Off-axis scanning hologram interferometer using reference mirror

Abstract

The present invention relates to an off-axis scanning hologram interferometer using a reference mirror. According to the present invention, provided is an off-axis scanning hologram interferometer comprising: a scan beam generation unit for modulating a phase of a first beam from a light source to convert the first beam into a first curvature beam, converting a second beam into a second curvature beam, and then interfering the first and second curvature beams to form a scan beam; a scan unit for controlling a scanning position of the scan beam in horizontal and vertical directions and transmitting the scan beam to an object so as to scan the object, which is a reflective object, using the scan beam; a beam splitter disposed between the scan unit and the object to transmit and reflect an incident beam so as to split the beam; a reference mirror installed on the upper side of the beam splitter so as to be inclined at a set angle with respect to a z-axis direction perpendicular to a surface (x, y plane) of the object, and reflecting the incident beam; a photodetector disposed on the lower side of the beam splitter to detect a beam reflected from the object and the reference mirror and passing through the beam splitter; and an electronic processing unit for processing a signal detected by the photodetector to generate a hologram of the object.

Description

Deaxial scanning holographic interferometer using a reference mirror

[0001] The present invention relates to an out-axis scanning holographic interferometer using a reference mirror, and more specifically, to an out-axis scanning holographic interferometer using a reference mirror that can obtain phase information according to the step difference of an object having a rough surface without speckle noise, unlike conventional interferometers.

[0002] A conventional scanning hologram recording device for acquiring phase information based on the step difference of an object generates a scan beam by superimposing a spherical wave and a plane wave, scans the object while moving it in the X and Y directions while the scan beam is stationary, then collects the scan beam reflected from the object and focuses it on a photodetector, and generates an electrical signal in the photodetector that is proportional to the intensity of the focused light.

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

[0004] As such, conventional interferometers are devices that obtain the step difference of an object by utilizing the coherence of a light source, but due to the coherence of the light source, there is a problem in that it is difficult to obtain interference patterns for objects with rough surfaces in wavelength units.

[0005] The technology forming the background of the present invention is disclosed in Korean Registered Patent No. 1304695 (published September 6, 2013).

[0006] The present invention aims to provide an out-of-axis scanning holographic interferometer using a reference mirror to obtain phase information according to the step difference of an object having a rough surface without speckle noise.

[0007] The present invention provides an off-axis scanning hologram 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 converts 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 horizontal and vertical directions and transmits it to the object, which is a reflective object, so as to scan the object using the scan beam; a beam splitter disposed between the scanning unit and the object and splits the beam by transmitting and reflecting the incident beam; a reference mirror installed above the beam splitter at an angle set with respect to the z-axis direction perpendicular to the plane (x,y plane) of the object and reflects the incident beam; a photodetector disposed below the beam splitter and detects the beam that passes through the beam splitter after being reflected from the object and the reference mirror; and an electronic processing unit that processes the signal detected by the photodetector to generate a hologram of the object.

[0008] In addition, the electronic processing unit sets the focal position of the first or second curvature beam projected onto the object as the origin, and the distance in the z-axis direction from the origin plane to the reference mirror is z 0ff (x,y), z is the distance in the z-axis direction from the focal position to the object. obj If defined as (x,y), the holographic information expressed by the following mathematical formula You can obtain.

[0009]

[0010] Here, is the hologram of the above-mentioned reference mirror, and represents a hologram of an object that is the above-mentioned reflective object, and

[0011] as, is the distance from the center of the reference mirror to the focal position, and is the degree of tilt in the x-axis and y-axis directions, and represents the angle of inclination in the x-axis and y-axis directions, respectively.

[0012] Additionally, the above-decompression scanning hologram interferometer may further include a numerical restoration unit that numerically processes the hologram information received from the electronic processing unit and restores the numerical reference light reflected from the reference mirror and the numerical object light reflected from the object in a numerical way.

[0013] In addition, the above-decompression 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 reconstruction.

[0014] In addition, the numerical interference unit can obtain step difference information of an object at a corresponding location by unwrapping the numerical interference image based on the interference pattern.

[0015] In addition, the numerical interference unit can obtain the interference pattern of the numerical reference light and the numerical object light using the following mathematical formula.

[0016]

[0017] 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 focal position of the first or second curvature beam is the origin, the direction of propagation of the first or second curvature beam is the z-axis, and planar axes perpendicular to the z-axis are the x-axis and y-axis, Z obj is the distance from the above focus position to the object, It indicates the distance between the reference mirror installed at an angle and the object.

[0018] In addition, the numerical interference unit can spatially separate the DC information region, the hologram information region of the object, and the biimage noise information region in the frequency domain by performing FFT processing on the result of numerically removing the DC component from the interference pattern, and then spatially filter only the hologram information of the object among the three separated regions, move it to the origin position of the space, and then perform IFFT processing again to obtain only the hologram information of the object from which background noise and biimage noise have been removed.

[0019] In addition, the deaxial angle in the x-axis or y-axis direction of the reference mirror to prevent the DC information region and the holographic information from overlapping in the frequency region is larger value ( It is set to ), It can represent the aperture of a Fresnel plate generated by interference phenomena.

[0020] Additionally, the scan beam generating unit may include: a transition means for phase modulating a first beam divided from the light source by frequency shifting or phase shifting; first and second curvature beam generators for converting the phase-modulated first beam and the second beam divided from the light source into a first curvature beam and a second curvature beam, respectively, having a set curvature; and an interference means for generating the scan beam having an interference pattern of a Fresnel plate by interfering the first curvature beam that has passed through the first curvature beam generator and the second curvature beam that has passed through the second curvature beam generator with each other.

[0021] In addition, the above-mentioned transition means is a frequency transition means for frequency transitioning the first beam, and the scan beam can be defined by the following mathematical formula as a Fresnel plate form that is heterodyne modulated over time.

[0022]

[0023] 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 propagation 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 as the curvature of the Fresnel plate formed by the interference of the first curvature beam and the second curvature beam, and Ω represents the frequency of transition.

[0024] In addition, the above-mentioned transition means is a phase transition means for phase transitioning the first beam, and the scan beam can be defined by the following mathematical formula as a phase-transitioned Fresnel plate shape in the region where the first curvature beam and the second curvature beam interfere.

[0025]

[0026] Here, λ is the wavelength of the beam used, (x,y,z) is a spatial coordinate system with the focal position of the first or second curvature beam as the origin, the direction of propagation of the first or second curvature beam as the z-axis, and planar axes parallel 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, a function representing the change in curvature along the z-axis, P n represents a set of n different phases used in the above phase transition.

[0027] Additionally, the electronic processing unit may include: a heterodyne detector that generates an in-phase output signal and a quartile 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 generation unit; an AD converter that receives the in-phase signal and the quartile 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 that stores the generated complex hologram; and a scan control unit that generates a control signal to change the scan position of the scan unit whenever hologram processing for any position of the object is completed.

[0028] Additionally, 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 of an object using the converted digital current signal and a phase shift value generated by a phase shift signal generator of the signal generation unit; a storage unit that stores the generated complex hologram; and a scan control unit that generates a control signal to change the scan position of the scan unit whenever hologram processing for any position of the object is completed.

[0029] Additionally, the scanning unit may include a horizontal scanning mirror and a vertical scanning mirror to control the scanning position of the scan beam with respect to the object in horizontal and vertical directions.

[0030] Additionally, the scanning unit may include a scanning mirror that controls the scan beam incident from the scan beam generating unit in a horizontal direction and transmits it to the target object to control the scanning position of the scan beam with respect to the target object in horizontal and vertical directions, and a translation stage that moves the target object in a vertical direction from the rear end of the target object.

[0031] According to the present invention, phase information according to the step difference of a reflective object having a rough surface can be obtained without speckle noise.

[0032] FIG. 1 is a diagram showing the configuration of an off-axis scanning holographic interferometer according to a first embodiment of the present invention.

[0033] Figure 2 is a diagram in which the transition means of Figure 1 is replaced with a phase transition means.

[0034] FIG. 3 is a diagram illustrating an example of implementation of a beam curvature generator according to an embodiment of the present invention.

[0035] FIG. 4 is a diagram showing an embodiment of the present invention in which distance information of a step difference on the surface of an object is obtained using a reference mirror.

[0036] Figure 5 is a diagram illustrating the x and y direction tilt angles of a reference mirror.

[0037] Figure 6 is a diagram showing a numerical processing process for restoring out-axis hologram information obtained from an out-axis scanning hologram interferometer without background noise and paired image noise.

[0038] FIG. 7 is a diagram illustrating a numerical processing process for obtaining a numerical interference image from holographic information obtained according to an embodiment of the present invention.

[0039] FIGS. 8A and FIGS. 8B are drawings showing the configuration of an off-axis scanning holographic interferometer according to a second embodiment of the present invention.

[0040] FIG. 9 is a diagram illustrating the spatial frequency conditions for acquiring holographic information without biimage noise and background (DC) noise according to an embodiment of the present invention.

[0041] Then, with reference to the attached drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification have been given similar reference numerals.

[0042] Throughout the specification, when a part is described as being "connected" to another part, this includes not only cases where they are "directly connected," but also cases where they are "electrically connected" with other components interposed between them. Furthermore, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0043] The present invention relates to an out-axis scanning holographic interferometer, and provides an out-axis scanning holographic interferometer capable of acquiring a hologram of a reflective object, which is a reflective object.

[0044] In particular, the present invention proposes a scanning hologram interferometer structure capable of obtaining phase information according to the step difference of an object without speckle noise when acquiring a hologram of an object having a rough surface with a step difference on its surface.

[0045] FIG. 1 is a diagram showing the configuration of an off-axis scanning holographic interferometer according to a first embodiment of the present invention, and FIG. 2 is a diagram in which the transition means of FIG. 1 is replaced with a phase transition means.

[0046] First, as shown in FIG. 1, the deaxial scanning holographic interferometer (300) according to the first embodiment of the present invention largely comprises a scan beam generating unit (110), a scanning unit (120), a reference mirror (330), a beam splitter (340), a photodetector (150), and an electronic processing unit (160a), and may further include a computational processing unit (170) and a signal generating unit (180a). At this time, the reference mirror is at a specific angle with respect to the object. It is characterized by being positioned to have the following. Here, the remaining parts excluding the electronic processing unit (160a) and the computer processing unit (170) correspond to the optical system part of the present invention.

[0047] First, the scan beam generating unit (110) modulates the phase of the first beam among the first and second beams divided from the light source to convert it into a first curvature beam through the first curvature beam generator (N1), converts the second beam into a second curvature beam through the second curvature beam generator (N2), and then interferes the first and second curvature beams to form a scan beam.

[0048] The scan beam generating unit (110) uses a Mark Zender interferometer structure that divides a light source into first and second beams to generate first and second curvature beams, and then combines the two generated beams.

[0049] 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.

[0050] The transition means (112; 112a, 112b) can phase-modulate the first beam split from the light source by frequency-shifting or phase-shifting. In an embodiment of the present invention, FIG. 1 implements the transition means (112) as a frequency-shifting means (112a), and FIG. 2, described later, implements it as a phase-shifting means (112b).

[0051] The first and second curvature beam generators (N1, N2) can convert the first beam, which is phase-modulated by the transition means (112), and the second beam, which is split from the light source, into the first curvature beam and the second curvature beam, respectively, having a set curvature. In this way, the first and second curvature beam generators (N1, N2) can change the incident beam into a beam of a specific curvature.

[0052] The interference means (117) can receive the first curvature beam and the second curvature beam and interfere with each other to generate a scan beam having an interference pattern of a Fresnel plate and transmit it to the scan unit (120).

[0053] Below, the configuration of the scan beam generating unit (110) is explained in more detail through FIG. 1.

[0054] First, the light source is the part that generates electromagnetic waves. The light source can include various means capable of generating electromagnetic waves, such as a laser generator, an LED (light emitting diode), or a low-coherence beam like halogen light with a short coherence length. In the following, a representative example is provided where the light source is implemented as a laser generator.

[0055] The beam output from such a light source is input to the 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 the frequency shifting means (112b), and transmits the second beam to the second mirror (M2). That is, the beam following the path of the first beam in the first beam splitter (111) is transmitted to the frequency shifting means (112b), and the beam following the path of the second beam is reflected by the second mirror (M2) and then transmitted to the second curvature beam generator (N2).

[0056] 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 that transmits a beam to the outside by guiding it through free space. Here, if a means capable of splitting a beam in-line, such as a geometric phase lens, is used, the beam may be split into a first beam and a second beam in-line. In the following, it is assumed that each optical splitter is implemented as a beam splitter.

[0057] The frequency shifting means (112a) shifts the frequency of the first beam and then 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 generation unit (180a) and transmit it to the first mirror (M1). Here, the frequency shifting means (112a) may 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 a PZT.

[0058] 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).

[0059] The first beam reflected from the first mirror (M1) is transmitted to the first beam curvature generating unit (N1). The second beam reflected from the second mirror (M2) is transmitted to the second beam curvature generating unit (N2).

[0060] Here, the first and second curvature beam generators (N1, N2) receive each beam incident and generate an enlarged beam having a curvature between negative and positive curvature, including the collimated beam. The first and second curvature beam generators (N1, N2) may be set to different curvatures or, if necessary, to the same curvature.

[0061] FIG. 3 is a diagram illustrating an example of implementation of a beam curvature generator according to an embodiment of the present invention. FIG. 3 shows a first curvature beam generator, (b) a second curvature beam generator, and (c) an example of a change in curvature of a beam passing through the first curvature beam generator.

[0062] 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 the spherical wave and generates a curvature beam (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 the spherical wave and generates a curvature beam (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).

[0063] In this way, the first and second curvature beam generators (N1, N2) may be composed of at least one lens, and the curvature of the first beam and the curvature of the second beam may be changed respectively by adjusting the distance between the lenses.

[0064] In addition, in all embodiments of the present invention, various scaling elements can be determined by adjusting the curvature of the two beams, such as setting the curvature of the first curvature beam and the curvature of the second curvature beam to be the same or different, by utilizing the first curvature beam generator (N1) and the second curvature beam generator (N2) in the method of FIG. 3.

[0065] 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) generates the first curvature beam by modulating the spatial distribution of the first beam.

[0066] 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) generates a second curvature beam by modulating the spatial distribution of the second beam.

[0067] The generated first and second curved beams 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.

[0068] The interference means (117) overlaps and interferes the first beam (first curvature beam) that has passed through the first beam curvature generating unit (N1) and the second beam (second curvature beam) that has passed through the second beam curvature generating unit (N2) to form a scan beam having an interference pattern of a Fresnel zone pattern.

[0069] At this time, the depth position on the focal axis of the first curvature beam and the depth position on the focal axis 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 shape of a Fresnel plate by interfering the first curvature beam and the second curvature beam, which have different focal positions, with each other.

[0070] 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 overlaps them with each other through the interference means (117) to form a scan beam.

[0071] At this time, as shown in FIG. 1, when the transition means is composed of a frequency transition means (112a), the generated scan beam can be defined as a Fresnel plate shape that is heterodyne modulated over time as shown in Equation 1 below.

[0072]

[0073] Here, λ is the wavelength of the beam used, (x,y,z) is a spatial coordinate system with the focal position of the first or second curvature beam as the origin, the direction of propagation of the first or second curvature beam as the z-axis, and planar 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, a function representing the change in curvature along the z-axis, and Ω represents the shifted frequency. Also, (x0 2 +y0 2 ) represents a cathartic coordinate system with (x0,y0) being a plane orthogonal to the optical axis of the first or second curvature beam.

[0074] For convenience of explanation, in the following embodiments of the present invention, (x,y,z) is exemplified as a spatial coordinate system in which the focal position of the first curvature beam is the origin and the axes of a plane perpendicular to the direction of travel of the first curvature beam are the x and y axes.

[0075] The scan beam generating unit (110) transmits the generated scan beam to the scanning unit (120). The scanning unit (120) scans an object using an interference beam formed by the interference means (117).

[0076] Referring again to FIG. 1, the scanning unit (120) controls the scanning position of the scan beam in the horizontal and vertical directions to scan the object, which is a reflective object, using the scan beam and transmits it to the object.

[0077] The beam incident on the scanning unit (120) is transmitted to the target object via the horizontal scanning mirror (121) (X scanner) and the vertical scanning mirror (122) (Y scanner). In this way, the scanning unit (120) may include an X scanner and a Y scanner to control the scanning position of the scan beam for the target object in the horizontal and vertical directions.

[0078] The present invention uses a mirror scanner as a scanning means, but the present invention is not necessarily limited thereto and can be replaced with various known scanning means.

[0079] A Fresnel plate-shaped beam is transmitted to a mirror-shaped scanning unit (120), and the scanning unit (120) enables scanning of an object by moving the Fresnel plate-shaped beam across the object. The scanning position can be adjusted according to a control signal from a scan control unit (165) provided in an electronic processing unit (160a).

[0080] The scanning unit (120) can be operated by receiving a scanning control signal from the scanning control unit (165) within the electronic processing unit (160a). In response to the control signal, a scan beam can be projected onto an object according to the movement of the scanning mirror. In this way, the scanning unit (120) can project an interference beam (a scan beam by the scanning unit) between the first and second curvature beams onto an object using the scanning mirror.

[0081] Of course, the scanning unit (120) can be changed to a scanning unit (420) structure utilizing a horizontal scanning mirror (121) (X scanner) and a vertical scanning mirror (122) (Y scanner) as shown in FIGS. 1 and 2, as shown in FIGS. 8a and 8b described later, utilizing a horizontal scanning mirror (421) and a translation stage (422).

[0082] In other words, in the present invention, instead of using two mirror scanners as described above, the object can be positioned on an objective plate and the object can be scanned by moving the objective plate horizontally. In addition, the object can be scanned using various methods, such as using an electron light deflector.

[0083] The scan beam transmitted through the scanning unit (120) is split into two beams corresponding to two paths through the beam splitter (340), and the beam reflected from the object and the beam reflected from the reference mirror (300) are detected through the focusing lens (1450) and the light detector (150).

[0084] Specifically, the beam splitter (340) is positioned between the scanning unit (120) and the target object to split the beam by transmitting and reflecting the incident beam. At this time, the reference mirror (330) is installed above the beam splitter (340) at a set angle relative to the z-axis direction perpendicular to the surface (x,y plane) of the target object and reflects the incident beam.

[0085] The light detector (150) is positioned below the beam splitter (340) and detects the beam that is reflected from the object and the reference mirror (330) and passes through the beam splitter (340).

[0086] To explain this more specifically, the scan beam passes through the beam splitter (340) to scan the object. The beam reflected from the object is reflected by the beam splitter (340) and proceeds toward the photodetector (150).

[0087] Additionally, the scan beam is reflected through the beam splitter (340) and travels toward the reference mirror (330). The beam reflected from the reference mirror (330) passes through the beam splitter (340) and travels toward the photodetector (150).

[0088] In this way, the photodetector (150) is positioned on the opposite side of the reference mirror (330) with respect to the beam splitter (340) and detects the scan beam reflected from the reference mirror (330) and the object. Then, the electronic processing unit (160a) processes the signal detected by the photodetector to generate a hologram of the object.

[0089] At this time, the reference mirror may be installed at a set angle with respect to at least one of the x-axis and y-axis with respect to the surface (x,y plane) of the object. Accordingly, the reference mirror may be installed at an angle with respect to both the x and y directions, or may be installed at an angle with respect to either the x or y direction.

[0090] The photodetector (150) receives and detects a beam reflected from the object and the reference mirror. A beam splitter is located between the reference mirror and the object, and the photodetector receives and detects a beam reflected from the beam splitter.

[0091] Here, a focusing lens (145) may be provided at the front end of the photodetector (150). The photodetector (150) can receive a beam focused through the focusing lens (145) and convert it into an electrical signal.

[0092] The condensing lens (145) can spatially condense a beam reflected from a beam splitter (140) and transmit it to a light detector (150). A beam reflected from an object at a scan position of a scan beam designated by a scan unit (120) can be spatially condensed by the condensing lens (145). The condensing lens (145) can be composed of various lenses, such as an image or non-image condenser including a concave reflector and a convex reflector.

[0093] In this way, the focusing lens (145) focuses the beam that is reflected from the object (reflective object) and the reference mirror (330) and passes through the beam splitter (140), and the photodetector (150) can detect the beam spatially focused through the focusing lens (145) and convert it into a current signal. At this time, the photodetector (150) can generate a current according to the intensity of the spatially focused beam. The photodetector can be implemented using a photodiode, but the present invention is not necessarily limited thereto, and various light detection means such as a light pipe may be applied. In addition, the present invention can directly detect light transmitted to the detection surface of the photodetector (150) without a focusing lens.

[0094] Next, the electronic processing unit (160a) processes the signal detected by the photodetector (150) to generate a hologram of the object.

[0095] 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).

[0096] The heterodyne detector (161) processes the current signal received from the photodetector (150) to generate an in-phase output signal and a quarter-phase output signal.

[0097] Specifically, the heterodyne detector (161) generates a homodyne output signal and a quartile output signal using a current signal detected by the photodetector (150) and a heterodyne modulation signal having a frequency Ω generated by the function generator of the signal generation unit (180a).

[0098] The heterodyne detector (161) multiplies the received current signal with a heterodyne modulated signal having a frequency Ω generated by the function generator of the signal generation unit (180a), and then performs low-frequency filtering to generate a first output signal in phase. At the same time, the signal phase of the frequency Ω generated by the function generator is shifted by Ω and multiplied with the received current signal, and then performs low-frequency filtering to generate a second output signal in phase. Accordingly, the heterodyne detector (161) produces two output signals (in-phase output signal and phase in phase output signal).

[0099] Here, the in-phase output signal and the quartile output signal correspond to the pattern of the object's 3D image encoded by the Fresnel plate and can be expressed by Equation 2 and Equation 3, respectively.

[0100]

[0101]

[0102] Here, is the three-dimensional distribution of reflectance for the object, and 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, representing a function that indicates the change in curvature along the z-axis.

[0103] The AD converter (162) receives these in-phase and quarter-phase signals through each channel and converts them into digital signals. The converted digital current signals are provided to the signal processing unit (163) along with the scanning position of the scanning unit (120).

[0104] The signal processing unit (163) generates a complex hologram of an object from the converted digital signal, and the storage unit (164) stores the generated complex hologram.

[0105] And, whenever hologram processing for any position of the object is completed, the scan control unit (165) generates a control signal to change the scan position of the scan unit (120) and transmits it to the scan unit (120).

[0106] To this end, the signal processing unit (163) can form a two-dimensional array according to each scan position by adding mathematical formula 2 and mathematical formula 3 using a complex number addition method as shown in mathematical formula 4 below, and the storage unit (164) can store this.

[0107] In addition, the signal processing unit (163) may form a three-dimensional array according to the respective scan positions for Equation 2 and Equation 3 and transmit it to the storage unit (164), and then, when the scan is finished, read it from the storage unit (164), add the two-dimensional array corresponding to Equation 2 and Equation 3 using the complex number addition method of Equation 4, and then store it back in the storage unit (164). The signal stored in the storage unit (164) refers to Equation 4 below.

[0108]

[0109] In addition, the present invention may obtain the outputs of Equations 2 and 3 by applying the heterodyne signal generated in the signal generation unit (180a) to the reference signal input part of the heterodyne detector and obtaining the in-phase output and the quartile output, but as is known in the field of scanning hologram technology, it is also possible to obtain the reference signal by detecting it by positioning a portion of the light interfered by the interference means, that is, the second beam splitter (117), at the second photodetector.

[0110] In addition, in the first embodiment of the present invention, heterodyne detection is performed before converting to a digital signal through the AD converter (162), but it is also possible to convert the current signal provided by the photodetector (150) and the signal generated by the signal generation unit (180a) into a digital signal through the AD converter (162), and then perform digital heterodyne detection using a digital signal processing method and transmit it to the signal processing unit (163).

[0111] Meanwhile, the spatial distribution of the scan beam may be modulated or distorted in cases such as when there are aberrations in the lens or mirror. 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 the cross-sectional image of the object. At this time, the modulated or distorted pattern element can be obtained by convolving the complex conjugate of the desired Fresnel plate with the modulated or distorted Fresnel plate. Furthermore, by forming an inverse filter, such as a power fringe adaptive filter, using the modulated or distorted pattern element, the hologram encoded by the modulated or distorted Fresnel plate can be converted 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 details are common to all embodiments of the present invention.

[0112] In addition, in an embodiment of the present invention, an arbitrary phase and amplitude pattern may be positioned in the path of the first curvature beam or the path of the second curvature beam to modulate the spatial distribution of the first curvature beam or the second curvature beam. 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 may be a pattern encoded with the image of the object and the 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 the complex conjugate of the desired Fresnel plate with the Fresnel plate having a spatial distribution modulated by an arbitrary phase and amplitude pattern. Furthermore, by forming an inverse filter, such as a power print adaptive filter, using the pattern element modulated by the arbitrary phase and amplitude pattern, the hologram encoded by the Fresnel plate modulated by the arbitrary phase and amplitude pattern can be converted into a hologram encoded by the desired Fresnel plate. It goes without saying that a Fresnel plate having a spatial distribution modulated by arbitrary phase and amplitude patterns is also a type of Fresnel plate. This information is also common to all embodiments of the present invention.

[0113] FIG. 4 is a diagram showing an embodiment of the present invention in which distance information of a step difference on the surface of an object is obtained through a reference mirror, and FIG. 5 is a diagram explaining the x and y direction tilt angles of the reference mirror.

[0114] As shown in FIG. 4, the focal position of the first or second curved beam projected onto the object is set as the origin, and the distance in the z-axis direction from the origin plane (indicated by the dotted line in FIG. 4) to the reference mirror is z off (x,y), z is the distance in the z-axis direction from the focal position to the object. obj If defined as (x,y), the electronic processing unit (160a) is hologram information expressed by the following mathematical formula 5. You can obtain.

[0115]

[0116] Here, is the hologram of the reference mirror, and represents a hologram of an object that is a reflective object having reflectance.

[0117] In addition, the distance in the z-axis direction from the origin plane to the reference mirror is It can be expressed as. Here, is the distance from the center of the reference mirror to the focal point, and and is the degree to which the reference mirror is tilted in the x-axis and y-axis directions, and represents the magnitude of the angle at which the reference mirror is tilted in the x-axis and y-axis directions, respectively, as shown in Fig. 5.

[0118] At this time, and The angle range is , It is desirable that this be the case. In addition, it is possible for the reference mirror to be rotated in only one of the x or y directions, in which case the angle in the direction that is not rotated becomes 0 degrees.

[0119] In this way, the hologram information obtained from the electronic processing unit (160a) includes both the hologram from the beam reflected from the reference mirror and the hologram from the beam reflected from the object.

[0120] The escape scanning hologram interferometer (300) 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 object.

[0121] More specifically, the deaxial scanning holographic interferometer (300) detects the light signal reflected from the object and the light signal reflected from the reference mirror together at the condensing lens (145) and the light detector (150), and then numerically processes the detected signal at the computer processing unit (170) so that, unlike conventional interferometers, holographic information of an object having a rough surface can be obtained without speckle noise. After obtaining holographic information from the object without speckle noise, the holographic information is restored at a specific depth position and only phase information is extracted to obtain a numerical interference image at a specific depth position, and by unwrapping this using a numerical method, step difference information at that position can finally be obtained.

[0122] Specifically, the computer processing unit (170) includes a numerical restoration unit (171) for reading a hologram stored in a storage unit (164) and restoring a complex reference light reflected from a reference mirror (330) and a complex object light reflected from an object by a numerical method, and a numerical interference unit (172) for obtaining an interference pattern of an object by interfering the complex reference light and the complex object light by a numerical method.

[0123] First, the numerical restoration unit (171) can numerically process the hologram information received from the electronic processing unit (160a) to restore the numerical reference light reflected from the reference mirror (330) and the numerical object light reflected from the object in a numerical way.

[0124] At this time, the numerical restoration unit (171) places the hologram at the position (z) of the object. obj Numerical reference light and numerical object light can be generated by reconstructing at (x,y) using a numerical method. Numerical reconstruction can be obtained by convolving the complex conjugate of the Fresnel plate at the reconstruction location of the stored hologram. This method is merely one example, and it goes without saying that holograms can be reconstructed using various methods known in the field.

[0125] Mathematical formula 6 below represents the restoration of a hologram in the numerical restoration unit (171) using the above method.

[0126]

[0127] Here, is a numerical reference light generated by reflection from a reference mirror (330). and the position of the object (z obj Numerical object light generated by reflection at (x,y) It is the sum of, and It indicates the distance (difference in distance on the x,y plane) between the reference mirror (330) installed at a specific angle and the object. At this time, z obj is z obj It can mean (x,y). And, is a component of 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 shown in Equation 7 below.

[0128] And, the numerical interference unit (172) obtains an interference pattern of an object by numerically interfering the numerical reference light and the numerical object light restored by numerical restoration, and obtains a specific location of the object (Z) from the result of numerically removing the DC component caused by background noise from the obtained interference pattern. obj Restores holographic information from ).

[0129] Here, the numerical interference unit (172) obtains an interference pattern through the squared sum of the restored numerical reference light and the numerical object light, as in Equation 7. That is, the numerical interference unit (172) obtains the 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 from the numerical restoration unit (171), i.e., the restored image.

[0130]

[0131] Here, is an interference pattern, is a numerical reference light and numerical object light The sum of, is as a background noise component It can be expressed as. In addition, λ and (x,y,z) are as explained earlier in Equation 1, and Z obj is the distance from the focal point to the object, It indicates the distance between a reference mirror installed at an angle and an object.

[0132] of this mathematical formula 7 is the value obtained by excluding the DC component corresponding to background noise from the result of Equation 7, and through this, it can be seen that precise out-of-axis interference information of the object is obtained using the embodiment of the present invention.

[0133] The numerical interference unit (172) can obtain a numerical interference image based on the acquired interference pattern and unwrap the numerical interference image to obtain step difference information of the object at the corresponding location. The above-mentioned process can be briefly illustrated as in FIG. 7.

[0134] FIG. 7 is a diagram illustrating a numerical processing process for obtaining a numerical interference image from holographic information obtained according to an embodiment of the present invention.

[0135] As shown in FIG. 7, an embodiment of the present invention can obtain a numerical interference image at a specific depth position by acquiring holographic information without speckle noise using the method described above, then restoring the holographic information at a specific depth position and extracting only the phase information. At this time, if the numerical interference image acquired at the specific depth position is unwrapped using a numerical method, step difference information at that position can finally be obtained.

[0136] Here, the numerical interference part (172) is the position (Z of the object) objNumerical interference images in ) can be processed stepwise using a numerical method such as Equation 8 below, and unwrapped repeatedly until the difference between the estimated value and the measured value becomes less than a threshold.

[0137]

[0138] 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 The Fourier transform value of, class is the phase information to be restored, and i represents the complex number representation.

[0139] At this time, , It can be expressed as.

[0140] The process from step 1 to step 4 of mathematical formula 8 is performed repeatedly until the difference between the estimated value and the measured value is minimized, and the final result value is used as the unwrap result.

[0141] The unwrap method mentioned above corresponds to a representative example, and in addition to the above example, various methods including the quad-tree decomposition method, the least-square method using FFT, the block least-square method, and the rounding-least-square method may be utilized.

[0142] In addition, holographic information without biaxial noise and background noise (DC) can be obtained by using a numerical signal processing method as in the embodiment of Fig. 6, using the eccentric scanning holographic interferometer mentioned above.

[0143] Figure 6 is a diagram showing a numerical processing process for restoring out-axis hologram information obtained from an out-axis scanning hologram interferometer without background noise and paired image noise.

[0144] 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 hologram information region of the object, and the biimage noise information region in the frequency domain. Then, among the three separated regions, only the hologram information of the object is spatially filtered and moved to the origin position in space, and then IFFT processing is performed again to obtain only the hologram information of the object from which background noise and biimage noise have been removed.

[0145] As shown in Fig. 6, when the deaxial hologram information obtained by the method of Equation 6 is converted into the frequency domain, (k x , k y In the frequency domain coordinate system, the DC information region, the hologram information region, and the biimage noise region can be separated. The DC information region exists at the origin of the coordinate system. If we look at the result of spatially filtering only the hologram information in the frequency domain coordinate system and shifting the coordinates to the origin, it can be seen that the hologram information is located at the origin. Subsequently, by performing IFFT processing on this to transform it into the spatial domain, hologram information with both background noise and biimage noise removed can be obtained. In Fig. 6 represents spatially filtered holographic information.

[0146] In the case of an embodiment of the present invention, the larger the tilt angle of the reference mirror in the x and y directions, the greater the positional deviation (k) of the hologram information from the DC information position in the frequency domain coordinate system. x , k y The deviation in direction also increases and does not overlap with each other, making it easier to spatially filter holographic information in the frequency domain.

[0147] The DC information region, holographic information region, and biimage noise information region in the spatial frequency domain can be represented as shown in Fig. 9, and the magnitude of the maximum spatial frequency of the DC information region Is It can be expressed as follows. Here, λ is the wavelength used, represents the number of apertures of the Fresnel plate generated by the interference phenomenon, which can be determined by the curvature of the first curvature beam and the difference in curvature of the first curvature beam.

[0148] Here, the deaxial angle of the reference mirror in the x-axis or y-axis direction to prevent the DC information region and the holographic information from overlapping in the frequency domain is larger value ( It can be set to ).

[0149] By numerically processing the spatial filtering and coordinate translation processes to obtain only the holographic information of the object among three spatially separated information domains, and then converting it back into a spatial domain using a numerical method such as IFFT, it becomes possible to obtain only the holographic information of the object that is not affected by background noise and paired image noise.

[0150] In this way, the de-axis scanning hologram interferometer (300) acquires information of light reflected from a reference mirror and information of light reflected from an object in the form of electrical signals using a photodetector (150) as shown in the example of FIG. 4, and acquires de-axis hologram information through an electronic processing unit (160a). At this time, if the de-axis hologram information is numerically restored at a specific location through a computer processing unit (170), precise height information (step difference information of the object surface) at that location can be acquired.

[0151] Meanwhile, FIG. 2 is a case in which the transition means is implemented as a phase transition means (112b) differently from FIG. 1, and since components having the same sign as FIG. 1 mean that they perform the same operation, a separate description of components with the same sign is omitted.

[0152] In the case of Fig. 2, the basic structure of the system is the same as in Fig. 1, but the configuration of the transition means (112b), the signal generation unit (180b), and the electronic processing unit (160b) is different.

[0153] The phase shifting means (112b) serves to discontinuously shift the phase of the divided first curvature beam. The operation of the phase shifting means (112b) is based on the phase shift signal generated by the signal generation 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} according to the phase shift signal generated by the signal generation unit (180b).

[0154] A phase optical modulator can be used as such a phase shifting means, but the present invention is not necessarily limited thereto, and various phase shifting means can be used, such as changing the phase of the beam in the order of {0, π / 2, π} using a PZT.

[0155] In this embodiment, the phase is divided into three different phases {0, π / 2, π}, but it is possible to capture images with even more detailed subdivisions, and it is also possible to capture images with only one or two phase changes if you do not want to remove biimage noise or background noise. However, when capturing with only one phase (single phase), a phase modulator is not required.

[0156] In FIG. 2, the phase transition means (112b) is formed on the side of the first divided curvature beam as an example, but the present invention is not necessarily limited thereto. That is, the phase transition means (112b) can, of course, be formed on the side of the second divided curvature beam.

[0157] 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 phase-transitioned Fresnel plate shape in the region where the first curvature beam and the second curvature beam are combined, as shown in Equation 9 below.

[0158]

[0159] Here, P n is a set of n different phases used for phase transition in the phase transition means (112b), i.e., It represents, and the definitions for the remaining factors are the same as those shown in Equation 1 above. Here, the three phase transitions shown are for illustrative purposes, and it is obvious that n phase transitions, such as 2, 3, or 4, are possible.

[0160] As shown in Fig. 2, when the frequency shifting means is replaced with a phase shifting means, the electronic processing unit (180b) does not need to be equipped with a heterodyne detector.

[0161] First, the current generated at the scan position of the response command beam specified by the scan unit (120) of FIG. 2 is given by Equation 10. This Equation 10 represents the current signal detected by the photodetector (150) of FIG. 2.

[0162]

[0163] is a current signal detected by a photodetector (150), and is the three-dimensional distribution of reflectance for the object, and is a convolution operation. And, (x,y) is a scan position of a 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 a Fresnel plate formed by the interference of the first curvature beam and the second curvature beam.

[0164] The electronic processing unit (180b) of FIG. 2 processes a current signal detected by a photodetector to extract holographic information of an object, and to this end, it may include an AD converter (166), a signal processing unit (167), a storage unit (168), and a scan control unit (169).

[0165] 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 as a signal processing unit (167) together with.

[0166] The signal processing unit (167) generates a complex hologram of an object using the converted digital current signal and the phase shift value generated by the phase shift signal generator of the signal generation unit (180b), and the storage unit (268) stores the generated complex hologram.

[0167] And, the scan control unit (169) can generate a control signal that changes the scan position of the scan unit (120) whenever holographic processing for any position of the object is completed.

[0168] 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} transitioned at each scanning position using Equation 11, thereby forming a pattern encoded with a 3D image of an object and a Fresnel plate. Acquires.

[0169]

[0170] In Figure 2, the phase is subdivided into three. Here, when the phase is subdivided into three or more, the images for three or more phases are combined in the manner of Equation 11 to obtain a pattern in which the image of the object being photographed and the Fresnel plate are encoded.

[0171] In the case where there are two phases, there is insufficient information for combining the image of the object being photographed and the Fresnel plate in Equation 11, so the encoded pattern of the cross-sectional image of the object being photographed and the real Fresnel plate is combined, and in this case, the reconstructed image is contaminated by paired image noise.

[0172] In the case of FIG. 2, the digital current signal, the scanning position of the scan unit (120), and the phase shift value P n The data 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.

[0173] FIGS. 8A and FIGS. 8B are drawings showing the configuration of an off-axis scanning holographic interferometer according to a second embodiment of the present invention.

[0174] As shown in FIG. 8a and FIG. 8b, the deaxial scanning hologram interferometer (500) according to the second embodiment of the present invention mainly comprises a scan beam generating unit (110), a scanning unit (420), a reference mirror (330), a beam splitter (340), a photodetector (150), and an electronic processing unit (160), and may further include a computer processing unit (170) and a signal generating unit (180).

[0175] In the case of FIGS. 8a and FIGS. 8b, the basic structure of the system is the same as FIGS. 1 and FIGS. 2, but the configuration of the scanning unit (420) is different, and the operating principle is as follows.

[0176] In FIGS. 8A and 8B, 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 so as to control the scanning position of the scan beam for 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) from the rear end of the target object.

[0177] The scan mirror (421) controls the scan beam received from the interference means (117) in a horizontal direction and transmits it to the object. Here, a third mirror (M3) may be added to convert the direction of the beam output from the interference means (117) and transmit it to the scan mirror (421). The translation stage (422) is installed at the rear end of the object to directly move the object receiving the scan beam in a vertical direction, thereby enabling scanning of the object in the y-direction through the scan beam.

[0178] The translation stage (422) is implemented to be movable in the y-axis direction on which the object is placed, and may correspond to a movable object plate. 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 for the object, and is therefore included as a component of the scan unit (420) together with the scan mirror (421).

[0179] In this way, the scanning unit (420) can control the scan beam in the horizontal direction (x direction) and the vertical direction (y direction) relative to the object using the scanning mirror (421) and the translation stage (422).

[0180] According to the present invention as described above, an out-of-axis scanning holographic interferometer can be provided that can obtain phase information according to the step difference of a reflective object having a rough surface without speckle noise.

[0181] The present invention has been described with reference to embodiments illustrated in the drawings, but this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom. Accordingly, the true technical scope of 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 and converts 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 horizontal and vertical directions to scan a reflective object using the scan beam and transmits it to the object; A beam splitter positioned between the above-mentioned scanning unit and the above-mentioned target body to split the beam by transmitting and reflecting the incident beam; A reference mirror installed at an angle of inclination relative to the z-axis direction perpendicular to the plane (x,y plane) of the object above the beam splitter, and reflecting the incident beam; A photodetector disposed below the beam splitter to detect a beam reflected from the object and the reference mirror and passing through the beam splitter; and A scanning holographic interferometer comprising an electronic processing unit that processes a signal detected by the photodetector to generate a hologram of the object.

2. In Claim 1, The above electronic processing unit is, The focal position of the first or second curved beam projected onto the object is set as the origin, and the distance in the z-axis direction from the origin plane to the reference mirror is z off (x,y), z is the distance in the z-axis direction from the focal position to the object. obj If defined as (x,y), the holographic information expressed by the following mathematical formula An out-of-axis scanning holographic interferometer acquiring: Here, is the hologram of the above-mentioned reference mirror, and represents a hologram of an object that is the above-mentioned reflective object, and as, is the distance from the center of the reference mirror to the focal position, and is the degree of tilt in the x-axis and y-axis directions, and represents the angle of inclination in the x-axis and y-axis directions, respectively.

3. In Claim 1, An axialized scanning hologram interferometer further comprising a numerical restoration unit that numerically processes the hologram information received from the electronic processing unit and restores the numerical reference light reflected from the reference mirror and the numerical object light reflected from the object in a numerical way.

4. In Claim 3, An out-of-axis scanning holographic interferometer further comprising a numerical interference unit that acquires 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 reconstruction above.

5. In Claim 4, The above numerical interference unit is, An unwrap scanning hologram interferometer that obtains step difference information of an object at a corresponding location by unwrapping a numerical interference image based on the above interference pattern.

6. In Claim 4, The above numerical interference unit is, An out-of-axis scanning holographic interferometer that acquires the interference pattern of the numeric reference light and numeric 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 focal position of the first or second curvature beam is the origin, the direction of propagation of the first or second curvature beam is the z-axis, and planar axes perpendicular to the z-axis are the x-axis and y-axis, Z obj is the distance from the above focus position to the object, It indicates the distance between the reference mirror installed at an angle and the object.

7. In Claim 4, The above numerical interference unit is, An exhaustive scanning hologram interferometer that spatially separates a DC information region, a hologram information region of an object, and a biimage noise information region in the frequency domain by performing FFT processing on the result of numerically removing the DC component from the interference pattern, spatially filters only the hologram information of the object among the three separated regions, moves it to the origin position of the space, and then performs IFFT processing again to obtain only the hologram information of the object from which background noise and biimage noise have been removed.

8. In Claim 7, The deaxial angle in the x-axis or y-axis direction of the reference mirror to prevent the DC information region and the holographic information from overlapping in the above frequency domain is larger value ( It is set to ), is an out-of-axis scanning holographic interferometer representing the numerical aperture of a Fresnel plate generated by interference phenomena.

9. In Claim 1, The above scan beam generating unit is, A transition means for phase modulating a first beam divided from the above light source by frequency shifting or phase shifting; A first and second curvature beam generator that converts the phase-modulated first beam and the second beam split from the light source into a first curvature beam and a second curvature beam, respectively, having a set curvature; and An axialized scanning hologram interferometer comprising an interference means for generating a scan beam having an interference pattern of a Fresnel plate by interfering the first curvature beam passed through the first curvature beam generator and the second curvature beam passed through the second curvature beam generator with each other.

10. In Claim 9, The above-mentioned shifting means is a frequency shifting means for frequency shifting the above-mentioned first beam, and The above scan beam is, An out-of-axis scanning holographic interferometer defined by the following mathematical formula as a time-heterodyne modulated Fresnel plate form: 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 propagation 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 as the curvature of the Fresnel plate formed by the interference of the first curvature beam and the second curvature beam, and Ω represents the frequency of transition.

11. In Claim 9, The above-mentioned transition means is a phase transition means for phase-shifting the above-mentioned first beam, and The above scan beam is, An out-of-axis scanning holographic interferometer defined by the following mathematical formula as a phase-shifted Fresnel plate shape in the region where the first and second curvature beams interfere: Here, λ is the wavelength of the beam used, (x,y,z) is a spatial coordinate system with the focal position of the first or second curvature beam as the origin, the direction of propagation of the first or second curvature beam as the z-axis, and planar axes parallel 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, a function representing the change in curvature along the z-axis, P n represents a set of n different phases used in the above phase transition.

12. In Claim 10, The above electronic processing unit is, A heterodyne detector that generates an in-phase output signal and a quartile output signal using a current signal detected by the above photodetector and a heterodyne modulation signal having a frequency Ω generated by a function generator of a signal generation unit; An AD converter that receives the above in-phase signal and quarter-phase signal through each channel and converts them into digital signals; A signal processing unit that generates a complex hologram of an object from the above converted digital signal; A storage unit for storing the complex hologram generated above; and An off-axis scanning hologram interferometer comprising a scan control unit that generates a control signal to change the scan position of the scan unit whenever hologram processing for any position of the object is completed.

13. In Claim 11, The above electronic processing unit is, 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 of an object using the above-mentioned converted digital current signal and a phase shift value generated by the phase shift signal generator of the signal generation unit; A storage unit for storing the complex hologram generated above; and An off-axis scanning hologram interferometer comprising a scan control unit that generates a control signal to change the scan position of the scan unit whenever hologram processing for any position of the object is completed.

14. In Claim 1, The above scanning unit is, An axialized scanning holographic interferometer comprising a horizontal scanning mirror and a vertical scanning mirror to control the scanning position of the scan beam with respect to the above object in horizontal and vertical directions.

15. In Claim 1, The above scanning unit is, An axialized scanning hologram interferometer comprising a scan mirror that controls the scan beam incident from the scan beam generating unit in the horizontal direction and transmits it to the target object 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 that moves the target object in the vertical direction at the rear end of the target object.

Images