Ellipsoidal Mirror Research Articles

Flexible degenerate cavity with ellipsoidal mirrors.

Here we present a design of a traveling-wave optical cavity containing four identical ellipsoidal mirrors arranged in a square. The cavity proves to support more than 21 Laguerre-Gaussian modes simultaneously. There is a polarization splitting in the cavity that can be used for polarization filtering with a high isolation level.

Flexible high flux solar simulator based on optical fiber bundles

High flux solar simulators have been widely used in solar thermal research due to their controllable flux intensity. Simulators based on optical-fiber transmission have recently gained further attention because of their superior flexibility. In this study, we developed a flexible, high-flux solar simulator that consists of a xenon lamp-truncated ellipsoidal mirror array, a multicomponent glass optical-fiber bundle and a secondary concentrator. The flexibility of the fibers allows the simulator to produce various flux distributions in 2D and 3D space through corresponding optical-fiber bundle arrangements. Each bundle has a diameter of 10 mm and contains 30,000 optical fibers that can transmit the high flux of a xenon lamp to a target. The density of the spot can reach 500 kW/m2. The intensity of the flux produced is determined by the power of the lamps, and the transmission properties and temperature resistance of the fiber bundle.

Experimental study on hybrid compensation testing of an off-axis convex ellipsoid surface.

Aspherical surfaces can provide significant benefits to a wide variety of optical systems, but manufacturing high-precision aspherical surfaces has historically been limited by the ability to measure them. Null testing has always been the ideal method in aspherical measurement. However, in many cases, it is hard to realize null testing for complex surfaces, especially for convex surfaces in complicated forms. In this paper, we propose a hybrid compensation method combining a spherical mirror and a computer generated hologram (CGH) to achieve the null testing of the convex aspherical surface. Firstly, we introduce our self-developed mathematical models in the hybrid compensation method, including optics alignment model, distortion correction model and spherical surface error removing model. Then the performance of our proposed method is analyzed by a null testing experiment of an off-axis convex ellipsoid mirror. The experimental result shows that the proposed method can accomplish the hybrid compensation testing of convex aspherical surfaces effectively, and it can also bring much to the application of our method in convex aspherical surface testing.

Focal shift induced by source displacements and optical figure errors.

In this work the longitudinal shifts of the focal plane of an ellipsoidal mirror induced by longitudinal shifts of the source and by the optical figure error of the mirror itself are investigated. The case of an ideal mirror illuminated by a Gaussian beam is considered first, deriving an analytical formula predicting the source-to-focus shift. Then the realistic case of a mirror affected by surface shape defects is examined, by taking into account metrological data and numerically solving the Huygens-Fresnel integral. The analytical and numerical solutions in the ideal and real cases are compared. Finally, it is shown that an additional dependence of the focal shift is introduced on the wavelength and the pointing angle of the source. Both effects are investigated by numerical computations. We limit the treatment in the XUV spectral range, choosing as a test bench the Kirkpatrick-Baez mirror system of the DiProI and LDM end-stations and at the FERMI seeded free-electron laser (FEL). The work is primarily aimed at disentangling the different causes of focal shift at FEL light sources, where source position, wavelength and pointing angle are either tunable or rapidly fluctuating. The method can be easily extended to parabolic reflectors and refractors (lenses) with other kinds of illuminating sources and wavelengths.

Intense sub-micrometre focusing of soft X-ray free-electron laser beyond 1016 W cm-2 with an ellipsoidal mirror.

Intense sub-micrometre focusing of a soft X-ray free-electron laser (FEL) was achieved by using an ellipsoidal mirror with a high numerical aperture. A hybrid focusing system in combination with a Kirkpatrick-Baez mirror was applied for compensation of a small spatial acceptance of the ellipsoidal mirror. With this system, the soft X-ray FEL pulses were focused down to 480 nm × 680 nm with an extremely high intensity of 8.8×1016 W cm-2 at a photon energy of 120 eV, which yielded saturable absorption at the L-edge of Si (99.8 eV) with a drastic increase of transmittance from 8% to 48%.

Light field display with ellipsoidal mirror array and single projector.

We present a method to create light field display using a single projector and an array of plane mirrors. Mirrors can reproduce densely arranged virtual projectors regardless of the physical size of the real projector, thus producing a light field display of competitive ray density. We propose an ellipsoidal geometric framework and a design pipeline, and use parametric modelling technique to automatically generate the display configurations satisfying target design parameters. Three units of mirror array light field display systems have been implemented to evaluate the proposed methodologies. More importantly, we have experimentally verified that the high-density light field produced by our method can naturally evoke accommodation of the eyes, thereby reducing the vergence-accommodation conflict. The mirror array approach allows flexible trading between the spatial and angular resolutions for accommodating different applications, thus providing a practical solution to realize projection-based light field display.

Dedicated optical systems of the Institute of Applied Optics

The paper presents a collection of selected optical systems recently developed in the Institute of Applied Optics-INOS. The collection includes the family of techniques where the continuously modified wavelength facilitates high accuracy measurements of optical and geometrical features of the object in question i.e. the variable wavelength interferometry and confocal chromatic sensors. In addition, the paper refers to the construction of a new type of a spectrometer with rotating plasma and an illumination system supporting the road safety. Full Text: PDF ReferencesM. Pluta, Advanced Light Microscopy (Vol. 3, PWN, Elsevier, Warszawa-Amsterdam-London-New York-Tokyo, 1993). DirectLink M. Pluta, "Object-adapted variable-wavelength interferometry. I. Theoretical basis", Journal of Opt. Soc. Am., A4(11), 2107 (1987). CrossRef M. Pluta, "Variable wavelength microinterferometry of textile fibres", J. Microscopy, 149(2), 97 (1988). CrossRef M. Pluta, "On double‐refracting microinterferometers which suffer from a variable interfringe spacing across the image plane", Journal of Microscopy, 145(2), 191 (1987). CrossRef K. A. El-Farahaty, A. M. Sadik, A. M. Hezma, "Study of Optical and Structure Properties of Polyester (PET) and Copolyester (PETG) Fibers by Interferometry", International Journal of Polymeric Materials 56(7),715 (2007). CrossRef J. Galas, D. Litwin, M. Daszkiewicz, "New approach for identifying the zero-order fringe in variable wavelength interferometry", Proc. SPIE 10142, 101421R (2016). CrossRef A. Sadik, W. A. Ramadan, D. Litwin, "Variable incidence angle method combined with Pluta polarizing interference microscope for refractive index and thickness measurement of single-medium fibres", Measurement Science and Technology, IOP Publishing 14(10), 1753 (2003). CrossRef J. Galas, S. Sitarek; D. Litwin; M. Daszkiewicz, "Fringe image analysis for variable wavelength interferometry", Proc. SPIE 10445, 1044504 (2017). CrossRef D. Litwin, A. M. Sadik, "Computer-aided variable wavelength Fourier transform polarizing microscopy of birefringent fibers.", Optica Applicata 28(2), 139 (1998). DirectLink D. Litwin, J. Galas, N. Błocki, "Automated variable wavelength interferometry in reflected light mode", Proc.SPIE 6188, 61880F (2006). CrossRef M. Pluta, "Variable wavelength interferometry of birefringent retarders", Opt. Laser Technology, 19(3), 131 (1987). CrossRef K. Fladischer et al. "An ellipsoidal mirror for focusing neutral atomic and molecular beams", New journal of Physics, 12(3) 033018 (2010). CrossRef K. Fladischer et al. "An optical profilometer for characterizing complex surfaces under high vacuum conditions", Precision engineering Elsevier 32(3), 182 (2008). CrossRef A.E. Weeks et al. "Accurate surface profilometry of ultrathin wafers", Semiconductor Science and Technology", IOP Publishing, 22(9), 997 (2007). CrossRef D. Litwin et al. "Overview of the measuring systems where a continuously altered light source plays a key role: Part I", Proc. SPIE 10808, 10 8080B (2018). CrossRef D. Litwin et al. "Noise reduction in an optical emission spectrometer with rotating diffraction grating", Proc. SPIE 10142 101421Q (2016). CrossRef D. Litwin et al. "Photonics approach to traffic signs", Proc SPIE 10142 1014214, (2016). CrossRef

Broadband nano-focusing of high-order harmonics in soft X-ray region with ellipsoidal mirror

We demonstrate broadband focusing of multiple high-order harmonics of intense femtosecond laser pulses using an ellipsoidal mirror. The ellipsoidal mirror, with a high numerical aperture and a highly accurate surface, was fabricated using a replication process. The multiple high-order harmonics in the wavelength range between 10 and 20 nm were focused to the nearly diffraction-limited size of 350 × 380 nm2. According to Rayleigh's quarter wavelength criteria, the wavefront aberration of the focused beam was estimated to be less than 5 nm, which corresponds to a temporal dispersion of 16 as. The developed focusing system is suited for producing an intense attosecond laser field with negligible wavefront aberration, with which nonlinear light-matter interactions in the attosecond time domain can be explored.

Annular subaperture interferometry for high-departure aspheres using paraboloidal parameterization.

A low-cost technique is presented for constructing stitched Fizeau interferometric measurements of high-spherical-departure concave aspheres of arbitrary conic constant without the use of null optics. The optical test configuration assembles the surface figure of the asphere using subapertures parameterized as variances from best-fit paraboloids. Subtracting the optical path difference between each idealized paraboloid and the corresponding annulus of measured data removes the annular wavefront aberrations without the need to fit Zernike polynomials. The proof-of-concept measurement and reconstruction of a 250mm diameter diamond-turned ellipsoidal mirror with more than 3000 waves of spherical departure are reported. The presented technique is an inexpensive addition to the array of tools used to measure large-aperture aspheres and high-departure freeform optics.

Brilliance improvement of laser-produced extreme ultraviolet and soft x-ray plasmas based on pulsed gas jets

Two methods improving the brilliance of laser-induced plasmas emitting in the extreme UV (EUV) and soft x-ray (SXR) regions were investigated, using three different gases (nitrogen, krypton, and xenon) from a pulsed gas jet. Utilizing a newly designed piezoelectric valve, up to almost ten times higher gas pressures were applied, resulting in increased target densities and thus, higher conversion efficiencies of laser energy into EUV and SXR radiation. Secondly, geometrically reducing the angle between the incoming laser beam and the observed plasma emission minimizes reabsorption of the emitted short wavelength radiation. Combining both methods, the source brilliance is increased by a factor of 5 for nitrogen. Furthermore, a compact EUV focusing system for metrological applications is presented utilizing the optimized plasma source. An energy density of 1 mJ/cm2 at wavelength λ = 13.5 nm in the focal spot of an ellipsoidal mirror is achieved with xenon as the target gas being sufficient for material removal of PMMA samples with an ablation rate of 0.05 nm/pulse.

Alignment of solid targets under extreme tight focus conditions generated by an ellipsoidal plasma mirror

The design of ellipsoidal plasma mirrors (EPMs) for the PEARL laser facility is presented. The EPMs achieve a magnification of 0.32 in focal spot size, and the corresponding increase in focused intensity is expected to be about 8. Designing and implementing such focusing optics for short-pulse (<100 fs) systems paves the way for their use in future high-power facilities, where they can be used to achieve intensities beyond 1023 W/cm2. A retro-imaging-based target alignment system is also described, which is used to align solid targets at the output of the ellispoidal mirrors (with a numerical aperture of 0.75 in this case).

Ellipsoidal mirror dark-field scanning for detection of circulating tumor cells

The detection of circulating tumor cells (CTCs) plays a very important role in the prevention and treatment of cancer. However, because of the low content of tumor cells in peripheral blood, these cells have always been difficult to detect. An efficient and accurate imaging method, the dark-field scanning imaging method, was innovatively proposed for the detection of CTCs in filtered and colored peripheral blood specimens. Here, the original dark-field scanning system was improved. By introducing an ellipsoidal mirror system, the noise in the sampling process is greatly reduced, and the sampling accuracy is significantly improved. Meanwhile, an automatic identification algorithm was developed to identify and screen CTCs in a large number of blood samples. Comparing with the other CTC detection methods, this method does not require a complex biological enrichment process, which may cause loss and destruction of CTCs.

Development of electroforming process for soft x-ray ellipsoidal mirror.

An x-ray ellipsoidal mirror is an ideal tool for focusing soft x-rays. Because nanometer-level shape accuracy is required in the internal surface of a mirror having a small diameter, it is difficult to fabricate the mirror by processing the surface directly. We developed a fabrication process for soft x-ray ellipsoidal mirrors in which the surface of a high-precision quartz mandrel with the inverted shape of the designed mirror is replicated by nickel sulfamate electroforming. In this study, an ellipsoidal mirror of 40-mm length was fabricated and the shape accuracy of the replicated surface was evaluated by a measurement method using a contact probe. The root mean square (RMS) of the replication error in the entire measured surface was 27.2 nm. When the evaluated area was half the replicated surface near the middle of the mirror, the RMS of the replication error was 14.7 nm. Wave-optical simulation suggested that it is possible to focus soft x-rays to a spot with a diameter of 400 nm.

Beam tracing study for design and operation of two-pass electron cyclotron heating at ASDEX Upgrade

The electron cyclotron resonance heating system at ASDEX Upgrade (AUG) is currently being extended to eight similar Gyrotrons in total. Each Gyrotron operates at 105 and 140 GHz and is designed for up to 1 MW millimetre wave output power. A substantial part of the AUG program will focus on experimental conditions, where the plasma density may be above the X-2 cut-off density at 140 GHz. In order to cope with the high density, the heating system will operate in the O-2 mode scheme with potentially incomplete absorption in the first pass. Reflecting gratings installed into the heat shield on AUG’s inner column allow for a controlled second pass of the beam’s unabsorbed fraction. Thermocouple measurements serve to control the beam position on the grating. The beam geometry is being finalized for the launchers #1-4. Beam propagation is simulated with the TORBEAM code and previous high density experiments are used as a database. The geometry is optimized using three criteria: central deposition, high absorption and robustness of the beam dump after the second pass. The experimental conditions, and the plasma electron density in particular, may vary such that the Gaussian beam parameters of the incoming beam on the grating deviate from the design values. It is proposed to model the effect of the grating with an equivalent ellipsoidal mirror. Laboratory measurements are shown, which support this model.

Off-axis ellipsoid focus method for a direct kilowatt-class laser diode stack for material processing

An off-axis ellipsoid focus system is designed to focus rectangular beams that are emitted by a direct high-power laser diode (LD) stack for material processing. This off-axis ellipsoid focus method can be applied to LD stacks with different spot sizes. Compared to other focusing methods, only this focus system designed an ellipsoid mirror to simultaneously focus the fast and slow axis laser beams in the same focal plane. The detailed process of the theoretical derivation is shown in this paper, and the corresponding formula is summarized finally. The focus system and light path are simulated by ZEMAX software, and the corresponding experiment is also performed. The spot size of the LD stack is 42 mm × 10 mm (fast axis × slow axis). This rectangular spot is focused into an ellipse spot whose size is 1.5 mm × 3.0 mm, with a 300-mm focal length. This focus system can be directly used for material processing.

Fabrication of a precise ellipsoidal mirror for soft X-ray nanofocusing.

In X-ray focusing, grazing incidence mirrors offer advantages of no chromatic aberration and high focusing efficiency. Although nanofocusing mirrors have been developed for the hard X-ray region, there is no mirror with nanofocusing performance in the soft X-ray region. Designing a system with the ability to focus to a beam size smaller than 100 nm at an X-ray energy of less than 1 keV requires a numerical aperture larger than 0.01. This leads to difficulties in the fabrication of a soft X-ray focusing mirror with high accuracy. Ellipsoidal mirrors enable soft X-ray focusing with a high numerical aperture. In this study, we report a production process for ellipsoidal mirrors involving mandrel fabrication and replication processes. The fabricated ellipsoidal mirror was assessed under partial illumination conditions at the soft X-ray beamline (BL25SU) of SPring-8. A focal spot size of less than 250 nm was confirmed at 300 eV. The focusing tests indicated that the proposed fabrication process is promising for X-ray mirrors that have the form of a solid of revolution, including Wolter mirrors.

<i>In Situ</i> Synchrotron X-Ray Topography Observation of Double-Ended Frank-Read Sources in PVT-Grown 4H-SiC Wafers

We present in-situ observations of the dynamical operation of multiple double-ended Frank-Read dislocation sources in a PVT-grown 4H-SiC wafer under thermal gradient stresses. The nucleation of these sources is facilitated by a specific configuration consisting of one basal plane dislocation (BPD) segment pinned by two threading edge dislocations (TEDs). This configuration is formed during PVT crystal growth by deflection of TEDs on to the basal planes by macrosteps and re-deflection of resulting BPDs back into TEDs. Under the influence of thermal gradient stresses induced by heating inside a double ellipsoidal mirror furnace, the pinned BPD segment glides and activates dislocation multiplication by the double Frank-Read source mechanism. A more intricate mechanism of swapping of TED pinning points between Frank-Read sources lying on same basal plane is identified, enabling one dislocation loop to effectively “pass through” the other dislocations on same basal plane.

Development of multiple-eye PIV using mirror array

In order to reduce particle image velocimetry measurement error, we manufactured an ellipsoidal polyhedral mirror and placed it between a camera and flow target to capture n images of identical particles from n (=80 maximum) different directions. The 3D particle positions were determined from the ensemble average of nC2 intersecting points of a pair of line-of-sight back-projected points from a particle found in any combination of two images in the n images. The method was then applied to a rigid-body rotating flow and a turbulent pipe flow. In the former measurement, bias error and random error fell in a range of ±0.02 pixels and 0.02–0.05 pixels, respectively; additionally, random error decreased in proportion to . In the latter measurement, in which the measured value was compared to direct numerical simulation, bias error was reduced and random error also decreased in proportion to .

Research on a wide-angle diagnostic method for shock wave velocity at SG-III prototype facility

A wide-angle diagnostic method for shock wave velocity is proposed in this paper. An ellipsoidal equation deduced for wide-angle diagnosis by using geometrical optical laws is presented. The combination of an ellipsoidal mirror and a traditional velocity interferometer system for any reflector (VISAR) forms a wide-angle VISAR. Several fundamental problems such as assembly, imaging, and interference in the wide-angle VISAR are discussed. The method is proven to be feasible based on the results of an eight-beam laser direct drive experiment at SG-III prototype facility. The diagnostic method is expected to be usable in a wide variety of experiments, especially those related to implosion compression, including high-pressure equation of state experiments, materials characterization experiments, shock characterization for Rayleigh–Taylor experiments, and shock timing experiments for inertial confinement fusion research.

Development of figure correction system for inner surface of ellipsoidal mirrors

X-ray mirrors are widely used in advanced x-ray facilities. An ellipsoidal mirror is used in soft x-ray focusing optics. To prevent a decrease in the intensity density or distortion of the wavefront of reflected x-ray beams, the inner surface of an ellipsoidal mirror should have high precision. Differential deposition is a method of fabricating a shape on a mirror surface. However, mirrors with a small diameter cannot be corrected by the conventional process.In this study, a figure correction method employing ion beam sputtering deposition was developed. The sputtering target is placed inside the ellipsoidal mirror. Then, a cylindrical tube with a small aperture is inserted inside the mirror to realize selective deposition. The figure accuracy of an ellipsoidal mirror is improved even when its diameter is less than 10 mm. This figure correction system can also be applied to various axisymmetric devices with a small diameter.