CN108802994A - A kind of image recording system and method - Google Patents

Abstract

The application relates to a microscopic image recording system and a recording method. The recording system divides the light emitted by the laser into two beams of light waves, one of which carries the information of the object, and the other beam of light waves is expanded and collimated to form a spherical light wave through the microscope objective lens; the two beams of light waves pass through the beam combining mirror Afterwards, a hologram is formed by interfering on the CCD, and the interference pattern is reproduced by a computer to obtain a three-dimensional microscopic image of the object. The computer can automatically control the rotation of the beam combiner, thereby adjusting the core position of the spherical light wave, so that the original image and the interfering item in the reconstructed image can be just separated, so as to obtain a high-quality reconstructed image.

Description

An image recording system and method

technical field

The application relates to a recording of microscopic images, which belongs to the field of optical imaging.

Background technique

The usual microscope is mainly obtained through the lens group, the microscopic image obtained in this way cannot be recorded and saved, and the details of the image will not be remembered very quickly after observation. With the continuous development of semiconductor technology and laser technology, a digital microscope has appeared at this stage, which can obtain the phase image of the imaged object while obtaining the intensity image of the imaged object, or it can obtain the three-dimensional image of the imaged object. And the obtained three-dimensional image can be permanently preserved.

Digital microscope technology, also known as digital holography, uses a CCD to collect a hologram of an imaging object, inputs the hologram into a computer, and uses an algorithm to simulate the actual hologram reproduction process in the computer, thereby reconstructing the three-dimensional image of the object in the computer. Compared with the image obtained by ordinary digital cameras, the reconstructed image of the hologram has not only the intensity image, but also the phase image, that is, the three-dimensional topographical image of the object. Therefore, the most important thing in digital holography is the phase of the object. information reconstruction. In the existing digital holography, most of the off-axis holographic methods are used to obtain digital holographic images. In the off-axis holographic recording system, the laser light emitted from the laser is divided into two beams after passing through the beam splitter, and one beam passes through the object (sample ) carries the information of the object (so called the object light wave), and reaches the CCD target surface after passing through the beam combiner BS, and the other beam (called the reference light wave) is reflected by the mirror _M2 after being collimated by the beam expander, and then combined The mirror reflection reaches the CCD target surface and interferes with the object light wave to form an interference image (that is, a hologram). In the prior art, off-axis digital holography is mainly divided into off-axis Fresnel digital holography and off-axis lensless Fourier transform digital holography. In the recording of off-axis Fresnel digital holography, the reference light adopts plane light waves. When using When recording a digital hologram with a plane reference light wave, the structure of the recording system determines that the frequency of interference fringes in some areas in the interference light field is low, and the frequency in some areas is high, so that the bandwidth of the CCD cannot be fully utilized, and the recording distance is limited by the size of the photosensitive surface of the CCD. Due to limitations, it is difficult to improve the resolution of the reproduced image.

Contents of the invention

The application provides a microscopic imaging system, which uses spherical reference light waves to record digital holograms, thereby improving the resolution of reconstructed images.

This application adopts the following technical solutions: a microscopic image recording system, including a laser 1, a first half-wave plate 2, a polarizing beam splitter 3, a first reflecting mirror 4, a first beam expander and collimating mirror 5, and a transparent object 6 , beam combining mirror 7 (semi-transmission and semi-reflection), CCD8, the second half-wave plate 9, the second beam expander collimating mirror 10, the second reflector 11, the microscopic objective lens 12 and the computer 13; the light beam that the laser emits is polarized After the beam splitter, it is divided into beam A and beam B. After passing through the first reflector, beam A enters the first beam expander and collimator to form parallel light and irradiate transparent objects to form object light waves. The object light waves reach the CCD after passing through the beam combiner mirror. Target surface; the light beam B after the polarization beam splitter passes through the second half-wave plate and the second beam expander collimating mirror 10 to form a plane light wave, and the plane light wave enters the microscopic objective lens through the second reflector to form a spherical reference light wave. The center of the spherical reference light wave is a reference point light source, and the spherical reference light wave reaches the CCD target surface and the object light wave to form a hologram after passing through the beam-combining mirror; the hologram recorded by the CCD is transmitted to a computer and saved, and the computer can automatically The rotation of the beam combiner is controlled, thereby controlling the position of the reference point light source to obtain the best hologram, and the original image, the conjugate image and the intermediate interference item in the reconstruction image obtained after the reconstruction of the interference pattern are just separated. It is characterized in that it also includes an angle adjustment system, and the angle adjustment system includes: a support platform, a rotating shaft, a pull rope, a displacement detector, and a driving motor; The beam mirror rotates to adjust the position of the reference point light source on the object plane. The rotation of the rotation axis drives the displacement of the pull rope. The moving distance of the pull rope is monitored by the displacement detector. The rotation angle of the axis.

This application uses spherical reference light waves to record holograms, and the fringe spatial frequency of the interference field is relatively low, so that the sampling conditions for digital hologram recording are easily satisfied, especially when the recording optical path is arranged according to the method of lensless Fourier transform holography, Since the interference fringes are close to parallel and equally spaced, the limited bandwidth of the CCD can be fully utilized. Moreover, the allowable minimum recording distance is not limited by the size of the CCD. For tiny objects, holograms can be recorded at a small distance, and more information can be obtained, which is conducive to the improvement of the resolution of the reproduced image. Therefore, spherical reference light waves are used to record lensless Fu Lie transform digital hologram is an effective way to realize high-resolution imaging.

Description of drawings

Figure 1: Schematic diagram of the coordinates recorded by the spherical reference lightwave digital hologram;

Figure 2: Off-axis lensless Fourier transform digital holographic recording system;

Figure 3: Angle adjustment automatic control system.

Detailed ways

The recording optical path and the coordinate system used for analysis of the spherical reference light wave digital hologram are shown in Figure 1, where the x ₀ -y ₀ plane is the object plane, the xy plane is the hologram plane, the z axis passes through the centers of the two planes vertically, and the reference point source The position coordinates of is (x _r , y _r , z _r ), where z _r represents the distance from the point source to the CCD plane. In practical applications, z _r >z ₀ is often taken.

According to the Fresnel diffraction formula, under the paraxial approximation condition, ignoring the constant phase factor, the object light wave and the reference light wave arriving at the CCD plane are respectively

The item representing the original image in the hologram is UO ^* , which can be obtained after sorting

in

The phase of each point in the diffraction field and the fringe spatial frequency along the x and y directions are respectively

Considering that both z ₀ and z _r are positive, and z _r ≥ z ₀ , the maximum and minimum spatial frequencies of the hologram stripes are respectively

According to the Nyquist sampling theorem, the requirement

From formulas (1-8) and (1-9), it can be obtained that the constraints imposed on the reference light bias in order to satisfy the sampling theorem are as follows:

The maximum value of the spatial frequency of the halo light |U| ² along the x and y directions is respectively

In order to separate the reproduced images from each other, it is only necessary to properly set the position of the reference light so that the spectra of the zero-order diffraction term, the original image and the conjugate image do not overlap each other, that is, it is required

Thus, in the spherical reference light wave off-axis holography, another constraint condition set on the position of the reference light source, that is, the separation condition of the reconstructed image is

The position of the reference point source can be determined by combining the formula (1-10), where the size of z _r is determined by the magnification requirements of the reproduced image and the form of the reproduced reference light wave.

In the methods of recording holograms using spherical reference light waves, off-axis lensless Fourier transform holography and coaxial phase shift lensless Fourier transform holography are widely used. The advantage of the off-axis optical path is that the zero-order, positive and negative first-order diffraction images are separated from each other, and it is easier to filter out interference items, and it can be reconstructed from a single hologram. Off-axis lensless Fourier transform holography is discussed below.

Off-axis lensless Fourier transform holography is one of the commonly used recording optical path structures in digital holography. The off-axis lensless Fourier transform digital holographic recording system is shown in Figure 2, including a laser 1, a first half-wave plate 2, a polarizing beam splitter 3, a first reflecting mirror 4, a first beam expander collimating mirror 5, Transparent object 6, beam combining mirror 7 (semi-transmission and semi-reflection), CCD8, second half-wave plate 9, second beam expander collimating mirror 10, second reflector 11, microscopic objective lens 12 and computer 13; The beam is divided into beam A and beam B after passing through the polarizing beam splitter. The beam A enters the first beam expander and collimator after passing through the first reflector to form parallel light and irradiates a transparent object to form an object light wave. The object light wave passes through the beam combiner Finally, it reaches the CCD target surface; the beam B after the polarization beam splitter passes through the second half-wave plate and the second beam expander collimator 10 to form a plane light wave, and the plane light wave enters the microscope objective lens through the second reflector to form a spherical reference The center of the light wave and the spherical reference light wave is a reference point light source, and the spherical reference light wave reaches the CCD target surface after passing through the beam combiner and forms a hologram with the object light wave. At this time, the recording reference point source is located on the object plane, z _r = z ₀ , and substituting (1-10) and (1-13) into equations to obtain the offset requirement that satisfies both the sampling condition and the reconstructed image separation condition

The equal sign represents the critical separation and critical sampling, and the solution can obtain the minimum recording distance

z _0min ＝max(4X/λΔx,4Y/λΔy) (1-15)

In the formula, max means to take the larger value of the two.

From the above analysis, it can be seen that the separation degree of the reconstructed image of the lensless Fourier transform holography is related to the coordinates of the reference point light source, and does not involve the angle between the object light wave and the reference light wave. However, through the analysis of the recording optical path, it can be seen that the reference point light source represented by the microscope objective lens and the object are mirror-symmetrical with respect to the semi-transparent mirror surface of the beam combiner, that is to say, the imaging of the reference point light source through the semi-transparent mirror surface It is located on the same plane as the object, and in the process of optical path arrangement, because the object light wave and the reference light wave are arranged parallel to the table, that is, the y coordinate of the reference point light source can be considered as zero. At this time, the lensless Fourier transform hologram The separation degree of the reconstructed image is only related to the x-coordinate of the reference point light source, and the x-coordinate of the above-mentioned point light source can be changed by rotating the beam combiner, thereby affecting the separation degree of the reconstructed image. In order to obtain a reconstructed image with sufficient separation and maximum resolution, a method for accurately adjusting the coordinates of the reference point light source is introduced below; specifically, the following steps are included:

₁ ) Measure and record the first distance d1 from the beam combiner to the CCD target surface;

2) collecting and saving the first hologram of the object light wave and the reference light wave;

3) Reconstructing the first hologram to obtain the reconstructed image 1, and judging the separation degree of the original image and the intermediate interference item in the reconstructed image 1 obtained;

4) If the original image in the reproduced image 1 overlaps or partially overlaps with the interfering item in the middle, the computer issues an instruction to control the beam combiner to rotate at a specified angle (for example, 0.1 degree);

5) Continue to collect and save the second hologram of the object light wave and the reference light wave;

6) Reconstructing the second hologram to obtain the reconstructed image 2, and judging the separation degree of the original image and the intermediate interference item in the reconstructed image 2 obtained;

7) If the original image and the intermediate interference item in the reproduction image 2 still partially overlap, then repeat the above steps 4)-6), until the original image and the intermediate interference item in the reproduction image are completely separated;

8) Continue to judge the reconstructed image that is completely separated from the original image and the intermediate interference item. If the distance between the original image and the intermediate interference item is too far, the computer sends an instruction to control the half-mirror to rotate in the opposite direction by half of the specified angle (for example 0.05 degrees);

9) Continue to collect the third hologram of the object light wave and the reference light wave and save it;

10) Reconstructing the third hologram to obtain the reconstructed image 3, and judging the separation degree of the original image and the intermediate interference item in the reconstructed image 3 obtained;

11) If the distance between the original image and the intermediate interference item is still too far, repeat the above steps 8)-10) until the original image and the intermediate interference item in the reconstructed image are just separated; at this time, the corresponding hologram is d ₁ The best hologram H ₁ corresponding to the distance; save the best hologram H ₁ in the database;

12) Control the CCD to move the specified distance Δd forward or backward, and then repeat the above steps 1)-11) until the best hologram H ₂ corresponding to the distance d ₁ ± Δd is obtained, and save the best hologram H ₂ in the database.

13) Establish a distance-hologram correspondence table from the obtained optimal holograms H ₁ , H ₂ ...H _n and the corresponding distances d ₁ , d ₂ ...d _n .

14) In the subsequent hologram recording, first measure the distance d from the CCD to the beam combiner, and after inputting the distance d, call out the required optimal hologram H from the above-mentioned distance-hologram correspondence table in the computer as a standard Hologram; secondly, the computer issues an instruction to control the rotation angle of the beam combiner to shoot the hologram M, and matches (ie, recognizes) the hologram M with the above-mentioned standard hologram. If the hologram does not match, continue to rotate the angle to shoot the hologram ; If the holograms match, save the hologram M captured at this time as the hologram for reconstructing the three-dimensional image of the object. In the matching process of the above holograms, since it is difficult for the two holograms to be completely consistent, an error threshold can be set. When the matching error value is less than the above threshold, it can be considered as a match, and if it is greater than the above threshold, it is not. match.

In this application, by collecting the best hologram corresponding to the distance and establishing a distance-hologram correspondence table, in the future adjustment of the digital microscope system, only need to input the distance from the CCD to the beam combiner, and the computer system will automatically control the beam combiner Rotate and obtain the optimal hologram, and through the optimal hologram, a more accurate three-dimensional reconstruction image can be obtained.

Further, the present application also provides an angle adjustment system that precisely controls the rotation angle of the beam combiner through a computer. As shown in FIG. 3 , the angle adjustment system includes: a supporting platform 14 , a rotating shaft 15 , a pull rope 16 , a displacement detector 17 , and a driving motor 18 . The beam combiner is fixed on the support platform, and the beam combiner is driven to rotate through the rotation of the rotating shaft, thereby adjusting the position of the reference point light source on the object plane. The rotation of the rotating shaft drives the displacement of the pull rope, and the moving distance of the pull rope is detected by the displacement. The displacement detector is used to obtain the moving distance of the pull rope, and then obtain the rotation angle of the rotating shaft. Since the moving distance of the pulling rope can be accurately obtained by the displacement detector, and when the diameter of the rotating shaft is a constant value, the rotating shaft The angle of rotation can also be accurately obtained. The computer 13 controls the driving motor to drive the rotating shaft to rotate. During the rotating process of the rotating shaft, it drives the displacement of the stay rope, and the displacement detector detects the linear displacement of the stay rope. When the linear displacement is equal to the preset value, the displacement detector sends a signal to the computer and then The rotation axis is controlled to stop rotating, and the preset value corresponds to the specified angle that the beam combiner needs to rotate. Through the above-mentioned angle adjustment system, the position of the reference point light source in the above-mentioned off-axis lensless Fourier transform digital holographic recording can be precisely adjusted, and the separation degree and resolution of the reconstructed image can be controlled, so as to obtain a high-quality reconstructed image.

Claims (3)

1. a kind of micro-image records system, including laser, the first half-wave plate, polarizing beam splitter mirror, the first speculum, the first expansion Beam collimating mirror, transparent substance, light combination mirror (half-transmitting and half-reflecting), CCD, the second half-wave plate, the second beam-expanding collimation mirror, the second reflection Mirror, microcobjective and computer；The light beam that laser is sent out is divided into light beam A and light beam B, light beam A warp after polarizing beam splitter mirror Directional light irradiation transparent substance formation Object light wave is formed after entering the first beam-expanding collimation mirror after first speculum, which penetrates Reach CCD target surfaces after light combination mirror；Light beam B after polarizing beam splitter mirror is formed by the second half-wave plate and the second beam-expanding collimation mirror Plane light wave, the plane light wave enter microcobjective by the second speculum and form spherical reference wave, the spherical reference The center of light wave is reference point source, and the spherical reference wave reaches CCD target surfaces after light combination mirror and forms holography with Object light wave Figure；The hologram of the CCD records is transmitted to computer and preserves, and the computer can automatically control the rotation of light combination mirror, To control the relative position of reference point source and plane where transparent substance, to obtain best hologram, the best holography Scheme it is reconstructed after in the reproduction image that can obtain original image, conjugate image and intermediate distracter just detach.It is characterized in that：Also Including angular adjustment system, the angular adjustment system includes：Support platform, rotary shaft, drawstring, displacement detector, driving electricity Machine；Light combination mirror is fixed in support platform, by the rotation of rotary shaft, light combination mirror rotation is driven, to adjust reference point source In the relative position of object plane, the rotation of rotary shaft drives the displacement of drawstring, the displacement distance of drawstring to be supervised by displacement detector It surveys, the displacement distance of drawstring is obtained by displacement detector, and then obtain the rotation angle of rotary shaft.

2. analysis of digital microscopy images as described in claim 1 records system, it is characterised in that：Computer controls driver driving rotation Shaft rotates, and during rotary shaft rotates, drives drawstring displacement, displacement detector detects the straight-line displacement of drawstring, when straight When displacement of the lines is equal to preset value, displacement detector sends out signal, and to computer, control rotary shaft is stopped rotating in turn, described default Value needs the predetermined angular rotated corresponding with light combination mirror.

3. a kind of micro-image recording method records system using the micro-image described in claims 1 or 22, records the object The best hologram that light wave and the reference light wave are formed, the reproduction image Central Plains that can be obtained after the best hologram is reconstructed Beginning picture, conjugate image and intermediate distracter just detach.