M2 Mirror Research Articles

Thermal analysis of a reflection mirror by fluid and solid heat transfer method.

High-repetition-rate free-electron lasers impose stringent requirements on the thermal deformation of beamline optics. The Shanghai HIgh-repetition-rate XFEL aNd Extreme light facility (SHINE) experiences high average thermal power and demands wavefront preservation. To deeply study the thermal field of the first reflection mirror M1 at the FEL-II beamline of SHINE, thermal analysis under a photon energy of 400 eV was executed by fluid and solid heat transfer method. According to the thermal analysis results and the reference cooling water temperature of 30 °C, the temperature of the cooling water at the flow outlet is raised by 0.05 °C, and the wall temperature of the cooling tube increases by a maximum of 0.5 °C. The maximum temperature position of the footprint centerline in the meridian direction deviates away from the central position, and this asymmetrical temperature distribution will directly affect the thermal deformation of the mirror and indirectly affect the focus spot of the beam at the sample.

Euclid: Ice Contamination Testing

Euclid is a medium-size ESA mission which will map the geometry of the Universe for a better understanding of dark matter and dark energy. Due to the mission profile and stringent performance requirements, the in-orbit contamination environment is a key aspect to control. Cryogenic operational temperatures root a particular concern over water/ice contamination on optical elements, since increased light scattering could potentially cause a significant impact on the performance of the payload. This challenging work under representative conditions closes the link between performance and ice contamination on specular surfaces (e.g. Mirror M1). The publication covers in detail the design and execution of the test campaign performed in ESA’s TEC-QEE Yuta vacuum facility, resulting in a data-set of spectral information at cryogenic temperatures. The optimised translation/rotation mechanisms incorporating fiber optics allowed scanning in different angular configurations: both the specular reflection as well as scattered light at different levels of surface contamination. The test results show that the effects of ice contamination are most noticeable in specular configuration. A summary is also given about ice-kinetics measured on the black paint used on the external baffle. The work supports Euclid’s calibration team in predicting expected performance and tuning the frequency and duration of in-flight decontamination processes.

Assessment of the Performance of Different Cooling Configurations for the Launcher Mirrors of the ECRH System of the DTT Facility

The launcher mirrors will allow the injection of microwave power from the gyrotrons in the plasma of the Divertor Tokamak Test facility, under construction in Italy. The active cooling of the elliptical M1 (curved and not-steerable) and M2 (flat and steerable) mirrors, both subject to a significant heat load, is investigated in this article. Several cooling solutions are analyzed: a spiral cooling for M1, both in a massive and in a lightened configuration, and also a radial-azimuthal cooling for M2, both in a massive and in a lightened configuration. Figures of merit are computed for the different configurations.

Effect of 3 T magnetic field on RF plasma sputtering in an ITER-relevant first mirror unit

The first mirror (FM) cleaning operations in ITER are expected to be executed in the presence of a T magnetic field. In the RF plasma cleaning configuration, this would have a significant influence on the plasma properties, ion energy, angle of incidence as well as flux spatial distribution. To this end, RF discharges were excited in an ITER-sized mock-up of a first mirror unit (FMU) consisting of a powered first mirror M1 and a grounded second mirror M2 placed in a homogeneous 3 T magnetic field. The plasma discharge was confined in a beam extending in the direction of the magnetic field, consequently wetting a limited portion of the FMU walls. In the DC-decoupled scheme (without λ/4 filter), this considerably influenced the self-bias voltage V DC that develops on M1. Changing the angle α between M1 normal and magnetic field, modified the plasma wetted wall area A g and the resulting V DC varied by over two orders of magnitude. Plasma exposure experiments were also done in the DC-coupled scheme (with λ/4 filter), wherein the angle and wetted surface determined the area of wall sputtered. Increasing α led to an increase in the sputtered wall area A g, and consequently the wall deposition on grounded M2. However, in all the cases M1 was entirely clean with the exception of edge deposits in some. In contrast, both M1 and M2 are coated with wall deposits in the absence of a magnetic field and a similar plasma exposure. The results show that plasma cleaning with λ/4 filter in a 3 T magnetic field at ITER could potentially prevent the parasitic wall deposition on FMs. The results also highlight the importance of FM orientation in the magnetic field and the wetted area in the plasma cleaning in both the DC-coupled and decoupled schemes within the ITER diagnostic systems.

Acute Mirror M1 Occlusions Treated With Endovascular First-Pass Contact Aspiration Technique

Patients with acute bilateral M1 occlusion are usually comatose at presentation and have a grave prognosis. There have been few reports of emergent treatment using endovascular reperfusion therapy (ERT). We describe a patient treated with simultaneous first-pass contact aspiration and review the literature for cases describing the successful use of ERT in patients with bilateral anterior circulation proximal large-vessel occlusion (LVO). A functionally independent 95-year-old woman with history of atrial fibrillation (AF) presented with altered mentation, aphasia, and weakness in all extremities. Her National Institutes of Health Stroke Scale (NIHSS) score was 13. CT angiogram and perfusion demonstrated acute mirror M1 occlusions with extensive bilateral middle cerebral artery (MCA) territory penumbra, respectively. Emergent ERT was performed with simultaneous contact aspiration within the bilateral M1s under concomitant flow arrest with a balloon guide catheter. Modified Thrombolysis in Cerebral Infarction (mTICI) grades 3 and 2c were achieved on the left and right, respectively. By postoperative day 1 (POD1), the patient had improved motor function, mentation, and communication.The technical feasibility of simultaneous contact aspiration thrombectomies for acute bilateral M1 occlusions was demonstrated with successful reperfusion of both vascular territories in a single pass lasting 28 minutes. Simultaneous thrombectomies yielded rapid recanalization and reperfusion and minimized radiation exposure. Previous cases demonstrating this technique utilized stent-retriever techniques in successive fashion, with a consequent increase in the patient’s total ischemic time. The technical success of our aggressive approach suggests it may have utility in the treatment of acute multivessel occlusions (MVOs).

Optimization of the performance of hand‐held FFOCT scanner

In this work, we have established an improved handheld full-field optical coherence tomography (FFOCT) system based on the tandem structure of Michelson interferometer and Fizeau interferometer. We have analyzed the influence of wave aberrations of the handheld FFOCT as a function of orientation deviation of mirror M2 on the system point spread function (PSF) by using the nodal aberration theory. It is found that the range of the orientation deviation of mirror M2 must be less than 0.1° to generate stable FFOCT images. The effect of wave aberrations of defocus as a result of the refractive index difference on the system PSF has also been calculated, the measuring depth in the case of the sample with refractive index of 1.5 and the propagation medium is air (n = 1) should be less than 20 μm. Theoretical analyses have been demonstrated by the experimental results of aluminum powder, onion and porcine myocardium. By comparing the defocused FFOCT images of aluminum powder with defocused FFOCT images of onion and porcine myocardium, it can be concluded that reducing the refractive index difference between the medium and sample can increase the imaging depth of handheld FFOCT system.

Development of the primary mirror for CAS500-1 (Compact Advanced Satellite 500-1)

AbstractCAS500-1 (Compact Advanced Satellite 500-1) launched in Mar. 2021 is the first Korean ground observation satellite localizing the entire mirror development, especially the primary mirror M1. M1 is a lightweight concave mirror with a diameter of 0.6 m, and it has 3 square bosses at the rim for flexure mounting. We present the whole development procedure of the flight model M1, including the optomechanical design, fabrication, environmental tests, and a coordinate mapping method for alignment and integration.

Design and Thermal-Structural Analyses of Ancillary Components for the Optical Steering Mirror (M4) for the ITER ECH Upper Launcher

Each of the four ITER Electron Cyclotron Heating Upper Launcher (ECHUL) features eight transmission lines (TLs) that are used to inject 170-GHz microwave power into the plasma at a level of up to 1.31 MW (at the TL diamond window) per line. The millimeter waves are guided through a quasi-optical section consisting of three fixed mirror sets (M1, M2, and M3) and one front steering mirror set (M4), with a steering range of [−7, +7]°. The M4 mirror assembly (upper and lower) will each reflect nearly four Gaussian beams at the correct location in the plasma for suppression of the ${q}\,\,=3$ /2 and ${q}\,\,=2$ /1 NTMs. EPFL-SPC has developed a novel steering mirror assembly (SMA) actuator system, which is based on four pressure-controlled, helium-filled bellows working against six helicoidally machined, preloaded, compressive springs, that rotate around two frictionless flexure pivots. This article will outline the design and thermal–mechanical analysis of such bellows, springs, housing (stator), and the remote-handling compatible support frame.

Beschichtungstechnik auf dem Gipfel

SummaryCoating technology on the summit – Mirror Layers for the Large Synoptic Survey Telescope in ChileThis article focuses on mirror coating for the Large Synoptic Survey Telescope, which is being installed in Chile. The LSST coating system consists of a coating chamber for the deposition of highly reflective optical coatings and a cleaning and stripping station for the M1M3 and M2 mirrors. With the help of the sputtering process, bare and protected silver/aluminum coating recipes can be deposited. The cleaning and stripping station consists of a rotating washing/drying boom, perimeter platforms, and an effluent handling system within the M1M3 mirror cell. The article describes the status of the assembly work on the coating system. Furthermore, it provides information about the progress of factory testing, a about the basic design features and reflective/coating requirements and the coating results.

Field stabilization control of the European Extremely Large Telescope under wind disturbance.

This paper discusses the field stabilization control of the M5 unit under wind disturbances. The first part is a literature survey of the spectral content of the wind disturbance. Next, a simplified model of a tip/tilt mirror control system is used to analyze the conditions for control-structure interaction. The influence of the asymptotic decay rate of the wind tilt disturbance on the magnitude and spectral content of the control torques is pointed out. A full telescope model is developed to justify a decoupled tip/tilt control design and to analyze the response of the primary mirror M1 to the disturbance generated by the control torques of the M5 unit.

Testing of sandwich molybdenum mirrors with radiative cooling for H-alpha and visible spectroscopy in ITER

The full-scaled mock-ups of the first spherical (M1) and the second flat (M2) mirrors for H-alpha and visible spectroscopy (HA&VS) in ITER were repeatedly heated within the temperature range of 100–350°C in a vacuum chamber (0.2–5Pa). The mock-ups were made of single crystal molybdenum segments bonded to a polycrystalline molybdenum substrate through a Ti interlayer by a hot isostatic pressure (HIP) technique. The goal of the test was to verify the stability of the mirror shape in ITER relevant conditions. The curvature of the mirror was optically measured in-situ. As a result, no damage or remarkable bending on the mirrors was observed. The maximum relative change of the M1 curvature at 350°C was −0.23%. The maximum curvature of the M2 mirror at 350°C was 1/670m−1. After cooling down to room temperature, the shape of the mock-ups was fully restored. Numerical simulation of HA&VS optics performance shows that the observed bending of the mirrors does not exceed the tolerable limits.

A soft X-ray plane-grating monochromator optimized for elliptical dipole radiation from modern sources.

A new but yet well proven way of making elliptically polarized dipole radiation from the BESSY II storage ring applicable to the SX700-type collimated plane-grating monochromator PM3 is described. It is shown that due to the limited vertical acceptance of the grating a simple use of vertical apertures is not possible in this case. Rather, deflecting the beam upwards or downwards by rotating the vertically collimating toroidal mirror M1 around the light axis leads to excellent performance. The resulting detuning of the photon energy can be taken into account by a readjustment of the monochromator internal plane mirror M2. The energy resolution of the beamline is not affected by the non-zero `roll' of the collimating mirror.

Corticospinal mirror neurons.

Here, we report the properties of neurons with mirror-like characteristics that were identified as pyramidal tract neurons (PTNs) and recorded in the ventral premotor cortex (area F5) and primary motor cortex (M1) of three macaque monkeys. We analysed the neurons’ discharge while the monkeys performed active grasp of either food or an object, and also while they observed an experimenter carrying out a similar range of grasps. A considerable proportion of tested PTNs showed clear mirror-like properties (52% F5 and 58% M1). Some PTNs exhibited ‘classical’ mirror neuron properties, increasing activity for both execution and observation, while others decreased their discharge during observation (‘suppression mirror-neurons’). These experiments not only demonstrate the existence of PTNs as mirror neurons in M1, but also reveal some interesting differences between M1 and F5 mirror PTNs. Although observation-related changes in the discharge of PTNs must reach the spinal cord and will include some direct projections to motoneurons supplying grasping muscles, there was no EMG activity in these muscles during action observation. We suggest that the mirror neuron system is involved in the withholding of unwanted movement during action observation. Mirror neurons are differentially recruited in the behaviour that switches rapidly between making your own movements and observing those of others.

Influence of resonator on sum-frequency CW generation power in an SRS-laser

Introduction. Laser radiation in the visible range is widely used in scientifi c research, chemistry, biology, medicine, and other areas. Therefore, research and development of all-solid-state lasers that generate effi ciently visible radiation are of great practical interest. (Quasi)-CW solid-state lasers with diode pumping, the cavity of which contains a stimulated-Ramanscattering (SRS) medium that increases the number of frequencies of generated IR radiation and a quadratically nonlinear medium that converts this radiation into the visible range by generating a harmonic and sum-frequency radiation (SFR), occupy a prominent place among such systems [1–7]. This results in a laser system in the cavity of which comparatively powerful beams of radiation exist and interact strongly. The radiation has at least four frequencies, i.e., the pumping, fundamental laser ωL, Stokes ωS, and sum ωG = ωL + ωS or harmonic ωG = 2ωS of the Stokes frequency. Such a system can also generate a harmonic ωG = 2ωL of the fundamental frequency [2, 4] but then there is no need to place an SRS medium in the cavity [8, 9]. Very high cavity gains at the fundamental and Stokes frequencies and a high transparency of the output mirror in the visible region are usually employed in order to obtain high generation effi ciency of visible radiation in the aforementioned systems. It is thought that there is no resonator at the visible radiation frequency, i.e., radiation generated during one pass of the nonlinear medium exits through the output mirror or dual-pass generation occurs if the system has surfaces that are refl ective at this frequency. Relationships describing the dependence of CW generation power of such a system on the pumping, active media, and resonator with no refl ection of the generated radiation at the output mirror have been published [10, 11]. Herein this limitation is lifted, i.e., the relationships defi ne the SFR generation power with a resonator and at the frequency of the generated radiation. Statement of the Problem. Let us examine as before SFR generation of a SRS-laser [10, 11]. Figure 1 shows a conceptual diagram of a laser system consisting of three (two for a self-Raman SRS-laser where media L and S are co-located) active media positioned co-axially in the cavity formed by mirrors M1 and M2. This is the active medium L of the primary laser generating radiation of frequency ωL (fundamental radiation); scattering (SRS) medium S that converts this radiation into Stokes component of frequency ωS; and a quadratically nonlinear medium N in which SFR generation occurs, ωG = ωL + ωS. Use of the third mirror M3 is desirable in order to direct the whole SFR output through a single mirror and avoid its losses in the active and SRS media. This mirror in system a should refl ect well radiation of frequency ωG and pass well radiation of frequencies ωL and ωS. In this instance, mirror M2 is the output mirror. It should pass SFR and be highly refl ective for the fundamental and laser radiation. Mirror M3 is the output mirror in system b and has high transmission for SFR and refl ects radiations ωL and ωS. In this instance, mirror M2 should refl ect well radiation of all three frequencies. The end surfaces of the active media can also fulfi ll to a certain extent the role of mirror M3.

Optical illusion alters M1 excitability after mirror therapy: a TMS study

The contralesional primary motor cortex (M1) has been suggested to be involved in the motor recovery after mirror therapy, but whether the ipsilesional M1 is influenced by the contralesional M1 via transcallosal interhemispheric inhibition (IHI) is still unclear. The present study investigated the change of IHI as well as the intracortical inhibition and intracortical facilitation of both M1 induced by training in a mirror with the use of transcranial magnetic stimulation (TMS). In this 2 × 2 factorial design (time × group), healthy subjects exercised standardized motor skills with their right hand on four consecutive days. Either a mirror (mirror group) or a board (control group) was positioned between their hands. Before and after training TMS was applied along with training tests of both hands. Tests were the same motor skills exercised daily by both groups. Tests of the untrained left hand improved significantly more in the mirror group than in the control group after training (P = 0.02) and showed a close correlation with an increase of intracortical inhibition of M1(left). IHI did not show any difference between investigation time points and groups. The present study confirms the previous suggestion of the involvement of the "contralesional" left-side (ipsilateral to the hand behind the mirror) M1 after mirror therapy, which is not mediated by IHI. Even with the same motor skill training (both groups performed same motor skills) but with different visual information, different networks are involved in training-induced plasticity.

High-Frequency Tunable EPR of Fe2+ in the Natural and Synthetic Forsterite

The natural forsterites and their synthetic analogs were investigated on a wide-band EPR spectrometer in the frequency region of 65–850 GHz. Two types of non-Kramers ions Fe2+ were discovered at the site M1 (inversion symmetry) and M2 (mirror plane symmetry). The ratio of concentrations of Fe2+ in these positions was measured in synthetic and natural crystals. The features of EPR spectra of synthetic and natural forsterite are discussed. Spin Hamiltonian with S = 1 was used for theoretical treatment of angular and field–frequency dependences.

Focusing light rays back to the vertex of a reflecting parabolic collector: the equivalent of Dionysius ear effect in optical systems

A vertical light ray coming from infinity is reflected by a primary parabolic mirror M1 having focus at F1. At a small distance from F1 a secondary mirror M2, symmetric with respect to the vertical axis, is placed. One would like to find the analytic equation of the mirror M2, so that all rays from infinity, incident on M1, could be sent back to the vertex V1 of the primary mirror M1. We denote the mirror M2 with the name of zozzaroid, after P Zozzaro, who first proposed the problem. Recalling the famous legend about Dionysius ear, we find that M2 has either an elliptic or a hyperbolic profile.

Mechanisms underlying mirror movements in Parkinson's disease: A transcranial magnetic stimulation study

The neural mechanisms underlying unintended mirror movements (MMs) of one hand during unimanual movements of the other hand in patients with Parkinson's disease (PD) are largely unexplored. Here we used surface electromyographic (EMG) analysis and focal transcranial magnetic stimulation (TMS) to investigate the pathophysiological substrate of MMs in four PD patients. Surface EMG was recorded from both abductor pollicis brevis (APB) and first dorsal interosseous (FDI) muscles. Cross-correlation EMG analysis revealed no common motor drive to the two APBs during intended unimanual tasks. Focal TMS of either primary motor cortex (M1) elicited normal motor-evoked potentials (MEPs) in the contralateral APB, whereas MEPs were not seen in the ipsilateral hand. During either mirror or voluntary APB contraction, focal TMS of the contralateral M1 produced a long-lasting silent period (SP), whereas stimulation of the ipsilateral M1 produced a short-lasting SP. During either mirror or voluntary finger tapping, 5 Hz repetitive TMS (rTMS) of the contralateral M1 disrupted EMG activity in the target FDI, whereas the effects of rTMS of the ipsilateral M1 were by far slighter. During either mirror or voluntary APB contraction, paired-pulse TMS showed a reduction of short-interval intracortical inhibition in the contralateral M1. These findings provide converging evidence that, in PD, MMs do not depend on unmasking of ipsilateral projections but are explained by motor output along the crossed corticospinal projection from the mirror M1.

Observation of nonlocal interference in separated photon channels.

A two-photon coincidence experiment of the kind recently proposed by J. D. Franson [phys. Rev. Lett. 62, 2205 (1989)] has been carried out with signal and idler photons produced in the process of parametric down-conversion. The coincidence rate registered by the two detectors is found to exhibit a cosine variation with the optical path difference, with periodicity equal to the wavelength. A number of fourth-order optical interference experiments have been carried out in recent years. [1-8] Unlike conventional second-order interference experiments, these depend on the detection of photon pairs and the interference of two two-photon probability amplitudes.[9] It The two-photon probability amplitude for the shorter is an interesting feature of those experiments that quantum mechanics allows the visibility of the interference to be larger for a two-photon state than is allowed by classical electromagnetic theory. A new and particularly simple form of fourth-order interference experiment with two photons has recently been proposed by Franson [10] as a test for locality violations. The outline of the experiment is shown in Fig. 1. Figure 1: Outline of the experiment proposed by Franson. Two photons emitted together by some common source travel along arms A and B to two detectors DA and DB, either directly along the shortest path or via a longer path involving reflections from two beam splitters and two mirrors, as shown. Franson supposed that the two photons might be produced by the cascade decay of an atom in which the initial excited state is very long lived. But we may also suppose that the two photons could arise from the down-conversion of a highly monochromatic laser beam, of long coherence time, in a nonlinear crystal.[11] In both cases the two photons are highly correlated in time and their state is an entangled quantum state. Let us suppose that the difference in propagation time between the longer and the shorter paths is the same in both channels and is much greater than the coherence time (reciprocal bandwidth 1/∆ω) of the light, or the length of each photon wave packet. Then one might naively suppose that there would be no interference. Indeed the mean detection rate registered by DA or DB would not show any dependence on path difference. However, we arrive at a different conclusion if we look for simultaneous detections by both DA and DB. The two-photon probability amplitude for the shorter paths, A to DA and B to DB, then interferes with the two-photon probability amplitude for the longer paths involving the two mirrors. After forming the sum of the two probability amplitudes and squaring we find that the coincidence rate exhibits a cosine variation with a path difference. This is so despite the fact that the two detectors are widely separated and the trajectories of the two photons never mix. We wish to report the results of an experiment in which this nonlocal interference effect, which has no direct classical counterpart, has been observed. The experiment is shown in Fig. 2. The source of the two photons is the process of spontaneous parametric down-conversion[11] in a crystal of LiIO3 that is optically pumped by the 351.1-nm line of an argon-ion laser. The signal (s) and idler (i) photons produced have wavelengths close to 700 nm but substantial bandwidth, which is restricted by interference filters to about 1012Hz. The main difference between the optical arrangement in our experiment and that proposed by Franson is that the variable delay is introduced via an unbalanced Michelson-type interferometer, rather than with the MachZehnder interferometer arrangement shown in Fig. 1. This requires only one beam splitter in each arm instead of two. One of the mirrors M1, of the Michelson interferometer is mounted on a motor-driven micrometer and can also be moved piezoelectrically, and this allows the optical path difference 2(BS−M1)k−2(BS−M2)k ≡ cTk (where k = s, i) to be nearly equalized in the two arms, and for Ti to be varied in submicron steps in a controlled manner about the fixed value cTi ≈ cTs ≈ 3 cm. The time difference Ts, Ti ∼ 10−10sec therefore greatly exceeds the coherence time 1/∆ω ∼ 10−12sec of the light. In order to make Ts and Ti equal to within 10−12sec in the signal and idler

Simon et al. Reply.

In our letter [1] the electric fields of both the incident beam and the beam reflected from the mirror m1 are described in the same transverse coordinate system (x,y), by the pair of complex electric field components Ex,Ey arranged as a column. ... Bhandari's difficulty [2] originates partly from a possible lack of clarity in the specification of the polarization states in our Letter and partly from a misconception that the return beam going through L will necessarily imply retracing of the circuit yielding a net zero geometric phase.