CN106325032B - A kind of adjustable digital hologram recording device of off-axis angle real-time accurate - Google Patents

Abstract

The invention discloses a digital holographic recording device whose off-axis angle can be precisely adjusted in real time. Compared with the digital holographic recording device in the prior art, the present invention adds a small monitoring optical path and a method of adjusting the fine-tuning screw of the mirror to control and measure the off-axis angle. Using the designed optical path generated by the digital holographic recording device of the present invention, the reflection direction of the detection reference light can be adjusted to realize the conversion of coaxial and off-axis holography; the off-axis angle can also be adjusted and detected to obtain the best off-axis in off-axis holography Angle, so that the original object image can be just separated, effectively using the resolution and spatial bandwidth of the CCD; it can also correct the object light recovery error caused by the slight tilt of the reference light in coaxial digital holography.

Description

A digital holographic recording device with real-time precision adjustable off-axis angle

technical field

The invention relates to a digital holographic recording device whose off-axis angle can be precisely adjusted in real time.

Background technique

Among many three-dimensional imaging and display technologies, holography is one of the most effective three-dimensional imaging technologies so far. This technology uses the reference light as the carrier wave to interfere with the object light wave to form interference fringes. The object light information (including amplitude and phase) is solidified into the interference fringes to form a hologram. Diffraction out, continue to propagate forward. In order to avoid the interference of direct light and negative primary image during reproduction, an off-axis recording method is usually used, that is, there is a certain angle between the reference light and the propagation direction of the object light. In holographic recording, the resolution of the recording medium limits the maximum value of the off-axis angle, while the size, resolution and recording distance of the recording object limit the minimum value of the off-axis angle. The off-axis angle should not be too large or too small. If the angle is too large, the interference fringes cannot be recorded accurately; if the angle is too small, the original object light cannot be completely separated.

Due to the omission of cumbersome procedures such as fixing, development and film processing of optical wet holography, the shortcomings of inaccurate positioning have been overcome, and digital holography that has emerged in recent years has been widely used in many aspects of scientific research, engineering technology, and biomedicine. Digital holography uses a modern photoelectric recording device CCD to replace the dry plate to record interference fringes, and uses a computer to process the interferogram, which can effectively utilize powerful modern computing technology. However, limited by the manufacturing process, the resolution of the existing CCD is on the order of microns, which is 1-2 orders of magnitude lower than that of the silver salt dry plate. This requires a smaller off-axis angle during digital holographic recording, generally below 2-3 degrees, while ensuring enough off-axis angle to separate the original image.

Existing digital holographic recording devices have the following problems in practical applications:

(1) The current off-axis holographic optical path adjustment mainly depends on the experience and skills of the experimenters to roughly determine. There is no mature technology to accurately determine the off-axis angle, and it is impossible to accurately control the off-axis angle.

(2) When determining the off-axis angle, the off-axis angle is calculated mainly by the ratio of the distance between the object light and the reference light spot and the propagation distance after beam splitting. However, since the object light and the reference light spot have a certain size , the distance between them is difficult to accurately measure, and it is easy to cause incorrect off-axis angles, which can only be adjusted repeatedly, and the efficiency is low.

(3) Accidental factors during the experiment, such as vibration, a single optical device being accidentally collided, causing the deflection of the reference optical path, it is necessary to restart the adjustment of the optical path; when the object to be recorded needs to be changed, if the size and resolution of the object to be recorded occur Changes, but also to re-adjust the optical path.

(4) The existing technology needs to adjust the off-axis angle in advance, and cannot change and detect the size of the off-axis angle in real time according to the needs of the experiment process, which brings inconvenience to the experiment and affects the experimental effect and accuracy.

(5) In the application of holographic measurement and imaging technology, the conversion of off-axis optical path and coaxial optical path needs to rebuild the optical path.

(6) Studies have shown that the tilt of the coaxial holographic reference light will introduce errors into the restored object light, causing the wavefront of the reconstructed object light to bend, reducing the measurement accuracy and imaging quality.

Contents of the invention

Aiming at the above-mentioned technical problems existing in the prior art, the present invention proposes a digital holographic recording device with real-time precision adjustable off-axis angle, which adopts the following technical solutions:

A digital holographic recording device with real-time precision adjustable off-axis angle, including laser light source, No. 1 beam splitter, No. 2 beam splitter, No. 1 beam combiner, No. 2 beam combiner, No. 1 reflector, No. 2 mirror, No. 3 mirror, No. 1 spatial filter beam expander collimation system, No. 2 spatial filter beam expander collimator system, No. 1 CCD, No. 2 CCD and computer; among them, based on No. 1 beam splitter, No. 2 combined The beam splitter, the first mirror and the third mirror form a rectangular interference light path for holographic interference recording; the second beam splitter, the first beam combiner, the second mirror and the third mirror form a The No. 2 rectangular interference optical path used to monitor the tilt angle of the reference light; the direction of the No. 1 rectangular interference optical path is: the laser beam emitted by the laser source passes through the No. 1 beam splitter and is divided into two beams. Among them, the laser beam transmitted through the No. 1 beam splitter The final beam is reflected by the No. 1 mirror and the No. 1 spatial filter beam expander and collimator system, and then becomes the object light illumination light. This plane wave irradiates the object to form a diffracted object light, which is reflected by the Fresnel diffraction and the No. 2 beam combiner When it arrives at the recording chip of the No. 1 CCD, the light beam reflected by the No. 1 beam splitter becomes the reference light. The reference light passes through the No. 2 beam splitter after passing through the No. 2 spatial filter beam expander and collimation system, and then is reflected by the No. 3 beam splitter. Mirror reflection, then transmitted through No. 1 beam combiner and No. 2 beam combiner in turn, and finally irradiated on the recording chip of No. 1 CCD; the direction of the No. 2 rectangular interference optical path is: the reference light is collimated by the No. 2 spatial filter beam expansion The system transmits through the No. 2 beam splitter, and then reflects through the No. 3 reflector and the No. 1 beam combiner in turn, and finally irradiates on the recording chip of the No. 2 CCD; the reference light reflected by the No. 2 beam splitter passes through the No. No. 1 mirror reflection and No. 1 beam combiner transmission reach the recording chip of No. 2 CCD; No. 1 rectangular interference optical path and No. 2 rectangular interference optical path are respectively provided with No. 1 for controlling the corresponding rectangular interference optical path to work or stop. Shutter and No. 2 shutter; An adjustment screw is provided on the rear side of the No. 3 reflector, which is used to adjust the pitch or horizontal angle of the No. 3 reflector; No. 1 CCD and No. 2 CCD are connected to the computer respectively.

Preferably, the No. 1 shutter is located between the No. 1 beam combiner and the No. 2 beam combiner; the No. 2 shutter is located between the No. 2 beam splitter and the No. 2 mirror.

Preferably, when the No. 1 shutter is open and the No. 2 shutter is closed, only the No. 1 rectangular interference light path is in working state; when the No. 2 shutter is opened and the No. 1 shutter is closed, only the No. 2 rectangular interference light path is in working state.

Preferably, the laser beam reflected on the No. 2 CCD recording chip through the No. 2 beam splitter and the No. 2 reflector interferes with the laser beam reflected on the No. 2 CCD recording chip through the No. 3 reflector and the No. 1 beam combiner Form detection interference fringes.

Preferably, before the digital holographic recording device is used, the No. 1 rectangular interference optical path and the No. 2 rectangular interference optical path are adjusted to be parallel and coaxial.

Preferably, the adjusting screws include horizontal adjusting screws and vertical adjusting screws.

Preferably, the No. 1 CCD and the No. 2 CCD have the same resolution.

Compared with the prior art, the present invention has the following advantages:

1. The present invention is equipped with a reference light monitoring optical path, and the off-axis angle can be accurately obtained by using the distribution of interference fringes, and at the same time, the off-axis angle can be precisely controlled to achieve the best angle of off-axis holography, so that the reproduced image can be just completely separated, Effective use of the resolution and spatial bandwidth of the CCD.

2. The present invention can adjust the off-axis angle in real time as needed during the experiment. Objects with different sizes and resolutions require different off-axis angles, which can be adjusted in real time as needed.

3. According to the needs of measurement and imaging, the present invention can realize the conversion of coaxial optical path and off-axis optical path only by precisely controlling the direction of reference light without changing the optical path during the experiment, so as to improve the experimental efficiency.

4. The reference light monitoring optical path in the present invention uses two-plane reference light to directly measure the inclination angle, which can be adjusted in real time.

5. The present invention is based on digital holographic technology, and the accuracy of angle measurement can reach one ten-thousandth of a radian. The construction of the digital holography experimental optical path is relatively simple, and the angle measurement method adopted is relatively easy to implement.

6. The present invention can also correct the object light recovery error caused by the slight tilt of the reference light in coaxial digital holography.

Description of drawings

Fig. 1 is an optical path diagram of a digital holographic recording device with real-time precision adjustable off-axis angle in the present invention;

Fig. 2 is the interferogram (when the reference light is not tilted) of No. two CCD record monitoring optical path among the present invention;

Fig. 3 is the interferogram (when the reference light is inclined) of No. two CCD record monitoring optical path among the present invention;

Fig. 4 is an object light and reference light interferogram (when the reference light is inclined) that No. 1 CCD records among the present invention;

Fig. 5 is another object light and reference light interferogram (when reference light is inclined) that No. 1 CCD records among the present invention;

Fig. 6 is the optical phase diagram of the reduced object when the reference light is tilted in the present invention;

Fig. 7 is an object light and reference light interferogram (when the reference light is not tilted) that No. 1 CCD records among the present invention;

Fig. 8 is another object light and reference light interferogram (when the reference light is not tilted) that No. 1 CCD records among the present invention;

Fig. 9 is the optical phase diagram of the reduced object when the reference light is not tilted in the present invention;

Fig. 10 is the optical phase diagram of the restored object corrected when the reference light is tilted in the present invention;

Among them, 1-laser light source, 2-beam splitter No. 1, 3-beam splitter No. 2, 4-beam combiner No. 1, 5-beam combiner No. 2, 6-reflector No. 1, 7-No. 2 beam Mirror, 8-mirror No. 3, 9-CCD No. 1, 10-CCD No. 2, 11-computer, 12-space filtering beam expansion collimation system No. 1, 13-space filtering beam expansion collimation system No. 2, 14-shutter one, 15-shutter two, 16-object.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment the present invention is described in further detail:

As shown in Figure 1, a digital holographic recording device with real-time precision adjustable off-axis angle, including a laser light source 1, No. 1 beam splitter 2, No. 2 beam splitter 3, No. 1 beam combiner 4, No. 2 combiner Beamer 5, No. 1 reflector 6, No. 2 reflector 7, No. 3 reflector 8, No. 1 spatial filter beam expander collimation system 12, No. 2 spatial filter beam expander collimator system 13, No. 1 CCD 9, No. 2 CCD10 and computer 11. in,

Based on the No. 1 beam splitter 2, the No. 2 beam combiner 5, the No. 1 mirror 6 and the No. 3 mirror 8, a No. 1 rectangular interference optical path is formed for holographic interference recording.

Based on the No. 2 beam splitter 3, the No. 1 beam combiner 4, the No. 2 reflector 7 and the No. 3 reflector 8, a No. 2 rectangular interference optical path is formed, which is used to monitor the tilt angle of the reference light.

In Figure 1, the solid line represents the optical path when the reference light and the object light are coaxial, that is, the on-axis holographic recording optical path; the dotted line represents the actual optical path when the reference light is off-axis, that is, the off-axis holographic recording optical path.

The functions of No. 1 spatial filtering beam expanding collimation system 12 and No. 2 spatial filtering beam expanding collimating system 13 are to carry out spatial filtering beam expanding and collimating the laser beam emitted by the laser light source. device.

The direction of the No. 1 rectangular interference light path is:

The laser beam emitted by the laser source 1 is divided into two beams after passing through the No. 1 beam splitter 2, and the beam transmitted through the No. Become the object light illumination light, this road plane wave irradiates on the object 16 to form diffracted object light, after Fresnel diffraction and No. The light beam becomes the reference light, and the reference light passes through the No. 2 beam splitter 3 after passing through the No. 2 spatial filtering beam expander collimation system 13, and then is reflected by the No. 3 mirror 8, and then transmits through the No. 1 beam combiner 4 and No. The beam combiner 5 finally irradiates on the recording chip of No. 1 CCD9.

The trend of the No. 2 rectangular interference optical path (located in the dotted line box in Figure 1) is:

The reference light is transmitted through the No. 2 beam splitter 3 after being passed through the No. 2 spatial filtering beam expander collimation system 13, and then reflected by the No. 3 mirror 8 and the No. 1 beam combiner 4 in turn, and finally irradiated on the recording chip of the No. 2 CCD 10 ; The reference light reflected by No. 2 beam splitter 3 is then reflected by No. 2 reflector 7 and transmitted by No. 1 beam combiner 4 and arrives on the recording chip of No. 2 CCD10.

The laser beam reflected by the No. 2 beam splitter and the No. 2 mirror and reaching the No. 2 CCD recording chip interferes with the laser beam reflected by the No. 3 mirror and No. 1 beam combiner and reaches the No. 2 CCD recording chip to form detection interference. stripe.

A first shutter 14 and a second shutter 15 for controlling the corresponding rectangular interference optical path to work or stop are respectively arranged on the first rectangular interference optical path and the second rectangular interference optical path.

Specifically, the No. 1 shutter 14 is located between the No. 1 beam combiner 4 and the No. 2 beam combiner 5 ; the No. 2 shutter 15 is located between the No. 2 beam splitter 3 and the No. 2 mirror 7 .

When No. 1 shutter 14 is opened and No. 2 shutter 15 is closed, only No. 1 rectangular interference light path is in working state; when No. 2 shutter 15 is opened and No. 1 shutter 14 is closed, only No. 2 rectangular interference light path is in working state.

In addition, an adjustment screw (not shown in the figure) is provided on the rear side of the third reflector 8 for adjusting the pitch or horizontal angle of the third reflector 8 . No. 1 CCD9 and No. 2 CCD10 are connected with computer 11 respectively.

The above-mentioned adjusting screws include horizontal adjusting screws and vertical adjusting screws. Wherein, the horizontal adjustment screw is used to adjust the horizontal angle of the third reflector 8 , and the vertical adjustment screw is used to adjust the pitch angle of the third reflector 8 .

Before using the digital holographic recording device, adjust the parallelism and coaxiality of the optical paths, so that the No. 1 rectangular interference optical path and the No. 2 rectangular interference optical path are both in the parallel and coaxial state. If the coaxial digital hologram needs to be recorded, the optical path has reached the working state. Under strict conditions, the reference light wave and the object light wave in coaxial digital holography need to be coaxial, but this requirement is often not met in experiments, and the reference light is more or less non-coaxial with the object light. The inclination of the reference light during the experiment can be monitored on the No. 2 CCD10 to ensure the success of the coaxial recording. Even if the reference light is tilted, the interference fringes can be recorded and processed to obtain the tilt angle and correct the measurement results. Of course, the horizontal or vertical adjustment screw behind the No. 3 reflector 8 can also be adjusted for on-line adjustment without readjusting the entire optical path. At this time, it is necessary to observe the width of the interference fringes on the No. 2 CCD10 to judge whether the optical path is coaxial. The wider the interference fringes, the smaller the off-axis angle; Obviously, adjusting the pitch or horizontal angle of the third reflector 8 adjusts the angle between the reference light and the object light, so that the optical path is in the off-axis or on-axis digital holographic recording state. Further analysis of the fringe distribution on the No. 2 CCD10 can accurately obtain the size of the off-axis angle, and realize real-time and accurate monitoring of the off-axis angle. Under the existing instrument conditions, the accuracy can reach one ten-thousandth of a radian. By calculating and controlling the off-axis angle, the optical path can be in the best state.

It should be noted that only the recording optical path of the transmissive object under test is shown in FIG. 1 , and the device in the present invention is also applicable to the recording optical path of the reflective object. Adding the detection optical path to any other reflective object digital holographic recording optical path can complete the function of real-time precise detection.

The specific process of utilizing the present invention to measure the off-axis angle is given below:

1. Maximum off-axis angle calculation

In the coaxial optical path, after passing through the No. 2 beam combiner 5, the reference beam and the object beam overlap in parallel. Keep the No. 2 beam splitter 3, the No. 2 reflector 7 and the No. 1 beam combiner 4 fixed, and the slight inclination angle θ of the No. 3 reflector 8 will cause the reference light entering the No. 2 beam combiner 5 to incline at an angle of θ, The reference light reflected by No. 3 reflector 8 and No. 1 beam combiner 4 successively and entering No. 2 CCD 10 also has the same inclination θ. The included angle θ is formed between the reference light reflected by No. 2 reflector 7 and transmitted by No. 1 beam combiner 4 successively, and the reference light reflected by No. 3 reflector 8 and No. 1 beam combiner 4 successively. Obvious interference fringes appear on the chip. The straight fringe spacing of the interference pattern captured by No. 2 CCD10 is:

d=λ/[2sin(θ/2)] (1)

In the formula, λ is the laser wavelength. The interference fringe width can be calculated by dividing the chip size of No. 2 CCD10 by the total number of fringes. Generally, the angle of inclination is small. Especially for digital holography, the off-axis angle is generally about 2 degrees, and the fringe width can be calculated to be about 29 wavelengths. If the laser wavelength is 0.532 microns and the chip size of No. 2 CCD10 is 0.5 cm, there will be hundreds of fringes. The fringe width d can be calculated by performing Fourier transform on the interferogram, finding the coordinates corresponding to the fringe frequency, and obtaining the fringe spacing. After calculating the fringe spacing d, the off-axis angle can be obtained:

θ=2arcsin[λ/(2d)] (2)

The fringe spacing during recording is at least twice the pixel size Δl, i.e.:

θ=2arcsin[λ/(4Δl)] (3)

If Δl is 6 microns and the wavelength is 0.532 microns, it can be calculated that the maximum off-axis angle is about 2.5 degrees.

When there is only one stripe on the recording surface and the size of the No. 2 CCD10 chip is 1 centimeter, the off-axis angle can be 0.00005 radians or three thousandths of a degree.

It can be seen from the above calculation results that the accuracy of the recording device in the present invention can reach one ten-thousandth of an arc.

2. Minimum off-axis angle calculation

In off-axis holography, the minimum recording angle that can separate the original image is determined by the wavelength of the recording laser and the resolution of the recording object. There is a relationship:

θ _min = arcsin(3λ/Δx) (4)

In the formula, λ is the wavelength of the recording laser, and Δx is the resolution of the object, that is, the smallest size that can be resolved.

Assuming that the resolution of the object is 50 microns and the laser wavelength is 0.532 microns, it can be calculated that the minimum off-axis angle is 1.8 degrees. As the object resolution increases, the required minimum off-axis angle becomes larger.

When calculating the angle, the angles in the horizontal and vertical directions can be calculated separately according to the needs, and then converted according to the relationship between the spatial directions to obtain the total off-axis angle.

If there is a small off-axis angle between the reference beam and the object beam when the device is used for coaxial digital holographic recording, there will be errors in the restored original object beam. After processing the interference fringe data recorded by the No. 2 CCD10 to obtain the tilt angle value, the spatial frequency of the fringe distribution in two directions can be obtained. Substituting it into the wavefront correction formula for recovering the object light on the No. 1 CCD9 recording surface can automatically eliminate this off-axis error due to angle. Similar work is introduced and confirmed in the following examples.

3. Example of off-axis angle monitoring

In order to verify the monitoring method of the device for the off-axis angle, the present invention uses the above-mentioned digital holographic recording optical path to conduct an off-axis angle measurement experiment. The angle between the two beams of plane waves corresponding to the interferogram recorded in the No. 2 CCD10 is the same as the off-axis angle in the holographic experimental optical path, that is, the interference fringe information collected by the No. 2 CCD10 can be used to represent the off-axis in the holographic interference optical path angle.

Close the No. 1 shutter 14, open the No. 2 shutter 15, and the off-axis angle measurement part starts to work. Use the No. 2 CCD10 to record the interferogram of the measuring light path, and the results are shown in Figure 2. Open No. 1 shutter 14, close No. 2 shutter 15, No. 1 CCD 9 records the holographic interferogram when the reference light is not tilted, and imports it into computer 11. Close No. 1 shutter 14 again, open No. 2 shutter 15, fine-tune the horizontal adjustment screw behind No. 3 reflector 8, make interference fringes appear on the recording surface of No. 2 CCD 10, import computer 11 after recording, the result is shown in Figure 3 . Open No. 1 shutter 14 again, close No. 2 shutter 15, and No. 1 CCD9 records the holographic interferogram when the reference light is tilted, and imports it into computer 11. In Figure 2, almost no interference fringes can be seen, because the two beams of interference light are in a parallel and coaxial state, and the interference fringes are very wide. Obviously, a lot of interference fringes appear in Figure 3, because one beam of light is tilted, the two beams of interference light have a small angle, and the interference fringes become narrower. Considering the inclination in the horizontal direction, it is necessary to observe the number of stripes in the horizontal direction, which is 16.5 in total. Considering the inclination in the vertical direction, it is observed that the number of stripes in the vertical direction is 6.5 in total. From formula (2), it can be calculated that the off-axis angle in the horizontal direction is 0.001 radians, which is equivalent to about 0.06 degrees; the off-axis angle in the vertical direction is 0.0005 radians, which is equivalent to about 0.03 degrees.

From the comparison of Figure 2 and Figure 3, it can be seen that when the reference light is not tilted, the image collected by the No. 2 CCD10 is a uniform light spot without obvious straight stripes. In the actual experiment, it needs to be patiently adjusted until there are no stripes on the screen. When the reference light is slightly inclined relative to the object light, fringes will appear on the No. 2 CCD10, and with the increase of the inclination angle, the fringes will become denser until the fringes are invisible, and it is necessary to carefully distinguish between the two types of invisible fringes. situation. From the inclination of the stripes in Figure 3, the inclination angle of the reference light can be calculated and provided to the correction algorithm for correction.

The experiment employs on-axis generalized phase-shift digital holography to observe a slightly tilted off-axis corrected reference light.

In order to test the accuracy of the measurement method, the reference light tilt detection method is applied in the phase-shift digital holography technology example, and the result obtained by bringing the off-axis angle obtained by this off-axis angle measurement method into the recovery object light correction formula is compared with the untilted The results of time-object optical reconstruction were compared and verified.

In the experiment, a slightly divergent spherical light wave is used as the object light wave. In the experimental light path in Fig. 1, the first shutter 14 and the second shutter 15 are used to isolate the interaction between the detection light path and the holographic recording light path.

The images collected on the recording surface of the No. 1 CCD9 are divided into two situations, which are two interference diagrams of the object light and the reference light when the reference light is inclined and non-inclined, as shown in Figure 4, Figure 5 and Figure 8, respectively. Figure 9 shows.

In the generalized phase-shift digital holographic two-step restoration algorithm, the extraction of the phase shift value needs to be extracted from two holograms, and the No. 1 CCD9 records two holograms (Fig. 4 and Fig. 5). The phase shift value between the two holograms extracted in the two-step restoration algorithm is 0.9241 rad, and the phase diagram of the restored object light has a large shift when the tilted reference light is not corrected, as shown in Figure 6. In order to display the details of the phase map more clearly, when restoring the phase map in Figure 6, we zero-filled the 1390×1024 pixels on the CCD recording surface to 1990×1990 pixels. It can be clearly seen that the ring of the phase diagram is not in the center of the diagram.

It can be seen from the above figure 6 that when the reference light is tilted, it will not only cause errors in the hologram collected by the No. 1 CCD9, but this error will always accompany the object light reconstruction process, resulting in phase distortion of the restored image relative to the original image. Using the reference light tilt correction algorithm can solve this problem.

After calculating the inclination angle of 0.06 degrees in the horizontal direction and 0.03 degrees in the vertical direction, the corrected restored image can be obtained through the tilt reference light correction algorithm. Comparing the optical phases of the restored object without tilting together, it can be found that the correction algorithm can well correct the distortion of the optical phase of the restored object caused by the tilt of the reference light.

Figure 7 and Figure 8, Figure 9, and Figure 10 are the two interferograms when no tilt occurs, the restored phase, and the phase diagram after the correction of the restored object light when tilted. From the phase distributions in Figure 6 and Figure 9, it can be seen that the central ring of the restored image with tilted reference light is significantly shifted compared with that without tilt, and the correction algorithm can effectively eliminate the distortion of the restored object light in this respect when the reference light is tilted. The error, shown in the figure, is that the off-center ring in Figure 6 is corrected to the center of Figure 10, and the phase distribution figure 10 is basically consistent with Figure 9. Since the range of object light information received by the CCD becomes smaller when the incidence is oblique, the fringe range in the corrected phase diagram 10 will naturally decrease. It can be seen that the off-axis angle measured in the experiment is correct, and the theoretical accuracy can reach one ten-thousandth of a radian.

The optical path design in the present invention uses the interference of two beams of reference light plane waves, and the interferogram is straight fringes distributed at equal intervals, which is not only beneficial for counting the number of fringes to measure the angle, but also beneficial for spectrum analysis of the interferogram.

The measurement accuracy of the method in the present invention is very high, and the maximum off-axis angle measured is limited by the resolution of the second CCD10. According to formula (2), if Δl is 5 microns and the laser wavelength is 0.532 microns, it can be calculated that the maximum off-axis angle is about 3 degrees. Improving the resolution of the No. 2 CCD10 can greatly increase the measurement range. If two CCDs have the same resolution, they can be used to detect the off-axis angle of digital holography. Due to the diffraction effect of the object light, the fringe density of the interference pattern of the diffracted object light and the reference light will be greater than the fringe density of the interference pattern of the two reference lights. When the off-axis angle reaches that No. 2 CCD10 cannot distinguish fringes, No. 1 CCD9 can no longer record holograms.

Of course, the above descriptions are only preferred embodiments of the present invention, and the present invention is not limited to the above-mentioned embodiments. It should be noted that all equivalent substitutions made by any person skilled in the art under the teaching of this specification , obvious deformation forms, all fall within the essential scope of this specification, and should be protected by the present invention.

Claims (5)

1. A digital holographic recording device with real-time and precise adjustable off-axis angle is characterized by comprising a laser light source, a first beam splitter, a second beam splitter, a first beam combiner, a second beam combiner, a first reflector, a second reflector, a third reflector, a first spatial filtering and beam expanding collimation system, a second spatial filtering and beam expanding collimation system, a first CCD, a second CCD and a computer; the holographic interference device comprises a first beam splitter, a second beam combiner, a first reflector and a third reflector, wherein a first rectangular interference light path for holographic interference recording is formed on the basis of the first beam splitter, the second beam combiner, the first reflector and the third reflector; a second rectangular interference light path for monitoring the inclination angle of the reference light is formed based on the second beam splitter, the first beam combiner, the second reflector and the third reflector; the first rectangular interference light path has the following trend: a laser beam emitted by a laser source is divided into two beams after passing through a first beam splitter, wherein the beam transmitted by the first beam splitter is reflected by a first reflector and is expanded by a first spatial filtering beam-expanding collimation system to form object light, the one path of plane wave irradiates an object to form diffracted object light, the diffracted object light is reflected by a Fresnel diffraction and a second beam combiner and reaches a recording chip of the first CCD, the beam reflected by the first beam splitter becomes reference light, the reference light passes through the second beam splitter after passing through the second spatial filtering beam-expanding collimation system, is reflected by a third reflector, then sequentially passes through the first beam combiner and the second beam combiner, and finally irradiates the recording chip of the first CCD; the direction of the second rectangular interference light path is as follows: the reference light is transmitted through a second beam splitter after passing through a second spatial filtering beam expanding collimation system, then is reflected by a third reflector and a first beam combiner in sequence, and finally is irradiated on a recording chip of a second CCD; the reference light reflected by the second beam splitter is reflected by the second reflecting mirror and transmitted by the first beam combiner to reach a recording chip of the second CCD; a first shutter and a second shutter for controlling the corresponding rectangular interference light path to be in a working or stopping state are respectively arranged on the first rectangular interference light path and the second rectangular interference light path; an adjusting screw is arranged on the rear side of the third reflector and used for adjusting the pitching or horizontal angle of the third reflector; the first CCD and the second CCD are respectively connected with a computer; the first shutter is positioned between the first combiner and the second combiner; the second shutter is positioned between the second beam splitter and the second reflector; when the first shutter is opened and the second shutter is closed, only the first rectangular interference light path is in a working state; when the second shutter is opened and the first shutter is closed, only the second rectangular interference light path is in a working state.

2. The real-time precise adjustable off-axis angle digital holographic recording device as claimed in claim 1, wherein the laser beam reflected by the beam splitter and the beam splitter II and reaching the CCD recording chip II interferes with the laser beam reflected by the beam splitter and the beam combiner I and reaching the CCD recording chip II to form the detection interference fringe.

3. The real-time precise off-axis angle adjustable digital holographic recording device as claimed in claim 1, wherein the first rectangular interference optical path and the second rectangular interference optical path are adjusted to be parallel and coaxial before the digital holographic recording device is used.

4. The apparatus of claim 1, wherein the adjusting screws comprise a horizontal adjusting screw and a vertical adjusting screw.

5. The real-time precise off-axis angle adjustable digital holographic recording device of claim 1, wherein the first CCD and the second CCD have the same resolution.