CN102122513B - Coaxial recording device for digital hologram of transparent substance based on beam-splitting property of Fresnel biprism - Google Patents

Abstract

The invention relates to a coaxial digital holographic measuring device for a transparent substance based on the beam-splitting property of a Fresnel biprism. The measuring device consists of a laser, a beam expander, a transparent object to be measured, a Fresnel biprism, a CCD (charge coupled device) camera and the like. In the invention, after light sent by the laser is expanded, one part of the light is projected on the Fresnel biprism through the object to be measured and then is split into two beams which form an included angle, and interference information between the two beams is recorded by the CCD camera; and meanwhile one coherent beam of the two beams passes through the object to be measured, thus forming a hologram carried with object information. The device has the advantages of fewer components, simple structure and good portability; and the recording device can be applied to testing structural and state parameters of the transparent substances such as a transparent medium, a living cell and the like.

Description

Coaxial transparent material digital hologram recording device based on Fresnel double prism

technical field

The invention relates to a coaxial transparent material digital holographic recording device based on Fresnel double prism light splitting, mainly used for measuring the structure and state parameters of transparent objects, that is, pure phase objects, such as living cells, optical fibers, micro slides, etc. Such as deformation and so on. the

Background technique

Digital holography technology is an important measurement technology developed in recent years, and has been widely used in object contour and state parameters. The recording methods used can be divided into two types, one is the coaxial recording method, the advantage is that only one beam of light is needed, and the device structure is often simple, but the digital hologram reproduction algorithm is more complicated, and there are certain requirements for the recording medium, such as transparency Advanced; the application is more off-axis recording method, the advantage is that when the digital hologram is reproduced, the object wave information is easy to separate, and the reproduction algorithm is easy to implement. The disadvantage is that it adopts the structure of split light path, and the composition of the light path is often complicated, requiring multiple optical devices, having high requirements for adjustment, and being greatly affected by vibration. the

The present invention attempts to invent a recording device to realize coaxial recording of off-axis holograms, so that when the hologram is digitally reproduced, the general off-axis hologram reproduction algorithm can be used to improve the anti-interference, easy adjustment and portability of the system sex. the

In the document "Transmission digital holographic microscopy based on a beam-splitter cube interferometer", a method of using a beam-splitting prism and basically incident along the beam-splitting plane to achieve single-beam coaxial recording is proposed. This method realizes single-beam recording of off-axis holograms, but the carrier frequency of holograms depends on the splitter prism, which requires the tester to have a certain understanding of the measurement principle to ensure that the state of the instrument meets the test requirements. the

Contents of the invention

The purpose of the device of the present invention is to provide a coaxial transparent material digital holographic recording device for Fresnel double prism light splitting in view of the defects in the prior art, which uses the coaxial optical path to realize the recording of off-axis holograms, and can facilitate adjust the recording magnification accordingly. the

For achieving the above object, design of the present invention is:

The present invention utilizes the spectroscopic characteristic of the Fresnel biprism and the crossing angle between the split beams to realize two performances of splitting and introducing carrier frequency, and does not need to adjust the optical path to introduce carrier frequency in the test. The recording device is composed of a laser, a beam expander, a Fresnel double prism and a CCD device. It has the following characteristics: it is a coaxial digital hologram recording system; there is a carrier wave in the interference signal and does not need to be adjusted during the measurement. The optical path is conducive to the separation of object-wave information in the digital reproduction of holograms; two functions of light splitting and carrier wave are realized by using a Fresnel biprism; the dynamic performance is good, not only can realize the three-dimensional structure measurement of transparent objects, but also can realize deformation detection ; The recording device records a lensless magnified hologram, which is convenient for flexible adjustment of the recording magnification; the device has few components, simple structure, and good portability; the recording device can be applied to transparent substances, such as transparent media and living bodies Structural and state parameter testing of cells etc.

According to above-mentioned inventive conception, the present invention adopts following technical scheme:

A digital hologram recording device for transparent matter based on Fresnel double prism light splitting, comprising a laser, a beam expander assembly, a Fresnel double prism, a CCD camera, a baffle plate and a computer, characterized in that The beam expander assembly is arranged on the optical path of the emitted beam of the laser, the object to be measured is arranged in the optical path between the beam expander assembly and the Fresnel prism, and on the optical path behind the Fresnel double prism The CCD camera is set to be aligned with the Fresnel double prism, and a baffle plate is set on the periphery of the CCD camera, and the CCD camera is connected to a computer; after the beam emitted by the laser passes through the beam expander assembly, a part of the light passes through the measured object, and then passes through the phoenix The Nel biprism splits the light, and the rest of the non-measurement beams are absorbed or blocked by the baffle plate, and the overlapping area signals of the two beams are received by the CCD camera, and the CCD camera transmits the collected image information to the computer.

In the above-mentioned digital hologram recording device, the beam expander assembly is composed of a reflector arranged on the optical path behind a spatial filter, and a negative lens arranged behind the reflector. Wherein the spatial filter (2) can obtain a spherical wave, and the mirror (3) plays the role of beam steering, so as to save the overall lateral length dimension of the recording system. the

In the above digital hologram recording device, the negative lens (4) can be moved to obtain light beams with different degrees of diffusion. the

In the above-mentioned digital hologram recording device, the measured object (5) is placed between the negative lens (4) and the Fresnel double prism (6), and the measured sample is a pure phase object, i.e. a transparent object, placed Below the centerline of the system, it is guaranteed that the wavefront passing through the sample remains intact after beam splitting. the

In the above digital hologram recording device, the CCD camera (8) can move laterally to change the magnification of the measured object. the

In the above digital hologram recording device, the CCD camera (8) is connected to a computer (9) equipped with an image acquisition card. the

In the above-mentioned digital hologram recording device, the structural requirement of the Fresnel double prism (6) is that the size of its vertex angle requires the introduction of an appropriate carrier frequency in the hologram to ensure that the object wave in the digital reproduction of the hologram Can be separated from zero-order and conjugate images. the

Description of drawings

Fig. 1 is a structural block diagram of an embodiment of the present invention. the

FIG. 2 is a schematic structural diagram of the example in FIG. 1 . the

FIG. 3 is a diagram of specific optical path parameters in FIG. 2 . the

FIG. 4 is a schematic diagram of interference fringes generated by the optical path in FIG. 3 . the

Fig. 5 is a process diagram of a digital reproduction method of a digital hologram. the

Detailed ways

Preferred embodiments of the present invention are described in detail as follows in conjunction with the accompanying drawings:

Embodiment one:

Referring to Fig. 1 and Fig. 2, the coaxial transparent material digital hologram recording device of this Fresnel double prism beam splitting device includes a laser (1), a beam expander assembly (2-4), and a Fresnel double prism (6), a CCD camera (8), a baffle plate (7) and a computer (9), characterized in that the beam expander assembly (2-4) is set on the optical path of the beam emitted by the laser (1) ), place the measured object (5) in the optical path between the beam expander assembly (2-4) and the Fresnel prism (6), and place the measured object (5) on the optical path behind the Fresnel double prism (6) The CCD camera (8) is set to align with the Fresnel double prism (6), and a baffle plate (7) is arranged around the CCD camera (8), and the CCD camera (8) is connected to a computer (9); After the beam passes through the beam expander assembly (2-4), part of the light passes through the measured object (5), and then passes through the Fresnel double prism (6) to split the light, and the rest of the non-measurement beam is absorbed or blocked by the baffle plate (7), Signals of the overlapping area of the two beams of light are received by the CCD camera (8), and the CCD camera (8) transmits the collected image information to the computer (9).

Embodiment two:

Referring to Fig. 2, the present embodiment is basically the same as the first embodiment and the special features are as follows:

The beam expander assembly (2-4) is composed of a mirror (3) arranged on the optical path behind the spatial filter (2), and a negative lens (4) is placed behind the mirror (3); the spatial filter (2) ) and the negative lens (4) play the role of beam expansion, wherein the negative lens (4) is required to be installed on the guide rail so that it can move along the optical axis; the function of the mirror (3) is to turn the beam direction to reduce the overall The transverse overall length dimension of the device.

The object to be measured (5) is a transparent object, placed between the negative lens (4) and the Fresnel biprism (5), and required to be within the space beam angle below the optical axis. the

，其顶角

大小的选取需要根据被测物体尺寸、仪器总体尺寸、载波频率选取，比传统测量中采用的菲涅耳双棱镜的顶角大。  The refractive index of the Fresnel double prism (4) is

, whose top angle

The selection of the size needs to be selected according to the size of the measured object, the overall size of the instrument, and the carrier frequency, which is larger than the vertex angle of the Fresnel double prism used in traditional measurement.

The installation of the CCD camera (8) requires that it can move back and forth along the optical axis to change the magnification of the measured object. the

Embodiment three:

Referring to Fig. 2 and 3, present embodiment is identical with embodiment two, and its working principle is as follows: the light beam that laser (1) sends is focused on point S after spatial filter (2), because negative lens (4) has divergence to light beam Therefore, after passing through the negative projection lens (4), the converging point of the light beam is S', that is, the light beam passing through the negative lens (4) can be regarded as being emitted through the point S'. Investigate the overlapping area (that is, the area received by the CCD camera (8)) of the two beams of light after passing through the Fresnel double prism (6), and set the included angle of the Fresnel double prism (6) as θ , the prism The refractive index is n , then the opening angle of the beam corresponding to the overlapping area is:

                                     (1)

(1)

                                      (2)

(2)

As shown in Figure 3, assuming that the distance between the beam converging point S of the spatial filter (2) and the negative lens (4) is -l , and the focal length of the negative lens (4) is f' , then according to the optical imaging theory, the virtual image The distance between point S' and the negative lens (4) is:

                                         (3)

(3)

As shown in Figure 3, if the distance between the negative lens (4) and the bottom surface of the Fresnel double prism (6) is p , and the distance between the bottom surface of the Fresnel double prism (6) and the CCD receiving surface is q , then The width of the interference area, that is, the range that the CCD should receive is:

                      (4)

(4)

As shown in Figure 4, it is the equivalent optical path of this recording system, that is, the light emitted from S' is divided into two beams through the Fresnel biprism, which can be equivalent to the light emitted from S ₁ ', S ₂ ' in space overlapping interference. Therefore, the object under test should be placed within the shaded area in Figure 4.

As shown in Figure 4, assuming that the distance between the equivalent light source points S ₁ ' and S ₂ ' is d , the introduced carrier frequency is:

                              (5)

(5)

As shown in Figure 4, suppose the distance between the measured object (5) and the CCD receiving surface is L, and the size of the receiving surface of the CCD is equal to the interference area width M, then the size of the object that can be recorded is:

     

  (菲涅耳算法)                    (6)

(Fresnel algorithm) (6)

                                          (7) 

(7)

     

  (卷积算法)                               (8)

(Convolution Algorithm) (8)

As shown in Figures 2, 3, and 4, by adjusting the negative lens (4), adjust the position of S', thereby achieving the purpose of adjusting the width of the CCD recording area (that is, the size of the interference area) and the carrier frequency.

As shown in Figures 2, 3 and 4, by adjusting the position of the CCD camera (8) and adjusting the distances L and D, the size and magnification of the recordable object can be realized. the

As shown in Figure 5, the collected digital hologram is first subjected to Fourier transformation, and the object wave information at the recording plane is extracted from the spectrogram, and then the Fresnel algorithm or convolution algorithm is used for digital reconstruction, and the object wave information obtained from the reconstruction From the original object wave information at the location, the amplitude and phase information of the recorded object is obtained. The calculation formula of Fresnel algorithm is:

             （9）

(9)

                  （10）

(10)

    （11）

(11)

为从频谱图中提出的记录平面处物波信息，

为再现参考光波，

代表CCD记录平面的坐标，

代表再现平面坐标，

，

为CCD摄像机两个方向的像素间隔，

 为被测物体到CCD记录平面的距离，

为记录光源的波长。 In the formula,

is the object wave information at the recording plane proposed from the spectrogram,

To reproduce the reference wave,

Represents the coordinates of the CCD recording plane,

represents the reproduction plane coordinates,

,

is the pixel interval of the CCD camera in two directions,

is the distance from the measured object to the CCD recording plane,

to record the wavelength of the light source.

The calculation formula of the convolution algorithm is:

(12)

          （13）

(13)

The amplitude distribution of the reproduced original object wave is:

                            （14）

(14)

表示绝对值运算。               In the formula:

Indicates an absolute value operation.

                            （15）

(15)

表示取相角运算。 In the formula:

Indicates the phase angle operation.

Claims (2)

1. A coaxial transparent material digital hologram recording device with a Fresnel double prism splitting light, comprising a laser (1), a beam expander assembly (2-4), a Fresnel double prism (6), A CCD camera (8), a baffle plate (7) and a computer (9), characterized in that the beam expander assembly (2-4) is provided with a reflective light on the optical path behind a spatial filter (2) mirror (3), a negative lens (4) is placed behind the mirror (3); the spatial filter (2) and the negative lens (4) play the role of beam expansion, and the negative lens (4) is required to be installed on the guide rail above, so that it can move along the direction of the optical axis; the role of the reflector (3) is to deflect the direction of the beam to reduce the overall lateral length of the device, and set the beam expander on the optical path of the laser (1) emitting beam component (2-4), the measured object (5) is placed in the optical path between the beam expander component (2-4) and the Fresnel double prism (6), and the Fresnel double prism ( 6) Set the CCD camera (8) on the rear optical path to align with the Fresnel double prism (6), set a shielding plate (7) around the CCD camera (8), and connect the CCD camera (8) to the computer (9 ); after the beam emitted by the laser passes through the beam expander assembly (2-4), a part of the light passes through the measured object (5), and then passes through the Fresnel double prism (6) to split the light, and the rest of the non-measurement beam is blocked by the baffle ( 7) Absorption or blocking, the overlapping area signal of the two beams of light is received by the CCD camera (8), and the CCD camera (8) transmits the collected image information to the computer (9); The measured object (5) is a transparent object placed between the negative lens (4) and the Fresnel double prism (5), and is required to be within the space beam angle below the optical axis; The refractive index of the Fresnel double prism (6) is

, whose top angle The selection of the size needs to be selected according to the size of the measured object, the overall size of the instrument, and the carrier frequency, which is larger than the vertex angle of the Fresnel double prism used in traditional measurement. 2. the coaxial type transparent material digital hologram recording device of Fresnel double prism light splitting according to claim 1, it is characterized in that described CCD camera (8) installation requirement can move back and forth along the optical axis direction, to change by The magnification of the measured object.

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