Light from an object (such as a tree) enters the eye first through the clear cornea and then through the pupil the circular aperture (opening) in the iris.  Next, the light is converged by the lens to a nodal point immediately behind the lens; at that point, the image becomes inverted.  The light progresses through the gelatinous vitreous humor and, ideally, back to a clear focus on the retina, the central area of which is the macula. In the retina, light impulses are changed into electrical signals and then sent along the optic nerve and back to the occipital (posterior) lobe of the brain, which interprets these electrical signals as visual images

Regular spherical contact lenses have an even curvature across the entire lens surface; in contrast, aspheric lenses have varying curvatures across the surface ...

Skinner, G. K. Design and imaging performance of achromatic diffractive-refractive x-ray and gamma-ray Fresnel lenses. Appl. Opt. 43, 4845–4853 (2004).

The photothermal process occurs first with the absorption of photon energy, producing a vibrational excited state in molecules, and then in elastic scattering with neighboring molecules, increasing their kinetic energy and creating a temperature rise. Under normal conditions the kinetic energy per molecule (kT) is about 0.025 eV. Heating effects are largely controlled by molecular target absorption such as free water, haemoproteins, melanin, and other macromolecules such as nucleic acids.

The cornea, lens and vitreous fluid are transparent to wavelengths. Damage to the retinal tissue occurs by absorption of light and its conversion to heat by the melanin granules in the pigmented epithelium or by photochemical action to the photoreceptor. The focusing effects of the cornea and lens will increase the irradiance on the retina by up to 100,000 times. For visible light 400 to 700 nm the aversion reflex which takes 0.25 seconds may reduce exposure causing the subject to turn away from a bright light source. However, this will not occur if the intensity of the laser is great enough to produce damage in less than 0.25 sec. or when light of 700 – 1400 nm (near infrared) is used, as the human eye is insensitive to these wavelengths.

Cowley, J. M. & Moodie, A. F. The scattering of electrons by atoms and crystals. I. A new theoretical approach. Acta Crystallogr. 10, 609–619 (1957).

a Principle of achromatic focusing: The chromaticity of the defocusing refractive lens (RL) acts as a corrector for the chromatic behaviour of the focusing Fresnel zone plate (FZP). b Scanning electron microscopy (SEM) image of a nickel FZP fabricated by electron-beam lithography and nickel electroplating, as used for the comparison measurements. c SEM image of the RL consisting of four stacked paraboloids 3D-printed using two-photon polymerisation lithography. d Sketch of the experimental setup for scanning transmission X-ray microscopy (STXM) and ptychography using the achromat as a focusing optic.

In the visible-light regime, chromatic aberration of refractive lenses was observed already centuries ago, impairing the performance of telescopes6. In the mid-18th century, Chester Moor Hall found a solution for tackling the chromaticity by stacking a focusing lens made of crown glass and a defocusing lens made of flint glass to form an achromatic doublet7. Owing to the dispersion being stronger for flint glass than for crown glass, a proper combination of the two lenses provided identical focal lengths for two distinct wavelengths and low chromatic aberration for the wavelength range between them, despite the strong chromaticity of each individual lens. The span between these two wavelengths over which the remaining change in focal length lies within the depth of focus (DOF) is commonly defined as the achromatic range.

Experiments were performed at the cSAXS beamline of the Swiss Light Source at the Paul Scherrer Institute, Villigen, Switzerland. Monochromatic X-rays of different energies were extracted from the undulator spectrum with a silicon double-crystal monochromator (relative energy bandwidth:~10−4). The experimental setup for the measurements is sketched in Fig. 1d. The beam-shaping slits upstream of the setup were set to a position that ensured fully coherent illumination of the lens aperture. Further downstream, the incident X-ray beam was reduced to the size of the lens aperture by a pinhole of 100 μm diameter. The beam was then focused with the achromat consisting of the RL and the blazed FZP that were separated by approximately 1 mm along the beam direction. Undesired diffraction orders of the FZP were removed by an order-sorting aperture (OSA) of 30 μm diameter mounted downstream of the achromat. The X-ray probe shaped this way illuminated a Siemens star test object, and the resulting diffraction pattern was recorded by a photon-counting detector located approximately 7 m downstream of the sample.

The layers of the skin, which are of concern in a discussion of laser hazards to the skin, are the epidermis and the dermis. The epidermis layer lies beneath the stratum corneum and is the outermost living layer of the skin. The dermis mostly consists of connective tissue and lies beneath the epidermis.

The exposure to a visible laser beam can be detected by a bright color flash of the emitted wavelength and an after-image of its complementary color (e.g., a green 532 nm laser light would produce a green flash followed by a red after-image). When the retina is affected, there may be difficulty in detecting blue or green colors secondary to cone damage and pigmentation of the retina may be detected.

Apochromatic vsachromatic

In the last decade, X-ray ptychography25,26 has been identified as a powerful tool for characterising X-ray optics27,28,29. The method was used here to retrieve the caustics of the X-ray beam illuminating the sample. The Siemens star test pattern was scanned over an area of 4 × 4 μm2 following a Fermat spiral pattern with a step size of 250 nm and the diffraction patterns were recorded with an Eiger 500k single-photon counting detector (chip size: 512 × 1024 pixels, pixel size: 75 × 75 μm2). The exposure time for each recorded pattern was 200 nm. The X-ray probe was retrieved from the measurements using the ptychographic reconstruction framework PtychoShelves30. The probe intensity was then numerically free-space propagated using an angular-spectrum propagator implemented in PtychoShelves. From the beam caustics retrieved this way, information on the position of the focal plane and the size of the focal spot was extracted at each X-ray energy for the achromat as well as the single FZP. The measured data points for the focal length in Fig. 3c represent the positions of the voxel with highest intensity in each caustic.

Photoablation is the photodissociation or direct breaking of intramolecular bonds in biopolymers, caused by absorption of incident photons and subsequent release of biological material. Molecules of collagen, for example, may dissociate by absorption of single photons in the 5–7 eV energy range. Excimer lasers at several ultraviolet wavelengths (ArF, 193 nm/6.4 eV; KrF, 248 nm/5 eV; XeCl, 308 nm/4 eV) with nanosecond pulses focused on tissue at power densities of about 108 W/cm2 can produce this photoablative effect. Ultraviolet radiation is extremely strongly absorbed by biomolecules, and thus absorption depths are small, of the order of a few micrometers.

Malinauskas, M., Farsari, M., Piskarskas, A. & Juodkazis, S. Ultrafast laser nano-structuring of photopolymers: a decade of advances. Phys. Rep. 533, 1–31 (2013).

Antireflection coatings minimize the reflection of one or many wavelengths and are typically used on the surface of lenses so that less light is lost.

Aug 21, 2023 — How to use Gel Nail Glue - Guide Preparation: Start by cleaning your hands and nails to remove dirt and impurities. Remove any old nail ...

The major danger of laser radiation is hazards from beams entering the eye. The eye is the organ most sensitive to light. A laser beam (400-1400 nm) with low divergence entering the eye can be focused down to an area 10 to 20 microns in diameter.

Light below 400 nm does not focus on the retina. The light can be laser output, ultraviolet (UV) from the pump light, or blue light from a target interaction. The effect is cumulative over a period of days. The ANSI standard is designed to account only for exposure to laser light. If UV light from a pump light or blue light from a target interaction is emitted, additional precautions must be taken.

Poulsen, S. O., Poulsen, H. F. & Bentley, P. M. Refractive and diffractive neutron optics with reduced chromatic aberration. Nucl. Instrum. Methods Phys. Res. A 767, 415–420 (2014).

The RL was modelled as a single lens with one refraction interface and a diameter of 100 μm, a height of 904 μm and an apex radius of 1.38 μm, made of a material with chemical formula C14H18O7 and density of 1.2 g/cm3, see above. It was sliced 100 times using multi-slice propagation32,33. The simulated FZP consisted of 2.2 μm-high nickel structures. It had a diameter of 100 μm and an outermost zone width of 415 nm. To obtain focusing in the correct plane, the separation of the two elements in the simulation was set to the physical separation of 1 mm plus the thickness of the RL, giving a total of 1.904 mm.

Fortunately the eye has a self-defense mechanism — the blink and aversion response. Aversion response is the closing of the eyelid, or movement of the head to avoid exposure to bright light. The aversion response is commonly assumed to occur within 0.25 sec and is only applicable to visible laser wavelengths. This response may defend the eye from damage where lower power lasers are involved, but cannot help where higher power lasers are involved. With high power lasers, the damage can occur in less time than a quarter of a second.

Thermal damage occurs because of the conversion of laser energy into heat. With the laser’s ability to focus on points a few micrometers or millimeters in diameter, high power densities can be spatially confined to heat target tissues. Depth of penetration into the tissue varies with wavelength of the incident radiation, determining the amount of tissue removal and bleeding control.

The solid red curve in Fig. 3c represents the BFL values calculated according to Eq. (6). The dashed red curve in Fig. 3c was obtained using tabulated values of the refractive index of the RL material at the different energies15. The slight difference between the two curves is due to the fact that the tabulated values take into account the material dispersion, whereas in Eq. (6) it is assumed to be negligible (D ≈ 0). For the X-ray energy range in our experiment, far from the absorption edges, this approximation holds well and the difference between the two curves is small.

X-ray techniques for the non-invasive investigation of the inner structure and elemental composition of matter at the micro- and nanoscale require high-performance X-ray optics. For this purpose, various types of reflective, refractive, and diffractive optical elements have been developed in the last decades1,2,3. Reflective X-ray optics rely on grazing incidence configuration and require complicated geometries to produce a magnified image of an extended field of view4,5, resulting in long focal lengths that are incompatible with a compact setup. While these limitations do not apply to refractive and diffractive optics, making them more suitable for the formation of magnified X-ray images, they suffer from inherent chromatic aberration, meaning that X-rays of different energies are not focused to the same focal plane. As a consequence, the performance of these optics for multi-energy or spectroscopic measurements at synchrotrons and for high-resolution microscopy at polychromatic X-ray tube sources has to date been severely limited.

a Caustics at energies from 5.2 keV to 8.0 keV obtained with the achromat. The red dashed line indicates the location of the focal plane at the different energies. b Comparison of the caustics obtained with the achromat and the FZP. While the position of the focal plane remains almost constant with the energy for the achromat (red dashed line), it changes rapidly for the FZP (blue dashed line). c Calculated curves (solid and dashed lines) and experimental data (dots) for the focal length versus energy for the FZP (blue) and the achromat (red; solid: based on Eq. (6), dashed: based on tabulated refractive index values for the calculation of fRL at each energy).

The achromat was designed in a way that the RL acted as a corrector for the chromaticity of the FZP. The efficiency of such an achromat can be approximated by the product of the diffraction efficiency of the FZP and the X-ray transmission through the RL, which results in a theoretical efficiency of about 24% at the design energy of 6.2 keV for our optics.

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The surface of the cornea absorbs all UV of these wavelengths which produce a photokeratitis (welders flash) by a photochemical process, which cause a denaturation of proteins in the cornea. This is a temporary condition because the corneal tissues regenerate very quickly.

The BFL is the position of the focus measured from the downstream optical element, here the FZP. The energy dependence of li(E) can be described by considering the energy dependences of fFZP(E) and fRL(E):

Matsuyama, S. et al. 50-nm-resolution full-field X-ray microscope without chromatic aberration using total-reflection imaging mirrors. Sci. Rep. 7, 46358 (2017).

The iris diaphragm regulates the amount of light passing though the microscope lenses, producing varying degrees of image brightness. It is identified by a ...

The RL was 3D-printed with two-photon polymerisation-induced lithography using a Nanoscribe Photonic Professional GT20. The flexible capabilities of two-photon polymerisation have been exploited previously for the fabrication of various types of X-ray optics such as compound RLs for focusing and phase plates for wavefront correction14,21.

A further dependency was found concerning the irradiated area on the retina, i.e. increasing the retinal spot from 6.4 to 9.4 mm2 up to 33.7 to 46.8 mm2 resulted in an increase of the blink reflex  percentage from 20 % to 33.3 %.

Monochromaticaberration

If a laser burn occurs on the fovea, most fine (reading and working) vision may be lost. If a laser burn occurs in the peripheral vision, it may produce little or no effect on vision.

Corneal tissue will absorb light with a wavelength longer than 1400 nm. Damage to the cornea results from the absorption of energy by tears and tissue water causing a temperature rise and subsequent denaturation of protein in the corneal surface.

Symptoms of a laser burn in the eye include a headache shortly after exposure, excessive watering of the eyes, and sudden appearance of floaters in your vision. Floaters are those swirling distortions that occur randomly in normal vision most often after a blink or when eyes have been closed for a couple of seconds. Floaters are caused by dead cell tissues that detach from the retina and choroid and float in the vitreous humor. Ophthalmologists often dismiss minor laser injuries as floaters due to the very difficult task of detecting minor retinal injuries. Minor corneal burns cause a gritty feeling, like sand in the eye.

Exposure to the Q-switched Nd:YAG laser beam (1064 nm) is especially hazardous and may initially go undetected because the beam is invisible and the retina lacks pain sensory nerves. Photoacoustic retinal damage may be associated with an audible “pop” at the time of exposure. Visual disorientation due to retinal damage may not be apparent to the operator until considerable thermal damage has occurred.

a Convolution of the simulated polychromatic X-ray beam of the achromat with the binarised image of the Siemens star in Fig. 2b. b Convolution of the same image with the simulated polychromatic X-ray beam of the FZP. Gaussian noise was added to both images after convolution to model the image noise in experimental data. c Line profiles of the simulated polychromatic X-ray beams (normalised to central peak) for the achromat (red) and the FZP (blue).

Achromaticdoublet formula

Dichroitische Strahlteiler erfüllen sehr enge Spektrumstoleranzen und stellen eine maximale spektrale Stabilität sowie einen sehr geringen.

where (1 − δ) and β are the real and imaginary parts of n, λ is the X-ray wavelength, re the classical radius of the electron, and na the number of atoms per volume. For the majority of the X-ray regime, the real part f1 of the atomic scattering factor changes only little with λ, meaning that the material dispersion D of f1 is close to zero, D = (Δf1/f1)/(Δλ/λ) ≈ 0, and δ can be approximated as δ ∝ λ2 for all materials (see Eq. (1)). Only near the absorption edges, D reaches large positive or even negative values, leading to anomalous dispersion. Combining two refractive X-ray lenses from different materials therefore cannot provide achromatic behaviour over an extended range of X-ray wavelengths.

Achromaticdoublet meaning

This type of damage requires beams of extremely high power density (109–1012 W/cm2) in extremely short pulses (ns) to delivery fluences of about 100 J/cm2 and very high electric fields (106–107 V/cm), comparable to the average atomic or intermolecular electric field. Such a pulse induces dielectric breakdown in tissue, resulting in a microplasma or ionized volume with a very large number of electrons. A localized mechanical rupture of tissue occurs due to the shock wave associated with the plasma expansion. Laser pulses of less than 10 microseconds duration can induce a shock wave in the retinal tissue that causes tissue rupture. This damage is permanent, as with a retinal burn. Acoustic damage is actually more destructive to the retina than a thermal burn. Acoustic damage usually affects a greater area of the retina, and the threshold energy for this effect is substantially lower. The ANSI MPE values are reduced for short laser pulses to protect against this effect.

Simulations of X-ray focusing were performed for both an achromat, consisting of a RL and a FZP, and a single FZP. In-house developed code in Matlab was used for the simulations, which is based on an angular-spectrum approach described in earlier publications31.

The cornea, lens and aqueous humour allow Ultraviolet radiation of these wavelengths and the principal absorber is the lens. Photochemical processes denature proteins in the lens resulting in the formation of cataracts.

Exposure in the shorter UV-C (0.200 µm-0.280 µm) and the longer UV-A ranges seems less harmful to human skin. The shorter wavelengths are absorbed in the outer dead layers of the epidermis (stratum corium) and the longer wavelengths have an initial pigment-darkening effect followed by erythema if there is exposure to excessive levels.

Sphericalaberration

Chapman, H. N. & Bajt, S. High-resolution achromatic X-ray optical systems for broad-band imaging and for focusing attosecond pulses. Proc. R. Soc. A 477, 20210334 (2021).

Refractive and diffractive X-ray lenses, on the other hand, scale differently regarding their chromaticity, which opens up the fundamental possibility of combining them to compensate for chromatic aberration and form an X-ray achromat8,9, see Fig. 1a. In the theoretical work by Wang et al.8, a general expression providing achromatic behaviour is derived for the ratio of the focal lengths fRL of the RL and fFZP of the diffractive FZP:

Achromaticlens

Exposure to the invisible carbon dioxide laser beam (10,600 nm) can be detected by a burning pain at the site of exposure on the cornea or sclera.

The chief concern over laser use has always been the possibility of eye injury. While skin presents a greater target, it is injury to one’s eyes that drives laser safety, funding, controls and application. The effect of laser radiation will vary with the wavelength and part of the eye it interacts with. In addition biological effects from direct exposure and diffuse reflection exposure will differ. The anatomy of the eye and skin will be explained and issues associated with biological effects.

The presented work describes the proof-of-principle of an X-ray achromat, leaving room for further improvements through advances in manufacturing techniques and design. Reducing the X-ray spot size will require RLs with stronger refracting power and thus higher structures with smaller radii of curvature. This challenge, along with the significant absorption losses in the RL, can be addressed by designing the RL with a stepped profile, as suggested previously8. Furthermore, while in its current implementation the diffractive and the refractive parts of the achromat are mounted on two separate support membranes, we will explore the fabrication as a single monolithic device in the future. This will simplify the alignment and use of the achromatic X-ray lens at the experimental setup.

A specular reflection, which is a reflection off a mirror like surface (keeping in mind different surfaces to different wavelengths may or may not be mirror like. Specular reflection will result when the surface roughness is smaller than the wavelength. Specular reflections are generally less than 100%.

Seiboth, F. et al. Perfect X-ray focusing via fitting corrective glasses to aberrated optics. Nat. Commun. 8, 14623 (2017).

Apochromaticaberration

Kewish, C. M. et al. Ptychographic characterization of the wavefield in the focus of reflective hard X-ray optics. Ultramicroscopy 110, 325–329 (2010).

Figure 2a presents the STXM images of the Siemens star test sample shown in Fig. 2b acquired with the achromat as a focusing optic at different X-ray energies. No significant change of the image quality is visible between 6.0 keV and 7.2 keV. The significant advantage of using the achromat is clear when directly comparing its performance with STXM data obtained with the FZP as an optical element, see Fig. 2c. While the achromat delivers images of consistently high contrast and spatial resolution over a wide energy range, the images taken with the FZP exhibit severe blurring already at X-ray energies deviating 200 eV from its design energy of 6.2 keV. The achromat is capable of resolving line widths below 400 nm over its achromatic range, however, it does not reach the image quality of the FZP at its design energy. This is due to shape imperfections in the refractive element resulting in aberrations and will be improved in future designs of the achromat.

The subcutaneous tissue is a layer of fat and connective tissue that houses larger blood vessels and nerves. This layer is important is the regulation of temperature of the skin itself and the body. The size of this layer varies throughout the body and from person to person.

There is quite a variation in depth of penetration over the range of wavelengths, with the maximum occurring around 700 to 1200 nm. Injury thresholds resulting from exposure of less than 10 seconds to the skin from far-infrared and far-ultraviolet radiation are superficial and may involve changes to the outer dead layer of the skin. A temporary skin injury may be painful if sufficiently severe, but it will eventually heal, often without any sign of injury. Burns to larger areas of the skin are more serious, as they may lead to serious loss of body fluids. Hazardous exposure of large areas of the skin is unlikely to be encountered in normal laser work.

The safest reflection is the diffuse reflection, a reflection off a surface that spreads out the laser radiation reducing its irradiance. A diffuse surface will be one where the surface roughness is larger that the wavelength.

Eskildsen, M. R. et al. Compound refractive optics for the imaging and focusing of low-energy neutrons. Nature 391, 563–566 (1998).

To the skin, UV-A (0.315 µm-0.400 µm) can cause hyperpigmentation and erythema. UV-B and UV-C, often collectively referred to as “actinic UV,” can cause erythema and blistering, as they are absorbed in the epidermis. UV-B is a component of sunlight that is thought to have carcinogenic effects on the skin. Exposure in the UV-B range is most injurious to skin. In addition to thermal injury caused by ultraviolet energy, there is the possibility of radiation carcinogenesis from UV-B (280 nm – 315 nm) either directly on DNA or from effects on potential carcinogenic intracellular viruses.

A sensation of warmth resulting from the absorption of laser energy normally provides adequate warning to prevent thermal injury to the skin from almost all lasers except for some high-power far-infrared lasers. Any irradiance of 0.1 W/cm2 produces a sensation of warmth at diameters larger than 1 cm. On the other hand, one tenth of this level can be readily sensed if a large portion of the body is exposed. Long-term exposure to UV lasers has been shown to cause long-term delayed effects such as accelerated skin aging and skin cancer.

Henke, B., Gullikson, E. & Davis, J. X-ray interactions: photoabsorption, scattering, transmission, and reflection at E = 50–30000 eV, Z = 1–92. At. Data Nucl. Data Tables 54, 181–342 (1992).

The manufacturing process of the RL was similar to the methods described by Lyubomirskiy et al.21. Nanoscribe IP-S resist in dip-in lithography mode with a 25× objective was used. The total writing time was approximately 17 h. The RL was printed in vertical geometry on a 250 nm-thick Si3N4 membrane and consisted of a stack of N = 4 individual paraboloid elements of R = 5.3 μm apex radius and 236 μm height each. Its focal length fRL is hence given by:

A dispersion of D ≪ − 2 can be found for wavelengths near the absorption edges in the extreme ultra-violet and the soft X-ray regimes. Wang et al. conclude that one can thus form an achromat by combining a focusing FZP with a weakly focusing RL. This elegant solution, however, is limited to narrow wavelength ranges where a material suitable for the fabrication of the refractive corrector shows strongly negative dispersion. In the broad wavelength ranges far from the absorption edges, where D ≈ 0, the focal length of a FZP is proportional to the inverse wavelength, fFZP ∝ λ−1, whereas the focal length of a RL scales as fRL ∝ λ−2. Therefore, according to Eq. (2), an X-ray achromat needs to be composed of a focusing diffractive part (FZP), see Fig. 1b, and a defocusing refractive part (RL), see Fig. 1c, fulfilling the relation fRL = −2fFZP. The focal length fA of such an achromat is then given by: fA = 2fFZP. These relations are valid for the case of direct contact of the two elements. When taking into account their separation along the beam direction, we arrive at slightly modified expressions, see Methods and Supplementary Material. This type of X-ray achromat has previously been proposed in the context of telescopes in X-ray astronomy10,11,12. More recently, the promising potential of X-ray achromats has been discussed for microscopy and spectroscopy and moreover for focusing of short pulses without distortion in time9,13,14. However, an experimental realisation has not been reported to date.

Anti reflective coated glasses have multiple layers of different metals deposited on the surface through vaporization/sublimation.

Diffraction limits resolution. For a circular aperture, lens, or mirror, the Rayleigh criterion states that two images are just resolvable when the center of ...

The experimental results for the location of the focal spot agree well with the corresponding calculated curves for both the achromat and the FZP, see Fig. 3c. The difference between the solid and dashed red curves for the achromat, which were calculated using Eq. (6) and inserting tabulated δ and β values15 into Eq. (4), respectively, is small. This indicates that the assumption of no material dispersion that was made in Eq. (6) holds well, see Methods. Looking at Fig. 3c, we expect in-focus imaging within the wide achromatic range δEAchromat from about 5.8 keV to 7.3 keV for the achromat but only within the relatively narrow range δEFZP ≈ 100 eV for the FZP, which is consistent with the results shown in Fig. 2.

Diffractive and refractive optical elements have become an integral part of most high-resolution X-ray microscopes. However, they suffer from inherent chromatic aberration. This has to date restricted their use to narrow-bandwidth radiation, essentially limiting such high-resolution X-ray microscopes to high-brightness synchrotron sources. Similar to visible light optics, one way to tackle chromatic aberration is by combining a focusing and a defocusing optic with different dispersive powers. Here, we present the first successful experimental realisation of an X-ray achromat, consisting of a focusing diffractive Fresnel zone plate (FZP) and a defocusing refractive lens (RL). Using scanning transmission X-ray microscopy (STXM) and ptychography, we demonstrate sub-micrometre achromatic focusing over a wide energy range without any focal adjustment. This type of X-ray achromat will overcome previous limitations set by the chromatic aberration of diffractive and refractive optics and paves the way for new applications in spectroscopy and microscopy at broadband X-ray tube sources.

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Figure 1c shows an SEM image of the RL used in the experiment. Vertical support structures were printed to stack the four paraboloids. The X-ray absorption and diffraction properties of the resist can be estimated using the material compound C14H18O7 with a density of 1.2 g/cm315. The transmission through the RL calculated using these properties is 23% at 5.2 keV, 44% at 6.2 keV, and 73% at 8.0 keV.

NAPA REWARDS · Home · Replacement Parts · Steering & Suspension · Rack & Pinions & Steering Boxes. Rack & Pinions & Steering Boxes.

The focusing properties of the achromat can also be analysed by looking at the evolution of the X-ray wavefield with the energy. For this purpose, ptychography measurements (see Supplementary Fig. 1 in the Supplementary Material) were conducted at the same energies as the STXM data, which allows for retrieving the illuminating X-ray wavefield. The intensity distribution of the wavefield at the sample position was then propagated computationally along the optical axis z to create an X-ray beam caustic at each energy. Cuts along the xz plane, see coordinate system in Fig. 1d, through the caustics of the achromat are shown in Fig. 3a, where the focus position is indicated with a red dashed line. A direct comparison of the caustics obtained with the achromat and the FZP, see Fig. 3b, confirms the significant gain in achromatic range achieved by the achromat, as already observed in the STXM images in Fig. 2.

Jacobsen, C. et al. Diffraction-limited imaging in a scanning transmission x-ray microscope. Opt. Commun. 86, 351–364 (1991).

Mohacsi, I. et al. Fabrication and characterization of high-efficiency double-sided blazed x-ray optics. Opt. Lett. 41, 281–284 (2016).

The part of the eye that provides the most acute vision is the fovea centralis (also called the macula lutea). This is a relatively small area of the retina (3 to 4%) that provides the most detailed and acute vision as well as color perception. This explains why eyes move when you read the image has to be focused on the fovea for detailed perception. The balance of the retina can perceive light and movement.

With the Vention USB 3.0 cable, you are set to benefit from high-quality construction that promotes rapid data transfer speeds coupled with long-lasting ...

Kubec, A., Zdora, MC., Sanli, U.T. et al. An achromatic X-ray lens. Nat Commun 13, 1305 (2022). https://doi.org/10.1038/s41467-022-28902-8

The code used for the reconstruction of the STXM data, the ptychography data, and for the propagation of the wavefront obtained with ptychography was developed by the cSAXS beamline at the Swiss Light Source and is freely available at https://www.psi.ch/en/sls/csaxs/software.

The epidermis is the outer layer of skin. The thickness of the epidermis varies in different types of skin. It is the thinnest on the eyelids at .05 mm and the thickest on the palms and soles at 1.5 mm.

Laser radiation injury to the skin is normally considered less serious than injury to the eye, since functional loss of the eye is more debilitating than damage to the skin, although the injury thresholds for both skin and eyes are comparable (except in the retinal hazard region, (400–1,400 nm). In the far-infrared and far-ultraviolet regions of the spectrum, where optical radiation is not focused on the retina, skin injury thresholds are about the same as corneal injury thresholds. Obviously, the possibility of skin exposure is greater than that of eye exposure because of the skin’s greater surface area.

The test pattern was a Siemens star made from 750 nm-high gold structures. It had a diameter of 10 μm and consisted of 18 spokes with inner spoke width of 50 nm and outer spoke width of 873 nm. The Siemens star was fabricated on a 250 nm-thick Si3N4 membrane with similar process steps as the FZPs, using electron-beam lithography and electroplating.

where E0 is the reference energy (optimum energy of the achromat), ΔE is the energy difference to E0 and fD = fFZP(E0), and fR = fRL(E0) the focal lengths at E0. This leads to the expression:

The concept of an achromatic doublet can be transferred to the X-ray regime. For X-rays, the refraction and absorption in matter are described by the complex refractive index n, which is related to the atomic scattering factor fa = f1 + if2 of the atoms in the given material:

One of the deciding factors on how hazardous a laser beam can be is how one is exposed. Is it a direct or intrabeam exposure (where all the energy is directed right at one’s eyes).

Wakonig, K. et al. PtychoShelves, a versatile high-level framework for high-performance analysis of ptychographic data. J. Appl. Crystallogr. 53, 574–586 (2020).

The lens focuses light to form images onto the retina. Over time, the lens becomes less pliable, making it more difficult to focus on near objects. With age, the lens also becomes cloudy and eventually opacifies. This is known as a cataract. Every lens develops cataracts eventually.

To demonstrate the potential of the presented achromat for imaging with polychromatic X-rays, we performed wavefield propagation simulations with an achromat and a single FZP, see Methods. Comparing the simulated data allows for assessing the gain in image quality over a FZP that is attainable with an optimised achromat without the effects manufacturing errors. Figure 4a shows the result of a convolution of the binarised SEM image of the Siemens star in Fig. 2b with the simulated polychromatic X-ray beam with an energy range between 5.6 keV and 6.8 keV obtained with an achromat. The gain in image quality compared to the image in Fig. 4b simulated analogously using a FZP as an optical element is striking. The image contrast is significantly improved with the achromat, which in the presence of noise enables the visualisation of much smaller features. The improvement in image quality can be understood from the simulated polychromatic beam profiles in Fig. 4c, where much stronger side lobes of the beam can be observed for the FZP than for the achromat.

Mohacsi, I. et al., High-efficiency x-ray nanofocusing by the blazed stacking of binary zone plates. In Lai, B. (ed.) X-Ray Nanoimaging: Instruments and Methods, vol. 8851, 142-149. International Society for Optics and Photonics (SPIE, 2013).

We have presented the experimental realisation of an X-ray achromat consisting of a focusing diffractive and a defocusing refractive optical element, which achieves steady imaging performance over a wide energy range without change of the focal settings. This feature will facilitate experiments with monochromatic X-rays that rely on rapid or frequent change of photon energy. Moreover, it will allow for more efficient use of broad-band radiation in X-ray microscopy and nanoanalysis, including the diffraction-limited focusing of the full radiation from an undulator at synchrotron or X-ray laser facilities. The presented achromat will be of particular benefit for use at polychromatic laboratory X-ray tube sources, as indicated by our simulations, which will enable efficient high-resolution microscopy at laboratory-based X-ray systems. Using chromatic lenses as available to date, the available spectrum had to be cut down to a narrow X-ray bandwidth in previous setups, which severely reduced the photon flux and hence led to long scan times and poor statistics. For the same reason, we expect the proposed achromatic optic to unfold microscopy applications for neutron beams16, as theoretically explored in a previous publication17.

STXM23,24 was performed by transversely raster-scanning the sample on a grid of 60 × 60 steps with a step size of 200 nm, recording a diffraction pattern at each position using a Pilatus 2M single-photon counting detector (chip size: 1475 × 1679 pixels, pixel size:172 × 172 μm2). The sample was positioned in the focal plane of the achromat at an energy of 6.4 keV. The exposure time for each recorded frame was 200 ms. Each pixel of the reconstructed STXM image was created by integrating the photon counts in the corresponding diffraction pattern over a region of interest of 192 × 192 pixels around the centre of the beam.

The data generated in this study are available under restricted access due to pending further analysis, access can be obtained from corresponding author M.-C.Z. upon reasonable request.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Vila-Comamala, J. et al. Angular spectrum simulation of X-ray focusing by Fresnel zone plates. J. Synchrotron Radiat. 20, 397–404 (2013).

Braig, C. & Predehl, P. Multiband imaging at the diffraction limit using Fresnel x-ray telescopes. Opt. Eng. 51, 096501 (2012).

This study states that even for the larger spot size on the retina the frequency of the blink reflex has been shown to be less than 35 % and the same is true for the maximum of the pupil size, i. e. for low ambient light conditions. The study states 503 volunteers have been irradiated in the lab and 690 in 4 different field trials with laser radiation. Out of these only 15.5 % or 18.26 % respectively have shown a blink reflex. The respective numbers as a function of wavelength are: 15.7 % (670 nm), 17.2 % (635 nm), and 22.4 % (532 nm). An increase from 4.2 % up to 28.1 % in blink reflex frequency was achieved when the ambient illuminance was decreased from 1 700 lx to 1 lx using an LED as a large extended stimulating optical source instead of a collimated laser beam.

The simulations were performed for energies in the range of 5.6 keV and 6.8 keV in steps of 50 eV. The X-ray probes obtained this way for both the achromat and the FZP were used to create simulated X-ray images of a Siemens star. For this, the SEM image of the Siemens star in Fig. 2b was binarised and then convolved with the simulated X-ray probe in the focal plane. Subsequently, Gaussian noise with a variance of 0.01 was added to the normalised images to better represent the properties of experimental data.

The energy density (measure of energy per unit of area) of the laser beam increases as the spot size decreases. This means that the energy of a laser beam can be intensified up to 100,000 times by the focusing action of the eye for visible and near infrared wavelengths. If the irradiance entering the eye is 1 mW/cm2, the irradiance at the retina will be 100 W/cm2. Even a 4% reflection off an optic can be a serious eye hazard. Remember a low power laser in the milliwatt range can cause a burn if focused directly onto the retina. A 40 mW laser is capable of producing enough energy (when focused) to instantly burn through paper.

The presented X-ray achromat consisted of a FZP fabricated using electron-beam lithography and nickel electroplating and a 3D-printed RL made by two-photon polymerisation. The achromat was installed as a focusing optic at the cSAXS beamline of the Swiss Light Source (Villigen, Switzerland) with the experimental setup shown in Fig. 1d. The fabrication, properties, and arrangement of the optical components are described in more detail in the Methods section. In order to demonstrate the achromatic behaviour of the optic, STXM as well as ptychography measurements were performed at multiple X-ray energies between 5.2 keV and 8.0 keV, with the sample placed in the focal plane of the achromat at its optimum energy of 6.4 keV. For comparison, reference measurements were taken with a conventional FZP (see Fig. 1b) instead of the achromat. Both optics had the same numerical aperture, limiting the achievable spot size to about 500 nm.

The dermis also varies in thickness depending on the location of the skin. It is .3 mm on the eyelid and 3.0 mm on the back. The dermis is composed of three types of tissue that are present throughout – not in layers. The types of tissue are collagen, elastic tissue, and reticular fibers.

Lyubomirskiy, M. et al. Ptychographic characterisation of polymer compound refractive lenses manufactured by additive technology. Opt. Express 27, 8639–8650 (2019).

155# Crimson Flocked Marquee. This flocked red material combines the looks of suede and the richness of velvet, with unparalleled quality and consistency.

Achromaticcolor

A.K. and C.D. conceived the experiment. A.K. and U.T.S. fabricated the refractive lens. M.-C.Z. fabricated the binary zone plate. A.K., U.T.S., M.-C.Z., J.V.-C., A.D., and C.D. planned and prepared the experiment. A.K., M.-C.Z., J.V.-C., U.T.S., A.D., and C.D. carried out the experiment. U.T.S. acquired the SEM images. A.K., J.V.-C., and M.-C.Z. analysed the data. J.V.-C., A.K., M.-C.Z., and C.D. performed the simulations and calculations. M.-C.Z. and C.D. wrote the manuscript with contributions from all authors.

The FZP that was used as part of the achromat was a double-sided blazed FZP with four steps. It consisted of nickel structures on the top and bottom of a 250 nm-thick silicon nitride (Si3N4) membrane, which were aligned with respect to each other and had heights of 1 μm (back) and 2.2 μm (front). The FZP had a diameter of 100 μm and an effective outermost zone width of 200 nm. The diffraction efficiency of the FZP was measured to be 54.7% at its design energy of 6.2 keV. The FZP used for the comparison measurements was binary and had a diameter of 100 μm and an outermost zone width of 415 nm. It consisted of 2.2 μm-high nickel structures on a 250 nm-thick Si3N4 membrane with a theoretical efficiency of 36.8% at 6.2 keV15. For the fabrication of both FZPs, the membranes were first covered with a chromium-gold-chromium plating base by evaporation and then spin-coated with a Poly(methyl methacrylate) (PMMA) resist layer, which was subsequently exposed by electron-beam lithography (Vistec EBPG 5000+ electron-beam writer at 100 kV acceleration voltage). The patterns were developed, resist trenches cleaned by plasma etching, and then filled with nickel via electroplating, which was followed by removal of the residual PMMA. For the blazed FZP, this process was performed for both sides of the chip. More details on the fabrication process of the FZPs can be found in earlier publications18,19.

Here, we present a compact optical system that can achieve achromatic focusing, delivering images of consistently high quality, over an X-ray photon energy range from 5.8 keV to 7.3 keV.

The cornea is the transparent layer of tissue covering the eye. Damage to the outer cornea may be uncomfortable (like a gritty feeling) or painful, but will usually heal quickly. Damage to deeper layers of the cornea may cause permanent injury.

Li, K., Wojcik, M. & Jacobsen, C. Multislice does it all–calculating the performance of nanofocusing X-ray optics. Opt. Express 25, 1831–1846 (2017).

Wang, Y., Yun, W. & Jacobsen, C. Achromatic Fresnel optics for wideband extreme-ultraviolet and X-ray imaging. Nature 424, 50–53 (2003).

The FZP and the RL were separated by a distance d = 1 mm along the optical axis (RL upstream of FZP), making the approximation in Eq. (2), which holds for d = 0, not strictly valid. In the case of d ≠ 0, the focal length of the achromat can be defined using the concept of the back focal length (BFL) li of a lens combination22:

a STXM images of the Siemens star sample shown in panel b obtained with the achromat, indicating an achromatic range of  > 1 keV around the optimum energy of ~ 6.4 keV. b SEM image of the Siemens star test sample. The radial lines and spaces (L/S) at the outer and inner concentric rings have widths of 400 nm and 200 nm, respectively, see red arrows. c Comparison of the STXM results in the energy range of 6.0 keV to 6.4 keV obtained with the achromat (top) and the conventional FZP (bottom). While the contrast of the FZP images changes rapidly with the energy, the image quality achieved with the achromat varies only little.

Vila-Comamala, J. et al. Characterization of high-resolution diffractive x-ray optics by ptychographic coherent diffractive imaging. Opt. Express 19, 21333–21344 (2011).

We thank Istvan Mohacsi (Paul Scherrer Institut) for the fabrication of the blazed Fresnel zone plate and the Siemens star test pattern. We acknowledge Nicholas Phillips (Paul Scherrer Institut) for support during the beamtime. This project has received funding from the Swiss Nanoscience Institute under Argovia Project 16.01 ‘ACHROMATIX’ (J.V.-C.) and the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 884104 (PSI-FELLOW-III-3i) (U.T.S.).

The study “A Critical Consideration of the Blink Reflex as a Means for Laser Safety Regulations, byH.-D. Reidenbach1,2,3, J. Hofmann1, K. Dollinger1,3, M. Seckler2.