CN114061769A - Device and method for measuring laser wavelength based on coaxial holographic self-focusing technology - Google Patents
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Abstract
The invention discloses a device and a method for measuring laser wavelength based on a coaxial holographic self-focusing technology, which comprises a laser input end, a collimation and beam expansion system, a resolution plate and a CCD (charge coupled device) which are sequentially arranged, wherein the resolution plate is irradiated by laser to generate object light containing object information, the CCD records the acquired light intensity distribution and generates a hologram, and the coaxial holographic self-focusing technology of the resolution plate is utilized and the function relation of the wavelength and the recording distance or the optimal reproduction distance is combined to measure unknown laser wavelength. The invention enriches the measuring method of the laser wavelength, has the advantages of simple structure, low cost, automatic calculation of the wavelength and the like, is convenient to popularize and apply, can greatly shorten the acquisition time of the hologram, does not need other focusing devices, enables the system to be simple and efficient, has higher precision of the measured wavelength, can be applied to the field of industrial measurement, and can also be applied to teaching experiments in the directions of coaxial holographic transmission, diffraction transmission and the like.
Description
Technical Field
The invention relates to a laser wavelength measuring device and method, in particular to a device and method for measuring laser wavelength based on a coaxial holographic self-focusing technology.
Background
Laser has been a great invention of human beings since the 20 th century, following atomic energy, computers, and semiconductors. It can make scientists effectively use the unprecedented advanced methods and means to obtain huge results, thereby promoting the development of human social productivity. With the rise of modern laser technology, laser wavelength measurement is also very important, and at present, various methods are available for laser wavelength measurement, such as a michelson interferometer manufactured according to a double-beam principle, and laser wavelength measurement by using a grating, but most experimental devices are complex in instrument manufacturing, expensive in price, complex to operate and complex to calculate. There is a strong need in the industry for a method that can accurately obtain a wavelength in a simple and easy manner. With the development of semiconductor and microelectronic technologies, the performance of photosensitive electronic components such as pixel points, resolution and the like of image sensors is continuously improved, and in addition to the rapid development of high speed and large capacity, the advantages of digital holography technology are gradually shown and are paid more and more attention by researchers. U.S. shnars and W.Juptner used Fresnel off-axis digital holograms recorded with diffusely reflecting objects in 1994, and proposed a fast algorithm for digital reconstruction, the Fresnel transform method. The method realizes the calculation of Fresnel diffraction by using one-time fast Fourier transform, and is one of the most common fast algorithms for digital representation at present. The application of the current digital holography is very wide, and comprises the fields of optical device measurement, precision circuit board detection, biological cell measurement, granularity analysis, data storage and the like. This provides a new direction for seeking laser wavelength measurement methods.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to provide a device and a method for measuring laser wavelength based on a coaxial holographic self-focusing technology, which can simply and quickly measure the wavelength.
The technical scheme is as follows: the laser beam splitting device comprises a laser input end, a collimation and beam expanding system, a resolution plate and a CCD which are sequentially arranged, wherein the laser input end, the collimation and beam expanding system, the resolution plate and the CCD are positioned on the same optical axis, the resolution plate is irradiated by laser to generate object light containing object information, and the CCD records the acquired light intensity distribution and generates a hologram.
The collimation and beam expansion system comprises a first lens and a second lens which are arranged in sequence.
When the distance from the resolution plate to the CCD is fixed, the laser with different wavelengths irradiates the resolution plate, and then the obtained holograms on the CCD are different.
The laser input end can be replaced by different light sources, the precision of laser wavelength measurement is related to the step length (namely the sampling interval delta d) selected by a self-focusing algorithm, and the smaller the sampling interval delta d is, the higher the precision is.
A method for measuring laser wavelength based on a coaxial holographic self-focusing technology comprises the following steps:
(1) using laser with known wavelength as light source, collecting hologram a with CCD, and calculating actual distance d by self-focusing algorithm and substituting known wavelength1；
(2) Maintaining the actual distance d1Invariant, using unknown wavelength λ1The laser is used as a light source, and a hologram b is collected through a CCD;
(3) using the hologram b, a certain wavelength λ is selected2Calculating to obtain the distance d corresponding to the wavelength2；
(4) According to the formula lambda1d1＝λ2d2And calculating the unknown wavelength as: lambda [ alpha ]1＝λ2d2/d1。
The distance is a reproduction distance or a recording distance.
The actual distance is the distance from the resolution plate to the CCD.
The actual distance range is d which is more than or equal to 10mm1≦ 100mm for better acquisition of the on-axis hologram of the resolution plate.
The measurement range of the unknown wavelength depends on the photosensitive range of the CCD, and the wavelength from visible light to infrared band can be measured by selecting the appropriate CCD 5.
Has the advantages that: the invention enriches the measuring method of the laser wavelength, has the advantages of simple structure, low cost, automatic calculation of the wavelength and the like, is convenient to popularize and apply, can greatly shorten the acquisition time of the hologram, does not need other focusing devices, enables the system to be simple and efficient, has higher precision of the measured wavelength, can be applied to the field of industrial measurement, and can also be applied to teaching experiments in the directions of coaxial holographic transmission, diffraction transmission and the like.
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FIG. 1 is a schematic structural diagram of the present invention.
Detailed Description
The invention will be further explained with reference to the drawings.
As shown in fig. 1, the present invention includes a laser input end 1, a collimating and beam expanding system (including a first lens 2 and a second lens 3), a resolution plate 4 and a CCD5, which are sequentially arranged, wherein the laser input end 1, the first lens 2, the second lens 3, the resolution plate 4 and the CCD5 are located on the same optical axis and fixed on a guide rail, which is convenient for adjustment.
The invention applies the coaxial digital holography to the field of wavelength measurement, establishes the relation between the reproduction wavelength lambda and the reproduction distance d according to the Fresnel diffraction integral formula, realizes the rapidity and the automation of wavelength calculation by utilizing the self-focusing algorithm, enriches the existing method for measuring the wavelength, has simple device structure and is easy to popularize and apply. The self-focusing algorithm means that a reproduced image is calculated once by using a diffraction integral formula at every same distance delta d, the definition of the image is evaluated by using an evaluation function, and the transmission distance corresponding to the image with the highest definition is found by calculation and is the optimal reproduction distance.
The object (resolution plate 4) is irradiated by monochromatic plane waves with the wavelength of lambda to generate object light containing object information, the emitted plane waves penetrate through an object plane to form strong and uniform plane waves and weak diffraction waves, the two parts meet the coherence condition, and the CCD5 records the collected light intensity distribution at a certain position away from the object to generate a hologram. According to the Fresnel diffraction integral formula, the complex amplitude distribution of the reconstructed light after the hologram is calculated by a computer, the diffraction process is simulated, and the clearest reconstructed image and the accurate distance d from the reconstructed image to the CCD5 are obtained by using a self-focusing algorithm.
When the distance from the resolution plate 4 to the CCD5 is fixed, holograms obtained on the CCD5 after the laser light of different wavelengths irradiates the object are different. Deducing and finding the light intensity distribution I of the reproduction surface by utilizing a Fresnel diffraction integral formulazIs a function of λ d, which can be written as IzF (λ d), where λ is the laser wavelength and d is the hologram to reconstruction surface distance. For a hologram obtained by irradiating an object with a certain wavelength, the following functional relationship is satisfied by calculating the optimal reproduction distance (or the recording distance) by using different wavelengths: lambda [ alpha ]1d1＝λ2d2Wherein d is1And d2Respectively substituting lambda into the self-focusing algorithm1And λ2The calculated optimal reproduction distance (or recording distance).
After holograms collected based on light waves with different wavelengths are reproduced, because an object does not change, the theoretically obtained complex amplitude distribution information is the same, and the relation between the optimal reproduction distance (or recording distance) d and the wavelength lambda is obtained by combining a Fresnel diffraction integral formula. When a light beam with unknown wavelength passes through the optical system, a hologram is obtained on the CCD and reproduced by computer simulation according to the function relation lambda of the distance d and the wavelength lambda1d1＝λ2d2The size of the unknown wavelength can be determined by calculation.
The laser wavelength measuring method comprises the following steps:
(1) using laser with known wavelength as light source, collecting hologram a with CCD5, and calculating actual recording distance d by self-focusing algorithm and substituting known wavelength1I.e. the distance from the resolution plate 4 to the CCD5, the distance from the resolution plate 4 to the CCD5 is within the range of 10mm < d > in order to better collect the coaxial hologram of the resolution plate 41≤100mm。
(2) Keeping the actual recording distance unchanged, and adopting unknown wavelength lambda1The laser is used as a light source, and the CCD5 is used for collecting the holographyIn the graph b, the measurement range of the unknown wavelength depends on the photosensitive range of the CCD5, and the wavelength from visible light to infrared band can be measured by selecting a proper CCD 5.
(3) Using the hologram b, a certain wavelength λ is selected2Calculating to obtain the recording distance d corresponding to the wavelength2。
(4) According to the formula lambda1d1＝λ2d2And calculating the unknown wavelength as: lambda [ alpha ]1＝λ2d2/d1。
In the process of measuring the wavelength, an optical device does not need to move, and only different light sources need to be replaced at the laser input end 1, the precision of laser wavelength measurement is related to the step length (namely the sampling interval delta d) selected by the self-focusing algorithm, and the smaller the sampling interval delta d is, the higher the precision is.
The present invention can calculate an optimum reproduction distance or recording distance.
Example one
(1) The hologram a is collected by the CCD5 using a red laser with a known wavelength as a light source, and the recording distance is the distance from the object plane to the hologram plane, and since there is a certain distance between the light entrance and the receiving plane of the CCD, it is difficult to measure the distance by a tool such as a ruler, and therefore, an accurate recording distance can be obtained by calculating the reproduction distance. In holographic reconstruction, a clear reconstructed image is only obtained if the reconstruction distance d (i.e. the distance from the holographic surface to the reconstruction surface) is exactly equal to the recording distance, so that the recording distance d is determined by means of a self-focusing algorithm1。
(2) Using unknown wavelength lambda1The position of the optical device is kept constant, and the hologram b is acquired by the CCD, wherein the recording distance is constant and is equal to d1。
(3) Using a hologram b and a known wavelength of lambda2The corresponding recording distance d is obtained by calculation through the brought-in self-focusing algorithm2。
(4) According to the formula lambda1d1＝λ2d2And calculating the unknown wavelength as: lambda [ alpha ]1＝λ2d2/d1。
Example two
(1) The hologram a is collected by the CCD5 using a red laser with a known wavelength as a light source, and the recording distance is the distance from the object plane to the hologram plane, and since there is a certain distance between the light entrance and the receiving plane of the CCD, it is difficult to measure the distance by a tool such as a ruler, and therefore, an accurate recording distance can be obtained by calculating the reproduction distance. In the holographic reproduction process, a clear reproduction image can be obtained only when the reproduction distance d (i.e. the distance from the holographic surface to the reproduction surface) is exactly equal to the recording distance, so that the best reproduction distance d is obtained by means of the autofocus algorithm3。
(2) Using unknown wavelength lambda3The position of the optics is kept constant, and the hologram b is acquired by the CCD, with the optimum reconstruction distance constant, equal to d3。
(3) Using a hologram b and a known wavelength of lambda4Is calculated by the carry-in self-focusing algorithm to obtain the corresponding optimal reproduction distance d4。
(4) According to the formula lambda3d3＝λ4d4And calculating the unknown wavelength as: lambda [ alpha ]3＝λ4d4/d3。
EXAMPLE III
An experimental device is built according to figure 1, laser with known wavelength is used as a light source, and according to an acquired light intensity graph a, a recording distance d calculated by using a self-focusing algorithm is used1＝21mm。
Keeping the recording distance of the experimental apparatus constant, i.e. d121mm, using a He-Ne laser as the light source, and a wavelength of λ1Assuming the quantity required for the experiment, the intensity map b is collected by the CCD.
Assuming the use of a known wavelength λ2The corresponding reconstruction distance or recording distance, which is the 532nm green light illumination hologram b, can be determined by means of a self-focusing algorithm, the calculated distance d being determined1＝25mm。
According to the formula lambda1d1＝λ2d2And calculating the unknown wavelength as: lambda [ alpha ]1＝λ2d2/d1≈633.3nm。
The wavelength of the He-Ne laser is known as 632.8nm, the wavelength calculated by the coaxial holographic self-focusing approaches an accurate value, and the existing error value can be reduced by the optimization of the algorithm and the reduction of the sampling distance interval. In the calculation process of the self-focusing algorithm, the value of delta d is 1mm, and the accuracy of wavelength calculation can be improved by reducing the value of delta d so as to meet the actual requirement.
Claims (9)
1. The utility model provides a device based on coaxial holographic self-focusing technique measures laser wavelength, is including laser input end (1), collimation beam expanding system, resolution ratio board (4) and CCD (5) that set gradually, its characterized in that, laser input end (1), collimation beam expanding system, resolution ratio board (4) and CCD (5) be located same optical axis, adopt laser irradiation resolution ratio board (4), produce the object light that contains object information to the light distribution who gathers and produce the hologram by CCD (5) record.
2. The device for measuring laser wavelength based on in-line holographic self-focusing technology of claim 1 is characterized in that the collimating beam expanding system comprises a first lens (2) and a second lens (3) which are arranged in sequence.
3. The device for measuring the laser wavelength based on the coaxial holographic self-focusing technology of claim 1, wherein when the distance from the resolution plate (4) to the CCD (5) is fixed, the holograms obtained on the CCD (5) after the laser with different wavelengths irradiates the resolution plate (4) are different.
4. The device for measuring laser wavelength based on in-line holographic self-focusing technique according to claim 1 is characterized in that the laser input end (1) can be replaced by different light source.
5. The method for measuring the laser wavelength based on the coaxial holographic self-focusing technology is characterized by comprising the following steps:
(1) make itUsing laser with known wavelength as light source, using CCD to collect hologram a, and using self-focusing algorithm and substituting known wavelength to obtain actual distance d1；
(2) Maintaining the actual distance d1Invariant, using unknown wavelength λ1The laser is used as a light source, and a hologram b is collected through a CCD;
(3) using the hologram b, a certain wavelength λ is selected2Calculating to obtain the distance d corresponding to the wavelength2；
(4) According to the formula lambda1d1＝λ2d2And calculating the unknown wavelength as: lambda [ alpha ]1＝λ2d2/d1。
6. The method for measuring laser wavelength based on in-line holographic self-focusing technique according to claim 5, wherein the distance of steps (1) and (3) is a reproducing distance or a recording distance.
7. The method for measuring laser wavelength based on in-line holographic self-focusing technique according to claim 5, wherein the actual distance of step (1) is the distance from the resolution plate to the CCD.
8. The method for measuring laser wavelength based on in-line holographic self-focusing technique as claimed in claim 5 or 7, wherein the actual distance range is 10mm ≦ d1≤100mm。
9. The method for measuring laser wavelength based on in-line holographic self-focusing technique as claimed in claim 5, wherein the measurement range of the unknown wavelength depends on the photosensitive range of CCD.
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| CN107421638A (en) * | 2017-08-25 | 2017-12-01 | 西京学院 | A kind of new optical diffraction analogy method and its device |
| CN108803293A (en) * | 2017-05-06 | 2018-11-13 | 北京微美云息软件有限公司 | Calculate holographic reproduction light path system |
| CN108871198A (en) * | 2018-05-24 | 2018-11-23 | 合肥工业大学 | Digital coaxial micro- holographic apparatus and recording distance and reproduction distance calibration method |
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Patent Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2006268933A (en) * | 2005-03-23 | 2006-10-05 | Alps Electric Co Ltd | Holography apparatus and method of reproducing holography medium |
| CN101206885A (en) * | 2006-12-15 | 2008-06-25 | 夏普株式会社 | Wavelength control method controlling the wavelength for recording or reproducing information with holography, hologram information processing apparatus and hologram recording medium |
| CN101740048A (en) * | 2008-11-20 | 2010-06-16 | 索尼株式会社 | Reproduction apparatus and reproduction method |
| CN102737658A (en) * | 2011-03-31 | 2012-10-17 | 通用电气公司 | Multi-wavelength- holographic systems and methods |
| CN106094487A (en) * | 2016-08-18 | 2016-11-09 | 中国工程物理研究院激光聚变研究中心 | Terahertz in-line holographic imaging systems based on multiple recording distances and formation method |
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