable from the core to edge just by means of changing the angle of the rotation mirror. The spatial resolution is about 1-3 cm according to the diagnosed radial position. The temporal resolution is 1 μs. Space calibration of the diagnostic system is done based on the reversibility of the optical path. The NBI modulation experiment shows the success of BES development.

An eight-channel Doppler backscattering system in the experimental advanced superconducting tokamak.

Doppler backscattering system can measure the perpendicular velocity and fluctuation amplitude of the density turbulence with intermediate wavenumber. An eight-channel Doppler backscattering system has been installed in the Experimental Advanced Superconducting Tokamak (EAST), which can probe eight different radial locations simultaneously by launching eight fixed frequencies (55, 57.5, 60, 62.5, 67.5, 70, 72.5, 75 GHz) into plasma. The quasi-optical system consists of circular corrugated waveguide transmission, a fixed parabolic mirror, and a rotatable parabolic mirror which are integrated with quasi-optics front-end of the profile reflectometer inside the vacuum vessel. The incidence angle can be chosen from 5° to 12°, and the wavenumber range is 2-15/cm with the wavenumber resolution Δk/k≤0.21. Ray tracing simulations are used to calculate the scattering locations and the perpendicular wavenumber. The dynamic range of this new eight-channel Doppler backscattering system can be as large as 40 dB in the EAST. In this article, the hardware design, the ray tracing, and the preliminary experimental results in the EAST will be presented.

Phase and frequency noise measurement using passive self-homodyne technique

For single longitudinal-mode lasers, the phase and frequency noises are very important parameters for their applications. The passive self-homodyne technique with an unbalanced Michelson interferometer is demonstrated to measure the phase and frequency noise characteristics. The Michelson interferometer for measurements is composed of a 3×3 optical fiber coupler and two Faraday rotator mirrors. The measurement performance is derived and discussed strictly from the transmission matrix of the coupler. The influence to the demodulation resulting from the asymmetry of the 3×3 optical fiber coupler is eliminated through the derived relationship between the differential phase fluctuation and the interferometer fringes. The technique is utilized to measure the phase and frequency noise features of a distributed feedback fiber laser. Based on the measured frequency noise spectrum, the lineshape, linewidth, and phase-error variance related to the laser coherence are able to be calculated and discussed well.

Mode-Locking Thulium-Doped Fiber Laser With 1.78-GHz Repetition Rate Based on Combination of Nonlinear Polarization Rotation and Semiconductor Saturable Absorber Mirror

We experimentally demonstrate a passively mode-locking thulium-doped fiber laser based on the combination of the nonlinear polarization rotation (NPR) and the semiconductor saturable absorber mirror (SESAM). In contrast to SESAM mode-locking merely, the fiber lasers based on NPR working together with SESAM have more advantages. By using two mode-locking mechanisms, the nonlinear effect can be enhanced tremendously; then, the threshold of high-order harmonic mode-locking (HML) pulse trains can be decreased, and the pulses width can be compressed. The shapes of the pulses can also be reshaped better, and the HML pulse trains stability can be improved. The high repetition rate of 1.78 GHz is obtained by both NPR and SESAM in the experiment. Because of the variation of the gain-and-loss distribution in the cavity, the output wavelength of mode-locking fiber laser can be tuned from 1839 to 1890 nm, and the multiwavelength HML is also observed in the experiment.

Calculation of the overlap factor for scanning LiDAR based on the tridimensional ray-tracing method.

The overlap factor is used to evaluate the LiDAR light collection ability. Ranging LiDAR is mainly determined by the optical configuration. However, scanning LiDAR, equipped with a scanning mechanism to acquire a 3D coordinate points cloud for a specified target, is essential in considering the scanning effect at the same time. Otherwise, scanning LiDAR will reduce the light collection ability and even cannot receive any echo. From this point of view, we propose a scanning LiDAR overlap factor calculation method based on the tridimensional ray-tracing method, which can be applied to scanning LiDAR with any special laser intensity distribution, any type of telescope (reflector, refractor, or mixed), and any shape obstruction (i.e., the reflector of a coaxial optical system). A case study for our LiDAR with a scanning mirror is carried out, and a MATLAB program is written to analyze the laser emission and reception process. Sensitivity analysis is carried out as a function of scanning mirror rotation speed and detector position, and the results guide how to optimize the overlap factor for our LiDAR. The results of this research will have a guiding significance in scanning LiDAR design and assembly.

Polarization modeling and predictions for Daniel K. Inouye Solar Telescope part 1: telescope and example instrument configurations

We outline polarization performance calculations and predictions for the Daniel K. Inouye Solar Telescope (DKIST) optics and show Mueller matrices for two of the first light instruments. Telescope polarization is due to polarization-dependent mirror reflectivity and rotations between groups of mirrors as the telescope moves in altitude and azimuth. The Zemax optical modeling software has polarization ray-trace capabilities and predicts system performance given a coating prescription. We develop a model coating formula that approximates measured witness sample polarization properties. Estimates show the DKIST telescope Mueller matrix as functions of wavelength, azimuth, elevation, and field angle for the cryogenic near infra-red spectro-polarimeter (CryoNIRSP) and visible spectro-polarimeter. Footprint variation is substantial and shows vignetted field points will have strong polarization effects. We estimate 2% variation of some Mueller matrix elements over the 5-arc min CryoNIRSP field. We validate the Zemax model by showing limiting cases for flat mirrors in collimated and powered designs that compare well with theoretical approximations and are testable with lab ellipsometers.

Erratum: Frequency stabilization of two orthogonally polarized external cavity laser diodes using a novel γ-type optical configuration consist of a phase modulator and a Faraday rotator mirror [IEICE Electronics Express Vol. 11 (2014) No. 10 pp. 20140169

Erratum: Frequency stabilization of two orthogonally polarized external cavity laser diodes using a novel γ-type optical configuration consist of a phase modulator and a Faraday rotator mirror [IEICE Electronics Express Vol. 11 (2014) No. 10 pp. 20140169