Mirror Variable Angle Absolute Reflectivity Method and Reflectometer

Abstract

This disclosure relates to a method for and a reflectometer with variable-angle absolute reflectivity of a mirror, the variable-angle absolute reflectometer including a light source and a mirror system in the optical path of the light source. The mirror system is configured to reflect a light beam from the light source to an optically reflective sample. The apparatus also includes an elliptical roof-shaped mirror disposed in the optical path after the sample, having an elliptical reflector surface configured to reflect the light beam back to the sample. The apparatus also includes a mechanism connected to the elliptical roof-shaped mirror. The mechanism is configured to rotate the elliptical roof-shaped mirror about an axis of the sample. The apparatus also includes a detector in the optical path after the elliptical roof-shaped mirror, such that the detector receives light that has been reflected from the elliptical roof-shaped mirror, thereby reflected back to the sample, thereby reflected back to the mirror system, and thereby reflected back to the detector.

Description

Technical Field

[0001] This article generally relates to methods and apparatuses for the absolute reflectivity of mirrors at variable angles. Background Technology

[0002] Specular reflectivity refers to the reflection of light from a surface such as a mirror, where light from the incident direction is reflected to the outgoing direction. Therefore, specular reflectivity is the behavior of light that can be measured using optical equipment. Measuring the specular reflectivity of a material is one way to determine the composition or other chemical, thermal, or optical properties of a sample material.

[0003] Precise absolute measurement of specular reflectivity has several applications. For example, this technique is used to establish reference standards for the calibration of other types of reflectivity measurements and optical measuring devices. In another example, the technique is used in the optical coating industry to develop coatings (e.g., mirrors) to improve the optical efficiency of mirrors. In yet another example, precise absolute measurement of specular reflectivity can be used to measure the thickness or refractive index of a single layer of optical coating.

[0004] However, measuring absolute specular reflectivity is challenging when a wide range of incident angles, wavelengths, and polarizations are desired for rapid testing. Specular reflectivity measurement devices struggle to align components and samples for accurate measurements. Furthermore, focusing the beam onto the sample and detector is difficult; for example, the beam tends to disperse along its length. Some specular reflectivity measurement devices, for instance, use laser sources. Improved techniques for measuring absolute specular reflectivity are desired. For example, devices with enhanced alignment mechanisms and techniques for improved reflectivity measurements are desired. Devices with focused beam paths and spot sizes on the sample are desired. Devices enabling extended-area sources are desired. Summary of the Invention

[0005] An example provides a mirror-mounted variable-angle absolute reflectometer. The mirror-mounted variable-angle absolute reflectometer includes a light source and a mirror system in the optical path of the light source. The mirror system is configured to reflect a light beam from the light source to an optically reflective sample. The mirror-mounted variable-angle absolute reflectometer also includes an elliptical roof-shaped reflector disposed in the optical path after the sample. The elliptical roof-shaped reflector is configured to reflect the light beam back to the sample. The sample is located at the focal point of an elliptical reflector surface of the elliptical roof-shaped reflector, and the elliptical reflector surface refocuses the light beam onto the sample. The mirror-mounted variable-angle absolute reflectometer also includes a mechanism connected to the elliptical roof-shaped reflector. This mechanism is configured to rotate the elliptical roof-shaped reflector about an axis of the sample. The mirror-mounted variable-angle absolute reflectometer also includes a detector in the optical path after the elliptical roof-shaped reflector, such that the detector receives light that has been reflected from the elliptical roof-shaped reflector, thereby reflected back to the sample, thereby reflected back to the mirror system, and thereby reflected back to the detector. Attached Figure Description

[0006] Figure 1A A prior art 10-degree "V" configuration optical path is shown for performing 100% reflectivity measurements;

[0007] Figure 1B A prior art 10-degree "W" configuration optical path is shown for performing reflectance measurements of a sample;

[0008] Figure 2 The prior art “VW” assembly and beam path are shown for both 100% reflectivity measurement and sample reflectivity measurement at incident angles of 10 degrees and 20 degrees.

[0009] Figure 3 A prior art method for measuring reflectivity samples at variable angles is shown;

[0010] Figure 4 A mirror variable-angle absolute reflectometer in a 100% reflectivity measurement configuration according to an illustrative embodiment is shown;

[0011] Figure 5 A 15-degree configuration of a variable-angle absolute reflectometer for measuring sample reflectance is shown according to an illustrative embodiment.

[0012] Figure 6 A 30-degree configuration of a variable-angle absolute reflectometer for measuring sample reflectance is shown according to an illustrative embodiment.

[0013] Figure 7 This is a side view of a mirror variable angle absolute reflectometer according to an illustrative embodiment;

[0014] Figure 8 This is a perspective view of a mirror variable angle absolute reflectometer configured for 100% reflectivity measurement according to an illustrative embodiment.

[0015] Figure 9 A 15-degree configuration of a variable-angle absolute reflectometer for measuring sample reflectance is shown according to an illustrative embodiment.

[0016] Figure 10 A 30-degree configuration of a variable-angle absolute reflectometer for measuring sample reflectance is shown according to an illustrative embodiment.

[0017] Figure 11 A flowchart is shown of a method for performing absolute reflectance measurement of a sample using a mirror-variable-angle absolute reflectometer, according to an illustrative embodiment.

[0018] Figure 12A mirror-mounted variable-angle absolute reflectometer according to an illustrative embodiment is shown;

[0019] Figure 13 A method for measuring the reflectance of a sample having a sample axis, according to an illustrative embodiment, is shown;

[0020] Figure 14 A flowchart illustrating a method for using a mirror-variable-angle absolute reflectometer according to an illustrative embodiment is shown; and

[0021] Figure 15 A data processing system according to an illustrative embodiment is shown. Detailed Implementation

[0022] The example recognizes and considers that precise absolute measurement of specular reflectance has several applications. First, and perhaps most widely used, is the technique for establishing reference standards for the calibration of other types of reflectance measurements and measuring devices. Most measuring instruments require a known reflectance standard to establish a reference system throughput or 100% reflectance level. In other words, the 100% reflectance level is defined as the reflectance measured without measuring a sample; or simply the reflectance of a component in the reflectometer. Not all known measuring systems use the same angle of incidence; some are variable.

[0023] The example recognizes and takes into account that these known techniques depend on a reference standard with variable wavelength, incident angle of the beam, and polarization capability of the reflectometer. Therefore, the example's Mirror Variable Angle Absolute Reflectometer (SVAAR) provides an absolute measurement technique and reflectometer that can be established independently of any reference standard with variable wavelength, incident angle, and polarization capability.

[0024] The example also recognizes and considers another application in the optical coating industry. For instance, laser mirrors require highly efficient, high-reflectivity coatings to maximize reflectivity and minimize heating due to absorption. These efficient mirror coatings are typically multilayer dielectric stacks designed for specific incident angles and possibly specific wavelengths of light. Due to uncertainties in the thickness or composition of each coating, the performance of the dielectric coating can differ from its original design. These variations in thickness or composition can affect the reflectivity and polarization of the reflected light.

[0025] Verification samples are typically included in each coating that is run and measured to verify that the coating batch meets the expected coating performance standards. For example, at a specific laser wavelength and design angle, although the mirror manufacturer or user may want to determine the absolute reflectivity at angles and polarizations outside the defined design angle (in the case of off-the-shelf mirror coatings used at non-design angles), the reflectivity of a laser mirror is typically greater than 99.98%. For this type of measurement, using a reference standard with additional uncertainties will increase the coating measurement uncertainty. Additionally, the example reflectometer can characterize the polarization effect of the coating. The example reflectometer can also support broadband mirror measurements or measurements at specific wavelengths, including laser lines and multiple angles and polarizations.

[0026] The example also recognizes and considers another application in the measurement of single-layer coating thickness or refractive index. One technique for measuring contamination within a vacuum chamber involves placing a reflective verification sample into the chamber during certain processes or procedures. For example, during satellite testing, components typically release volatile substances when under vacuum, especially when heated, such as during thermal or operational testing. Contaminants condense on the mirrored verification sample during the procedure. The verification sample can be measured in the example reflectometer, and the thickness or refractive index of the contaminant layer, derived from the polarization of the reflected light, varies at specific angles and wavelengths.

[0027] The example also recognizes and considers that measuring the reflectance or transmittance of a material is a way to determine the composition or other chemical, thermal, or optical properties of the test substance. Specifically, the example considers measurements of various properties at optical (visible, near-visible) or infrared (often called thermal infrared) wavelengths of light. Typically, optical measurements are the ratio of the amplitude of the test sample to the amplitude of a well-characterized "reference" or "standard" or "reference standard" workpiece. However, the accuracy of these relative measurements is limited by the accuracy of the "reference standard," which in many cases is calibrated relative to other "reference standards." Each level of the calibration process increases the uncertainty in the accuracy of the "reference standard" we are working with, often resulting in significant uncertainty. Therefore, in some cases, the "reference standard" becomes almost useless. As an example, if the accuracy of the purchased reference standard has an uncertainty of + / -4%, the reference standard is of no help when performing measurements with a measurement accuracy of + / -1%.

[0028] The example also recognizes and considers that, ideally, a “reference standard” used in optical measurements is measured via an “absolute” measurement technique that is not used for comparison with a known standard as a source of accuracy. The example also recognizes and considers that techniques currently exist for measuring reflectivity using “absolute” techniques, but they have practical limitations. A major limitation is the range of incident angles covered by the technique. Other limitations of known techniques include excessively large sample sizes for a given test or system alignment problems. For example, currently used devices have a diverging cone of the beam, which greatly increases the desired sample size required for the light's rebound point and necessitates large light-collecting optics for detection.

[0029] Therefore, the example provides a measurement technique capable of relatively quickly and accurately measuring the absolute reflectance of a specular sample across a wide range of incident angles, wavelengths, and polarizations. The example also provides absolute reflectance measurements at infrared wavelengths. The example also recognizes and takes into account the existence of a limited number of absolute reflectance standards (if any) available at thermal infrared wavelengths.

[0030] For most reflectivity standards, the relationship between reflectivity and angle and polarization is derived from the basic optical properties of the reflective material. For example, an optical system might use a polished copper plate with widely accepted basic optical properties, but not covering the full range of calibrated wavelengths. Extrapolation and interpolation of values ​​from multiple sources are used when deriving the relationship between reflectivity and wavelength, polarization, and angle. For such a system, it is unclear which copper alloy is effective for the accepted optical properties.

[0031] In summary, the example has several advantages over known techniques. The example can perform absolute reflectivity measurements of specular samples at variable angles, polarizations, and wavelengths, which existing reflectometers cannot. A unique feature of the example is the use of an elliptical roof mirror. An elliptical roof mirror has an elliptical reflector surface for reflecting the light beam back to the sample and detector. The elliptical reflector surface focuses the reflected beam onto the sample surface. The elliptical roof mirror can rotate about a sample rotation axis at twice the angular distance from the sample incident point. The sample rotation axis lies on the sample surface. The angle of incidence of light on the sample is measured relative to the sample normal (a line perpendicular to the sample surface).

[0032] The second unique feature of the example is the shape of the elliptical reflector surface and its positioning relative to the sample, which allows the first and second reflections from the sample to coincide. The third unique feature is the ability to sequentially measure the sample, laser power, and background light level to compensate for source drift and background conditions. The fourth unique feature is the limitation of the measured footprint to a range equal to the beam diameter divided by the cosine of the incident angle. The beam can be focused at the detector, maximizing the signal and minimizing alignment criticality. The fifth unique feature is that the measurement technique uses the same optical path and optics during both the 100% measurement phase and the sample measurement phase. The sample-to-100% ratio is an absolute measure of the square of the sample reflectance.

[0033] Therefore, this example provides a method for absolute reflectivity of a mirror with variable angles and a reflectometer that has several advantages over known techniques. Now, let us turn our attention to the accompanying drawings.

[0034] Figure 1A A prior art 10-degree “V” configuration optical path is shown for performing 100% reflectivity measurements. Figure 1B This illustrates a prior art 10-degree "W" configuration optical path for performing reflectance measurements of a sample. (The following should be read together.) Figure 1A and Figure 1B Although dashed line 101 is the axis of sample 114, Figure 1A and Figure 1B The lines in the diagram show the optical path.

[0035] Figure 1A The “V” configuration 100 shown is used to measure the 100% reflectivity of an optical reflectometer, which includes a light source 102, a reflector 104, a reflector 106, a reflector 108, and a detector 110. Because a sample is not present, the term “100%” reflectivity is used, and when a sample is present in the reflectometer, the reflectivity will be reduced by at least a small percentage. In the absence of a sample, the maximum possible reflectivity of the system is achieved, and this maximum possible reflectivity is considered either “100% reflectivity” or simply “100%”.

[0036] In the "W" arrangement of the optical path between sample 114 and mirror 106, Figure 1B The “W” configuration 112 shown adds sample 114 to the configuration. Figure 1A In the reflectometer shown, the reflectivity of the system is recalculated and compared with the 100% reflectivity to determine the reflectivity of sample 114.

[0037] therefore, Figure 1A and Figure 1BThis indicates a known method for measuring the absolute reflectance of a specular sample. This method, known as the "VW" absolute reflectance measurement accessory, is commercially available from many spectrophotometers and Fourier transform infrared (FTIR) measurement systems. The measurement paths for "100%" and "sample" are shown below. Figure 1A and Figure 1B The reason for the names "V" and "W" is quite obvious. The "absolute" measurement capability is derived from the use of the same three mirrors in the "V" configuration when measuring the "100%" value of the sample in the "W" configuration. Because the only change in the optical path is the addition of a sample, the ratio of the "W" / "V" value is the absolute reflectance ratio directly attributable to the sample reflectance. However, it should be noted that there are two reflections or "bounces" from the sample. This is because the measured value is R... sample *R sample The result is that the reflectance or R of the sample... sample It equals the square root of ("W" / "V"). This relationship helps improve the accuracy of sample reflectance measurements.

[0038] Figure 2 The illustration shows a prior art “VW” assembly and beam path for both 100% reflectance measurement and sample reflectance measurement at incident angles of 10 degrees and 20 degrees, according to an illustrative embodiment. Figure 2 The “VW” arrangement 200 shown is Figure 1A The "V" configuration 100 and Figure 1B The “W” configuration 112 is a variation or combination thereof. The reflectometer of the “VW” arrangement 200 includes a light source 202, a reflector 204, a reflector 206, a sample 208, a sample axis 210, a reflector 212, a reflector 214, a reflector 216, a reflector 218, and a detector 220.

[0039] Figure 1A and Figure 1B as well as Figure 2 The described technique is limited in its ability to change the angle of incidence. Typically, reflectometers are configured for a single angle of incidence of 10° + / - and are not intended to be varied. The sample angle of incidence is the degree to which the sample 208 rotates relative to the incident light about the sample axis 210. Therefore, the sample angle of incidence is the angle between the incident light ray and the normal to the sample at the point of intersection. Another way to define the sample angle of incidence is that it is half the angle between the incident ray and the reflected ray at the point of intersection with the sample.

[0040] Figure 2This illustrates one of the problems associated with changing and increasing the angle of incidence, increasing the sample size or beam footprint, and requiring the repositioning of the source and detector mirrors. A 20° angle of incidence is the maximum shown. At larger angles of incidence, the sample size requirements become significant and are often impractical. Furthermore, repositioning and realigning the mirrors represents a significant time commitment. Even at a 10° angle of incidence, the required sample size exceeds the standard 1” size. Therefore, as further described below, refer to... Figure 1A , Figure 1B as well as Figure 2 The existing reflectometer technology described has drawbacks that are addressed by example.

[0041] Figure 3 A prior art method for measuring the reflectivity of a variable-angle sample, according to an illustrative embodiment, is shown. The reflectometer system 300 includes a light source 302, a mirror M1304, a sample 306, mirrors M2308, M3310, and M4312, a polarizer pair 314, and a detector 316. The sample 306 and mirror M2308 can rotate together with a rotating platform 318, which may include mirror apertures. Figure 3 The arrows and lines in the diagram represent the optical path taken by the beam emitted by the light source 302.

[0042] Harrick Scientific Corp of Pleasantville, NY, manufactured... Figure 3 The diagram shows a variable measurement system that can be used to perform variable angle measurements of specular reflection. In other words, Figure 3 This is a diagram of the Harik Science Crop Variable Angle Reflectometer.

[0043] The instrument is used to perform a scan sequence similar to that used for near-normal reflectivity to obtain relative values. As with the near-normal case, the relative value is multiplied by the absolute reflectivity of the reference standard at the same angle and polarization to obtain absolute calibration. To obtain absolute calibration of the reference standard mirror, the mirror is calibrated at a near-normal angle to give absolute calibration.

[0044] However, this technique is not a direct absolute measurement; rather, it is based on the absolute value of a reference standard relative to an angle, derived from the absolute value measured at a single angle (via the “VW” technique), and this absolute value is associated with a variable measurement at the same angle. Reference values ​​at larger angles are provided through the available literature and fitted optical constants. In summary, variable angle measurements are based on a reference standard with a mixed reflectivity derived from the absolute angle and polarization of a single measurement, and based on published and fitted optical constants projected onto other angles and polarizations.

[0045] Figure 3 The limitation of the variable angle technique shown is the requirement for relatively restricted sample sizes. Sample sizes are limited in terms of maximum thickness, as well as minimum and maximum height and width. For fixed-size samples outside these ranges, different instruments must be used.

[0046] Figure 4 The following is shown based on the measurement sample 800 ( Figure 5 and Figure 6 An exemplary embodiment of a mirror variable-angle absolute reflectometer 700 (shown) is illustrated. The mirror variable-angle absolute reflectometer 700 is shown in a configuration for measuring 100% reflectivity. Figure 4 Indicates relative to Figure 1 to Figure 3 The present invention represents a substantial improvement over existing reflectometers.

[0047] The mirror-mounted variable-angle absolute reflectometer 700 includes a light source 702, a selectable polarizer 704, a mirror system 706, an elliptical roof-shaped reflector 708, a selectable polarizer 710, a detector 712, and a selectable light trap 714. Another term for the elliptical roof-shaped reflector 708 is "elliptical roof reflector." Because... Figure 4 The calibration or 100% reflectivity configuration is shown, so it is specifically from... Figure 4 Sample 800 is omitted. However, sample axis 802 is shown as a dashed line, and the sample is placed at this dashed line for later sample measurement. Similarly, sample axis 802 lies on the face or surface of the sample. Figure 4 The remaining lines shown represent the optical path of the beam. Different parts of the beam can converge or diverge.

[0048] 700 Mirror Variable Angle Absolute Reflectometer and Figure 1A , Figure 1B , Figure 2 as well as Figure 3 Compared to traditional "V", "W", and "VW" type angle reflectometers, the mirror variable angle absolute reflectometer 700 offers several advantages. It provides multiple bounce absolute reflectance at variable angles and polarizations for samples with minimal size constraints.

[0049] In an exemplary embodiment, the mirror-variable-angle absolute reflectometer 700 includes an elliptical roof-shaped reflector 708. The reflector system 706 and the elliptical roof-shaped reflector 708 are arranged to provide an incident beam and a returned beam that coincide at the sample location (e.g., at the sample axis 802). In the exemplary embodiment, the incident beam and the returned beam are in a vertical plane; however, in alternative embodiments, other orientations are possible. The elliptical roof-shaped reflector 708 provides a first and a second bounce of the beam to redirect the returned beam at the sample location.

[0050] For illustrative purposes and as a suggested source, a wavelength-tunable laser with optional polarization control and a polarization analyzer via polarizers 704 and 710 is shown. However, both polarizers are optional. Additionally, the light source 702 need not be a wavelength-tunable laser, but can be a fixed-wavelength laser, a single-line laser, a broadband source, a light-emitting diode source, a filtered broadband source, a sunlight simulator, actual sunlight directed into the system, or any other suitable light source for the intended measurement configuration.

[0051] The elliptical roof-type reflector 708 includes an upper portion 720 and a lower portion 722. The upper portion 720 and the lower portion 722 meet at a vertex 724 of the elliptical roof-type reflector 708. The elliptical roof-type reflector 708 includes an elliptical reflector surface 726 along the interior of the upper portion 720 and the lower portion 722. The elliptical reflector surface 726 is defined by a curved surface (such as a continuous curve) extending between the top and bottom of the elliptical roof-type reflector 708. The elliptical reflector surface 726 is recessed between the upper portion 720 and the lower portion 722. The elliptical reflector surface 726 is configured to face the sample 800. The vertex 724 is set along the major axis 728 of the ellipse defining the elliptical reflector surface 726.

[0052] A two-dimensional ellipse is a closed object with two foci, so the sum of the distances from any point on the ellipse to the foci is constant. An ellipsoid is a solid that rotates about an axis passing through its two foci. An elliptical reflector surface 726 is defined by an ellipsoid cut in the front and sides to form the elliptical reflector surface 726. The elliptical reflector surface 726 is a hollow surface, wherein the interior of the surface is reflective. The elliptical reflector surface 726 curves from top to bottom and from one side to the opposite side to control the direction of beam reflection. The elliptical shape of the elliptical reflector surface 726 eliminates the alignment control degree of freedom used to focus the beam at the sample 800. The elliptical reflector surface 726 has an elliptical shape, rather than a flat surface, to control the beam spot position and beam spot size at the sample. Passing the beam through one focal point of the inner reflecting ellipsoid will necessarily cause the beam to pass through the other focal point. The elliptical reflector surface 726 is used to redirect the beam reflected from the sample 800 back to the sample 800. The elliptical reflector surface 726 includes one focus of an ellipse, with a second focus at the measurement point of the sample 800, such that any light reflected from the sample 800 along the direction of the elliptical roof-type reflector 708 is reflected at the same focus and refocused back onto the sample 800. The elliptical roof-type reflector 708 performs absolute reflectivity measurements of the mirror sample with variable angles, polarization, and wavelengths.

[0053] An elliptical reflector surface 726 is shaped to reflect a light beam back to detector 712 and sample 800. In an exemplary embodiment, the elliptical reflector surface 726 is configured to converge the light beam at a coincident beam spot 804 on sample 800. For example, when the light beam is reflected from the elliptical reflector surface 726, the beam is focused at the focal point of the ellipse defining the elliptical reflector surface 726. Sample 800 is configured to be positioned at a focal point (telefocal) such that the light beam converges to sample 800.

[0054] The elliptical reflector surface 726 includes a first beam spot 730 and a second beam spot 732. In the illustrated embodiment, the first beam spot 730 is disposed on the upper portion 720, and the second beam spot 732 is disposed on the lower portion 722. A light beam is configured to be guided from the light source 702 and / or the sample 800 (if present) to the first beam spot 730. The light beam is guided from the first beam spot 730 to the second beam spot 732. The light beam is guided from the second beam spot 732 back to the sample 800 and / or the detector 712. In an exemplary embodiment, the first beam spot 730 and the second beam spot 732 are axially aligned with a first focal point 734 of the ellipse defining the elliptical reflector surface 726. In an exemplary embodiment, the sample 800 is configured to be axially aligned with a second focal point 736 of the ellipse defining the elliptical reflector surface 726. The elliptical reflector surface 726 is configured to converge the light beam to a beam spot 738 at the second focal point 736 of the sample 800. Therefore, the system can use a smaller sample size and a smaller light-collecting optics at detector 712.

[0055] There are various configurations available for source and detector redirection. Figure 4 The configuration shown is presented as 100% measurement or system 100% value. Of course, although the prior art system does not include the arrangement of the elliptical roof-type reflector 708 or the reflector system 706, this arrangement corresponds to Figure 1 or... Figure 2 The “V” configuration measurement value is shown in the “VW” system.

[0056] Figure 4 The mirror system 706 is shown as including a first mirror 715 having a first surface 716 and a second mirror 717 having a second surface 718. Each surface 716, 718 is mirrored to reflect the light beam. However, the mirror system 706 can be a different mirror system, such as having a single block or having, for example... Figures 7 to 8 The two surfaces shown are single reflectors, etc. Alternatively, the reflector system 706 can have more than two reflectors, depending on the desired arrangement for a specific application.

[0057] Figure 5A 15-degree configuration of a variable-angle absolute reflectometer 700 for measuring sample reflectance is shown according to an illustrative embodiment. Figure 6 A 30-degree configuration of a mirror variable-angle absolute reflectometer 700 for measuring sample reflectance is shown according to an illustrative embodiment. Figure 5 and Figure 6 The sample 800 is shown arranged at the sample axis 802. A sample holder with a flat surface or a three-point sphere position can be manufactured to position the sample surface on the plane containing the sample axis 802. The left, right, top, and bottom positioning of the sample 800 is not critical, as long as the largest incident laser spot is contained within the sample 800. A kinematic base mount is another option.

[0058] The elliptical roof-shaped reflector 708 rotates in the same direction as the light source 702 by twice the desired sample incident angle to intercept and return the reflected beam. Figure 5 An elliptical roof-shaped reflector 708 is shown, which is rotated 30 degrees around the sample axis 802 to measure orientation, and a sample 800 is shown, which is rotated 15 degrees around the sample axis 802 to measure orientation or grazing angle. Figure 6 The diagram illustrates an elliptical roof-type reflector 708 rotated 60 degrees around a sample axis 802 for measurement orientation, and a sample 800 rotated 30 degrees around the sample axis 802 for measurement orientation or grazing angle. The grazing angle is the angle between the elliptical roof-type reflector 708 and the surface of the sample 800. The measurement orientation angle of the elliptical roof-type reflector 708 is complementary to the sample surface. The measurement orientation angles of the elliptical roof-type reflector 708 and the sample are measured from a 100% position.

[0059] If the sample 800 facing the light source 702 and detector 712 is considered zero, and the sample 800 normally parallel to both the light source and detector is considered zero, the sample incident angle can be achieved by rotating the desired incident angle clockwise or counterclockwise. If the elliptical roof-type reflector 708 is in calibration or 100% configuration, such as... Figure 4 As shown, if the elliptical roof mirror angle is considered to be 180°, then when the elliptical roof mirror 708 is located between the source beam and the detector beam closest to the detector 712 and the light source 702, the elliptical roof mirror angle is zero. One method for removing the sample from the optical path to perform a 100% measurement is as follows: If the elliptical roof mirror 708 and the sample 800 are coupled, then when the sample incident angle is 90°, the elliptical roof mirror 708 will be at 180° in the 100% or calibration position. This arrangement makes the sample surface parallel to the source beam and the return beam. The sample 800 only needs to move about half the beam diameter to leave the beam. A fixed cam or other mechanical or electromechanical device can push the sample holder backward relative to the sample surface normal. The procedure will also include mounting the sample 800 on a linear translation stage parallel to the sample normal.

[0060] The elliptical roof-shaped reflector 708 is configured to rotate about the sample axis 802 to measure the reflectivity of the sample 800 at various measurement angles. The elliptical roof-shaped reflector 708 can be moved using a moving device (such as, but not limited to, an electromechanical motor, a movable bracket holding the elliptical roof-shaped reflector 708, a series of gears or knobs, or any convenient mechanical mechanism for rotating the elliptical roof-shaped reflector 708 about the sample axis 802).

[0061] exist Figure 5 In the illustrative embodiment shown, the elliptical roof-shaped reflector 708 is relative to Figure 4 The 0-degree reference of the light path direction is rotated 30 degrees around the sample axis 802. The sample 800 is positioned with its sample surface at the sample axis 802, facing the light source 702 and detector 712, and the sample 800 is rotated to the desired angle of incidence. In this case, the sample 800 is rotated 15° counterclockwise from the light beam. Figure 5 As shown, the elliptical roof-shaped reflector 708 is rotated to intercept the reflected beam and redirect the reflected beam so that it is reflected a second time away from the sample 800.

[0062] exist Figure 6 In the illustrative embodiment shown, the elliptical roof-shaped reflector 708 is rotated 60 degrees about the sample axis 802 relative to a 0-degree reference. The sample 800 is positioned with its sample surface at the sample axis 802, facing the light source 702 and detector 712, and the sample 800 is rotated to the desired angle of incidence. In this case, the sample 800 is rotated 30° counterclockwise from the light beam. Figure 6 As shown, the elliptical roof-shaped reflector 708 is rotated to intercept the reflected beam and redirect the reflected beam so that it is reflected a second time away from the sample 800.

[0063] The elliptical roof-shaped reflector 708 rotates in the same direction as the light source 702 by twice the desired sample incident angle to intercept and return the reflected beam. Because these relative angular rates are constant, mechanical coupling between the two can be achieved, or, for alignment versatility, the rotational motion can be controlled independently.

[0064] In an exemplary embodiment, the beam spot size can be kept small on the sample, such as to keep the sample size relatively small. The beam footprint can vary with the sampling angle. The size of the beam footprint is the beam diameter divided by the cosine of the angle of incidence. Keeping the beam small minimizes the sample size requirement. In an exemplary embodiment, the mirror system 706 and the elliptical roof mirror 708 focus the beam at a coincident beam spot on the sample 800. The beam can be converged at the sample 800 to reduce the beam spot footprint. By controlling the positional orientation of the mirror system 706, the elliptical roof mirror 708, and the sample 800, the same optical path and optics can be used during 100% measurement and sample measurement. The system is used to sequentially measure the sample 800, laser power, and background level to compensate for source drift and background conditions. The ratio of sample measurement to 100% measurement is an absolute measure of the square of the sample reflectivity.

[0065] An optical trap 714 is used to provide a zero-measurement. The optical trap 714 can be placed in or near the mirror system 706, and it will intercept the source output as the mirror system 706 moves accordingly. For example, a first mirror 715 can be rotated so that its first surface 716 faces the optical trap 714. The first mirror 715 can be moved by a motor, a manual dial, or other convenient mechanical mechanism. In other embodiments, the first mirror 715 can be moved in other directions of movement, such as by translation. In other embodiments, the first mirror 715 and the second mirror 717 can be moved to allow for total source power measurement. For example, a light beam can be directed from the light source 702 directly or by using the first mirror 715 and the second mirror 717 to the detector 712 without directing the beam to the elliptical roof reflector 708. The total source power is used to compensate for any source drift that varies over time. When the first reflector 715 returns to its normal operating position, the light beam can be guided to the sample 800 and the elliptical roof reflector 708 for 100% horizontal measurement (sample removed) or sample measurement (sample in the optical path).

[0066] The first reflector 715 and the second reflector 717 can be mounted on a single mechanical device (motor and bracket or other device) or on separate mechanical devices (motor and bracket or other device) to move reflectors 715, 717. The reflector system 706 can be rotated in opposite directions to rotate the first reflector 715 and the second reflector 717, and can be mechanically coupled to minimize control requirements or controlled independently as needed. A source zero level provided by the optical trap 714 can be achieved by rotating the first reflector 715 and the second reflector 717 of the reflector system 706 by approximately 90° from their normal operating position.

[0067] In other embodiments, a chopper may be introduced at the source output before or after the optional polarizer 704. The chopper may be used to extract source and / or detector signals from background noise caused by light leakage or light scattered within the mirrored variable-angle absolute reflectometer 700.

[0068] In an exemplary embodiment, a light beam is guided from a first reflector 715 to a sample 800 and converges at a beam spot 804. A first surface 716 is shaped to form a converging beam so that the beam is focused on the sample 800 to form a small-diameter beam spot. In an exemplary embodiment, a light beam is guided from an elliptical reflector surface 726 to a sample 800 and converges at a beam spot 804. The elliptical reflector surface 726 is shaped to form a converging beam so that the beam is focused on the sample 800 to form a small-diameter beam spot.

[0069] Figure 7 It is based on the measurement sample 800 ( Figure 9 and Figure 10 A side view of a mirror variable-angle absolute reflectometer 700, an exemplary embodiment of the reflectivity shown. Figure 8 It is based on the measurement sample 800 ( Figure 9 and Figure 10 A perspective view of a specular variable-angle absolute reflectometer 700, illustrating an exemplary embodiment of reflectivity (shown). The specular variable-angle absolute reflectometer 700 is shown in a configuration for measuring 100% reflectivity.

[0070] In the illustrated embodiment, the mirror system 706 includes a central mirror 750, which includes a first surface 752 and a second surface 754. The central mirror 750 is used in place of the first mirror 715 and the second mirror 717. Figure 5 and Figure 6 (As shown). The central reflector 750 is positioned to receive a light beam from a light source (not shown) and guide the light beam to a sample 800, and the central reflector 750 is also positioned to receive a light beam from a sample 800 and guide the light beam to a detector (not shown). A reflector moving device 756 can be used to move the central reflector 750, such as by rotating and / or translating the central reflector 750, to control the direction of light beam reflection.

[0071] The mirror-mounted variable-angle absolute reflectometer 700 includes an elliptical roof-type reflector 708, specifically a first elliptical roof-type reflector 708. The reflector system 706 includes a second elliptical roof-type reflector 760 disposed in the optical path. The second elliptical roof-type reflector 760 has a second elliptical reflector surface 762 configured to reflect a light beam. The second elliptical roof-type reflector 760 includes an upper portion 764 and a lower portion 766. The second elliptical reflector surface 762 is formed along the upper portion 764 and the lower portion 766 and is shaped to reflect a light beam to or from the sample 800. The second elliptical roof-type reflector 760 is used for focusing the source beam (to the sample 800) and collecting the reflected beam (from the sample 800).

[0072] A central reflector 750 is located within the concave interior of an elliptical roof-shaped reflector 760. A first surface 752 of the central reflector 750 is configured to reflect light from the light source 702 to a second elliptical reflector surface 762, and thereby to the sample 800. The second elliptical reflector surface 762 is configured to reflect light from the sample 800 back to the central reflector 750. A second surface 754 of the central reflector 750 is configured to reflect light from the sample 800 to the detector 712.

[0073] The second elliptical reflector surface 762 includes a first beam spot 770 and a second beam spot 772. A light beam is guided from a first surface 752 of the central mirror 750 to the first beam spot 770. The light beam is guided from the first beam spot 770 to the sample 800. The light beam is guided from the sample 800 to the second beam spot 772. The light beam is guided from the second beam spot 772 to a second surface 754 of the central mirror 750. The first beam spot 770 and the second beam spot 772 are axially aligned with a first focal point 774 of the ellipse defining the elliptical reflector surface 762. The central mirror 750 is located at the first focal point 774. The sample 800 is axially aligned with a second focal point 776 of the ellipse defining the elliptical reflector surface 762. For example, the second focal point 776 of the ellipse defining the elliptical reflector surface 762 may be aligned with a second focal point 736 of the ellipse defining the elliptical reflector surface 726, such as at the sample axis 802. The two ellipses defining the first elliptical reflector surface 726 and the second elliptical reflector surface 762 have a common focal point at the surface of the sample (measurement point). The elliptical reflector surface 762 causes the light beam to converge to the beam spot 778 at the sample 800.

[0074] Figure 9 A 15-degree configuration of a variable-angle absolute reflectometer 700 for measuring sample reflectance is shown according to an illustrative embodiment. Figure 10 A 30-degree configuration of a mirror variable-angle absolute reflectometer 700 for measuring sample reflectance is shown according to an illustrative embodiment. Figure 9 and Figure 10 The sample 800 is shown arranged at the sample axis 802. Figure 9 and Figure 10 A mirror system 706 is shown, comprising a second elliptical roof-shaped mirror 760 and a central mirror 750.

[0075] An elliptical roof-shaped reflector 708 is configured to rotate about a sample axis 802 to measure the reflectivity of a sample 800 at various measurement angles. The elliptical roof-shaped reflector 708 rotates to twice the desired sample incident angle of the sample 800 to intercept and return the reflected beam. Figure 9 An elliptical roof-shaped reflector 708 is shown, rotated 30 degrees around the sample axis 802 to a measurement orientation, and a sample 800 is shown, rotated 15 degrees around the sample axis 802 to a corresponding measurement orientation. Figure 10 An elliptical roof-shaped reflector 708, rotated 60 degrees around the sample axis 802 for measurement orientation, and a sample 800, rotated 30 degrees around the sample axis 802 for corresponding measurement orientation, are shown.

[0076] Figure 11 A flowchart illustrating a method for performing an absolute reflectance measurement of a sample using a specular variable-angle absolute reflectometer, according to an illustrative embodiment, is shown. The order of the steps can be changed or altered, such as to change the order of measurements. Method 1100 can be using... Figures 4 to 10 As shown and below Figure 12 The methods described herein are applicable to any mirror-variable angle absolute reflectometer. In other words, multiple loop sequences can be used in the methods described herein to optimize measurement speed.

[0077] Method 1100 can begin by removing the sample from the SVAAR (Spiral Variable Angle Absolute Reflectometer) and verifying that the sample holder does not restrict the 100% beam (Operation 1102). The term "100% beam" refers to the beam path used in the reflectometer when the sample is not present.

[0078] Method 1100 also includes aligning the elliptical roof-type reflector with a 100% configuration (operation 1104). The term "100% configuration" means that the sample is not present in the reflectometer, so that the maximum possible light from the light source will reach the detector via other components in the reflectometer.

[0079] Optionally, method 1100 also includes configuring the polarizer and analyzer (operation 1106). In some implementations, this operation is considered optional because the polarizer and / or analyzer may not be present.

[0080] Method 1100 also includes rotating the elliptical roof-shaped reflector to a complementary reflection angle (operation 1108). The term "complementary reflection angle" refers to an angle complementary to the angle at which the sample is positioned relative to the sample axis once it is repositioned in the reflector.

[0081] Method 1100 also includes measuring the sample reflector and total optical power (operation 1110). This operation is also performed with the reflectometer in 100% configuration, so that the maximum possible light and optical power reach the detector.

[0082] Method 1100 also includes configuring the laser reflector to 0% using an optical trap (operation 1112). The optical trap absorbs all light from the light source. This operation is intended for the next operation. Specifically, method 1100 also includes measuring the background noise within the reflectometer at the detector (operation 1114).

[0083] Method 1100 also includes configuring the light source, detector, and elliptical roof reflector to 100% readout (operation 1116). The term "100% readout" means measuring the light received by the detector when the reflectometer is in 100% configuration. The light source can be any number of light sources such as lasers (fixed wavelength or tunable wavelength), light-emitting diodes (LEDs), ordinary light bulbs, actual sunlight, sunlamps, or any other suitable light source for the intended application.

[0084] Method 1100 also includes measuring 100% path (operation 1118). The term “measuring 100% path” refers to measuring the path length of the beam traveling within the reflectometer.

[0085] Method 1100 also includes optionally selecting the wavelength of the light (operation 1120). Because this operation is only applicable when the light source is tunable, such as using a tunable laser or a tunable light-emitting diode, this operation is considered optional.

[0086] Method 1100 also includes configuring a light source, detector, and mirror system for measuring light source power drift (operation 1122). The purpose of this operation is to measure how the power measured at the detector changes over time in order to compensate for the error when performing sample measurements.

[0087] Method 1100 further includes measuring the total power of the light source at the detector (operation 1124). Then, method 1100 includes configuring the light source to a 0% configuration (operation 1126). Similarly, method 1100 includes measuring the background noise (operation 1128). At this point, method 1100 includes calculating the 100% path as the ratio of the total power of the light source to the background compensation (operation 1130).

[0088] Method 1100 further includes repositioning the sample into the reflectometer and rotating the sample to the desired angle of incidence (operation 1132). Method 1100 also includes calculating the reflectance as the ratio of a 100% measurement to background compensation (operation 1134). This operation compares the total reflectance measured in this operation with the background compensation and the 100% measurement, allowing the actual reflectance of the sample to be determined as close as possible. Specifically, method 1100 also includes calculating the absolute reflectance as the reflectance divided by the square root of the 100% measurement (operation 1136).

[0089] Method 1100 also includes determining whether a wavelength measurement has been completed (operation 1138). If not, method 1100 returns to operation 1108. If yes, or if operation 1120 is skipped, the process continues. Specifically, method 1100 then includes determining whether polarization has been completed (operation 1140). If no, method 1100 returns to operation 1106. If yes, or if operation 1106 is skipped, method 1100 terminates. In an exemplary embodiment, for each sample measurement (angle, polarization, wavelength), sample reflected power, background, and laser power measurements are acquired. 100% power measurement, background measurement, and source power measurement can be performed before or after the sample measurement. Each combination of polarization and wavelength will have 100% throughput (e.g., watts of the reading for background correction / watts of source power) for each combination of polarization and wavelength. Each combination of polarization, wavelength, and angle will have sample throughput (e.g., watts of the sample reading for background correction / watts of source power again).

[0090] Method 1100 is only relative to Figures 4 to 10 The description provides one example of the use of the reflectometer. Other examples are possible. Therefore, method 1100 does not necessarily limit the claimed invention.

[0091] Figure 12 A mirror-mounted variable-angle absolute reflector according to an illustrative embodiment is shown. The mirror-mounted variable-angle absolute reflector 1200 is relative to... Figures 4 to 10 The deformation shown.

[0092] The mirror-mounted variable-angle absolute reflectometer 1200 includes a light source 1202. The mirror-mounted variable-angle absolute reflectometer 1200 also includes a mirror system 1204 in the optical path of the light source. The mirror system 1204 can be configured to reflect the light beam from the light source 1202 to an optically reflected sample 1206.

[0093] The mirror-mounted variable-angle absolute reflectometer 1200 also includes an elliptical roof-shaped reflector 1208 disposed in the optical path following the sample 1206. The elliptical roof-shaped reflector 1208 includes an elliptical reflector surface along the interior of the elliptical roof-shaped reflector 1208. The elliptical roof-shaped reflector 1208 is configured to reflect the light beam back to the sample 1206.

[0094] The variable-angle absolute reflectometer 1200 also includes a mechanism 1210 connected to the elliptical roof-shaped reflector 1208. The mechanism 1210 can be configured to rotate the elliptical roof-shaped reflector 1208 about a sample axis 1211 of the sample 1206. The mechanism 1210 can be a motor, bracket, microelectromechanical device, gear set, knob, or any other suitable device for translating and / or rotating the elliptical roof-shaped reflector 1208.

[0095] The mirror-variable-angle absolute reflectometer 1200 also includes a detector 1212 located in the optical path after the elliptical roof-shaped reflector 1208, such that the detector 1212 receives light that has been reflected from the elliptical roof-shaped reflector 1208, thereby reflected back to the sample 1206, thereby reflected back to the reflector system 1204, and thereby reflected back to the detector 1212. In an exemplary embodiment, the reflector system 1204 may include a second elliptical roof-shaped reflector having an elliptical reflector surface along the interior of the second elliptical roof-shaped reflector.

[0096] In another example, the light source could be a tunable laser. However, the light source can be any suitable light source for different applications, including but not limited to fixed-wavelength lasers, light-emitting diodes (LEDs), sunlamps, light bulbs, natural sunlight, or other light sources suitable for a particular application.

[0097] In another example, the mirror-mounted variable-angle absolute reflectometer 1200 may also include a polarization controller 1214 disposed in the optical path between the light source 1202 and the mirror system 1204. In a related but different example, the mirror-mounted variable-angle absolute reflectometer 1200 may additionally include a second polarization controller 1216 disposed in the optical path between the mirror system 1204 and the detector 1212.

[0098] The second polarization controller 1216, often referred to as a polarization "analyzer," is used to determine the rotation or change in the polarization of the light from the sample 1206. Typically, for a given input polarization, the second polarization controller 1216 rotates relative to the polarization controller 1214 between approximately 0 and 90 degrees. If the sample 1206 has no effect on the polarization of the light, a maximum signal will appear on the detector 1212 when the second polarization controller 1216 is parallel to the polarization controller 1214 corresponding to "0" degrees.

[0099] In different illustrative embodiments, the mirror system 1204 may be a single mirror having a first surface on a first side of the single mirror and a second surface on a second side of the single mirror. In this case, the first surface is configured to reflect light from the light source 1202 to the sample 1206, and the second surface is configured to reflect light from the sample 1206 to the detector 1212.

[0100] In yet another illustrative embodiment, the mirror system 1204 may be a first mirror and a second mirror. In this case, the first mirror is configured to reflect light from the light source 1202 to the sample 1206, and the second mirror is configured to reflect light from the sample 1206 to the detector 1212.

[0101] In yet another illustrative embodiment, the variable-angle absolute reflectometer 1200 may include an optical trap 1218 associated with a mirror system. In this context, the term "associated with" means that the optical trap is positioned in the optical path such that when the position of the mirror system 1204 is adjusted or when the position of the optical trap 1218 is adjusted, the optical trap 1218 can intercept light from the light source 1202. For example, the optical trap 1218 is configured to intercept light from the light source 1202 by utilizing forward movement of the mirror system 1204, and to intercept a direct path from the light source 1202 to the detector 1212 when the mirror system 1204 retracts due to light interception. The variable-angle absolute reflectometer 1200 may also include a movement system 1220 connected to the mirror system 1204, which is configured to move the mirror system 1204.

[0102] In different examples, the elliptical roof-shaped reflector 1208 is rotated about the sample axis 1211 by a first angle, which is approximately twice the angular distance by which the sample 1206 rotates about the sample axis 1211. In yet another example, the first reflection from the sample 1206 coincides with the second reflection.

[0103] Figure 13 A method for measuring the reflectance of a sample having a sample axis, according to an illustrative embodiment, is shown. Method 1300 is... Figure 11 Method 1100 is an optional method. Use Figures 4 to 10 as well as Figure 12 Any reflectometer shown can implement method 1300. Method 1300 can be characterized as a method for measuring the reflectance of a sample having a sample axis.

[0104] Method 1300 includes projecting a light beam from a light source onto a mirror system (operation 1302). Method 1300 also includes reflecting the light beam from the mirror system onto a sample that has been rotated about a sample axis by a first angle (operation 1304).

[0105] Method 1300 further includes reflecting the light beam from the sample to an elliptical roof-shaped reflector, which is rotated about the sample axis by a second angle, approximately twice the first angle (operation 1306). The elliptical roof-shaped reflector includes an elliptical reflector surface along the interior of the elliptical roof-shaped reflector. Method 1300 further includes reflecting the light beam from the elliptical roof-shaped reflector back to the sample (operation 1308).

[0106] Method 1300 further includes reflecting the light beam from the sample back to the mirror system (operation 1310). Method 1300 also includes reflecting the light beam from the mirror system to a detector to generate a corrected light beam (operation 1312). Method 1300 further includes calculating the reflectivity of the sample based on the optical properties of the corrected light beam detected by the detector (operation 1314). In one illustrative embodiment, the method may then be terminated.

[0107] However, method 1300 can be further modified. For example, method 1300 may also include compensating for source drift and background-introduced errors by sequentially measuring the power of the sample, the light source, and the background error before calculation. In another example, method 1300 may also include limiting the measured footprint to the diameter of the beam divided by the cosine of the angle of incidence of the beam on the sample.

[0108] In yet another example, method 1300 may further include: focusing the beam at the detector to maximize the signal and minimize the alignment criticality. In yet another example, method 1300 may further include: determining the 100% reflectivity level of the elliptical roof mirror before projection by using a light source, a mirror system, and a detector, but without measuring the reflectivity of the elliptical roof mirror with a sample. In this case, calculating the reflectivity may be calculating the absolute reflectivity of the sample. Furthermore, when calculating the reflectivity, the ratio of the sample's reflectivity to 100% reflectivity is an absolute measure of the square of the sample's reflectivity.

[0109] Other variations are possible. For example, in another variation, method 1300 may further include: intercepting the source output using an optical trap when the mirror system retracts due to intercepting the source beam. In yet another variation, method 1300 may further include: extracting the source signal from the background using a chopper disposed at the output of the light source.

[0110] Several other variations are possible. For example, in another variation, method 1300 may further include: reflecting the beam using a second elliptical roof-shaped reflector of a reflector system. The second elliptical roof-shaped reflector includes a second elliptical reflector surface along the interior of the second elliptical roof-shaped reflector.

[0111] Some other variations are possible. Therefore, refer to Figure 13 The examples provided do not necessarily limit the inventions for which protection is claimed.

[0112] Figure 14 A method for using a mirror-mounted variable-angle absolute reflectometer according to an illustrative embodiment is shown. Method 1400 is... Figure 11 Method 1100 or Figure 13 Another variation of method 1300. Through the methods described herein, including... Figures 4 to 10 as well as Figure 12 Any reflectometer shown can implement method 1400. Method 1400 can be characterized as a method using a mirror-variable-angle absolute reflectometer comprising: a light source; a mirror system in the optical path of the light source configured to reflect a light beam from the light source to an optically reflective sample; an elliptical roof-shaped reflector disposed in the optical path after the sample, the elliptical roof-shaped reflector configured to reflect the light beam back to the sample, the elliptical roof-shaped reflector including an elliptical reflector surface along the interior of the elliptical roof-shaped reflector; a mechanism connected to the elliptical roof-shaped reflector configured to rotate the elliptical roof-shaped reflector about an axis of the sample; and a detector in the optical path after the elliptical roof-shaped reflector, such that the detector receives light that has been reflected from the elliptical roof-shaped reflector, thereby reflected back to the sample, thereby reflected back to the mirror system, and thereby reflected back to the detector.

[0113] Method 1400 includes removing the sample and verifying that the sample holder does not restrict the beam (operation 1402). Method 1400 also includes aligning the elliptical roof-shaped reflector with a 100% configuration (operation 1404).

[0114] Method 1400 further includes measuring the signal at the detector to form a 100% measurement (operation 1406). Method 1400 also includes measuring the total source power at the detector (operation 1408). The method may include moving a reflector to collect the total source power at the detector.

[0115] Method 1400 further includes, subsequently, moving the mirror system such that the beam is projected into the light trap to interrupt the light source (operation 1410). Method 1400 also includes, subsequently, measuring the background noise at the detector (operation 1412).

[0116] Method 1400 also includes, subsequently, moving the mirror system back to receive the beam (operation 1414). Method 1400 also includes repositioning the sample in the path of the beam (operation 1416).

[0117] Method 1400 also includes rotating the sample to the desired angle of incidence (operation 1418). Method 1400 also includes rotating the elliptical roof-shaped mirror to the complementary angle of reflection (operation 1420).

[0118] Method 1400 further includes measuring sample reflection at the detector to form a measurement (operation 1422). Method 1400 also includes measuring total source power at the detector (operation 1424). The method may include moving a reflector to collect the total source power at the detector.

[0119] Method 1400 further includes, subsequently, moving the mirror system such that the beam is projected into the light trap to interrupt the light source (operation 1426). Method 1400 also includes, subsequently, measuring the background noise at the detector (operation 1428).

[0120] Method 1400 also includes subsequently moving the mirror system back to receive the beam (operation 1430). Method 1400 also includes calculating the reflectivity of the sample as a ratio of 100% measurement to background and total light source power compensation (operation 1432).

[0121] Method 1400 also includes calculating the absolute reflectance of the sample as the square root of the reflectance with respect to 100% of the measurement (operation 1434). In one illustrative embodiment, the method may then be terminated.

[0122] Turn now Figure 15 An illustration of a data processing system is depicted according to an illustrative embodiment. Figure 15 The data processing system 1500 is an example of a data processing system that can be used to implement the data processing of the detected optical signal described in the above example. In this illustrative example, the data processing system 1500 includes a communication structure 1502 that provides communication between the processor unit 1504, the memory 1506, the permanent storage 1508, the communication unit 1510, the input / output (I / O) unit 1512, and the display 1514.

[0123] Processor unit 1504 is used to execute instructions for software that can be loaded into memory 1506. This software may be associative memory, content-addressable memory, or software for implementing processes described elsewhere herein. Thus, for example, the software loaded into memory 1506 may be for executing... Figure 11 Method 1100 Figure 13 Method 1300 or Figure 14The software of method 1400. Processor unit 1504 can be multiple processors, multiprocessor cores, or some other type of processor, depending on the specific implementation. As used in the references herein, numbers refer to one or more. Furthermore, processor unit 1504 can be implemented using multiple heterogeneous processor systems, in which the main processor and auxiliary processors coexist on a single chip. As another illustrative example, processor unit 1504 can be a symmetric multiprocessor system containing multiple processors of the same type.

[0124] Memory 1506 and persistent storage 1508 are examples of storage device 1516. A storage device is any hardware capable of storing information on a temporary and / or permanent basis, such as, but not limited to, data, program code in a functional form, and / or other suitable information. In these examples, storage device 1516 may also be referred to as a computer-readable storage device. In these examples, for example, memory 1506 may be random access memory or any other suitable volatile or non-volatile storage device. Persistent storage 1508 can take various forms depending on the specific implementation.

[0125] For example, persistent storage 1508 may include one or more components or devices. For example, persistent storage 1508 may be a hard disk drive, flash memory, rewritable optical disc, rewritable magnetic tape, or a combination thereof. The media used in persistent storage 1508 may also be removable. For example, a removable hard disk drive may be used for persistent storage 1508.

[0126] In these examples, communication unit 1510 provides communication with other data processing systems or devices. In these examples, communication unit 1510 is a network interface card. Communication unit 1510 can provide communication by using one or both of physical and wireless communication links.

[0127] Input / output (I / O) unit 1512 allows data input and output using other devices that can be connected to data processing system 1500. For example, I / O unit 1512 can provide connectivity for user input via a keyboard, mouse, and / or other suitable input devices. Furthermore, I / O unit 1512 can send output to a printer. Display 1514 provides a mechanism for displaying information to the user.

[0128] Instructions for operating systems, applications, and / or programs may reside in a storage device 1516 that communicates with processor unit 1504 via communication structure 1502. In these illustrative examples, the instructions exist in functional form on permanent storage 1508. These instructions may be loaded into memory 1506 for execution by processor unit 1504. Processes of different implementations may be performed by processor unit 1504 using computer-implemented instructions that may reside in memory such as memory 1506.

[0129] These instructions are referred to as program code, computer-usable program code, or computer-readable program code that can be read and executed by the processor in processor unit 1504. The program code in different embodiments may be embodied on different physical or computer-readable storage media (such as memory 1506 or persistent storage 1508).

[0130] Program code 1518 is functionally located on a selectively removable computer-readable medium 1520 and can be loaded onto or transferred to the data processing system 1500 for execution by the processor unit 1504. In these examples, program code 1518 and computer-readable medium 1520 form a computer program product 1522. In one example, computer-readable medium 1520 may be a computer-readable storage medium 1524 or a computer-readable signal medium 1526. For example, computer-readable storage medium 1524 may include an optical disc or disk inserted or placed into a drive or other device as part of permanent storage 1508 for transfer to a storage device such as a hard disk drive as part of permanent storage 1508. Computer-readable storage medium 1524 may also take the form of permanent storage connected to the data processing system 1500, such as a hard disk drive, thumb drive, or flash memory. In some instances, computer-readable storage medium 1524 cannot be removed from the data processing system 1500.

[0131] Optionally, program code 1518 can be transferred to data processing system 1500 using computer-readable signal medium 1526. For example, computer-readable signal medium 1526 can be a propagated data signal containing program code 1518. For example, computer-readable signal medium 1526 can be an electromagnetic signal, an optical signal, and / or any other suitable type of signal. These signals can be transmitted via a communication link such as a wireless communication link, fiber optic cable, coaxial cable, wire, and / or any other suitable type of communication link. In other words, in the illustrative example, the communication link and / or connection can be physical or wireless.

[0132] In some examples, program code 1518 can be downloaded from another device or data processing system via a network to persistent storage 1508 for use within data processing system 1500 via computer-readable signal medium 1526. For example, program code stored in a computer-readable storage medium of a server data processing system can be downloaded from a server to data processing system 1500 via a network. The data processing system providing program code 1518 can be a server computer, a client computer, or some other device capable of storing and transmitting program code 1518.

[0133] The different components shown for the data processing system 1500 are not intended to impose architectural limitations on the ways in which different implementations can be achieved. Different examples of data processing systems may be implemented that include components other than or replacing those shown for the data processing system 1500. Figure 15 Other components shown may differ from the illustrative example. Different implementations can be implemented using any hardware device or system capable of running program code. As an example, a data processing system may include organic components integrated with inorganic components and / or may consist entirely of organic components excluding human intervention. For example, a storage device may include organic semiconductors.

[0134] In another illustrative example, the processor unit 1504 may take the form of a hardware unit with circuitry manufactured or configured for a particular use. This type of hardware can perform operations without loading program code from a storage device configured to perform operations into memory.

[0135] For example, when the processor unit 1504 is implemented as a hardware unit, it can be a circuit system, an application-specific integrated circuit (ASIC), a programmable logic device, or some other suitable type of hardware configured to perform multiple operations. Using a programmable logic device, the device is configured to perform multiple operations. The device can be reconfigured at a later time or can be permanently configured to perform multiple operations. Examples of programmable logic devices include programmable logic arrays, programmable array logic, field-programmable logic arrays, field-programmable gate arrays, and other suitable hardware devices. Because different implementation methods are implemented using hardware units, program code 1518 can be omitted using this type of implementation.

[0136] In yet another illustrative example, processor unit 1504 can be implemented using a combination of processors found in computer and hardware units. Processor unit 1504 may have multiple hardware units and multiple processors configured to run program code 1518. Using the examples described, some processes can be implemented with multiple hardware units, while other processes can be implemented with multiple processors.

[0137] As another example, the storage device in the data processing system 1500 is any hardware device capable of storing data. Memory 1506, persistent storage 1508, and computer-readable medium 1520 are examples of storage devices in tangible form.

[0138] In another example, a bus system can be used to implement communication structure 1502 and may include one or more buses, such as a system bus or input / output bus. Of course, any suitable type of architecture that provides data transfer between different components or devices attached to the bus system can be used to implement the bus system. Additionally, the communication unit may include one or more devices for transmitting and receiving data, such as a modem or network adapter. Furthermore, for example, memory may be memory 1506 or cache, which may be found in the interface and storage controller hub that may be present in communication structure 1502.

[0139] The data processing system 1500 may also include associative memory. The associative memory may communicate with the communication structure 1502. The associative memory may also communicate with or be considered part of the storage device 1516 in some examples. Although one associative memory is shown, additional associative memories may exist.

[0140] As used herein, the term "associative memory" refers to multiple data items and multiple associations between them. Multiple data items and multiple associations can be stored in a non-volatile computer-readable storage medium. Multiple data items can be collected into groups of associations. In addition to direct associations between multiple data items, associative memory can be configured to be queried based at least on indirect relationships between them. Therefore, associative memory can be configured to be queried based only on direct relationships, at least only on indirect relationships, and based on a combination of direct relationships and at least indirect relationships. Associative memory can be content-addressable memory.

[0141] Therefore, associative memory can be characterized as multiple data sets and multiple associations between them. Multiple data sets can be collected into associative groups. Furthermore, associative memory can be configured to be queried based on at least one relationship between multiple data sets, selected from groups including direct relationships and at least indirect relationships, or relationships other than direct correlations between the data sets. Associative memory can also take the form of software. Therefore, associative memory can also be viewed as a process of collecting information into associative groups to gain new insights based on relationships rather than direct correlations. Associative memory can also take the form of hardware such as dedicated processors or field-programmable gate arrays.

[0142] As used herein, the term "entity" refers to a distinct, independently existing object, although such existence need not be a physical entity. Therefore, abstract and legitimate constructs can be considered entities. As used herein, an entity does not have to be an animation. Associative memory works with entities.

[0143] Different examples can take the form of a completely hardware implementation, a completely software implementation, or an implementation that includes both hardware and software elements. Some implementations are implemented in software, including but not limited to, firmware, resident software, and microcode.

[0144] Furthermore, different implementations may take the form of a computer program product accessible by a computer-usable medium or a computer-readable medium, which provides a program for use by or in connection with a computer or any device or system that executes instructions. For the purposes of this disclosure, a computer-usable medium or a computer-readable medium can generally be any tangible device that can contain, store, communicate, propagate, or transmit a program for use by or in connection with an instruction execution system, device, or apparatus.

[0145] Computer-usable media or computer-readable media can be, for example, but not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems or propagation media. Non-limiting examples of computer-readable media include semiconductor or solid-state memory, magnetic tape, removable computer disks, random access memory (RAM), read-only memory (ROM), hard disks, and optical discs. Optical discs can include CD-ROM, CD-R / W, and DVDs.

[0146] Furthermore, the computer-usable medium or computer-readable medium may contain or store computer-readable program code or computer-usable program code such that, when the computer-readable program code or computer-usable program code is executed on a computer, the execution of the computer-readable program code or computer-usable program code causes the computer to transmit another computer-readable program code or computer-usable program code via a communication link. This communication link may use, for example, but not limited to, physical or wireless media.

[0147] A data processing system suitable for storing and / or executing computer-readable or computer-usable program code includes one or more processors that are directly or indirectly coupled to memory elements via a communication structure such as a system bus. Memory elements may include local memory, mass storage, and cache memory used during the actual execution of the program code, which provides temporary storage for at least some of the computer-readable or computer-usable program code to reduce the number of times code is retrieved from mass storage during code execution.

[0148] Input / output (I / O) devices can be coupled to the system directly or via an intermediate I / O controller. These devices may include, for example, but are not limited to, keyboards, touchscreen displays, and indicating devices. Different communication adapters may also be coupled to the system, enabling the data processing system to become coupled to other data processing systems or remote printers or storage devices via an intermediate proprietary or public network. The non-limiting examples of modems and network adapters are only a few of the currently available types of communication adapters.

[0149] Various examples have been described for illustrative and descriptive purposes, and these descriptions are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those skilled in the art. Furthermore, different examples may provide different features compared to other examples. One or more embodiments have been selected and described in order to best explain the principles of the embodiments, their practical application, and to enable those skilled in the art to understand the disclosure of various embodiments with various modifications suitable for their intended use.

[0150] It should be understood that the above description is intended to be illustrative and not restrictive. For example, the embodiments described above (and / or aspects thereof) may be used in combination with each other. Furthermore, many modifications may be made to adapt to specific situations or materials to suit the teachings of the invention without departing from its scope. The dimensions, material types, orientations of the various components, and the number and position of the various components described herein are intended to define parameters of a particular embodiment and are not intended to limit in any way and are merely exemplary embodiments. Many other embodiments and modifications within the spirit and scope of the claims will be apparent to those skilled in the art upon review of the above description. Therefore, the scope of the invention should be determined by reference to the appended claims and the full scope of their equivalents. In the appended claims, the terms “including” and “in which” are used as plain English equivalents to the corresponding terms “comprising” and “wherein”. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc., are used only as designations and are not intended to impose numerical requirements on other objects.

[0151] Furthermore, this disclosure includes examples based on the following:

[0152] Item 1: A mirror-mounted variable-angle absolute reflectometer, comprising:

[0153] light source;

[0154] A mirror system in the optical path of the light source, the mirror system being configured to reflect the light beam from the light source to an optically reflective sample;

[0155] An elliptical roof-shaped reflector is positioned in the optical path behind the sample. The elliptical roof-shaped reflector has an elliptical reflector surface configured to reflect the light beam back to the sample.

[0156] A mechanism, connected to an elliptical roof-shaped reflector, configured to rotate the elliptical roof-shaped reflector about the axis of the sample; and

[0157] The detector in the optical path is configured to receive light from the optical path.

[0158] Item 2: According to the mirror variable angle absolute reflectometer of Item 1, wherein the elliptical roof-shaped reflector includes an upper part and a lower part, and the elliptical reflector surface is concave towards the sample between the upper and lower parts.

[0159] Item 3: According to the mirror variable angle absolute reflectometer of Item 1, wherein the elliptical reflector surface includes a first beam spot and a second beam spot, a beam is guided from the sample to the first beam spot, a beam is guided from the first beam spot to the second beam spot, a beam is guided from the second beam spot back to the sample, the first beam spot and the second beam spot are aligned with the first focal axis of the ellipse defining the elliptical reflector surface, and the sample is aligned with the second focal axis of the ellipse defining the elliptical reflector surface.

[0160] Item 4: According to the mirror variable angle absolute reflectometer of Item 1, wherein the mirror system includes a second elliptical roof-shaped mirror disposed in the optical path, the second elliptical roof-shaped mirror having a second elliptical reflector surface configured to reflect the light beam, the mirror system including a central mirror having a first surface on a first side of the central mirror and a second surface on a second side of the central mirror, wherein the first surface is configured to reflect light from the light source to the second elliptical reflector surface and thereby to the sample, wherein the second elliptical reflector surface is configured to reflect light from the sample to the central mirror, and wherein the second surface is configured to reflect light from the sample to the detector.

[0161] Item 5: According to the mirror variable angle absolute reflectometer of Item 4, wherein the second elliptical reflector surface includes a first beam spot and a second beam spot, a beam is guided from a first side of the central reflector to the first beam spot, a beam is guided from the first beam spot to the sample, a beam is guided from the sample to the second beam spot, a beam is guided from the second beam spot to the second side of the central reflector, the first beam spot and the second beam spot are aligned with the first focal axis of the ellipse defining the second elliptical reflector surface, and the sample is aligned with the second focal axis of the ellipse defining the second elliptical reflector surface.

[0162] Item 6: According to Item 1, a mirror-variable angle absolute reflectometer, wherein the elliptical reflector surface converges the beam into a beam spot at the sample.

[0163] Item 7: The mirror-variable angle absolute reflectometer according to Item 1, wherein the light source includes a tunable laser.

[0164] Item 8: The mirror variable angle absolute reflectometer according to Item 1 further includes a polarization controller disposed in the optical path between the light source and the mirror system.

[0165] Item 9: The mirror variable angle absolute reflectometer according to Item 8 further includes a second polarization controller disposed in the optical path between the mirror system and the detector.

[0166] Item 10: The mirror variable angle absolute reflectometer according to Item 1, wherein the mirror system includes a single mirror having a first surface on a first side of the single mirror and a second surface on a second side of the single mirror, wherein the first surface is configured to reflect light from a light source to a sample, and wherein the second surface is configured to reflect light from the sample to a detector.

[0167] Item 11: The mirror variable angle absolute reflectometer according to Item 1, wherein the mirror system includes a first mirror and a second mirror, wherein the first mirror is configured to reflect light from a light source to a sample, and wherein the second mirror is configured to reflect light from the sample to a detector.

[0168] Item 12: The mirror variable-angle absolute reflectometer according to Item 1 further includes:

[0169] An optical trap associated with a mirror system, configured to intercept light from a light source by forward movement of the mirrors, and to intercept the direct path from the light source to the detector when the mirror system retracts due to the intercepted light; and

[0170] A moving system, connected to and configured as a moving mirror system.

[0171] Item 13: According to the mirror variable angle absolute reflectometer of Item 1, the elliptical roof-shaped reflector rotates about the sample axis at a first angle, which is approximately twice the angular distance of the sample rotation about the sample axis.

[0172] Item 14: According to Item 1, the mirror variable angle absolute reflectometer, wherein the first and second reflections from the sample coincide.

[0173] Item 15: A method for measuring the reflectance of a sample having a sample axis, the method comprising:

[0174] A beam of light from a light source is projected onto a mirror system.

[0175] Then, the beam of light from the mirror system is reflected onto the sample, which rotates around the sample axis by a first angle;

[0176] The beam of light from the sample is then reflected to an elliptical roof-shaped reflector having an elliptical reflector surface. The elliptical roof-shaped reflector rotates about the sample axis by a second angle, which is approximately twice the first angle.

[0177] Then, the light beam from the elliptical reflector surface of the elliptical roof-shaped reflector is reflected back to the sample;

[0178] Then, the beam of light from the sample is reflected back to the mirror system;

[0179] Then, the beam from the mirror system is reflected back to the detector, thereby generating a corrected beam; and

[0180] The reflectivity of the sample is calculated based on the optical properties of the corrected beam detected by the detector.

[0181] Item 16: According to the method of Item 15, it further includes: compensating for source drift and background-introduced errors by sequentially measuring the power of the sample, the light source, and the background error before calculation.

[0182] Item 17: The method according to Item 15 further includes: limiting the measured area to the diameter of the beam divided by the cosine of the incident angle of the beam on the sample.

[0183] Item 18: The method according to Item 15 further includes: focusing the beam at the detector to maximize the signal and minimize the alignment criticality.

[0184] Item 19: The method according to Item 15 further includes: determining the 100% reflectivity level of the elliptical roof reflector by using a light source, a reflector system, and a detector, but without measuring the reflectivity of the elliptical roof reflector before projection.

[0185] Item 20: According to the method of Item 19, wherein calculating reflectance includes: calculating the absolute reflectance of the sample.

[0186] Item 21: According to the method of Item 20, wherein, when calculating reflectance, the ratio of the reflectance of the sample to 100% reflectance is an absolute measure of the square of the reflectance of the sample.

[0187] Item 22: The method according to Item 15 further includes: when the mirror system retracts due to intercepting the source beam, intercepting the output from the light source using an optical trap.

[0188] Item 23: A method using a mirror-variable-angle absolute reflectometer, the mirror-variable-angle absolute reflectometer comprising: a light source; a mirror system in the optical path of the light source, the mirror system being configured to reflect a light beam from the light source to an optically reflective sample; an elliptical roof-shaped mirror disposed in the optical path after the sample, the elliptical roof-shaped mirror having an elliptical reflector surface configured to reflect the light beam back to the sample; a mechanism connected to the elliptical roof-shaped mirror, the mechanism being configured to rotate the elliptical roof-shaped mirror about an axis of the sample; and a detector in the optical path after the elliptical roof-shaped mirror, such that the detector receives light that has been reflected from the elliptical roof-shaped mirror, thereby reflected back to the sample, thereby reflected back to the mirror system, and thereby reflected back to the detector, the method comprising:

[0189] Remove the sample and verify that the sample holder does not restrict the beam;

[0190] Align the elliptical roof-shaped reflector with 100% configuration;

[0191] The signal is measured at the detector to form a 100% measurement value;

[0192] Measure the total light source power at the detector;

[0193] Then, the mirror system is moved so that the beam of light is projected into the light trap to interrupt the light source;

[0194] Then, the background noise was measured at the detector;

[0195] Then, the mirror system is moved back to receive the beam;

[0196] Reposition the sample onto the path of the beam;

[0197] Rotate the sample to the desired angle of incidence;

[0198] Rotate the elliptical roof-shaped reflector to the complementary reflection angle;

[0199] The sample reflectance is measured at the detector to form a measurement value;

[0200] Measure the total light source power at the detector;

[0201] Then, the mirror system is moved so that the beam of light is projected into the light trap to interrupt the light source;

[0202] Then, the background noise was measured at the detector;

[0203] Then, the mirror system is moved back to receive the beam;

[0204] The reflectance of the sample was calculated as the ratio of 100% measurement to background compensation; and

[0205] The absolute reflectance of the sample is calculated as the square root of the reflectance as measured at 100%.

Claims

1. A mirror-mounted variable-angle absolute reflectometer, comprising: light source; A mirror system in the optical path of the light source, the mirror system being configured to reflect the light beam from the light source to an optically reflective sample; An elliptical roof-shaped reflector is disposed in the optical path behind the sample, the elliptical roof-shaped reflector having an elliptical reflector surface configured to reflect the light beam back to the sample; A mechanism connected to the elliptical roof-shaped reflector is configured to rotate the elliptical roof-shaped reflector about the axis of the sample by an angle, the angle being twice the angular distance through which the sample rotates about the axis; as well as The detector in the optical path is configured to receive light from the optical path.

2. The mirror-mounted variable-angle absolute reflectometer according to claim 1, wherein, The elliptical roof-shaped reflector includes an upper part and a lower part, and the surface of the elliptical reflector is recessed between the upper part and the lower part facing the sample.

3. The mirror-mounted variable-angle absolute reflectometer according to claim 1, wherein, The elliptical reflector surface includes a first beam spot and a second beam spot. The light beam is guided from the sample to the first beam spot, from the first beam spot to the second beam spot, and from the second beam spot back to the sample. The first beam spot and the second beam spot are aligned with the first focal axis of the ellipse defining the elliptical reflector surface, and the sample is aligned with the second focal axis of the ellipse defining the elliptical reflector surface.

4. The mirror-mounted variable-angle absolute reflectometer according to claim 1, wherein, The mirror system includes a second elliptical roof-shaped mirror disposed in the optical path, the second elliptical roof-shaped mirror having a second elliptical reflector surface configured to reflect the light beam, the mirror system including a central mirror having a first surface on a first side of the central mirror and a second surface on a second side of the central mirror, wherein the first surface is configured to reflect light from the light source to the second elliptical reflector surface and thereby to the sample, wherein the second elliptical reflector surface is configured to reflect light from the sample to the central mirror, and wherein the second surface is configured to reflect light from the sample to the detector.

5. The mirror-mounted variable-angle absolute reflectometer according to claim 4, wherein, The second elliptical reflector surface includes a first beam spot and a second beam spot. The light beam is guided from the first side of the central reflector to the first beam spot, the light beam is guided from the first beam spot to the sample, the light beam is guided from the sample to the second beam spot, and the light beam is guided from the second beam spot to the second surface of the central reflector. The first beam spot and the second beam spot are aligned with the first focal axis of the ellipse defining the second elliptical reflector surface, and the sample is aligned with the second focal axis of the ellipse defining the second elliptical reflector surface.

6. The mirror-mounted variable-angle absolute reflectometer according to claim 1, wherein, The elliptical reflector surface at the sample causes the light beam to converge into a beam spot.

7. The mirror-mounted variable-angle absolute reflectometer according to claim 1, wherein, The light source includes a tunable laser.

8. The mirror-mounted variable-angle absolute reflectometer according to claim 1, further comprising a polarization controller disposed in the optical path between the light source and the mirror system.

9. The mirror-mounted variable-angle absolute reflectometer according to claim 8, further comprising a second polarization controller disposed in the optical path between the mirror system and the detector.

10. The mirror-mounted variable-angle absolute reflectometer according to claim 1, wherein, The mirror system includes a single mirror having a first surface on a first side and a second surface on a second side, wherein the first surface is configured to reflect light from the light source to the sample, and wherein the second surface is configured to reflect light from the sample to the detector.

11. A method for measuring the reflectance of a sample having a sample axis, the method comprising: A beam of light from a light source is projected onto a mirror system; The light beam from the mirror system is then reflected onto the sample, which rotates about the sample axis by a first angle. The beam of light from the sample is then reflected to an elliptical roof-shaped reflector having an elliptical reflector surface, the elliptical roof-shaped reflector being rotated about the sample axis by a second angle, the second angle being twice the first angle; Then, the light beam from the elliptical reflector surface of the elliptical roof-shaped reflector is reflected back to the sample; The beam of light from the sample is then reflected back to the mirror system; The beam from the mirror system is then reflected to the detector, thereby generating a corrected beam; and The reflectivity of the sample is calculated based on the optical properties of the corrected beam detected by the detector.

12. The method of claim 11, further comprising: Before calculation, source drift and background introduction errors are compensated by sequentially measuring the power of the sample, the light source, and the background error.

13. The method of claim 11, further comprising: The measured area is limited to the diameter of the beam divided by the cosine of the angle of incidence of the beam on the sample.

14. The method of claim 11, further comprising: The beam is focused at the detector to maximize the signal and minimize the alignment criticality.

15. The method of claim 11, further comprising: Before projection, the 100% reflectivity level of the elliptical roof-shaped reflector is determined by measuring the reflectivity of the elliptical roof-shaped reflector using the light source, the reflector system, and the detector, but without the sample. Calculating the reflectivity includes calculating the absolute reflectivity of the sample, and wherein, in calculating the reflectivity, the ratio of the reflectivity of the sample to the 100% reflectivity is an absolute measure of the square of the reflectivity of the sample.

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