Off-axis scanning hologram interferometer

Abstract

The present invention relates to an off-axis scanning hologram interferometer. The present invention provides an off-axis scanning hologram interferometer comprising: a scan beam generation unit which modulates the phase of a first beam from a light source to convert the first beam into a first curvature beam, converts a second beam into a second curvature beam, and then causes the first and second curvature beams to interfere with each other to form a scan beam; a scan unit for controlling the scanning position of the scan beam in the horizontal and vertical directions and transferring the scan beam to a target, which is a reflective object, to scan the target by using the scan beam; a transparent or translucent plate which is placed in front of the target to transmit the beam and is installed to be inclined at a predetermined angle in least one of the X-axis and Y-axis directions with respect to the surface (X, Y plane) of the target; a photodetector for receiving and detecting beams reflected from the target and the plate; and an electronic processing unit for processing a detected signal to generate the hologram of the target. According to the present invention, phase information based on the step of a reflective object having a rough surface can be obtained without speckle noise.

Description

Off-axis scanning holographic interferometer

[0001] The present invention relates to an off-axis scanning holographic interferometer, and more particularly, to an off-axis scanning holographic interferometer that, unlike existing interferometers, can obtain phase information according to a step difference of an object having a rough surface without speckle noise.

[0002] A conventional scanning hologram recording device for obtaining phase information according to the step of an object generates a scan beam by superposing a spherical wave and a plane wave, scans the object while moving the scan beam in the X and Y directions while the object is fixed, then collects the scan beam reflected from the object and focuses it on a light detector, and generates an electric signal proportional to the intensity of the focused light in the light detector.

[0003] Here, a very small mask, such as a pin-hole, is placed in front of the photodetector to filter and acquire only the light information corresponding to the focus area of ​​the light collecting lens. However, in the case of such a pin-hole mask structure, not only is the light collecting efficiency low, but since the scan is performed by mechanically moving the stage on which the object is placed in the X and Y directions, it takes a long time to acquire the phase information of the object step, and there is a problem that the acquired phase information of the step is contaminated with speckle noise.

[0004] In this way, the existing interferometer is a device that obtains the step of an object by using the coherence of a light source, but has the problem that it is difficult to obtain an interference pattern for an object with a rough surface in units of wavelengths due to the coherence of the light source.

[0005] The technology underlying the present invention is disclosed in Korean Patent No. 1304695 (announced on September 6, 2013).

[0006] The purpose of the present invention is to provide an off-axis scanning holographic interferometer for obtaining phase information according to a step of an object having a rough surface without speckle noise.

[0007] The present invention provides an off-axis scanning holographic interferometer, comprising: a scan beam generating unit that modulates the phase of a first beam from a light source to convert it into a first curvature beam and a second beam into a second curvature beam, and then interferes the first and second curvature beams to form a scan beam; a scanning unit that controls the scanning position of the scan beam in the horizontal and vertical directions and transmits the scan beam to the object, which is a reflective object, so as to scan the object using the scan beam; a transparent or translucent plate that is arranged in front of the object, transmits the beam, and is installed so as to be inclined at a set angle with respect to at least one direction of the x-axis and the y-axis with respect to a plane (x, y plane) of the object; a light detector that receives and detects a beam reflected from the object and the plate; and an electronic processing unit that processes a signal detected by the light detector to generate a hologram of the object.

[0008] In addition, the off-axis scanning holographic interferometer may further include a light splitter disposed between the scanning unit and the plate to transmit a scan beam received from the scanning unit to an object and to reflect a beam reflected from the object and the plate back to the light detector.

[0009] Additionally, the plate may be installed at a set distance from the front of the object.

[0010] In addition, the electronic processing unit sets the focal point of the first or second curvature beam projected on the object as the origin and the distance in the z-axis direction from the origin plane to the plate as z off (x,y), the distance in the z-axis direction to the target object based on the focus position is z obj If defined as (x,y), the hologram information is expressed by the mathematical formula below. can be obtained.

[0011]

[0012] Here, is a hologram of the above plate, represents a hologram of the object, which is the reflective object,

[0013] as, is the distance from the center of the above plate to the above focus position, and is the degree of twist in the x-axis and y-axis directions, and represent the angles of inclination in the x-axis and y-axis directions, respectively.

[0014] In addition, the off-axis scanning holographic interferometer may further include a numerical restoration unit that numerically processes the hologram information received from the electronic processing unit and numerically restores the numerical reference light reflected from the plate and the numerical object light reflected from the object.

[0015] In addition, the off-axis scanning holographic interferometer may further include a numerical interference unit that obtains an interference pattern of the numerical reference light and the numerical object light by calculating the square of the sum of the numerical reference light and the numerical object light obtained by the numerical restoration.

[0016] In addition, the numerical interference unit can obtain step information of the target object at the corresponding location by unwrapping the numerical interference image by the interference pattern.

[0017] In addition, the numerical interference unit can obtain the interference pattern through the square of the sum of the restored numerical reference light and the numerical object light, and numerically restore the hologram information of the object by removing the DC component formed by the sum of the square of the numerical reference light and the square of the numerical object light from the interference pattern.

[0018] In addition, the numerical interference unit can obtain an interference pattern between the numerical reference light and the numerical object light using the mathematical formula below.

[0019]

[0020] Here, is an interference pattern, is the above numerical reference light and the above numerical object light The sum of, The component is the sum of the square of the numerical reference light and the square of the numerical object light, λ is the wavelength of the beam used, (x, y, z) is a spatial coordinate system in which the origin is the focus position of the first or second curvature beam, the direction of travel of the first or second curvature beam is the z-axis, and the plane axis perpendicular to the z-axis is the x-axis and the y-axis, Z obj is the distance from the above focus position to the object, It indicates the distance between the plate installed at an angle and the target object.

[0021] In addition, the numerical interference unit performs FFT processing on the result of numerically removing the DC component from the interference pattern to spatially separate a DC information region, an object hologram information region, and a twin image noise information region in the frequency domain, and then spatially filters only the object hologram information among the three separated regions, moves it to the origin position in space, and then performs IFFT processing again to obtain only the object hologram information from which background noise and twin image noise have been removed.

[0022] In addition, the off-axis angle of the plate in the x-axis or y-axis direction to prevent the DC information area and the hologram information from overlapping in the frequency domain is A larger value ( ) is set to can represent the numerical aperture of the Fresnel plate generated by the interference phenomenon.

[0023] In addition, the scan beam generating unit may include a shifting means for modulating a phase by frequency shifting or phase shifting a first beam split from the light source; first and second curvature beam generators for converting the phase-modulated first beam and the second beam split from the light source into a first curvature beam and a second curvature beam having a set curvature, respectively; and an interference means for interfering the first curvature beam passing through the first curvature beam generator and the second curvature beam passing through the second curvature beam generator to generate the scan beam having an interference pattern of a Fresnel plate.

[0024] In addition, the above transition means is a frequency transition means that frequency-shifts the first beam, and the scan beam can be defined as a Fresnel plate shape heterodyned over time by the following mathematical formula.

[0025]

[0026] Here, λ is the wavelength of the beam used, (x,y,z) is a spatial coordinate system in which the focal point of the first or second curvature beam is the origin, the direction of travel of the first or second curvature beam is the z-axis, and the plane axis perpendicular to the z-axis is the x-axis and the y-axis, C(z) is the curvature of the Fresnel plate formed by the interference of the first and second curvature beams, and is a function representing the change in curvature along the z-axis, and Ω represents the frequency at which the transition is made.

[0027] In addition, the above transition means is a phase shifting means for phase shifting the first beam, and the scan beam can be defined by the following mathematical formula as a Fresnel plate shape that is phase shifted in an area where the first curvature beam and the second curvature beam interfere.

[0028]

[0029] Here, λ is the wavelength of the beam used, (x, y, z) is a spatial coordinate system with the focal point of the first or second curvature beam as the origin, the direction of travel of the first or second curvature beam as the z-axis, and the plane axis parallel to the z-axis as the x-axis and y-axis, C(z) is a function representing the change in curvature along the z-axis as the curvature of the Fresnel plate formed by the interference of the first and second curvature beams, P n represents a set of n different phases used in the above phase transition.

[0030] In addition, the electronic processing unit may include a heterodyne detector that generates an in-phase output signal and a quadrature output signal using a current signal detected by the photodetector and a heterodyne modulation signal having a frequency Ω generated by a function generator of the signal generating unit; an AD converter that receives the in-phase signal and the quadrature signal through each channel and converts them into digital signals; a signal processing unit that generates a complex hologram for an object from the converted digital signal; a storage unit that stores the generated complex hologram; and a scan control unit that generates a control signal for changing a scan position of the scan unit whenever hologram processing for an arbitrary position of the object is completed.

[0031] In addition, the electronic processing unit may include an AD converter that converts a current signal detected by the photodetector into a digital signal; a signal processing unit that generates a complex hologram for an object using the converted digital current signal and a phase shift value generated by a phase shift signal generator of the signal generating unit; a storage unit that stores the generated complex hologram; and a scan control unit that generates a control signal for changing a scan position of the scan unit whenever hologram processing for an arbitrary position of the object is completed.

[0032] Additionally, the scanning unit may include a horizontal scan mirror and a vertical scan mirror to control the scanning position of the scanning beam with respect to the target object in horizontal and vertical directions.

[0033] In addition, the scanning unit may include a scan mirror that controls the scanning position of the scan beam with respect to the target object in the horizontal and vertical directions and transmits the scan beam incident from the scan beam generating unit to the target object in the horizontal direction, and a translation stage that moves the target object in the vertical direction at the rear end of the target object.

[0034] In addition, the present invention provides an off-axis scanning holographic interferometer including: a scan beam generating unit that modulates the phase of a first beam from a light source to convert it into a first curvature beam and a second beam into a second curvature beam, and then interferes the first and second curvature beams to form a scan beam; a scanning unit that controls the scanning position of the scan beam in the horizontal and vertical directions and transmits the scan beam to the object, which is a reflective object, so as to scan the object using the scan beam; a light splitter that is arranged between the scan unit and the object and splits the beam by transmitting and reflecting an incident beam; a reference mirror that is installed above the light splitter at a set angle with respect to the z-axis direction that is perpendicular to a surface (x, y plane) of the object and reflects the incident beam; a light detector that is arranged below the light splitter and detects a beam that is reflected from the object and the reference mirror and passes through the light splitter; and an electronic processing unit that processes a signal detected by the light detector to generate a hologram of the object.

[0035] According to the present invention, phase information according to the step of a reflective object having a rough surface can be obtained without speckle noise.

[0036] FIG. 1 is a drawing showing the configuration of an off-axis scanning holographic interferometer according to a first embodiment of the present invention.

[0037] Figure 2 is a drawing of a form in which the transition means of Figure 1 is replaced with a phase transition means.

[0038] FIG. 3 is a drawing illustrating an example of an implementation of a beam curvature generator according to an embodiment of the present invention.

[0039] Figure 4 is a drawing showing an example of a modification of Figure 1.

[0040] Figures 5 and 6 are drawings showing a configuration with a beam splitter added to Figures 1 and 2, respectively.

[0041] FIG. 7 is a drawing showing the configuration of an off-axis scanning holographic interferometer according to a second embodiment of the present invention.

[0042] Figure 8 is a drawing of a form in which the transition means of Figure 7 is replaced with a phase transition means.

[0043] FIG. 9a is a drawing showing an embodiment of obtaining distance information of a step difference on a surface of an object using a transparent or translucent plate in an embodiment of the present invention.

[0044] Figure 9b is a drawing explaining the x, y direction tilt angles of the plate.

[0045] Figure 10 is a diagram showing a numerical processing process for restoring off-axis hologram information obtained from an off-axis scanning hologram interferometer without background noise and twin image noise.

[0046] Fig. 11 is a drawing showing the configuration of an off-axis scanning holographic interferometer according to a third embodiment of the present invention.

[0047] Figure 12 is a drawing of a form in which the transition means of Figure 11 is replaced with a phase transition means.

[0048] FIG. 13 is a drawing illustrating a numerical processing process for obtaining a numerical interference image from hologram information obtained according to an embodiment of the present invention.

[0049] FIG. 14a and FIG. 14b are drawings showing the configuration of an off-axis scanning holographic interferometer according to the fourth embodiment of the present invention.

[0050] FIG. 15a and FIG. 15b are drawings showing the configuration of an off-axis scanning holographic interferometer according to the fifth embodiment of the present invention.

[0051] FIG. 16 is a drawing showing a specific example of a process for obtaining off-axis hologram information according to an embodiment of the present invention.

[0052] FIG. 17 is a diagram illustrating conditions of spatial frequency for obtaining hologram information without twin image noise and background (DC) noise according to an embodiment of the present invention.

[0053] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily practice the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein. In addition, in the drawings, parts irrelevant to the description have been omitted to clearly explain the present invention, and similar parts have been designated with similar reference numerals throughout the specification.

[0054] Throughout the specification, when a part is said to be "connected" to another part, this includes not only the cases where the parts are "directly connected" but also the cases where the parts are "electrically connected" with other elements intervening. Furthermore, when a part is said to "include" a component, this does not exclude other components, but rather includes other components, unless otherwise stated.

[0055] The present invention relates to an off-axis scanning holographic interferometer, and provides an off-axis scanning holographic interferometer capable of obtaining a hologram for a reflective object (reflective object).

[0056] In particular, the present invention proposes a scanning hologram interferometer structure capable of obtaining phase information according to the step of an object without speckle noise when acquiring a hologram of an object having a rough surface with a step on the surface.

[0057] FIG. 1 is a drawing showing the configuration of an off-axis scanning holographic interferometer according to a first embodiment of the present invention, and FIG. 2 is a drawing showing a form in which the transition means of FIG. 1 is replaced with a phase transition means.

[0058] First, as shown in Fig. 1, the off-axis scanning holographic interferometer (100) according to the first embodiment of the present invention largely includes a scan beam generating unit (110), a scanning unit (120), a transparent or translucent plate (130), a light detector (150), and an electronic processing unit (160a), and may further include a computer processing unit (170) and a signal generating unit (180a). At this time, the transparent or translucent plate (130) is positioned at a specific angle with the target object. It is characterized by being positioned to have . Here, the remaining parts excluding the electronic processing unit (160a) and the computer processing unit (170) correspond to the optical system part in the present invention.

[0059] First, the scan beam generator (110) modulates the phase of the first beam among the first and second beams split from the light source and converts it into a first curvature beam through the first curvature beam generator (N1), and then converts the second beam into a second curvature beam through the second curvature beam generator (N2), and then forms a scan beam by interfering the first and second curvature beams.

[0060] The scan beam generation unit (110) uses a Mark-Zehnder interferometer structure that divides a light source into first and second beams to generate first and second curvature beams and then recombines the two generated beams.

[0061] The scan beam generating unit (110) includes a first beam splitter (111), a transition means (112), first and second mirrors (M1, M2), first and second beam curvature beam generators (N1, N2), and an interference means (117), and may further include a light source.

[0062] The transition means (112; 112a, 112b) can phase-shift the first beam split from the light source by frequency-shifting or phase-shifting it. In the embodiment of the present invention, FIG. 1 illustrates the transition means (112) implemented as a frequency shifting means (112a), and FIG. 2, described below, illustrates the transition means (112) implemented as a phase shifting means (112b).

[0063] The first and second curvature beam generators (N1, N2) can convert the first beam phase-modulated by the transition means (112) and the second beam split from the light source into the first and second curvature beams having set curvatures, respectively. In this way, the first and second curvature beam generators (N1, N2) can change the incident beam into a beam with a specific curvature.

[0064] The interference means (117) can receive the first curvature beam and the second curvature beam, cause them to interfere with each other, and generate a scan beam having an interference pattern of a Fresnel plate, which can then be transmitted to the scan unit (120).

[0065] Below, the configuration of the scan beam generation unit (110) is described in more detail through Fig. 1.

[0066] First, a light source is a component that generates electromagnetic waves. A light source can include various means capable of generating electromagnetic waves, such as a laser generator, a light-emitting diode (LED), or a beam with low coherence, such as halogen light with a short coherence length. The following example illustrates a light source implemented as a laser generator.

[0067] A beam output from such a light source is input to a first beam splitter (111). The first beam splitter (111) separates the incident beam into a first beam and a second beam, transmits the first beam to a frequency shifting means (112b), and transmits the second beam to a second mirror (M2). That is, a beam following the path of the first beam in the first beam splitter (111) is transmitted to the frequency shifting means (112b), and a beam following the path of the second beam is reflected by the second mirror (M2) and then transmitted to a second curvature beam generator (N2).

[0068] Here, the first beam splitter (111) may be composed of an optical fiber coupler, a beam splitter, a geometric phase lens, etc., and may be implemented in a manner of transmitting the beam to the outside by waveguide in free space. Here, if a means for splitting the beam in-line, such as a geometric phase lens, is used, the beam may be split in-line into the first beam and the second beam. In the following, it is assumed that each optical splitter is implemented as a beam splitter.

[0069] The frequency shifting means (112a) shifts the frequency of the first beam and transmits it to the first mirror (M1). The frequency shifting means can shift the frequency of the first beam by Ω using the frequency generated by the function generator of the signal generating unit (180a) and transmit it to the first mirror (M1). Here, the frequency shifting means (112a) can use a phase optical modulator, but the present invention is not necessarily limited thereto, and it is also possible to perform frequency shifting using an acousto-optic frequency shifter or PZT.

[0070] Here, the frequency shifting means (112a) is formed between the first beam splitter (111) and the first curvature beam generator (N1) as an example, but the present invention is not necessarily limited thereto. That is, the frequency shifting means (112a) can of course be formed between the first beam splitter (111) and the second curvature beam generator (N2).

[0071] The first beam reflected from the first mirror (M1) is transmitted to the first beam curvature generator (N1). The second beam reflected from the second mirror (M2) is transmitted to the second beam curvature generator (N2).

[0072] Here, the first and second curvature beam generators (N1, N2) receive the respective beams and generate an enlarged beam having a curvature ranging from negative to positive curvature, including a collimated beam. The first and second curvature beam generators (N1, N2) may be set to different curvatures or may be set to the same curvature as needed.

[0073] Fig. 3 is a drawing illustrating an example of an implementation of a beam curvature generator according to an embodiment of the present invention. Fig. 3 (a) shows a first curvature beam generator, (b) shows a second curvature beam generator, and (c) shows an example of a change in curvature of a beam passing through the first curvature beam generator.

[0074] A specific implementation example of the first curvature beam generator (N1) is a beam expander having a first lens (113) that converts a first beam reflected from a first mirror (M1) into a spherical wave, and a second lens (115) that receives a spherical wave and generates a beam with a curve (a first curvature beam), and the curvature of the beam can be adjusted by adjusting the distance between the first lens (113) and the second lens (115). A specific implementation example of the second curvature beam generator (N2) is a beam expander having a third lens (114) that converts a second beam reflected from a second mirror (M2) into a spherical wave, and a fourth lens (116) that receives a spherical wave and generates a beam with a curve (a second curvature beam), and the curvature of the beam can be adjusted by adjusting the distance between the third lens (114) and the fourth lens (116).

[0075] In this way, the first and second curvature beam generators (N1, N2) can be composed of at least one lens, and the curvature of the first beam and the curvature of the second beam can be changed respectively by adjusting the spacing between the lenses.

[0076] In addition, in all embodiments of the present invention, by using the first curvature beam generator (N1) and the second curvature beam generator (N2) in the method of FIG. 3, the curvatures of the first curvature beam and the second curvature beam can be set to be the same or different, thereby adjusting the curvatures of the two beams to determine various scaling factors.

[0077] The first curvature beam generator (N1) converts the first beam into a first curvature beam of a specific curvature and transmits it to the interference means (117). That is, the first curvature beam generator (N1) modulates the spatial distribution of the first beam to generate the first curvature beam.

[0078] The second curvature beam generator (N2) converts the second beam into a second curvature beam of a specific curvature and transmits it to the interference means (117). That is, the second curvature beam generator (N2) modulates the spatial distribution of the second beam to generate the second curvature beam.

[0079] The first and second curvature beams generated are transmitted to the scanning unit (120) after interfering with each other while passing through the interference means (117). The interference means (117) can be implemented as a beam splitter, and is referred to as a second beam splitter in the drawing.

[0080] The interference means (117) overlaps and interferes the first beam (first curvature beam) that has passed through the first beam curvature generation unit (N1) and the second beam (second curvature beam) that has passed through the second beam curvature generation unit (N2) to form a scan beam having an interference pattern of a Fresnel zone pattern.

[0081] At this time, the depth position on the axis of the focus of the first curvature beam and the depth position on the axis of the focus of the second curvature beam can be different from each other. Accordingly, the interference means (117) can form an interference beam (scan beam) in the form of a Fresnel plate by interfering the first curvature beam and the second curvature beam having different focus positions.

[0082] In this way, the scan beam generating unit (110) converts the first beam and the second beam separated from the light source into first and second curvature beams and then superimposes them with each other through the interference means (117) to form a scan beam.

[0083] At this time, as in Fig. 1, when the transition means is configured as a frequency transition means (112a), the generated scan beam can be defined as a Fresnel plate shape heterodyned over time, as in the following mathematical expression 1.

[0084]

[0085] Here, λ is the wavelength of the beam used, (x, y, z) is a spatial coordinate system with the focal point of the first or second curvature beam as the origin, the direction of travel of the first or second curvature beam as the z-axis, and the plane axes perpendicular to the z-axis as the x-axis and y-axis, C(z) is the curvature of the Fresnel plate formed by the interference of the first and second curvature beams, which is a function representing the change in curvature along the z-axis, and Ω represents the frequency at which the transition was made. In addition, (x0 2 +y0 2 ) represents a Cathartic coordinate system with (x0,y0) as the plane orthogonal to the optical axis of the first or second curvature beam.

[0086] For convenience of explanation, in the following embodiments of the present invention, (x, y, z) is a representative example of a spatial coordinate system in which the focal point of the first curvature beam is the origin and the axes of the plane perpendicular to the direction of travel of the first curvature beam are the x, y axes.

[0087] The scan beam generation unit (110) transmits the generated scan beam to the scan unit (120). The scan unit (120) scans the target object using the interference beam formed by the interference means (117).

[0088] Referring again to FIG. 1, the scanning unit (120) controls the scanning position of the scanning beam in the horizontal and vertical directions to scan the target object, which is a reflective object, using the scanning beam and transmits it to the target object.

[0089] The beam incident on the scan unit (120) is transmitted to the target object through the horizontal scan mirror (121) (X scanner) and the vertical scan mirror (122) (Y scanner). In this way, the scan unit (120) may include an X scanner and a Y scanner to control the scanning position of the scan beam with respect to the target object in the horizontal and vertical directions.

[0090] Although the present invention uses a mirror scanner as a scanning means, the present invention is not necessarily limited to this and may be replaced with various known scanning means.

[0091] A Fresnel plate-shaped beam is transmitted to the mirror-shaped scan unit (120), and the scan unit (120) scans the object by moving the Fresnel plate-shaped beam across the object. The scanning position can be adjusted according to a control signal from the scan control unit (165) provided in the electronic processing unit (160a).

[0092] The scan unit (120) can be operated by receiving a scanning control signal from the scan control unit (165) within the electronic processing unit (160a). In response to the control signal, a scan beam can be projected onto the target object according to the movement of the scan mirror. In this way, the scan unit (120) can project an interference beam (a scan beam by the scan unit) between the first and second curvature beams onto the target object by using the scan mirror.

[0093] Of course, the scanning unit (120) may be changed to a scanning unit (420) structure utilizing a horizontal scanning mirror (421) and a translation stage (422) as shown in FIGS. 14a, 14b, 15a, and 15b, in addition to a structure using a horizontal scanning mirror (121) (X scanner) and a vertical scanning mirror (122) (Y scanner) as shown in FIGS. 1 and 2, which will be described later.

[0094] That is, in the present invention, instead of using two mirror scanners as described above, the target can be positioned on an objective plate and the objective plate can be horizontally moved to scan the target. Furthermore, the target can be scanned using various methods, such as using an electronic optical deflector.

[0095] Next, a transparent or translucent plate (130) (hereinafter, “plate”) is placed on the front (front) of the object and transmits the incident beam. This plate (130) can be implemented as an object having transparent or translucent properties (e.g., a glass plate), and any material having transparent or translucent properties is acceptable.

[0096] At this time, the plate (130) is installed so as to be tilted at a set angle with respect to at least one direction of the x-axis and the y-axis with respect to the surface (x, y plane) of the object. Accordingly, the plate (130) may be installed so as to be tilted in both the x and y directions, or may be installed so as to be tilted in either the x and y directions.

[0097] The light detector (150) receives and detects a beam reflected from the target and the plate (130). If, as in FIG. 5 described below, a light splitter (140) is added between the plate (130) and the target, the light detector (150) receives and detects a beam reflected from the light splitter (140).

[0098] Here, a condenser lens (145) may be provided at the front end of the light detector (150). The light detector (150) can receive a beam collected through the condenser lens (145) and convert it into an electrical signal.

[0099] The condenser lens (145) can spatially collect the beam reflected from the light splitter (140) and transmit it to the light detector (150). The beam reflected from the target object at the scan position of the scan beam specified by the scan unit (120) can be spatially collected by the condenser lens (145). The condenser lens (145) can be composed of various lenses, such as an image or non-image condenser including a concave reflector and a convex reflector.

[0100] In this way, the condenser lens (145) collects the beam reflected from the target (reflective target) and the plate (130) and passed through the light splitter (140), and the light detector (150) can detect the spatially concentrated beam through the condenser lens (145) and convert it into a current signal. At this time, the light detector (150) can generate current according to the intensity of the spatially concentrated beam. The light detector can be implemented using a photodiode, but the present invention is not necessarily limited thereto, and various light detection means such as an optical multiplier pipe can be applied. In addition, the present invention can directly detect light transmitted to and entering the detection surface of the light detector (150) without a condenser lens.

[0101] Next, the electronic processing unit (160a) processes the signal detected by the photodetector (150) to generate a hologram for the target object.

[0102] Referring to FIG. 1, the electronic processing unit (160a) includes a heterodyne detector (161), an AD converter (162), a signal processing unit (163), a storage unit (164), and a scan control unit (165).

[0103] The heterodyne detector (161) processes the current signal received from the photodetector (150) to generate an in-phase output signal and a quadrature output signal.

[0104] Specifically, the heterodyne detector (161) generates an in-phase output signal and a quadrature output signal using a current signal detected by the photodetector (150) and a heterodyne modulation signal having a frequency Ω generated by a function generator of the signal generation unit (180a).

[0105] The heterodyne detector (161) multiplies the received current signal by a heterodyne modulation signal having a frequency Ω generated by a function generator of the signal generating unit (180a), and then performs low-pass filtering to generate an in-phase signal as a first output. At the same time, the signal phase of the frequency Ω generated by the function generator is shifted by Ω, multiplied by the received current signal, and then performs low-pass filtering to generate a quadrant signal as a second output. Accordingly, two output signals (in-phase output signal, quadrant output signal) are output from the heterodyne detector (161).

[0106] Here, the same phase output signal and the quarter phase output signal correspond to the pattern encoded by the Fresnel plate of the 3D image of the object, and can be expressed by mathematical expressions 2 and 3, respectively.

[0107]

[0108]

[0109] Here, is the three-dimensional distribution of reflectance for the target object, is a convolution operation. And (x,y) is the scan position of the scan beam specified by the scan unit (120), and C(z) is the curvature of the Fresnel plate formed by the interference of the first curvature beam and the second curvature beam, and represents a function representing the change in curvature along the z-axis.

[0110] The AD converter (162) receives these in-phase signals and quadrature phase signals through each channel and converts them into digital signals. The converted digital current signal is provided to the signal processing unit (163) along with the scanning position of the scanning unit (120).

[0111] The signal processing unit (163) generates a complex hologram for the target object from the converted digital signal, and the storage unit (164) stores the generated complex hologram.

[0112] In addition, the scan control unit (165) generates a control signal for changing the scan position of the scan unit (120) whenever hologram processing for an arbitrary position of the target object is completed, and transmits the control signal to the scan unit (120).

[0113] To this end, the signal processing unit (163) adds mathematical expressions 2 and 3 using a complex number addition method as in mathematical expression 4 below to form a two-dimensional array according to each scan position, and the storage unit (164) can store this.

[0114] In addition, the signal processing unit (163) forms a three-dimensional array according to each scan position for mathematical expressions 2 and 3 and transmits it to the storage unit (164), and when the scan is finished, reads it from the storage unit (164), adds the complex number addition method of mathematical expression 4 to the two-dimensional array corresponding to mathematical expressions 2 and 3, and then stores it in the storage unit (164) again. The signal stored in the storage unit (164) refers to mathematical expression 4 below.

[0115]

[0116] In addition, the present invention can obtain the outputs of mathematical expressions 2 and 3 by applying the heterodyne signal generated in the signal generating unit (180a) to the reference signal input portion of the heterodyne detector and then obtaining the in-phase output and the quadrant output, but as is known in the field of scanning hologram technology, it is also possible to obtain the outputs by detecting the reference signal by positioning a part of the light interfered by the interference means, i.e. the second beam splitter (117), on the second photodetector.

[0117] In addition, in the first embodiment of the present invention, heterodyne detection was performed before conversion to a digital signal through an AD converter (162), but it is also possible to convert the current signal provided from the photodetector (150) and the signal generated from the signal generator (180a) into a digital signal through an AD converter (162), and then perform digital heterodyne detection on the signal using a digital signal processing method and transmit it to the signal processing unit (163).

[0118] Meanwhile, the spatial distribution of the scan beam may be modulated or distorted, for example, when there is an aberration in the lens or reflector. In this case, the pattern detected by the photodetector corresponds to a pattern encoded by a Fresnel plate having a modulated or distorted spatial distribution from a cross-sectional image of the object. In this case, the modulated or distorted pattern element can be obtained by convolving the conjugate complex number of the desired Fresnel plate with the modulated or distorted Fresnel plate. In addition, the modulated or distorted pattern element can be used to form an inverse filter, such as a power fringe adaptive filter, to convert the hologram encoded by the modulated or distorted Fresnel plate into a hologram encoded by the desired Fresnel plate. It goes without saying that the modulated or distorted Fresnel plate is also a type of Fresnel plate. These contents are common to all embodiments of the present invention.

[0119] And, in an embodiment of the present invention, by positioning an arbitrary phase and amplitude pattern in the path of the first curvature beam or the path of the second curvature beam, the spatial distribution of the first curvature beam or the second curvature beam can be modulated. At this time, the scan beam is a Fresnel plate modulated by an arbitrary phase and amplitude pattern, and accordingly, the pattern detected by the photodetector can be a pattern encoded by an image of the object and a Fresnel plate having a spatial distribution modulated by an arbitrary phase and amplitude pattern. Here, a pattern element modulated by an arbitrary phase and amplitude pattern can be obtained by convolving a complex conjugate of a desired Fresnel plate with a Fresnel plate having a spatial distribution modulated by an arbitrary phase and amplitude pattern. In addition, by using the pattern elements modulated by the arbitrary phase and amplitude patterns, an inverse filter such as a power-print adaptive filter can be formed to convert a hologram encoded with a Fresnel plate modulated by an arbitrary phase and amplitude pattern into a hologram encoded with a desired Fresnel plate. It goes without saying that a Fresnel plate having a spatial distribution modulated by an arbitrary phase and amplitude pattern is also a type of Fresnel plate. This content is also common to all embodiments of the present invention.

[0120] FIG. 9a is a drawing showing an embodiment of obtaining distance information of a step difference on a surface of an object through a transparent or translucent plate in an embodiment of the present invention, and FIG. 9b is a drawing explaining the x, y direction inclination angle of the plate.

[0121] As shown in Fig. 9, the focal point of the first or second curvature beam projected on the object is set as the origin, and the distance in the z-axis direction from the origin plane (indicated by a dotted line in Fig. 9) to the plate is z off (x,y), the distance in the z-axis direction to the object based on the focus position is z obj If defined as (x,y), the electronic processing unit (160a) is expressed as the hologram information in the mathematical expression 5 below. can be obtained.

[0122]

[0123] Here, is a hologram of the plate (130), represents a hologram of an object that is a reflective object with reflectance.

[0124] In addition, the distance in the z-axis direction from the origin plane to the plate (130) is can be expressed as . Here, is the distance from the center of the plate (130) to the focus position, and is the degree to which the plate (130) is twisted in the x-axis and y-axis directions, and As shown in Fig. 9b, the plate (130) represents the angle size at which it is tilted in the x-axis and y-axis directions, respectively.

[0125] At this time, and The angular range of , It is preferable. In addition, it is also possible for the plate (130) to be twisted in only one of the x and y directions, and in this case, the angle in the direction in which it is not twisted becomes 0 degrees.

[0126] In this way, the hologram information acquired from the electronic processing unit (160a) includes both a hologram by a beam reflected from the plate (130) and a hologram by a beam reflected from the object.

[0127] The off-axis scanning hologram interferometer (100) may additionally include a computer processing unit (170) that numerically processes the hologram information obtained from the electronic processing unit (160a) to restore the hologram of the target object.

[0128] In detail, the off-axis scanning holographic interferometer (100) detects the light signal reflected from the target object and the light signal reflected from the transparent or translucent plate together with the condenser lens (145) and the photodetector (150), and then processes the detected signal numerically in the computer processing unit (170), so that, unlike the existing interferometer, hologram information of an object with a rough surface can be obtained without speckle noise. After obtaining hologram information from the object without speckle noise, the hologram information is restored at a specific depth location and only the phase information is extracted, thereby obtaining a numerical interference image at the specific depth location, and by unwrapping this numerically, step information at the corresponding location can be finally obtained.

[0129] Specifically, the computer processing unit (170) includes a numerical restoration unit (171) for reading a hologram stored in a storage unit (164) and numerically restoring the complex reference light reflected from the plate (130) and the complex object light reflected from the object, and a numerical interference unit (172) for numerically interfering the complex reference light and the complex object light to obtain an interference pattern of the target object.

[0130] First, the numerical restoration unit (171) numerically processes the hologram information received from the electronic processing unit (160a) to restore the numerical reference light reflected from the plate (130) and the numerical object light reflected from the object using a numerical method.

[0131] At this time, the numerical restoration unit (171) displays the hologram at the position (z) of the target object. obj (x,y)) can be numerically restored to generate a numerical reference light and a numerical object light. The numerical restoration can be obtained by convolving the complex conjugate of the Fresnel plate at the restored position of the stored hologram. This method is only one example, and it is obvious that various methods known in the art can be used to restore holograms.

[0132] Mathematical expression 6 below shows the restoration of a hologram in the numerical restoration unit (171) using the above method.

[0133]

[0134] Here, is a numerical reference light generated by reflection from the plate (130). and the position of the object (z) obj Numerical object light generated by reflection at (x,y)) is the sum of, It represents the distance (difference in distance on the x,y plane) between the plate (130) installed at a specific angle and the target. At this time, z obj is z obj can mean (x,y). And, corresponds to background noise, and is expressed as the sum of the square of the numerical reference light and the square of the numerical object light, as in mathematical expression 7 described below.

[0135] And, the numerical interference unit (172) obtains the interference pattern of the target object by numerically interfering the numerical reference light and the numerical object light restored by the numerical restoration, and numerically removes the DC component due to the background noise from the obtained interference pattern to obtain the position (Z) of the target object, which is a specific position. obj ) restores holographic information.

[0136] Here, the numerical interference unit (172) obtains an interference pattern through the square of the sum of the restored numerical reference light and the numerical object light, as in mathematical expression 7. That is, the numerical interference unit (172) obtains an interference pattern of the numerical reference light and the numerical object light by calculating the sum of the numerical reference light and the numerical object light obtained by the numerical restoration unit (171), i.e., the square of the restored image.

[0137]

[0138] Here, is an interference pattern, is a numerical reference light and numerical object light The sum of, is a background noise component can be expressed as . In addition, λ and (x,y,z) are as explained in mathematical expression 1 above, and Z obj is the distance from the focus position to the object, It indicates the distance between the plate installed at an angle and the target.

[0139] This mathematical formula 7 is a value obtained by excluding the DC component corresponding to background noise from the result of mathematical expression 7, and through this, it can be seen that precise off-axis interference information of the target object is obtained using the embodiment of the present invention.

[0140] The numerical interference unit (172) acquires a numerical interference image based on the acquired interference pattern, and unwraps the numerical interference image to acquire step information of the target object at the corresponding location. The above-mentioned process can be briefly represented as shown in Fig. 13.

[0141] FIG. 13 is a drawing illustrating a numerical processing process for obtaining a numerical interference image from hologram information obtained according to an embodiment of the present invention.

[0142] As illustrated in FIG. 13, an embodiment of the present invention acquires holographic information without speckle noise using the aforementioned method, then restores the holographic information at a specific depth location and extracts only phase information, thereby obtaining a numerical interference image at that specific depth location. At this time, by numerically unwrapping the numerical interference image acquired at the specific depth location, step information at that location can ultimately be obtained.

[0143] Here, the numerical interference unit (172) is the position of the object (Z obj) can be repeatedly unwrapped by processing the numerical interference image in steps using a numerical method such as Equation 8 below until the difference between the estimated value and the measured value becomes less than the threshold.

[0144]

[0145] Here, x is the spatial coordinate system, u is the spatial frequency coordinate system, are each The estimated value of, is the function value of the object, Is Fourier transform value of, class is the phase information to be restored, and i represents a complex number representation.

[0146] At this time, , can be expressed as

[0147] The process from step 1 to step 4 of mathematical formula 8 is repeatedly performed until the difference between the estimated value and the measured value becomes the smallest, and the final result value is used as the unwrap result.

[0148] The unwrap method mentioned above is a representative example, and in addition to the above example, various methods can be utilized, including the quad-tree decomposition method, the least-square method using FFT, the block least-square method, and the rounding-least-square method.

[0149] In addition, the off-axis hologram information obtained by the above-mentioned off-axis scanning hologram interferometer can be used to obtain hologram information without twin image noise and background noise (DC) through a numerical signal processing method as in the embodiment of FIG. 10.

[0150] Figure 10 is a diagram showing a numerical processing process for restoring off-axis hologram information obtained from an off-axis scanning hologram interferometer without background noise and twin image noise.

[0151] The numerical interference unit (172) performs FFT processing on the result of numerically removing the DC component from the interference pattern to spatially separate the DC information region, the object's hologram information region, and the twin image noise information region in the frequency domain. Then, among the three separated regions, only the object's hologram information is spatially filtered and moved to the spatial origin position, and then IFFT processed again, so that only the object's hologram information with the background noise and twin image noise removed can be obtained.

[0152] As shown in Fig. 10, if the off-axis hologram information obtained by the method of mathematical expression 6 is converted to the frequency domain, (k x , k y ) can be separated into the DC information region, the hologram information region, and the twin image noise region in the frequency domain coordinate system. The DC information region is located at the origin of the coordinate system. Looking at the result of spatially filtering only the hologram information in the frequency domain coordinate system and then moving the coordinates to the origin, it can be seen that the hologram information is located at the origin. Afterwards, if this is converted to the spatial domain by IFFT processing, the hologram information with both the background noise and twin image noise removed can be obtained. In Fig. 10 represents spatially filtered holographic information.

[0153] In the embodiment of the present invention, the larger the tilt angle of the plate (130) in the x and y directions, the greater the positional deviation (k) of the hologram information from the DC information position on the frequency domain coordinate system. x , k y The directional deviation) also increases and they do not overlap each other, making it easier to spatially filter holographic information in the frequency domain.

[0154] The DC information area, hologram information area, and twin image noise information area in the spatial frequency domain can be represented as in Fig. 17, and the size of the maximum spatial frequency of the DC information area Is can be expressed as . Here, λ is the wavelength used, represents the numerical aperture of the Fresnel plate generated by the interference phenomenon, which can be determined by the difference in curvature between the first curvature beam and the second curvature beam.

[0155] Here, the off-axis angle of the plate (130) in the x-axis or y-axis direction to prevent the DC information area and the hologram information from overlapping in the frequency domain is A larger value ( ) can be set.

[0156] By going through the process of spatially filtering only the hologram information of the object among three spatially separated different information domains, numerically processing the coordinate movement process, and then converting it back to the spatial domain using a numerical method such as IFFT, it becomes possible to obtain only the hologram information of the object that is not affected by background noise and pair image noise.

[0157] FIG. 16 is a diagram showing a specific example of a process for obtaining off-axis hologram information according to an embodiment of the present invention. FIG. 16 (a) is a diagram showing an experimental environment for obtaining hologram information of an object, and FIG. 16 (b) shows the obtained hologram information. FIG. 16 (c) is a diagram showing how the information of the obtained hologram information is distributed in the frequency domain, and FIG. 16 (d) is a diagram showing the phase information of a numerical interference image after spatial filtering. FIG. 16 (e) is a diagram showing the result of unwrapping the information of FIG. 16 (d).

[0158] In this way, the off-axis scanning hologram interferometer (100) obtains information on light reflected from a transparent or translucent plate (130) and information on light reflected from an object in the form of electrical signals using a photodetector (150), as shown in the example of FIG. 9, and obtains off-axis hologram information through an electronic processing unit (160a). At this time, if the off-axis hologram information is numerically restored at a specific location through a computer processing unit (170), precise height information (step difference information on the object surface) at that location can be obtained.

[0159] The above-mentioned content is an example of use when a transparent or translucent plate is used, and another embodiment can be configured by using a beam splitter and a mirror instead of a transparent or translucent plate, as shown in FIGS. 11 and 12, and FIGS. 15a and 15b described below.

[0160] Meanwhile, Fig. 2 is a case where the transition means is implemented as a phase transition means (112b) differently from Fig. 1, and components having the same symbols as Fig. 1 mean that they perform the same operation, so a separate description of the components having the same symbols is omitted.

[0161] In the case of Fig. 2, the basic structure of the system is the same as Fig. 1, but the configuration of the transition means (112b), signal generation unit (180b), and electronic processing unit (160b) is different.

[0162] The phase shifting means (112b) serves to discontinuously shift the phase of the divided first curvature beam. The operation of this phase shifting means (112b) is based on the phase shift signal generated by the signal generating unit (180b). For example, the phase shifting means (112b) can shift the phase of the laser beam following the path of the first curvature beam in the order of {0, π / 2, π} based on the phase shift signal generated by the signal generating unit (180b).

[0163] A phase shifting means may be a phase light modulator, but the present invention is not necessarily limited thereto, and various phase shifting means may be used, such as changing the phase of a beam in the order of {0, π / 2, π} using PZT.

[0164] In this embodiment, the phase is divided into three different phases of {0, π / 2, π}, but it is of course possible to shoot in more detailed phases, and of course, it is also possible to shoot with only one or two phase changes to avoid removing twin image noise or background noise. However, if shooting with only one phase (single phase), a phase modulator is not required.

[0165] In this drawing 2, the phase shifting means (112b) is formed on the side of the divided first curvature beam, but the present invention is not necessarily limited thereto. That is, of course, the phase shifting means (112b) can be formed on the side of the divided second curvature beam.

[0166] As shown in Fig. 2, when the transition means is composed of a phase transition means (112b), the scan beam generated by the scan beam generation unit (110) can be defined as a Fresnel plate shape that is phase-shifted in the region where the first curvature beam and the second curvature beam are combined, as in the following mathematical expression 9.

[0167]

[0168] Here, P n is a set of n different phases used for phase transition in the phase transition means (112b), i.e., , and the definitions of the remaining factors are the same as those shown in mathematical expression 1 above. The three phase transitions shown here are exemplary, and of course, n phase transitions such as 2, 3, and 4 are possible.

[0169] In the case where the frequency shifting means is replaced with a phase shifting means as in Fig. 2, there is no need for the electronic processing unit (180b) to be equipped with a heterodyne detector.

[0170] First, the current generated at the scan position of the response command beam specified by the scan unit (120) of Fig. 2 is as shown in mathematical expression 10. This mathematical expression 10 represents the current signal detected by the photodetector (150) of Fig. 2.

[0171]

[0172] is a current signal detected by the photodetector (150), is the three-dimensional distribution of reflectance for the target object, is a convolution operation. In addition, (x,y) is the scan position of the scan beam specified by the scan unit (120), and C(z) is a function representing the change in curvature along the z-axis as the curvature of the Fresnel plate formed by the interference of the first curvature beam and the second curvature beam.

[0173] The electronic processing unit (180b) of FIG. 2 processes the current signal detected by the photodetector to extract hologram information of the target object, and for this purpose, may include an AD converter (166), a signal processing unit (167), a storage unit (168), and a scan control unit (169).

[0174] The AD converter (166) converts the current signal detected by the photodetector (150) into a digital signal. The converted digital current signal is a phase shift value P generated by the phase shift signal generator of the signal generation unit (180b). n It is provided together with a signal processing unit (167).

[0175] The signal processing unit (167) uses the converted digital current signal and the phase shift value generated from the phase shift signal generator of the signal generating unit (180b) to generate a complex hologram for the target object, and the storage unit (268) stores the generated complex hologram.

[0176] In addition, the scan control unit (169) can generate a control signal for changing the scan position of the scan unit (120) whenever hologram processing for an arbitrary position of the target object is completed.

[0177] Here, the signal processing unit (167) synthesizes the converted digital signals in three cases (p1, p2, p3) of the phase values ​​{0, π / 2, π} shifted at each scanning position by using mathematical expression 11, thereby generating a 3D image of the object and a pattern encoded with a Fresnel plate. Obtain .

[0178]

[0179] In Fig. 2, the phase is subdivided into three. Here, when the phase is subdivided into three or more, the image of the object to be photographed and the pattern encoded with the Fresnel plate can be obtained by synthesizing the images for the three or more phases using the method of mathematical expression 11.

[0180] In the case where there are two phases, the information required for synthesizing the image of the photographed object and the Fresnel plate in Equation 11 is insufficient, so the encoded pattern of the cross-sectional image of the photographed object and the real Fresnel plate is synthesized, and in this case, there is a problem that the restored image is contaminated by twin image noise.

[0181] In this case of Figure 2, the digital current signal and the scanning position of the scanning unit (120), and the phase shift value P n It can be stored in the storage unit (168), and after scanning is completed, it can be read from the storage unit (168) and transmitted to the electronic processing unit (167) to perform the signal processing process described above.

[0182] Fig. 4 is a drawing showing an example of a modification of Fig. 1. Fig. 4 shows only a different arrangement of objects, and the basic operating principle of the system is the same as Fig. 1, so duplicate description is omitted.

[0183] In addition, the structure of FIG. 2, in which the transition means is changed to a phase transition means, can also be applied to a modified example such as FIG. 4 described above, and it is obvious that such an example of a layout change can be applied to all embodiments described below.

[0184] FIG. 5 and FIG. 6 are drawings showing a configuration in which an optical splitter is added to FIG. 1 and FIG. 2, respectively. More specifically, the optical splitter (140) is placed between the scan unit (120) and the plate (130) to transmit the scan beam received from the scan unit (120) to the target object, and can reflect the beam reflected from the target object (reflective object) and the plate (130) back to the optical detector (150).

[0185] For convenience of explanation, the following FIGS. 7 to 15b illustrate a holographic interferometer structure with an added optical splitter (140, 340) as a representative example. However, as in the cases of FIGS. 1 and 2 described above, it goes without saying that the optical splitter (140, 340) may be omitted in all the following embodiments.

[0186] FIG. 7 is a drawing showing the configuration of an off-axis scanning holographic interferometer according to a second embodiment of the present invention.

[0187] As shown in FIG. 7, the off-axis scanning holographic interferometer (200) according to the second embodiment of the present invention largely includes a scan beam generation unit (110), a scan unit (120), a transparent or translucent plate (230), a light splitter (140), a light detector (150), and an electronic processing unit (160a), and may further include a computer processing unit (170) and a signal generation unit (180a).

[0188] Fig. 7, unlike the first embodiment of Fig. 1, has a structure in which a transparent or translucent plate (230) is installed at a set distance from the front of the object. Components having the same symbols as those in Fig. 1 perform the same operation, and therefore, a separate description of the components having the same symbols is omitted.

[0189] At this time, in the case of FIG. 7, compared to FIG. 1, it is characterized by differences in not only the position but also the size of the plate (230). In the first embodiment of FIG. 1, the plate (230) is positioned almost attached to or close to the target object, but in the embodiment of FIG. 7, the plate (230) is positioned closer to the scan unit (120) (X scanner & Y scanner) than the target object, and the size is also set to a smaller size to match the size of the scan unit (120) rather than the size of the target object.

[0190] Accordingly, as shown in FIG. 7, the closer the plate (230) is installed to the scanning unit (120) by a set distance from the target object, the more advantageous it is to create a hologram with a smaller size (area) of the plate (230).

[0191] The embodiment of Fig. 7 uses the same frequency shifting means (112a) and signal generation unit (180a) as the embodiment of Fig. 1, so the configuration of the electronic processing unit (180a) is the same as the embodiment of Fig. 1.

[0192] Fig. 8 is a diagram showing a form in which the transition means of Fig. 7 is replaced with a phase transition means. In the case of Fig. 8, the basic structure of the system is the same as Fig. 7, but the configurations of the transition means (112b), the signal generation unit (180b), and the electronic processing unit (160b) are different from Fig. 7. Since the configurations of the transition means (112b), the signal generation unit (180b), and the electronic processing unit (160b) of Fig. 8 are the same as those of the embodiment of Fig. 2, a duplicate description will be omitted.

[0193] The embodiments of FIGS. 7 and 8 are both embodiments in which the plate (230) is positioned between the scan unit (120) and the object regardless of the size of the object. In this case, it is more preferable that the size of the plate (230) be selected so as to be able to cover the scan beam by considering the size and angle of the beam output from the scan unit (120).

[0194] Fig. 11 is a drawing showing the configuration of an off-axis scanning holographic interferometer according to a third embodiment of the present invention.

[0195] As shown in FIG. 11, the off-axis scanning holographic interferometer (300) according to the third embodiment of the present invention largely includes a scan beam generation unit (110), a scan unit (120), a reference mirror (330), a light splitter (340), and an electronic processing unit (160a), and may further include a light detector (150), a computer processing unit (170), and a signal generation unit (180a).

[0196] This Fig. 11 corresponds to a case where a reference mirror (330) is used instead of a plate (130), unlike the first embodiment. Here, a separate description of components having the same symbols as in Fig. 1 is omitted.

[0197] Specifically, Fig. 11 is characterized in that, unlike the first embodiment of Fig. 1, a light splitter (340) and a reference mirror (330) are positioned between the scanning unit (120) and the target object. In addition, the reference mirror (330) is installed to be tilted at a set angle based on the z-axis direction that is perpendicular to the surface (x, y plane) of the target object, and the same effect as Fig. 1 can be obtained through this structure.

[0198] In the embodiment of FIG. 1, a feature is that a signal reflected from a plate (130) and a signal reflected from an object are detected by a light detector (140), whereas in the embodiment of FIG. 11, a scan beam transmitted through a scan unit (120) is split into beams corresponding to two paths through a light splitter (340), and a beam reflected from an object and a beam reflected from a mirror are detected by a condenser lens (145) and a light detector (150), which is a feature different from the embodiment of FIG. 1.

[0199] Specifically, in the case of FIG. 11, the optical splitter (340) is placed between the scanning unit (120) and the target object to split the beam by transmitting and reflecting the incident beam.

[0200] The reference mirror (330) is installed at a set angle with respect to the z-axis direction perpendicular to the surface (x, y plane) of the target object on the upper side of the beam splitter (340) and reflects the incident beam. The light detector (150) is placed on the lower side of the beam splitter (340) and detects the beam reflected from the target object and the reference mirror (330) and passing through the beam splitter (230).

[0201] To explain this more specifically, the scan beam scans the target object by passing through the optical splitter (340). The beam reflected from the target object is reflected by the optical splitter (340) and moves toward the photodetector (150).

[0202] Additionally, the scan beam is reflected through the optical splitter (340) and travels toward the reference mirror (330). The beam reflected from the reference mirror (330) passes through the optical splitter (340) and travels toward the photodetector (150).

[0203] In this way, the photodetector (150) is placed on the opposite side of the reference mirror (330) with respect to the light splitter (340), and receives and detects the scan beam reflected from the reference mirror (330) and the target object. Then, the electronic processing unit (160a) processes the signal detected by the photodetector to generate a hologram for the target object.

[0204] In addition, since the embodiment of FIG. 11 uses the same frequency shifting means (112a) and signal generation unit (180a) as the embodiment of FIG. 1, the configuration of the electronic processing unit (180a) is the same as the embodiment of FIG. 1.

[0205] Fig. 12 is a diagram showing a form in which the transition means of Fig. 11 is replaced with a phase transition means. In the case of Fig. 12, the basic structure of the system is the same as Fig. 11, but the configurations of the transition means (112b), the signal generation unit (180b), and the electronic processing unit (160b) are different from Fig. 11. The configurations of the transition means (112b), the signal generation unit (180b), and the electronic processing unit (160b) of Fig. 11 are the same as those of the embodiment of Fig. 2, and therefore, a duplicate description will be omitted.

[0206] Here, a cube-shaped beam splitter (340) was selected as the optical splitter, but it can be replaced with a flat-plate-shaped beam splitter or an optical fiber-shaped coupler.

[0207] FIG. 14a and FIG. 14b are drawings showing the configuration of an off-axis scanning holographic interferometer according to the fourth embodiment of the present invention.

[0208] As shown in FIGS. 14a and 14b, the off-axis scanning holographic interferometer (400) according to the fourth embodiment of the present invention largely includes a scan beam generation unit (110), a scan unit (420), a plate (130), a light splitter (140), a light detector (150), and an electronic processing unit (160), and may further include a computer processing unit (170) and a signal generation unit (180).

[0209] In the case of FIGS. 14a and 14b, the basic structure of the system is the same as in FIGS. 1 and 2, but the configuration of the scanning unit (420) is different, and its operating principle is as follows.

[0210] In FIGS. 14a and 14b, the scanning unit (420) includes a scanning mirror (421) (X scanner) that controls the scanning beam incident from the scanning beam generating unit (110) in the horizontal direction and transmits it to the target object to control the scanning position of the scanning beam with respect to the target object in the horizontal and vertical directions, and a translation stage (422) that moves the target object in the vertical direction (y direction) at the rear end of the target object.

[0211] The scan mirror (421) controls the scan beam received from the interference means (117) in the horizontal direction and transmits it to the object. Here, a third mirror (M3) that changes the direction of the beam output from the interference means (117) and transmits it to the scan mirror (421) may be added. The translation stage (422) is installed at the rear end of the object and directly moves the object receiving the scan beam in the vertical direction, thereby enabling y-direction scanning of the object using the scan beam.

[0212] The translation stage (422) may correspond to a moving target plate, which is implemented so that the target plate on which the target is placed can move in the y-axis direction. Although such a translation stage (422) is physically separated from the scan mirror (421), it corresponds to a means for controlling the scanning position of the beam with respect to the target, and is therefore included as a component of the scan unit (420) together with the scan mirror (421).

[0213] In this way, the scanning unit (420) can control the scanning beam in the horizontal direction (x direction) and vertical direction (y direction) with respect to the object by using the scanning mirror (421) and the translation stage (422).

[0214] Here, it goes without saying that the structure of the modified scan section can also be applied to the structure of the second embodiment of FIGS. 7 and 8.

[0215] FIG. 15a and FIG. 15b are drawings showing the configuration of an off-axis scanning holographic interferometer according to the fifth embodiment of the present invention.

[0216] As shown in FIGS. 15a and 15b, the off-axis scanning holographic interferometer (500) according to the fifth embodiment of the present invention largely includes a scan beam generation unit (110), a scan unit (420), a reference mirror (330), a light splitter (340), a light detector (150), and an electronic processing unit (160), and may further include a computer processing unit (170) and a signal generation unit (180).

[0217] In the case of FIGS. 15a and 15b, the basic structure of the system is the same as in FIGS. 11 and 12, but the configuration of the scan unit (420) is different. The operating principle of the scan unit (420) composed of the scan mirror (421) and the translation stage (422) has been described through FIGS. 14a and 14b, and therefore, a duplicate description will be omitted.

[0218] According to the present invention as described above, an off-axis scanning holographic interferometer capable of obtaining phase information according to a step of a reflective object having a rough surface without speckle noise can be provided.

[0219] While the present invention has been described with reference to the embodiments illustrated in the drawings, these are merely exemplary, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible. Therefore, the true scope of technical protection of the present invention should be determined by the technical spirit of the appended claims.

Claims

1. A scan beam generating unit that modulates the phase of a first beam from a light source to convert it into a first curvature beam, converts a second beam into a second curvature beam, and then forms a scan beam by interfering the first and second curvature beams; A scanning unit that controls the scanning position of the scan beam in the horizontal and vertical directions and transmits the scan beam to the target object, which is a reflective object, using the scan beam; A transparent or translucent plate disposed in front of the object, transmitting a beam, and installed so as to be tilted at a set angle with respect to at least one of the x-axis and the y-axis with respect to the plane (x, y plane) of the object; An off-axis scanning holographic interferometer comprising: a photodetector for receiving and detecting a beam reflected from the target object and the plate; and an electronic processing unit for processing a signal detected by the photodetector to generate a hologram of the target object.

2. In claim 1, An off-axis scanning holographic interferometer further comprising a light splitter disposed between the scanning unit and the plate to transmit a scan beam received from the scanning unit to a target object and to reflect a beam reflected from the target object and the plate back to the light detector.

3. In claim 1, The above plate, An off-axis scanning holographic interferometer installed at a set distance from the front of the above target object.

4. In claim 1, The above electronic processing unit, The focal point of the first or second curvature beam projected on the target object is taken as the origin, and the distance in the z-axis direction from the origin plane to the plate is z off (x,y), the distance in the z-axis direction to the target based on the focus position is z obj When defined as (x,y), the hologram information is expressed by the mathematical formula below. Off-axis scanning holographic interferometer to obtain: Here, is a hologram of the above plate, represents a hologram of the object, which is the reflective object, as, is the distance from the center of the above plate to the above focus position, and is the degree of twist in the x- and y-axis directions, and represent the angles of inclination in the x-axis and y-axis directions, respectively.

5. In claim 1, An off-axis scanning holographic interferometer further comprising a numerical restoration unit that numerically processes the holographic information received from the electronic processing unit and numerically restores the numerical reference light reflected from the plate and the numerical object light reflected from the target object.

6. In claim 5, An off-axis scanning holographic interferometer further comprising a numerical interference unit that obtains an interference pattern of the numerical reference light and the numerical object light by calculating the square of the sum of the numerical reference light and the numerical object light obtained by the above numerical restoration.

7. In claim 6, The above numerical interference part is, An off-axis scanning holographic interferometer that unwraps a numerical interference image using the above interference pattern to obtain step information of an object at a corresponding location.

8. In claim 6, The above numerical interference part is, Off-axis scanning holographic interferometer that obtains the interference pattern of the numerical reference light and the numerical object light using the mathematical formula below: Here, is an interference pattern, is the above numerical reference light and the above numerical object light The sum of, The component is the sum of the square of the numerical reference light and the square of the numerical object light, λ is the wavelength of the beam used, (x, y, z) is a spatial coordinate system in which the origin is the focus position of the first or second curvature beam, the direction of travel of the first or second curvature beam is the z-axis, and the plane axis perpendicular to the z-axis is the x-axis and the y-axis, Z obj is the distance from the above focus position to the object, It represents the distance between the plate installed at an angle and the target.

9. In claim 6, The above numerical interference part is, An off-axis scanning holographic interferometer that numerically removes the DC component from the above interference pattern, performs FFT processing to spatially separate a DC information region, an object hologram information region, and a paired image noise information region in the frequency domain, and then spatially filters only the object hologram information among the three separated regions, moves it to the origin position in space, and then performs IFFT processing again to obtain only the object hologram information with background noise and paired image noise removed.

10. In claim 9, The off-axis angle of the plate in the x-axis or y-axis direction to prevent the DC information area and the holographic information from overlapping in the above frequency domain is A greater value ( ) is set to An off-axis scanning holographic interferometer that shows the numerical aperture of a Fresnel plate generated by interference phenomena.

11. In claim 1, The above scan beam generating unit, A shifting means for performing phase modulation by frequency shifting or phase shifting the first beam split from the above light source; First and second curvature beam generators that convert the phase-modulated first beam and the second beam split from the light source into first and second curvature beams having set curvatures, respectively; and An off-axis scanning holographic interferometer including an interference means for generating a scan beam having an interference pattern of a Fresnel plate by interfering the first curvature beam passing through the first curvature beam generator and the second curvature beam passing through the second curvature beam generator.

12. In claim 11, The above transition means is a frequency transition means that shifts the frequency of the first beam, The above scan beam is, An off-axis scanning holographic interferometer in the form of a time-dependent heterodyned Fresnel plate, defined by the following mathematical equation: Here, λ is the wavelength of the beam used, (x, y, z) is a spatial coordinate system in which the origin is the focus position of the first or second curvature beam, the direction of travel of the first or second curvature beam is the z-axis, and the plane axes perpendicular to the z-axis are the x-axis and y-axis, C(z) is a function representing the change in curvature along the z-axis, and the curvature of the Fresnel plate formed by the interference of the first and second curvature beams, and Ω represents the transition frequency.

13. In claim 11, The above transition means is a phase transition means that phase-shifts the first beam, The above scan beam is, An off-axis scanning holographic interferometer defined by the following mathematical formula as a Fresnel plate type with phase shift in the region where the first curvature beam and the second curvature beam interfere: Here, λ is the wavelength of the beam used, (x, y, z) is a spatial coordinate system in which the focal position of the first or second curvature beam is the origin, the direction of travel of the first or second curvature beam is the z-axis, and the plane axis parallel to the z-axis is the x-axis and the y-axis, C(z) is a function representing the change in curvature along the z-axis as the curvature of the Fresnel plate formed by the interference of the first and second curvature beams, P n represents a set of n different phases used in the above phase transition.

14. In claim 12, The above electronic processing unit, A heterodyne detector that generates an in-phase output signal and a quadrature output signal by using a current signal detected by the above-mentioned photodetector and a heterodyne modulation signal having a frequency Ω generated by a function generator of a signal generating unit; An AD converter that receives the above-mentioned in-phase signal and the quadrature signal through each channel and converts them into digital signals; A signal processing unit that generates a complex hologram of an object from the converted digital signal; A storage unit for storing the above generated complex hologram; and An off-axis scanning holographic interferometer comprising a scan control unit which generates a control signal for changing a scan position of the scan unit whenever hologram processing for an arbitrary position of the target object is completed.

15. In claim 13, The above electronic processing unit, An AD converter that converts the current signal detected by the above photodetector into a digital signal; A signal processing unit that generates a complex hologram for an object by using the converted digital current signal and the phase shift value generated from the phase shift signal generator of the signal generating unit; A storage unit for storing the above generated complex hologram; and An off-axis scanning holographic interferometer comprising a scan control unit which generates a control signal for changing a scan position of the scan unit whenever hologram processing for an arbitrary position of the target object is completed.

16. In claim 1, The above scanning section, An off-axis scanning holographic interferometer comprising a horizontal scan mirror and a vertical scan mirror to control the scanning position of the scan beam with respect to the target object in the horizontal and vertical directions.

17. In claim 1, The above scanning section, An off-axis scanning holographic interferometer comprising a scan mirror for controlling a scan beam incident from the scan beam generating unit in the horizontal direction and transmitting the scan beam to the target object so as to control the scanning position of the scan beam with respect to the target object in the horizontal and vertical directions, and a translation stage for moving the target object in the vertical direction at the rear end of the target object.

18. A scan beam generating unit that modulates the phase of a first beam from a light source to convert it into a first curvature beam, converts a second beam into a second curvature beam, and then forms a scan beam by interfering the first and second curvature beams; A scanning unit that controls the scanning position of the scan beam in the horizontal and vertical directions and transmits the scan beam to the target object, which is a reflective object, using the scan beam; An optical splitter positioned between the scanning unit and the target object to split the beam by transmitting and reflecting the incident beam; A reference mirror that is installed at a set angle with respect to the z-axis direction perpendicular to the surface (x, y plane) of the target object on the upper side of the optical splitter and reflects the incident beam; A light detector positioned below the optical splitter to detect a beam reflected from the target object and the reference mirror and passing through the optical splitter; and An off-axis scanning holographic interferometer comprising an electronic processing unit for processing a signal detected by the photodetector to generate a hologram of the object.

19. In claim 18, The above scanning section, An off-axis scanning holographic interferometer comprising a horizontal scan mirror and a vertical scan mirror to control the scanning position of the scan beam with respect to the target object in the horizontal and vertical directions.

20. In claim 18, The above scanning section, An off-axis scanning holographic interferometer comprising a scan mirror for controlling a scan beam incident from the scan beam generating unit in the horizontal direction and transmitting the scan beam to the target object so as to control the scanning position of the scan beam with respect to the target object in the horizontal and vertical directions, and a translation stage for moving the target object in the vertical direction at the rear end of the target object.

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