Abstract: A quantity (or dispersion value) of a distribution of edge position due to random noise is expected to be reduced statistically to 1/N when N edge position data items are averaged. Using this property, the single page image is averaged in a vertical direction with various values of parameter S, and then the edge roughness index is calculated. The S-dependence of the edge roughness index is analyzed and a term of a dispersion value directly proportional to 1/S is determined as being due to noise.

Abstract: The accuracy of a library of simulated-diffraction signals for use in optical metrology of a structure formed on a wafer is evaluated by utilizing an identity relationship inherent to simulated diffraction signals. Each simulated diffraction signal contains at least one set of four reflectivity parameters for a wavelength and/or angle of incidence. One of the four reflectivity parameters is selected. A value for the selected reflectivity parameter is determined using the identity relationship and values of the remaining three reflectivity parameters. The determined value for the selected reflectivity parameter is compared to the value in the obtained set of four reflectivity parameters to evaluate and improve the accuracy of the library. The identity relationship can also be used to reduce the data storage in a library.

Abstract: A method for determining a mobility of foot comprising: measuring at least a portion of a shape of the foot under a first weight load; measuring the at least the portion of the shape of the foot under a second weight load; and comparing the measurement under the first weight load to the measurement under the second weight load, thereby determining a mobility of at least the portion of the foot.

Abstract: A surface inspection system, as well as related components and methods, are provided. The surface inspection system includes a beam source subsystem, a beam scanning subsystem, a workpiece movement subsystem, an optical collection and detection subsystem, and a processing subsystem. The optical collection and detection system features, in the front quartersphere, a light channel assembly for collecting light reflected from the surface of the workpiece, and a front collector and wing collectors for collecting light scattered from the surface, to greatly improve the measurement capabilities of the system. The light channel assembly has a switchable edge exclusion mask and a reflected light detection system for improved detection of the reflected light.

Abstract: The present invention provides a method of determining certain propeller parameters for a boat propeller that has a hub, a central axis and a plurality of propeller blades attached to the hub. The method includes providing a laser displacement sensor in proximity to the propeller. The laser displacement sensor has a laser head that generates a laser beam. The laser displacement sensor is used to measure the distance from the laser head to the propeller. The laser head is moved and the laser again measures the distance from the laser head to the propeller after the laser head is moved in relation to the propeller. The movement can be along either or both of the two axes including a first axis that is a linear axis and a second axis that is curved. The method includes computing a selected parameter or parameters by using the measurements that are obtained, the parameters being selected from a group that includes pitch, rake and squareness.

Abstract: For determining a space coordinate of a measurement point on a measuring object, the measurement point is approached with a probe head arranged on a displacement mechanism having at least two supports movable parallel to one another. Each support is moved by its own drive. The space coordinate of the measurement point is determined as a function of the respective displacement position of the supports. The two drives are controlled by a common regulator.

Abstract: A computer-implemented method for measuring a selected portion of a curved surface of an object is disclosed. The method includes the blocks of displaying a straight-line across an object, stretching the straight-line to form a plane, determining intersection points between the plane and the curved surface of the object, determining a vertical point of each point-cloud around the straight-line on the curved surface, a corresponding vertical distance, and a corresponding normal vector, projecting the vertical points onto the plane vertically, determining measured points, up tolerance points, and down tolerance points for the point-clouds around the straight-line on the plane, connecting the corresponding points to lines, and determining if one or more the dimensions of a selected portion around the straight-line of the object is acceptable according to the connected lines.

Abstract: A component is deployed into a well on a carrier line having an optical cable. An optical signal is transmitted into the optical cable, and a travel time of the optical signal in the optical cable is determined. A profile of a characteristic along the optical cable is determined, and a length of the carrier line deployed into the well is determined based on the determined profile and the travel time.

Abstract: A reflection type optical sensor can include a light emitting and receiving unit. The light emitting and receiving unit can include both a light emitting unit and a light receiving unit having light receiving sensitivity to light emitted from the light emitting unit. The light emitting unit and the light receiving unit can be arranged such that the optical axis of the light emitting unit intersects at a predetermined angle with the optical axis of the light receiving unit. The light emitting and receiving unit can be movably supported.

Abstract: The method of measuring a peripheral tilt angle in accordance with the present invention, to address the problems, is a method of measuring a peripheral tilt angle on an inspection object having surface mounds, the method including: the step A of projecting light onto the inspection object; the step B of sensing distribution of light reflected off the inspection object; the step C of obtaining a feature point of the distribution of the reflected light from result of the sensing of the distribution of the reflected light; and the step D of obtaining a peripheral tilt angle which is a tilt angle near a periphery of each of the surface mounds based on an angle of projection of the light in step A to a position which, on the inspection object, corresponds to the feature point and an angle of sensing of the reflected light in step B off a position which, on the inspection object, corresponds to the feature point.

Abstract: A measurement probe 1 for measuring a surface of sample S comprises a base section 10, a head section 30 having a probe tip 31, and a support structure section 15 which supports the head section 30 with the base section 10 along a support axis substantially orthogonal to the vertical axis in the direction of protrusion of the probe tip 31. The support structure section 15 includes two spring structure sections of a first spring structure section 20 deformable in the direction of the vertical axis; and a second spring structure section 25 deformable in the direction of the lateral axis, and a reflection surface 32 which is formed with a reflection pattern varying the reflectance within the surface is provided at the side opposite to the probe tip 31 of the head section 30.

Abstract: A surface inspection system, as well as related components and methods, are provided. The surface inspection system includes a beam source subsystem, a beam scanning subsystem, a workpiece movement subsystem, an optical collection and detection subsystem, and a processing subsystem. The system features a variable scan speed beam scanning subsystem, preferably using an acousto-optic deflector, with beam compensation, so that variable scanning speeds can be achieved. Also included are methods and systems for improving the signal to noise ratio by use of scatter reducing complements, and a system and method for selectively and repeatedly scanning a region of interest on the surface in order to provide additional observations of the region of interest.

Abstract: A laser beam system for measuring an aspect of a surface wherein a laser beam is reshaped into a corrected shaped laser beam having a corrected energy profile and subsequently reshaped into a measurement shaped laser beam having an measurement energy profile shaped to be effected by the at least one aspect of the surface. The measurement shaped laser beam is reflected from the surface, being modified by the aspect of interest of the surface, and to a sensor array wherein the sensors measure the reflected laser beam to determine the aspect of interest of the surface.

Abstract: A system and a method for investigating and/or determining the condition or the state of a ship's hull, in particular its outer skin, for making it possible to select, in particular to lengthen, the docking time interval for ships depending on the condition or the state of the ship's hull. The outer skin is provided with a subdivision, in particular by means of at least one grid or network, which subdivision cooperates functionally with at least floating/submersible investigation/determination unit for investigating and/or for determining the condition or the state of the ship's hull.

Abstract: A sample stage for performing measurements using an optical metrology system includes at least one sample section for retention of a sample, and components for controlling orientation of the sample section with relation to the optical metrology system. A method and a computer program product are provided.

Abstract: In order to provide light guides, in particular in the form of glass rod portions, with improved end faces, the invention provides a method for examining glass rods, in particular light guides, in which the glass rods are arranged in front of two cameras, the cameras recording the end faces from the sides, in two different radial viewing directions with respect to the longitudinal axis of the glass rods, and the planarity and angularity of the contour of the end faces being optically and contactlessly determined with both cameras on the basis of the recordings, and a glass rod automatically being rejected and/or sorted by means of a rejecting/sorting device if there is any deviation of the planarity or angularity of the end faces of the glass rod from a respectively prescribed set range.

Abstract: An imaging method and system are presented for use in sub-wavelength super resolution imaging of a subject. The imaging system comprises a spatial coding unit configured for collecting light coming from the scanned subject and being spaced from the subject a distance smaller than a wavelength range of said light; a light detection unit located upstream of the spatial coding unit with respect to light propagation from the object, and configured to define a pixel array and a spatial decoding unit, which is associated with said pixel array and is configured for applying spatial decoding to a magnified image of the scanned subject, thereby producing nanometric spatial resolution of the image.

Abstract: Disclosed are apparatus and methods for measuring a characteristic, such as overlay, of a semiconductor target. In general, order-selected imaging and/or illumination is performed while collecting an image from a target using a metrology system. In one implementation, tunable spatial modulation is provided only in the imaging path of the system. In other implementations, tunable spatial modulation is provided in both the illumination and imaging paths of the system. In a specific implementation, tunable spatial modulation is used to image side-by-side gratings with diffraction orders ±n. The side-by-side gratings may be in different layers or the same layer of a semiconductor wafer. The overlay between the structures is typically found by measuring the distance between centers symmetry of the gratings. In this embodiment, only orders ±n for a given choice of n (where n is an integer and not equal to zero) are selected, and the gratings are only imaged with these diffraction orders.

Abstract: The present invention describes a method for an apparatus for examining surface properties. Properties of effect pigments are to be examined in particular. A surface (9) to be examined is examined at different emission and reception angles and any curvature of the effect pigments is deduced on the basis of these different angles.

Abstract: A structure formed on a semiconductor wafer can be examined using a support vector machine. A profile model of the structure is obtained. The profile model is defined by profile parameters that characterize the geometric shape of the structure. A set of values for the profile parameters is obtained. A set of simulated diffraction signals is generated using the set of values for the profile parameters, each simulated diffraction signal characterizing the behavior of light diffracted from the structure. The support vector machine is trained using the set of simulated diffraction signals as inputs to the support vector machine and the set of values for the profile parameters as expected outputs of the support vector machine. A measured diffraction signal off the structure is obtained. The measured diffraction signal is inputted into the trained support vector machine. Values of profile parameters of the structure are obtained as an output from the trained support vector machine.

Abstract: A dark field surface inspection tool and system are disclosed herein. The tool includes an illumination source capable of scanning a light beam onto an inspection surface. Light scattered by each inspection point is captured as image data by a photo detector array arranged at a fourier plane. The images captured are adaptively filtered to remove a portion of the bright pixels from the images to generate filtered images. The filtered images are then analyzed to detect defects in the inspection surface. Methods of the invention include using die-to-die comparison to identify bright portions of scattering patterns and generate unique image filters associated with those patterns. The associated images are then filtered to generate filtered images which are then used to detect defects. Also, data models of light scattering behavior can be used to generate filters.

Abstract: The present invention uses ISTS to measure trenches with near- or sub-micron width. The trenches can be etched in a thin film on in a silicon substrate. One step of the method is exciting the structure by irradiating it with a spatially periodic laser intensity pattern in order to generate surface acoustic waves. Other steps are diffracting a probe laser beam off the thermal grating to form a signal beam; detecting the signal beam as a function of time to generate a signal waveform; determining surface acoustic wave phase velocity from the waveform; and determining at least one property of the trench structures based on the dependence of surface acoustic wave phase velocity on the parameters of the structure.

Abstract: An imaging system is provided. The imaging system includes a sample to be scanned by the imaging system. An absorbance modulation layer (AML) is positioned in close proximity to the sample and is physically separate from the sample. One or more sub-wavelength apertures are generated within the AML, whose size is determined by the material properties of the AML and the intensities of the illuminating wavelengths. A light source transmits an optical signal through the one or more sub-wavelength apertures generating optical near-fields that are collected for imaging.

Abstract: A device for examining the optical properties of surfaces includes at least one first radiation device which emits radiation to a surface to be examined at a first predetermined spatial angle, at least one first detector device for capturing the radiation emitted to and reflected back from the surface wherein the first detector device, allowing a local resolution of detected radiation, is positioned at least at a second predetermined spatial angle relative to the surface, and at least one further radiation device or second detector device emitting radiation to the surface to be examined at a third predetermined spatial angle or detecting radiation emitted to and reflected back from the surface.

Abstract: A method of calibrating or compensating a sensor for measuring property of target surface is provided. In one embodiment, a liquid reference surface is formed on a platen. A sensor is used to measure a feature property of the reference surface. The measured feature property of the reference surface may be used to calibrate the sensor. Further, the sensor is used to measure the feature property of a polishing pad. The measured feature property of the reference surface may be used to compensate the measured feature property of the polishing pad.

Abstract: A measurement probe 1 for measuring a surface of sample S comprises a base section 10, a head section 30 having a probe tip 31, and a support structure section 15 which supports the head section 30 with the base section 10 along a support axis substantially orthogonal to the vertical axis in the direction of protrusion of the probe tip 31. The support structure section 15 includes two spring structure sections of a first spring structure section 20 deformable in the direction of the vertical axis; and a second spring structure section 25 deformable in the direction of the lateral axis, and a reflection surface 32 which is formed with a reflection pattern varying the reflectance within the surface is provided at the side opposite to the probe tip 31 of the head section 30.

Abstract: The invention relates to an optical measurement device (10) for measuring an optical appearance of a surface (16) of a sample (18), in particular the surface (16) of a human skin, comprising a measuring head (30) which can be brought into contact with the surface (16) of the sample (18), the measuring head (30) comprising: an illumination device (12, 46) for illuminating the surface (16) with an illumination beam (14); a detection device (23) for detecting a response beam (20), wherein the response beam (20) is the response of the sample (18) to the illumination beam (14). The detection device (23) comprises a screen (22, 52) for intercepting the response beam (20), wherein the screen (22, 52) extends approximately a quarter hemisphere in order to realize measuring head (30) with a small contact area with the surface.

Abstract: A system to process requests for wafer structure profile determination from optical metrology measurements off a plurality of structures formed on one or more wafer includes a diffraction signal processor, a diffraction signal distributor, and a plurality of profile search servers. The diffraction signal processor is configured to obtain a plurality of measured diffraction signals of the plurality of structures. The diffraction signal distributor is coupled to the diffraction signal processor. The diffraction signal processor is configured to transmit the plurality of measured diffraction signals to the diffraction signal distributor. The plurality of profile search servers is coupled to the diffraction signal distributor. The diffraction signal distributor is configured to distribute the plurality of measured diffraction signals to the plurality of profile search servers.

Abstract: This invention addresses a contact mode hybrid scanning system (HSS), which can be used for measuring topography. The system consists of a cantilever or a cantilever array, a scanning stage, a light source, and instrumentation to synchronize and control the individual components. Detection of the cantilever's movement is achieved by directly measuring the change in disposition of the cantilever including its height, rotation at one or more points on the cantilever thereby providing a partial three-dimensional reconstruction without the need for actuating the cantilever. This is achieved by employing a displacement meter such as a triangulation meter or a confocal meter.

Abstract: A device for recognizing particles in milk comprising a measuring surface and a housing. The measuring surface is structured so as to cause the milk to spread on the measuring surface in that the measuring surface has a specific surface roughness.

Abstract: The present invention provides an apparatus and method for detecting flatness and/or unevenness of a surface of an overcoat layer on a colored pixel layer of a color filter with a high degree of accuracy. The apparatus includes: a light source 34, placed almost directly above the surface of a plate 30, for emitting an emission-line spectrum corresponding to at least one color of coloring particles in a color filter 32; a photo-receiver 36, placed obliquely upward with respect to the surface of the plate 30 and having a spectral sensitivity corresponding to the emission-line spectrum of the light source, for receiving reflected light from the color filter 32 on the plate 30 during inspection; and a detection means 42 for creating a brightness distribution for a color using a color signal output from the photo-receiver 36 as corresponding to its spectral sensitivity to detect the flatness (unevenness) of the surface of an overcoat layer 16.

Abstract: A device for examining the optical properties of surfaces includes at least one first radiation device which emits radiation to a surface to be examined at a first predetermined spatial angle; at least one first detector device for capturing the radiation emitted to and reflected back from the surface, wherein the first detector device, allowing a local resolution of detected radiation, is positioned at least at a second predetermined spatial angle relative to the surface; and at least one further radiation device or second detector device emitting radiation to the surface to be examined at a third predetermined spatial angle or detecting radiation emitted to and reflected back from the surface.

Abstract: A method for correlating line width roughness of gratings first performs a step (a) generating a characteristic curve of a predetermined grating having a known line width, and a step (b) performing a comparing process to select a matching spectrum from a plurality of simulated diffraction spectrum of known line width, and setting the known line width of the matching spectrum as the virtual line width of the predetermined grating. Subsequently, the method performs a step (c) changing a measuring angle and repeating the steps (a) and (b) to generate a virtual line width curve, and calculating the deviation of the virtual line width curve. The method then performs a step (d) changing the line width roughness of the predetermined grating and repeating the steps (a), (b) and (c), and a step (e) correlating the line width roughness and the deviation of the virtual line width curve to generate a correlating curve.

Abstract: The number of diffraction orders to use in generating simulated diffraction signals for a two-dimensional structure in optical metrology is selected by generating a first simulated diffraction signal using a first number of diffraction orders and a hypothetical profile of the two-dimensional structure. A second simulated diffraction signal is generated using a second number of diffraction orders using the same hypothetical profile used to generate the first simulated diffraction signal, where the first and second numbers of diffraction orders are different. The first and second simulated diffraction signals are compared. Based on the comparison of the first and second simulated diffraction signals, a determination is made as to whether to select the first or second number of diffraction orders.

Abstract: A control portion of an optical image pickup apparatus includes a scan driver, a lock-in amplifier, and an A/D converter. The scan driver outputs a predetermined drive signal to a Y-scanning mirror and an X-scanning mirror and scans the Y-scanning mirror and the X-scanning mirror. The lock-in amplifier detects a signal level Vout of a frequency component of the drive signal of the scan driver among signals detected by a detector portion. The A/D converter converts a signal detected by a detector portion and a signal level of the detected signal of a frequency component of a drive signal detected by the lock-in amplifier to digital signals and outputs the digital signals to an image processor. Thus, mirror scan operations of the scanning mirrors can be securely detected.

Abstract: A surface inspection system, as well as related components and methods, are provided. The surface inspection system includes a beam source subsystem, a beam scanning subsystem, a workpiece movement subsystem, an optical collection and detection subsystem, and a processing subsystem. The system features masking positioned in the collection and detection subsystem arranged to selectively prevent a portion of scattered light from passing through. Also included is a scatter absorbing system having a series of scatter absorbing elements for minimizing unrelated to the scatter associated with a desired location on the surface.

Abstract: A quantity (or dispersion value) of a distribution of edge position due to random noise is expected to be reduced statistically to 1/N when N edge position data items are averaged. Using this property, the single page image is averaged in a vertical direction with various values of parameter S, and then the edge roughness index is calculated. The S-dependence of the edge roughness index is analyzed and a term of a dispersion value directly proportional to 1/S is determined as being due to noise.

Abstract: A roughness evaluation method for evaluating a roughness of lines formed on a substrate includes a measuring step of irradiating light onto a plurality of locations of the substrate and measuring a state of reflected light by a scatterometry; and an analyzing step of evaluating the roughness of the lines based on a variation in value measured in the measuring step. A roughness evaluation system includes an optical device for irradiating light onto the substrate and measuring a state of reflected light by a scatterometry; a moving device for moving the substrate in at least one of an x-direction and a y-directions on a horizontal plane; a controller for controlling the moving device such that the optical device measures a plurality of locations on the substrate; and an analysis unit for evaluating the roughness based on a variation in measured values at the plurality of locations on the substrate.

Abstract: A device has first and second units that lights an object at first or second incident angles; a unit that generates image signals according to the intensity of the received light; units that guides diffusely and specularly reflected light from the object to the image-input unit; units that generates glossiness information, and texture information for the object, and image data based on image signals generated; a unit that generates and outputs the image data from glossiness information, texture information, and image data.

Abstract: An automated optical inspection system, comprising at least one camera having a field of view; and at least one image scanning module comprising a plurality of objective modules arranged to have fields of view covering a portion of an article during inspection, and an image selection mirror mechanism, such as a pentaprism movable to sequentially select and transfer images of the fields of view from the objective modules to the at least one camera, and a beam splitter operative to simultaneously direct illumination from at least one illumination source to a portion of the article and to direct an image of the portion of the article to at least one camera, wherein the beam splitter is operative to pivot about at least one axis, thereby to create motion of the image of the article within the field of view of the camera. The objective modules may be arranged in a pair of back-to-back arcs each served by and partially encircling its own optical head.

Abstract: The invention concerns a process and apparatus for monitoring the level of surface irregularity in a moving threadline, comprising: (a) illuminating the threadline via a light source positioned incident to the thread line at an entrance angle of greater than 0 degrees and less than 90 degrees to the threadline to produce spectral reflectance energy and diffuse reflectance energy; (b) measuring the amount of spectral reflectance energy from the threadline with a first receiver positioned incident to the threadline at an exit angle that is substantially equal to the entrance angle; (c) measuring the amount of diffuse reflectance energy from the threadline with a second receiver positioned at an angle that is different than the entrance angle and the exit angle, (d) determining the ratio of the amount of diffuse reflectance energy to the amount of spectral reflectance energy; and (e) relating said ratio to the level of surface irregularity.

Abstract: The present invention relates to a device and method for making quantified determinations of the quality of surfaces and wherein the device comprises an optical system with a first optical means and a second optical means as well as a control and evaluation means and an output (display) means. Said first optical means comprises an illuminating means having at least one LED as its light source and serves the function of illuminating the measurement surface at a predetermined angle. Said second optical means is likewise directed at a predetermined angle to the measurement surface and receives the reflected light. A photo sensor of said second optical means emits an electrical measurement signal which is characteristic of said reflected light. The light emitted from the illuminating means is configured such that its spectral characteristic comprises blue, green and red spectral components in the visible light spectrum.

Abstract: Surface roughness measurements are made by illuminating a surface with coherent light to generate a speckle pattern and studying characteristics of the speckle pattern. The disclosed techniques may be applied to measuring the surface roughness of skin or other biological surfaces. Skin roughness information may be used in the diagnosis of conditions such as malignant melanoma. Methods and apparatus for measuring the coherence length of optical sources involve extracting information about speckle patterns resulting when light from the optical sources interacts with a surface having a known roughness.

Abstract: Measurement of sample surface flatness of a continuously moving sample. A conveyor continuously conveys a sample beneath a grating disposed at a non-zero angle with respect to the plane of conveyance. The relative distance between the sample and the angled grating changes with the horizontal translation of the sample. A camera disposed above the sample and the grating captures, at constant time intervals, a sequence of images, each image comprising a shadow moiré fringe pattern that is indicative of the sample's surface flatness. The continuous change in relative distance between the sample and the grating introduces a known or unknown phase step between the shadow moiré fringe patterns of each successive image. A computer associated with the camera processes the images to determine phase values of pixels at, and the relative height of the sample surface at, selected pixel locations of the sample.

Abstract: An apparatus and a method for detecting low frequency specular surface flaws on coated substrates is disclosed. A method for detecting low frequency specular surface flaws may comprise: impinging visible electromagnetic radiation or light from an electromagnetic radiation source onto the coated substrate at an oblique angle, reflecting the visible electromagnetic radiation off the coated substrate onto a screen material to form a specular surface flaw reflected image, and recording the reflected image off the screen material with a photosensitive device to form a recorded reflected image.

Abstract: In a scatterometric method, a roughness value can be obtained by using a model including a surface layer having a variable parameter relating to its refractive index.

Abstract: In the present invention, since light beams are irradiated from a back face of a glass disk through the glass disk on to an outer peripheral chamfered portion at a front face side of the glass disk, a difference between extinction amounts in a received light due a foreign matter and a flaw increases, and the received light signal representing a defect detection signal in response to this difference can be obtained.

Abstract: An optical surface analysis system for scanning the surface of a (silicon) wafer and detect if any residual material is still on the wafer surface in order to determine an appropriate end-point in a polishing process. An Optical Surface Analyzer (OSA), of the present invention, is generally used to identify composition, measure surface area, and measure thickness variations of thin film layers of material. The difference in optical properties (index of refraction) of different materials on the surface allows the system of the present invention to separate different materials on the wafer surface using the histogram plots generated by the OSA. This method is used to detect and make a quantitative assessment regarding the amount of residual material to be removed by the polishing process and, therefore, when an appropriate end-point has been reached in the polishing process.

Abstract: Provided are a detection apparatus, a detection method and an optically transparent member, which can detect a decrease in a precision. A convolution is performed by a convolution portion 80 contained in an image processing portion 38, to acquire the distribution information indicating the light intensity distribution of a light beam, which is totally reflected at the interface and which is incident at a plurality of angles to an dielectric block 52 so as to be totally reflected at the interface of the dielectric block 52. A spatial frequency resolution is performed on the light intensity distribution indicated by the distribution information acquired, by a detection precision evaluating portion 86 contained in the image processing portion 38, to thereby derive the light intensity distribution of each spatial frequency of the light beam. The precision is detected by comparing the light intensity distribution derived, with a threshold value predetermined for each spatial frequency.

Abstract: A scatterometer comprising light source means (11) for providing an incident light beam (8) at different angles in the direction of a sample (5) to be analyzed, and a concave screen (1,2) for receiving the reflection (19) of the incident light beam (8). The screen (1,2) has substantially the shape of a portion of a sphere, for example a hemisphere, whereby the location of the sample (5) is in its center. The screen (1,2) having an aperture (9) through which the incident light beam (8) passes towards said sample (5). Said light source means (11) and at least a portion of the screen (2) including said aperture (9) can rotate relative to the sample (5), around an axis (3) through said center and substantial perpendicular to said direction of the incident radiation beam.