CN119758690A - Micro-off-axis digital holography method and device based on Mach-Zehnder interference structure - Google Patents
Micro-off-axis digital holography method and device based on Mach-Zehnder interference structure Download PDFInfo
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Abstract
A micro-off-axis digital holographic method and device based on Mach-Zehnder interference structure belong to the technical field of optical imaging based on holography. The method is characterized by comprising the steps of a step of obtaining linearly polarized light with amplitude of A 0, a step of obtaining a virtual light source of an object light spot light source, a step of enabling two point light sources of the object light and a reference light to be in a coaxial state, a step of enabling the object light spot light source and the reference light spot light source to reach an equal optical path state, a step of enabling the reference light to quantitatively translate in the transverse direction and enabling the reference light to continuously pass through the center of a reference light path again, a step of f obtaining a background hologram, an object hologram and an object intensity map, and a step of carrying out numerical value reproduction. By the micro-off-axis digital holographic method and the device based on the Mach-Zehnder interference structure, the object light filtering aperture and the reference light spot light source are not coplanar, and the aperture size and the position of the point light source can be independently regulated and controlled.
Description
Technical Field
A micro-off-axis digital holographic method and device based on Mach-Zehnder interference structure belong to the technical field of optical imaging based on holography.
Background
Digital holography has received much attention in recent years as an important quantitative phase imaging technique because of its ability to quantitatively measure complex wave front amplitudes (particularly phase information) of objects, and has been widely used in research fields such as physics, biology, and chemistry. Conventional digital holography can be classified into two types, i.e., on-axis digital holography and off-axis digital holography, according to the difference of the included angle between object light and reference light in a recording device. In coaxial digital holography, the included angle between object light and reference light is close to zero. Such a recording device can fully utilize the resolution capability of the image sensor to realize high-spatial resolution image reconstruction. The main problem is that the reconstructed image of the in-line hologram is often affected by auto-correlation and conjugate term noise, which can be eliminated or suppressed by phase shifting or other time consuming algorithms. In off-axis digital holography, the autocorrelation and conjugation terms can be well separated in the spatial frequency domain of the hologram. Therefore, the autocorrelation terms and conjugate terms can be removed in the image reconstruction process by only spatially filtering the off-axis digital hologram, but at the cost of high bandwidth requirements for the image sensor. In general, in order to separate the spatial frequency of the object light from the spatial frequency of the autocorrelation and conjugation terms, it is required that the bandwidth of the image sensor is four times that of the object light to be recorded.
In recent years, a new solution has been proposed between conventional on-axis and off-axis digital holography, called micro-off-axis digital holography. The micro-off-axis digital hologram does not need to completely separate the spatial frequency of the object light from the spatial frequency of the autocorrelation term, but only needs to separate the spatial frequency of the object light from the spatial frequency of the conjugate term, i.e. the spatial frequency of the reference light is set to be equal to or slightly larger than the maximum spatial frequency of the light wave of the object light to be recorded. Therefore, compared with off-axis digital holography, the transverse resolution of the reconstructed image based on micro-off-axis digital holography can be greatly improved. Meanwhile, micro-off-axis digital holography is also superior to on-axis digital holography in the aspect of observing dynamic process, because the phase reconstruction algorithm and the process are simpler, such as phase reconstruction algorithm based on Hilbert transformation, nonlinear filtering and phase derivative. In summary, micro-off-axis digital holography has the advantage of low bandwidth requirements for the image sensor compared to off-axis digital holography, which has the advantage of a simple information recovery process compared to on-axis digital holography.
While most phase reconstruction algorithms for micro-off-axis digital holography are equally applicable to conventional off-axis holography, in order to obtain the best resolution of the reconstructed image, the carrier frequency of the reference light should be calibrated as precisely as possible to be close to the maximum spatial frequency of the recorded object light when designing the recording device. However, most of the designed micro-off-axis digital hologram devices are directly based on the existing off-axis digital hologram recording devices, in which the maximum spatial frequency of the recorded object light and the carrier frequency of the reference light are difficult to quantitatively determine and control, and thus there is a difficulty in satisfying the optimal frequency condition of the micro-off-axis digital hologram.
In recent years, an optical system based on a micro-off-axis digital hologram algorithm and capable of better satisfying an optimal frequency condition has been described in the prior art. The system irradiates an object by adopting a converging spherical light beam, places a specially designed aperture filter on the plane of the spatial frequency of the object light, and simultaneously adopts a point light source emitted from the edge of the aperture as reference light, thereby ensuring the optimal frequency condition of micro-off-axis digital holography. In addition, the magnification of the field of view of the object to be measured in the system can be quantitatively regulated and controlled by changing the distance between the aperture filter and the object. However, the system is designed based on a1×2 single-mode fiber splitter, so that the requirements on external stability are higher, and the aperture filter is mechanically designed and cannot be flexibly regulated.
Disclosure of Invention
The technical problem to be solved by the invention is to overcome the defects of the prior art and provide the micro-off-axis digital holographic method and device based on the Mach-Zehnder interference structure, which can realize the non-coplanarity of the object optical filtering aperture and the reference light spot light source and the independent regulation and control of the aperture size and the position of the point light source.
The technical scheme adopted by the invention for solving the technical problems is that the micro-off-axis digital holographic method based on the Mach-Zehnder interference structure is characterized by comprising the following steps:
Step a, turning on a laser to obtain linearly polarized light with amplitude of A 0, wherein the linearly polarized light is incident to a Mach-Zehnder interference system comprising an object light path and a reference light path;
Step b, obtaining a virtual light source S 1' of the object light spot light source S 1 according to the reflection imaging principle;
step c, according to the Michelson interference principle, the change of interference fringes is utilized to adjust the object light path to enable the object light and the reference light to be in a coaxial state;
Step d, adjusting the position of a lens of a reference light path in the axial direction to enable an object light spot light source and a reference light spot light source to reach an equal optical path state;
step e, moving the reference light path in a transverse direction perpendicular to the optical axis, enabling the reference light to quantitatively translate in the transverse direction and enabling the reference light to continuously pass through the center of the reference light path again;
Step f, obtaining a background hologram through an image sensor, and obtaining an object hologram and an object intensity map through the image sensor after placing an object to be detected in an object light path;
and g, performing numerical reproduction.
Preferably, in step b, the object light spot light source S 1 is mirror-symmetrical with respect to the mirror M1 to obtain the virtual light source S 1 ' according to the reflection imaging principle, and the virtual light source S 1 ' is mirror-symmetrical with respect to the NPBS2 to obtain the virtual light source S 1 '.
Preferably, in step c, according to michelson interference principle, the mirror M1 is adjusted to make the inclined interference fringe on the image sensor gradually become vertical, then the mirror M1 is adjusted to make the fringe gradually become thicker until the concentric ring appears, and the mirror M1 is further adjusted to make the concentric ring be in the center of the visual field of the image sensor, so that the object light and the reference light spot light source reach the state of equal optical path.
Preferably, in step d, the front-rear axial position of the lens L2 on the reference light path is adjusted to make the stripe gradually swallow and become thicker, and when the stripe is thickest, the object light and the reference light spot source reach a coaxial aplanatic state.
Preferably, in step e, lens L2 and aperture stop FA2 in the reference light path are moved the same distance x r in the same lateral direction, then the parallel plates in the reference light path are rotated to laterally displace reference spot source S 2 by x r and the reference light is redirected through the center of lens L2 and aperture stop FA 2.
Preferably, in step g, the intensity pattern of the object is subtracted from the object hologram, then fourier transformation is performed, then a correct frequency spectrum is selected, inverse fourier transformation and numerical diffraction are performed to obtain the complex amplitude of the object to be measured, finally the background noise of the system is recovered from the background hologram, the complex conjugate of the complex noise is multiplied by the complex amplitude of the reconstructed object to further eliminate the background noise, and finally the amplitude and phase distribution diagram of the reconstructed object after noise elimination are obtained.
A micro-off-axis digital holographic system based on a Mach-Zehnder interference structure is characterized by comprising a laser used for emitting a laser light source, a Mach-Zehnder interference system consisting of two unpolarized beam splitting prisms NPBS 1-NPBS 2 and two reflectors M1-M2, wherein an attenuation plate used for adjusting the intensity of input laser light and a conversion mechanism used for converting the laser light source into linear polarized light are arranged between the laser and the Mach-Zehnder interference system;
An object light path is arranged between the non-polarized beam splitting prism NPBS1 and the reflecting mirror M1, a reference light path is arranged between the reflecting mirror M2 and the non-polarized beam splitting prism NPBS2, the reflecting mirror M2 is arranged on the propagation path of the light beam reflected by the non-polarized beam splitting prism NPBS1, the reflecting mirror M1 is arranged on the propagation path of the light beam transmitted by the non-polarized beam splitting prism NPBS1, the light reflected by the M2 and the M1 simultaneously enters the non-polarized beam splitting prism NPBS2, and the image sensor is arranged on the output light path of the non-polarized beam splitting prism NPBS 2.
Preferably, an attenuation sheet ND for adjusting the intensity of the input laser and a laser polarization state conversion mechanism polarizer P are sequentially arranged between the laser and the Mach-Zehnder interference system.
Preferably, the object light path comprises a pinhole filter SF, a lens L1 and an aperture diaphragm FA1 which are sequentially arranged, and the reference light path comprises a parallel flat plate PL, a lens L2 and an aperture diaphragm FA2 which are sequentially arranged.
Compared with the prior art, the invention has the following beneficial effects:
By the micro-off-axis digital holographic method and the device based on the Mach-Zehnder interference structure, the non-coplanarity of the object aperture diaphragm and the reference light spot light source and the independent regulation and control of the size of the diaphragm and the position of the point light source can be realized, and the micro-off-axis state can be well determined and realized.
The aperture of the object light path and the point light source of the reference light path in the micro-off-axis digital holographic device based on the Mach-Zehnder interference structure are not actually coplanar, the aperture size and the position of the point light source can be respectively and independently regulated and controlled, the practicability of the system is improved, and the interference mode of the point light source can also realize imaging of different amplification factors of an object to be detected, so that the application of the micro-off-axis digital holographic device in the field of high-resolution quantitative phase imaging of biological samples is further expanded.
According to the micro-off-axis digital holographic method and device based on the Mach-Zehnder interference structure, two point light source interference is generated by introducing a lens into two paths of light of a Mach-Zehnder interference system consisting of two unpolarized beam splitting prisms and two reflecting mirrors, an object to be detected is inserted between the lens and an aperture diaphragm of an object light path, a parallel flat plate and an aperture diaphragm are respectively introduced at two sides of a reference light path lens, and the transverse displacement of the light path along the direction perpendicular to an optical axis is realized by rotating the parallel flat plate, so that micro-off-axis digital holographic is realized.
Drawings
FIG. 1 is a schematic diagram of a micro-off-axis digital holographic device based on Mach-Zehnder interference structures.
Fig. 2 is a graph of a spatial spectrum corresponding to a theoretical micro-off-axis digital hologram.
FIG. 3 is a flow chart of a micro-off-axis digital holographic method based on Mach-Zehnder interference structure.
Fig. 4 is a state diagram of the theoretical equivalent of object light and reference spot light sources into coaxial and aplanatic states using the principle of reflection imaging.
Fig. 5 to 12 are schematic diagrams of interference fringe changes corresponding to different interference states of two point light sources of object light and reference light.
Fig. 13 is a schematic diagram showing the spatial distribution of the mirror image of the object aperture FA1 and the reference spot light source S 2 on the plane of the point light source S 2 in the coaxial aplanatic state.
Fig. 14 shows the mirror image of the object aperture FA1 and the spatial distribution of the reference spot light source S 2 in the slightly off-axis state.
Fig. 15 is a background hologram taken by the image sensor at the recording parameter z 1＝262.4mm,z2 =133.4 mm, object magnification m= 0.5084.
Fig. 16 is an object hologram photographed by the image sensor at the recording parameter z 1＝262.4mm,z2 =133.4 mm and the object magnification m= 0.5084.
Fig. 17 is an object intensity map captured by the image sensor at the recording parameter z 1＝262.4mm,z2 =133.4 mm and the object magnification m= 0.5084.
Fig. 18 is a spectrum diagram of an object hologram after fourier transform.
FIG. 19 is an amplitude distribution diagram of an object under test reproduced by a computer under the reconstruction effect of micro-off-axis digital holography.
FIG. 20 is a graph showing the phase distribution of an object under test reproduced by a computer under the reconstruction effect of micro-off-axis digital holography.
Fig. 21 to 22 are effect graphs of reproduction amplitude and phase of objects to be measured of different distance parameters and object magnification under the condition that a recording distance parameter z 1＝121.8mm,z2 =133.4 mm and an object magnification m= 1.0952.
Detailed Description
Fig. 1 to 22 are diagrams illustrating preferred embodiments of the present invention, and the present invention is further described below with reference to fig. 1 to 22.
As shown in FIG. 1, the micro-off-axis digital hologram device based on Mach-Zehnder interference structure comprises a Laser (Laser), a parallel flat plate PL, an attenuation sheet ND, a polaroid P, a pinhole filter SF, two unpolarized beam-splitting prisms including an unpolarized beam-splitting prism NPBS1, an unpolarized beam-splitting prism NPBS2, two Fourier lenses including a lens L1 and a lens L2, two aperture diaphragms including an aperture diaphragm FA1 and an aperture diaphragm FA2, two reflectors including a reflector M1, a reflector M2 and an image sensor CCD.
The device comprises an attenuation sheet ND, a polarizing sheet P, a non-polarized beam splitting prism NPBS1, a non-polarized beam splitting prism NPBS2, a pinhole filter SF, a lens L1, an aperture diaphragm FA1 and a reflecting mirror M1, wherein the pinhole filter SF, the lens L1, the aperture diaphragm FA1, the reflecting mirror M1 and the non-polarized beam splitting prism NPBS2 are sequentially arranged in an object light path corresponding to a transmitted light beam after being split by the non-polarized beam splitting prism NPBS1, the reflecting mirror M2 is arranged on a reference light path corresponding to a reflected light beam after being split by the non-polarized beam splitting prism NPBS1, and in the reference light path, the reflecting mirror M2, a parallel flat plate PL, the lens L2, the aperture diaphragm FA2 and the non-polarized beam splitting prism NPBS2 are sequentially arranged, and the object light path and the reference light path are non-common and spatially separated.
Light rays emitted from the reflecting mirror M2 are sequentially emitted into the non-polarized beam splitting prism NPBS2 through the parallel flat plate PL, the lens L2 and the aperture diaphragm FA2, light rays reflected by the reflecting mirror M1 in an object light path are simultaneously emitted into the non-polarized beam splitting prism NPBS2, and the image sensor CCD is arranged on an output light path of the non-polarized beam splitting prism NPBS 2.
After passing through the attenuation sheet ND and the polaroid P, the Laser emitted by the Laser enters a Mach-Zehnder interference system consisting of two non-polarized beam splitting prisms NPBS1 and NPBS2 and two reflectors M1 and M2. The object light in the object light path sequentially passes through the pinhole filter SF, the lens L1, and the aperture stop FA1 (the lens L1 converges light at the aperture stop FA1 to form a point light source), and the reference light in the reference light path sequentially passes through the parallel flat plate PL, the lens L2, and the aperture stop FA2 (the lens L2 converges light near the aperture stop FA2 to form a point light source).
The lens L2 and aperture stop FA2 in the reference light path are moved the same distance x r in the transverse direction perpendicular to the optical axis, and then the parallel plate PL is rotated to bring about a quantitative translation x r in the transverse direction of the reference light and to allow the reference light to pass again continuously through the centers of the lens L2 and aperture stop FA2 in the reference light path. Finally, an object OBJ to be detected is inserted between the lens L1 of the object light path and the aperture diaphragm FA1 (the radius of FA1 is R), and a micro-off-axis digital hologram of the object OBJ to be detected can be obtained on the image sensor CCD surface.
The principle of the micro off-axis digital holographic device based on the Mach-Zehnder interference structure shown in fig. 1 is as follows:
First, assume that the laser illumination wavelength is λ, the distance from an object OBJ to be measured in the object light path to the plane of the aperture stop FA1 is z 1, and the distances from the aperture stop FA1 and the aperture stop FA2 in the reference light path to the image sensor CCD are z 2. The complex transmittance of an object to be measured is represented by t (x 1,y1), meanwhile, the coordinates of the FA1 and FA2 surfaces are defined as (x 2,y2), and the coordinates of the CCD recording surface of the image sensor are defined as (x 3,y3);
In the micro-off-axis digital hologram device based on the mach-zehnder interference structure shown in fig. 1, if the reference light has been laterally displaced (assuming that the displacement occurs on the x-axis) by x r, and assuming that the reference light amplitude constant after passing through the non-polarizing beam splitter NPBS1, the mirror M2, and the parallel plate PL is a r, the complex amplitude of the reference light spot light source reaching the CCD plane can be theoretically expressed as:
wherein A r is a reference light amplitude constant, (x 3,y3) is an image sensor CCD recording surface coordinate, lambda represents a laser illumination wavelength, z 2 is a distance between an aperture diaphragm FA1 and an aperture diaphragm FA2 in a reference light path and the image sensor CCD, x r is a reference light lateral displacement, and i represents an imaginary unit.
The complex amplitude of the corresponding object light wave reaching the CCD plane can be expressed as:
Wherein, Representing the corresponding spatial spectrum after t (x 1,y1) fourier transform; A i is the amplitude constant of object light after passing through an unpolarized beam splitting prism NPBS1 and a pinhole filter SF, i is the imaginary unit, k is the wave number, lambda is the laser illumination wavelength, z 1 is the distance from an object to be detected OBJ in an object light path to the plane of the aperture diaphragm FA1, z 2 is the distance from the aperture diaphragm FA1 and an aperture diaphragm FA2 in a reference light path to an image sensor CCD, (x 2,y2) is the coordinates of the surfaces FA1 and FA2, (x 3,y3) is the coordinates of the recording surface of the CCD, and in micro-off-axis digital holography, x r is required to be equal to or slightly larger than R;
Further by variable substitution, with AndRepresenting spatial frequency domain coordinates such that the object light complex amplitude on the CCD face of the image sensor can be expressed as:
In the formula, Representing the Fourier transform, C is a constant and defines a magnification factor dependent on z 1 and z 2 R represents the aperture radius, z 1 is the distance from an object OBJ to be measured in an object light path to the plane of an aperture diaphragm FA1, z 2 is the distance from an aperture diaphragm FA1 and an aperture diaphragm FA2 in a reference light path to an image sensor CCD, (x 2,y2) is the coordinates of the planes where FA1 and FA2 are located, (x 3,y3) is the coordinates of a CCD recording surface, lambda represents the laser illumination wavelength, and i represents an imaginary unit. In particular, by substitution of the variables mentioned above,Representing the corresponding spatial spectrum after fourier transform of t (x 1,y1),The transmittance function of an aperture stop (stop radius R) on the FA1 plane is shown.
The intensity of interference of object light and reference light on the image sensor CCD plane can then be expressed as:
IH(x3,y3)＝|O(x3,y3)+R(x3,y3)2
＝|O(x3,y3)2+|R(x3,y3)2+O(x3,y3)R*(x3,y3)+O*(x3,y3)R(x3,y3)
wherein, the asterisk represents the complex conjugate operator, O (x 3,y3) represents the complex amplitude of the object light wave reaching the CCD surface, and R (x 3,y3) refers to the complex amplitude of the light spot source reaching the CCD surface of the image sensor.
Next, fourier transform is performed on the interference intensity, and the spatial spectrum formulas of the object wave (the third term O (x 3,y3)R*(x3,y3) above) and the conjugate term (the fourth term O *(x3,y3)R(x3,y3) above) of the object to be measured in the spatial frequency domain are simplified and can be expressed as:
wherein, C' represents a constant, AndRepresenting |o (x 3,y3)|2 and |r (x 3,y3)|2 spatial spectrum, M represents the magnification factor depending on z 1 and z 2,R represents the aperture radius, z 1 is the distance from the object to be measured OBJ in the object light path to the plane of the aperture diaphragm FA1, z 2 is the distance from the aperture diaphragm FA1 and the aperture diaphragm FA2 in the reference light path to the image sensor CCD,AndThe spatial frequency domain coordinates, (x 2,y2) are coordinates of the FA1 and FA2 planes, λ represents the laser illumination wavelength, asterisks represent complex conjugate operators, and i represents imaginary units.
As can be seen from the above formula, as long as x r is ensured to be greater than or equal to R, the spatial spectrum of the object light wave and the conjugate term thereof can be obviously separated, and the specific spectrum distribution situation refers to fig. 2. In summary, the micro-off-axis digital hologram shot by the micro-off-axis digital hologram optical system based on the Mach-Zehnder interference structure can always meet the optimal frequency condition required by the micro-off-axis.
The analysis can also determine that the magnification coefficient of the object to be detected of the micro-off-axis digital holographic device based on the Mach-Zehnder interference structure is determined by z 1 and z 2, when z 1<z2, the magnification coefficient is larger than 1, the micro-off-axis system can achieve higher spatial resolution and smaller view field of the object, and is particularly suitable for recording the object smaller than the CCD size of the image sensor, and when z 1>z2, the micro-off-axis system is particularly suitable for recording the object information larger than the CCD size of the image sensor.
Based on the micro-off-axis digital holographic device based on the Mach-Zehnder interference structure shown in fig. 1 and the principle thereof, the micro-off-axis digital holographic method based on the Mach-Zehnder interference structure shown in fig. 3 is obtained, and specifically comprises the following steps:
Step 1, starting a laser to obtain linearly polarized light;
And starting the Laser, so that the Laser emitted by the Laser sequentially passes through the attenuation sheet ND and the polaroid sheet P to obtain linearly polarized light with the amplitude of A 0, and ensuring a better interference effect.
Step 2, constructing a Mach-Zehnder interference system;
The Mach-Zehnder interference system shown in fig. 1 is constructed by using two non-polarized beam splitting prisms NPBS1 and NPBS2 and two reflectors M1 and M2, a pinhole filter SF, a lens L1 and an aperture diaphragm FA1 are sequentially inserted into an object light path to obtain object light with the amplitude of A i, and simultaneously a parallel flat plate PL, a lens L2 and an aperture diaphragm FA2 are sequentially inserted into a reference light path to obtain reference light with the amplitude of A r.
Step 3, obtaining linear polarized light of a virtual light source corresponding to the object light spot light source;
According to the reflection imaging principle, the object light spot light source S 1 is mirror-symmetrical with respect to the mirror M1 to obtain a virtual light source S 1 ', and then the virtual light source S 1' is mirror-symmetrical with respect to the NPBS2 to obtain a virtual light source S 1 ", as shown in fig. 4.
Step 4, adjusting the reflecting mirror to enable the object light path and the reference light path to be coaxial with the two point light sources;
According to the michelson interference principle, the mirror M1 is adjusted so that the inclined interference fringes on the image sensor CCD gradually become vertical as shown in fig. 5. Then, the reflector M1 is adjusted to make the stripes become thicker gradually until concentric rings appear, as shown in fig. 6-8, the reflector M1 is further adjusted to make the concentric rings be positioned at the center of the view field of the CCD of the image sensor, and at the moment, the object light point light source and the reference light point light source are coaxial.
Step 5, adjusting the lens to enable the object light path and the reference light path to reach a coaxial aplanatic state;
The front and rear axial positions of the lens L2 on the reference light path are adjusted to enable the stripe to be gradually swallowed and become thick gradually, as shown in fig. 9-12, when the stripe is thickest, the optical paths between the two point light sources and the image sensor CCD are almost equal, at the moment, the object light and the reference light point light source reach a coaxial equal optical path state, namely the state shown in fig. 4, the cross section state is shown in fig. 13, the circle in fig. 13 shows the mirror image of FA1 on the S 2 plane, and the radius is R.
Step 6, adjusting the reference light path to enable the reference light to pass through the lens and the aperture diaphragm center in the reference light path again;
Moving the lens L2 and aperture stop FA2 in the same lateral direction (x-direction) by 3mm, then rotating the parallel plate to cause the reference spot light source S 2 to generate lateral displacement x r and to allow the reference light to pass through again the center of the lens L2 and aperture stop FA2 (x r represents the distance from the reference light source S 2 to the center of the mirror circular hole of FA 1), i.e., r=x r =3 mm, indicates that a micro-off-axis state is experimentally achieved (the object aperture stop and the reference spot light source are not actually coplanar in space, and both R and x r can be individually flexibly adjusted according to actual needs), as shown in fig. 14, at which time the distance z 2 from FA2 to the image sensor CCD is 133.4mm.
And 7, shooting a background hologram by using the image sensor CCD in a dark environment under the condition of keeping the light path stable, as shown in fig. 15.
Step 8, shooting an object hologram by using an image sensor CCD in a dark environment;
An object OBJ to be measured is inserted between the lens L1 and the aperture stop FA1 of the object light path, wherein the distance z 1 from the plane of the object to be measured to the plane of the aperture stop FA1 is 262.4mm, and then, an object hologram is photographed by using the image sensor CCD in a dark environment while keeping the light path stable, as shown in fig. 16.
And 9, under the condition of blocking the reference light and keeping the light path stable, shooting an object intensity diagram by using the image sensor CCD in a dark environment, as shown in figure 17.
Step 10, numerical value reproduction;
The computer is used for numerical reconstruction, specifically, firstly, subtracting the intensity graph of the object from the hologram of the object, then performing Fourier transform, and then selecting the correct frequency spectrum, wherein the dotted circle frame shown in figure 18 is taken as a filtering area, and the frequency spectrum information of the corresponding object The complex amplitude of the object to be measured can be obtained by performing inverse Fourier transform and numerical diffraction, finally, the background noise of the system is recovered from the background hologram, the complex conjugate of the complex amplitude is multiplied by the complex amplitude of the reconstructed object to further eliminate the background noise, and finally, the amplitude and the phase distribution diagram of the reconstructed object after noise elimination are respectively shown in figures 19-20.
The recording distance parameter corresponding to the amplitude and phase of the playback object shown in fig. 21 to 22 is z 1＝121.8mm,z2 =133.4 mm, and the object magnification is m= 1.0952. Meanwhile, the amplitudes and phases shown in fig. 21 to 22 correspond to the amplitudes and phases of the objects within the dashed boxes in fig. 19 to 20. Comparing fig. 19 to 20 with fig. 21 to 22, the control of the magnification of the object to be measured can be achieved by controlling z 1 and z 2.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the invention in any way, and any person skilled in the art may make modifications or alterations to the disclosed technical content to the equivalent embodiments. However, any simple modification, equivalent variation and variation of the above embodiments according to the technical substance of the present invention still fall within the protection scope of the technical solution of the present invention.
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