CN118311551A - Michelson interference frequency discrimination device and method for ultra-wide band and ultra-large view field - Google Patents
Michelson interference frequency discrimination device and method for ultra-wide band and ultra-large view field Download PDFInfo
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Abstract
The invention discloses a Michelson interference frequency discrimination device and method of ultra-wide band and ultra-large view field, comprising a Michelson interferometer of ultra-wide band and ultra-large view field, a sealing cavity and an air pressure tuning mechanism; the Michelson interferometer comprises a glass arm compensation reflector, a mixing arm gap block and a beam splitting prism; the external light beam is divided into two beams after entering from one side of the beam splitting prism, and the two beams are reflected by the glass arm compensation mirror and the mixed arm compensation mirror respectively and then are combined to interfere through the beam splitting prism again; the interference light beam has two paths, one of which returns to be called a reflection channel, and the other of which is turned by 90 degrees to be emitted to be called a transmission channel; the sealed cavity is communicated with the air pressure tuning mechanism, and the Michelson interferometer is arranged in the sealed cavity and isolated from the external environment; when the air pressure tuning mechanism operates, the air pressure in the sealing cavity changes, so that the refractive index of air in the sealing cavity changes, and further the interference optical path difference and the center frequency of the device are changed, and tuning is realized.
Description
Technical Field
The invention belongs to the technical field of laser radars, and particularly relates to a Michelson interference frequency discrimination device and method for ultra-wide band and ultra-large field of view.
Background
The high-spectral-resolution laser radar (HSRL) is a laser radar technology which is newly developed in recent years, and by introducing a narrow-band spectral discriminator, the Rayleigh scattering of atmospheric molecules or the Brillouin scattering of water body are separated, so that the detection precision of the optical characteristics of the atmosphere and the water body is greatly improved. Common spectral discriminators include atomic or molecular vapor absorption cells, F-P interferometers, michelson interferometers, mach zehnder interferometers, and the like. The iodine molecule vapor absorption tank has excellent frequency discrimination effect near the characteristic spectral line 532 nm, but cannot be used at other wavelengths; the F-P interferometer can be suitable for any wavelength, but the effective field of view is small (half field of view is about 0.2 degrees), the energy utilization rate is low, an alignment error can be introduced, and the actual frequency discrimination effect can not meet the requirement of HSRL high-precision detection yet.
In order to solve the problem of high-precision spectrum frequency discrimination of non-532 nm wave bands and promote the development of ultraviolet, blue-violet, infrared and other wave band HSRL systems, relevant scholars propose a Michelson interferometer (CN 201410025286.9) and a Mach-Zehnder interferometer (CN 202211713674.7) with field broadening. The two interferometers expand the effective half field angle of the interference discriminator to 3-5 degrees by matching the optical paths in the air and the glass of the two interference arms, so that the inherent problem of smaller field of view of the F-P interferometer is solved to a certain extent, and the interferometer has been used in HSRL systems for atmospheric aerosol detection.
However, for application scenes such as water optical characteristic detection, echo signals received by a HSRL system have larger scattering angles, the half field of view of 3-5 degrees still cannot completely meet the requirements, and frequency discrimination devices with larger field of view still need to be developed. Meanwhile, most of the existing field broadening designs are sensitive to wavelength and can only be used under single wavelength, which means that HSRL systems are required to be equipped with a single longitudinal mode continuous laser with the same wavelength besides the single longitudinal mode pulse laser, so that the frequency discriminator is assembled and tested, and the research and development cost is increased. In addition, for a multi-wavelength HSRL system, the interference discriminator of different wave bands needs to be designed and manufactured separately, which further increases the complexity and manufacturing cost of the system, and hinders the development of the multi-wavelength HSRL system to some extent.
Disclosure of Invention
In order to solve the problems of smaller visual field and narrower working wave band of the existing interference frequency discrimination technology, the invention provides the Michelson interference frequency discrimination device and method with ultra-wide wave band and ultra-large visual field, which are suitable for any single-wavelength and multi-wavelength HSRL system, can effectively improve the frequency discrimination performance of the HSRL system, reduce the complexity and cost of the system, and have important significance for the development of HSRL technology.
The Michelson interference frequency discrimination device with the ultra-wide band and the ultra-large view field has an effective half view angle exceeding 10 degrees in the ultra-wide band of hundreds of nm magnitude, and comprises a Michelson interferometer with the ultra-wide band and the ultra-large view field, a sealing cavity and an air pressure tuning mechanism;
The Michelson interferometer with the ultra-wide band and the ultra-large view field comprises a glass arm compensation reflector, a mixing arm gap block and a beam splitting prism; the glass arm compensation reflector is directly bonded with the beam splitting prism, and the mixing arm compensation reflector is bonded with the beam splitting prism through two mixing arm gap blocks; the external light beam is divided into two beams after entering from one side of the beam splitting prism, and the two beams are reflected by the glass arm compensation mirror and the mixed arm compensation mirror respectively and then are combined to interfere through the beam splitting prism again; the interference light beam has two paths, one path returns to be called a reflection channel, and the other path is turned by 90 degrees to be emitted to be called a transmission channel;
The sealing cavity is communicated with the air pressure tuning mechanism, and the Michelson interferometer with ultra-wide wave band and ultra-large visual field is arranged in the sealing cavity and isolated from the external environment; when the air pressure tuning mechanism operates, the air pressure in the sealing cavity changes, so that the refractive index of air in the sealing cavity changes, and further the interference optical path difference and the center frequency of the whole Michelson interference frequency discrimination device are changed, and tuning is realized.
By using the device provided by the invention, the effective half-field angle exceeds 10 degrees in the ultra-wide wave band of hundreds of nm magnitude, the full-field wave front PV is better than 1/20 wavelength, and the multi-wavelength spectrum frequency discrimination under the ultra-wide field can be realized by a single frequency discrimination device.
Further, the coated wave bands of the glass arm compensation reflector, the mixed arm gap block and the beam splitting prism are the same. The optical elements are bonded by adopting a mode of optical glue or ultraviolet gluing.
Further, the glass arm compensation reflector is made of optical glass, and is marked as G 1, the refractive index is n 1, the thickness is d 1, the inner surface and the outer surface are parallel, and the outer surface is plated with a high-reflection film; wherein the inner surface refers to an optical surface close to the beam splitting prism, and the outer surface refers to an optical surface far from the beam splitting prism;
The material of the mixing arm compensation reflector is optical glass, G 3 is marked, the refractive index is n 3, the thickness is d 3, and the inner surface and the outer surface are parallel; the inner surface is plated with an antireflection film, the outer surface is plated with a high-reflection film, and the reflectivity of the high-reflection film is the same as that of the glass arm compensation reflector;
the thickness of the mixing arm gap block is d 2, and the two bonding surfaces are parallel and well polished;
The material of the light-splitting prism substrate is optical glass, G 4 is marked, and the light-splitting ratio is 50:50.
Further, when G 4 is the same as G 1, the interface of the beam splitting prism and the glass arm compensation reflector is not coated with a film; when G 4 is different from G 1, an anti-reflection film is plated on the bonding interface of the beam splitting prism and the glass arm compensation reflector; the other 3 optical surfaces of the beam-splitting prism are plated with antireflection films.
Further, in order to achieve an effective half field of view exceeding 10 degrees in the range [ lambda min, λmax ] and to ensure that the device is as compact as possible, said optical glass G 1、G3 meets the following requirements:
；
Where λ 1 and λ 2 are design reference wavelengths, and λ min < λ1 < λ2 < λmax,λmin and λ max are minimum and maximum wavelengths, respectively. Inequality M < 5 x 10 -5 means that the interferometer can achieve 1 st order and 2 nd order field stretching almost simultaneously in the selected band.
Further, for a selected optical glass G 1、G3, to achieve a given free spectral range FSR at wavelength λ 0, the thickness parameter d 1、d2、d3 satisfies the following requirement:
；
Wherein lambda 0 is the design center wavelength, lambda min < λ1 ≤ λ0 ≤ λ2 < λmax,θ1 and theta 2 are the 1-order and 2-order field broadening angles of the Michelson interferometer respectively, FSR is the free spectrum range of the Michelson interference frequency discrimination device, and c is the light speed; θ 1、θ2 and FSR are set as required.
Further, window sheets are arranged at the incidence port and the emergence port of the Michelson interference frequency discrimination device in the sealing cavity, the optical axis of the window sheets coincides with the optical axis of the Michelson interferometer, and an antireflection film is plated on the surface of the window sheets.
Further, the air pressure tuning mechanism is at least provided with two working modes of scanning and stepping, and when in scanning operation, the absolute air pressure in the sealing cavity can be continuously changed within the range of 1+/-delta P/2 atm, so that the refractive index of air in the sealing cavity is changed, and the interference optical path difference and the center frequency of the device are further changed.
Further, in order to ensure that the center frequency of the device is always tuned to the position with the optimal frequency discrimination effect, namely, the spectrum frequency discrimination curve is matched with the center wavelength of the incident laser, the tuning range should exceed half a period. For this purpose, the maximum air pressure change Δp satisfies Δp > λ/4χd 2, where d 2 is the thickness of the hybrid arm gap block, χ is the refractive index-air pressure slope, and the calculation formula is as follows, in relation to wavelength λ and temperature T:
；
Wherein n air is the refractive index of air, and P is the air pressure.
The Michelson interference frequency discrimination device with the ultra-wide band and the ultra-large view field comprises a processing and adjusting method of the Michelson interference frequency discrimination device, a single-channel multi-wavelength time-sharing detection method based on pulse synchronization and a multi-channel multi-wavelength scanning detection method based on a dichroic mirror;
the processing and adjusting method of the Michelson interference frequency discrimination device comprises the following steps:
(1-1) completing the design of each parameter of the Michelson interference frequency discrimination device according to the requirement, wherein the design comprises the steps of determining a free spectral range FSR of the Michelson interference frequency discrimination device, selecting optical glass G 1 of a glass arm compensation reflector, selecting optical glass G 3 of a mixed arm compensation reflector, determining the thickness d 1 of the glass arm compensation reflector, determining the thickness d 2 of a mixed arm gap block and determining the thickness d 3 of the mixed arm compensation reflector;
(1-2) finishing the shape processing and polishing of the beam splitting prism, the mixing arm compensating mirror and the mixing arm gap block;
(1-3) measuring the actual thickness d 2'、d3 'of the hybrid arm gap block and the hybrid arm compensation reflector, calculating the corrected thickness d 1' of the glass arm compensation reflector, carrying out shape processing and polishing on the glass arm compensation reflector according to d 1 ', and calculating the actual FSR';
(1-4) plating all the antireflection films and bonding all the optical elements;
(1-5) measuring the relative wavefront error delta W of the Michelson interferometer, and performing secondary polishing and finishing on the outer surface of the glass arm compensation reflector according to the measurement result until the wavefront error converges;
(1-6) plating all high-reflection films, and connecting and assembling the Michelson interferometer with a sealing cavity and an air pressure tuning mechanism;
the single-channel time-sharing detection method based on pulse synchronization comprises the following steps:
(2-1) respectively starting a light source of the multi-wavelength HSRL system, wherein N corresponding wavelengths are lambda c1、λc2, …, λcN respectively, aligning a telescope to a standard reference object, setting an air pressure tuning mechanism as a scanning mode, obtaining a transmission light intensity curve of a Michelson interference frequency discrimination device, and recording an optimal working point P c1, Pc2, …, PcN of each central wavelength; the optimal working point P c1, Pc2, …, PcN is the position of the light intensity minimum value on the transmission light intensity curve with the wavelength lambda c1、λc2, …, λcN;
(2-2) simultaneously starting a light source of the multi-wavelength HSRL system, aligning the telescope to a test target area, and adjusting pulse laser parameters to ensure that the repetition frequencies f of pulses with different wavelengths are consistent, wherein the time interval is deltat; the time interval Deltat satisfies Deltat < 1/Nf;
(2-3) setting an air pressure tuning mechanism to be in a stepping mode, setting a stepping time interval to be delta t, and setting a stepping signal to be synchronous with laser pulses; after synchronization is completed, the telescope is aligned to the target area for detection; after the acquisition of k periods is completed, a multi-wavelength frequency discrimination detection DATA matrix DATA and DATA sequences I 1, I2, …, IN of N wavelengths lambda c1、λc2, …, λcN are obtained for subsequent processing;
；
The multichannel scanning detection method based on the dichroic mirror comprises the following steps:
(3-1) setting N-1 dichroic mirrors and detectors with corresponding wavelengths at the exit port of the Michelson interference frequency discrimination device with ultra wide band and ultra large field of view for a HSRL system with lambda c1、λc2, …, λcN and total N wavelengths, thereby constructing N detection channels with different wavelengths; n-1 dichroic mirrors separate light beams having wavelengths of lambda c1 and lambda c2,…,λc(N-1) and lambda cN, respectively;
(3-2) setting an air pressure tuning mechanism as a scanning mode, and collecting m data points in one scanning period; simultaneously, a light source of the multi-wavelength HSRL system is started, and the telescope is aimed at the target area for detection; after the data acquisition of k periods is completed, respectively obtaining a scanning detection data sequence I 1', I2', …, IN' of a lambda c1、λc2, …, λcN channel for subsequent processing; wherein the m data points of each period form a sine curve with period T and length lT, and l is more than 0.5 to ensure that the data has a minimum value.
In the step (1-3), the actual thickness is measured by a micrometer gauge, and the corrected thickness d 1 'and the actual FSR' are determined by the following expressions:
；
；
Wherein c is the speed of light; lambda 0 is the design center wavelength, theta 1 and theta 2 are the 1 st order and 2 nd order field broadening angles of the Michelson interferometer, respectively, and theta 1、θ2 and FSR are set according to requirements.
In the step (1-5), the relative wavefront error DeltaW is usually measured by using a wavelength phase shift interference method, and only constant terms, tilt, defocus terms and the like are removed from the test result.
Compared with the prior art, the invention has the following beneficial effects:
1. The device and the method realize the design and the application of the ultra-wide band and ultra-large field interference frequency discrimination device for the first time by matching the glass material and the thickness of the interferometer;
2. The device is based on achromatic 2-order view field widening design, realizes an effective half view field exceeding 10 degrees in an ultra-wide wave band of hundreds of nm magnitude, and has a wave front PV better than 1/20 wavelength in the full view field range; the key indexes are obviously superior to the prior art, the characteristics of ultra-wide band and ultra-large view field are possessed, the alignment error can be obviously eliminated, and the energy utilization rate and the frequency discrimination detection performance of HSRL systems are effectively improved;
3. based on the ultra-wide band and ultra-large visual field characteristic of the device, the invention further provides a high-precision tool adjusting method and two multi-wavelength detection methods for HSRL systems, and the multi-wavelength spectrum frequency discrimination under the ultra-wide visual field can be realized by using only a single frequency discrimination device, so that the complexity, the research and development cost and the manufacturing cost of the multi-wavelength HSRL system can be effectively reduced, the method has important significance for the development of HSRL technology, and has wide application prospects in the laser radar field.
Drawings
Fig. 1 is a schematic diagram of a michelson interference frequency discrimination device with ultra wide band and ultra large field of view in the present invention.
Fig. 2 is a plan optical structure diagram of a michelson interferometer with ultra-wide band and ultra-large field of view according to the present invention.
Fig. 3 is a three-dimensional optical structure diagram of a michelson interferometer with ultra-wide band and ultra-large field of view according to the present invention.
Fig. 4 is a schematic diagram of a seal chamber and an implementation of an air pressure tuning mechanism according to an embodiment of the present invention.
FIG. 5 shows the main technical indexes of an interferometer designed by the embodiment of the present invention, including an optical path difference-field angle curve at a short wave cut-off wavelength, and an effective half-field-wavelength curve for representing a dispersion effect.
FIG. 6 is an interference pattern of an interferometer designed according to an embodiment of this invention at 6 typical wavelengths.
Detailed Description
The invention will be described in further detail with reference to the drawings and examples, it being noted that the examples described below are intended to facilitate the understanding of the invention and are not intended to limit the invention in any way.
As shown in FIG. 1, the Michelson interference frequency discrimination device with the ultra-wide band and the ultra-large view field comprises a Michelson interferometer with the ultra-wide band and the ultra-large view field, a sealing cavity and an air pressure tuning mechanism.
The Michelson interferometer with ultra-wide band and ultra-large view field consists of a glass arm compensation reflector 1, a mixed arm gap block 2, a mixed arm compensation reflector 3 and a beam splitting prism 4. The interferometer is enclosed in a sealed cavity 5, isolated from the external atmosphere. Wherein the sealed cavity 5 has a window sheet coated with an antireflection film at both the entrance port and the exit port of the interferometer (corresponding to both sides of the dichroic prism 4, respectively) for the light beam to pass through. The air pressure tuning mechanism 6 is communicated with the sealing cavity 5, and when the air pressure tuning mechanism 6 operates, the absolute air pressure in the sealing cavity 5 can continuously change within the range of 1+/-delta P/2 atm, so that the refractive index of air in the sealing cavity 5 changes, and the interference optical path difference and the center frequency of the whole device are changed.
Further, the optical structure of the michelson interferometer with ultra wide band and ultra large field of view is shown in fig. 2 and 3. The glass arm compensation reflector 1 is made of optical glass G 1, has the thickness d 1 and is coated with a high-reflection film on the outer surface S101; the material of the mixing arm gap block 2 is quartz, and the thickness is d 2; the material of the hybrid arm compensation reflector 3 is optical glass G 3, the thickness is d 3, the outer surface S301 is plated with a high-reflection film, and the inner surface S302 is plated with an anti-reflection film; the beam splitting prism 4 is made of G 1, and the beam splitting surface S401 is plated with a 50:50 beam splitting film, the surface S402 is not plated with a film, and the surfaces S403, S404 and S405 are plated with antireflection films, similar to the glass arm compensation reflector 1.
An external light beam (usually from a receiving telescope of HSRL system) enters from the surface S405 (or the surface S404), is split into two beams by the beam splitting surface S401, is reflected by the outer surface S101 of the glass arm compensating mirror and the outer surface S301 of the mixing arm compensating mirror 3 respectively, and then is combined and interfered again by the beam splitting surface S401. One path of the interference beam returns from the surface S405 (or the surface S404) to be called a reflection channel; the other path is turned by 90 degrees and exits from the surface S404 (or the surface S405), which is called a transmission channel. It is typically only necessary to receive the frequency discrimination signal from the transmission channel, the interference phases of the two channels being 180 deg. apart.
In the embodiment of the invention, the specific implementation manner of the sealing cavity 5 and the air pressure tuning mechanism 6 is shown in fig. 4. The pneumatic tuning mechanism is composed of a pneumatic hose 601, an air cylinder 602 and an electric push rod 603. The cylinder 602 is communicated with the sealing cavity 5 through a pneumatic hose, a piston rod of the cylinder 602 is coaxially connected with the electric push rod 603 through threads, and the maximum stroke of the cylinder 602 is the same as that of the electric push rod 603. After the sealing cavity 5 and the air pressure tuning mechanism 6 are combined, the air pressure tuning range delta P of the device is approximately equal to 0.2 atm. The electric push rod 603 can be controlled by a host computer and has various working modes including scanning and stepping.
In the embodiment of the invention, the FSR of the interferometer is set to be 18.5 GHz, the optical glass G 1 is selected to be F5, the optical glass G 3 is selected to be H-ZLaF, and the thickness parameters d 1、d2、d3 are 21.463 mm, 1.962 mm and 21.489 mm respectively. The effective half-field-of-view (PV) wave band exceeding 10 degrees can cover [ lambda min, λmax ] = [450, 1550] nm with the full-field-of-view (PV) being better than 1/20 wavelength as standard. The actual operating band of the interferometer will no longer be limited by the field stretching conditions, but by the optical coating. The simulated optical path difference-field angle curve at the short cut-off wavelength 450 nm, and the effective half-field-wavelength curve characterizing the dispersion effect are shown in fig. 5.
In the embodiment of the invention, the optical axis of the input light beam can be coincident with or slightly inclined to the optical axis of the interferometer, and the interferometer has the largest effective field of view when the optical axes are coincident, and the simulated interferograms under 6 typical wavelengths are shown in fig. 6, wherein the half field of view corresponding to the marked circle in the figure is 10 degrees.
The Michelson interference frequency discrimination method of the ultra-wide band and ultra-large view field based on the device is as follows, wherein steps 1-4 are processing and adjusting methods of the device, and steps 5-8 are single-channel time-sharing detection methods based on pulse synchronization.
Step 1: according to the design result, finishing the appearance processing and polishing of the beam splitting prism 4, the mixed arm compensating mirror 3 and the mixed arm gap block 2; the actual thickness d 2'、d3 'of the hybrid arm gap block and the hybrid arm compensating mirror is measured, the corrected thickness d 1' of the glass arm compensating mirror is calculated, the contour machining and polishing are carried out according to d 1 ', and the actual FSR' is calculated. The formulas required for the above calculations are as follows:
；
；
Step 2: the light splitting surface S401 is plated with a light splitting film, the inner surfaces S302, S403, S404 and S405 are plated with an antireflection film, and the light splitting surface S401, S402, S403 and inner surface S302 are bonded by using a photoresist method;
Step 3: measuring the relative wavefront error delta W of the interferometer, and performing secondary polishing refinement on the outer surface S101 according to the measurement result until the wavefront error such as inclination, defocus and the like is eliminated to the maximum extent;
Step 4: the outer surfaces S101 and S301 are plated with high-reflection films, connection and assembly of an interferometer, the sealing cavity 5 and the air pressure tuning mechanism 6 are completed, a Michelson interference frequency discrimination device with ultra-wide wave band and ultra-large view field is installed in a multi-wavelength HSRL system light path, and matching of optical, mechanical and circuit interfaces is completed;
step 5: respectively starting a light source of the multi-wavelength HSRL system, enabling N corresponding wavelengths to be lambda c1、λc2, …, λcN, aligning a telescope with a standard reference object, setting an electric push rod 603 as a continuous scanning mode, obtaining a transmission light intensity curve of the device, recording a light intensity minimum value position z c1, zc2, …, zcN corresponding to each center wavelength, namely an optimal working point (without converting coordinates into air pressure) of the corresponding wavelength, and completing calibration data acquisition;
Step 6: simultaneously, a light source of the multi-wavelength HSRL system is started, a telescope is aligned to a test target area, pulse laser parameters are adjusted, so that the repetition frequencies f of pulses with different wavelengths are consistent, the time interval is deltat, and delta t < 1/Nf is met, so that the pulses with different wavelengths can be separated in time, aliasing is avoided, and system preparation and preheating are completed;
Step 7: setting the electric push rod 603 as a stepping mode, setting a stepping time interval as deltat, and setting a stepping signal to be synchronous with laser pulses, so that when the pulse lambda c1、λc2, …, λcN appears, the air pressure in a sealing cavity is z c1, zc2, …, zcN respectively, the device is always at an optimal working point, and the system calibration is completed;
Step 8: the multi-wavelength HSRL system starts detection and DATA acquisition, and after the acquisition of k periods is completed, a multi-wavelength frequency discrimination detection DATA matrix DATA and detection DATA sequences I 1, I2, …, IN of N wavelengths lambda c1、λc2, …, λcN are obtained for subsequent processing.
When the multichannel scanning detection method based on the dichroic mirror is used, the steps 5-8 are changed into the following steps 5 '-6', external devices are added, and the calibration and synchronization processes are omitted:
Step 5': arranging N-1 dichroic mirrors and detectors with corresponding wavelengths outside an exit port of the interferometer, namely a surface S404 (or a surface S405), respectively separating light beams with wavelengths lambda c1, lambda c2,…,λc(N-1) and lambda cN, and constructing N detection channels with different wavelengths;
Step 6': the air pressure tuning mechanism is set into a scanning mode, and m data points are acquired in one scanning period. And simultaneously, a light source of the multi-wavelength HSRL system is started, and the telescope is aimed at the target area for detection. After the data acquisition of k periods is completed, a scanning detection data sequence I 1', I2', …, IN' of the lambda c1、λc2, …, λcN channel is obtained respectively for subsequent processing.
The foregoing embodiments have described in detail the technical solution and the advantages of the present invention, it should be understood that the foregoing embodiments are merely illustrative of the present invention and are not intended to limit the invention, and any modifications, additions and equivalents made within the scope of the principles of the present invention should be included in the scope of the invention.
Claims (10)
1. The Michelson interference frequency discrimination device with the ultra-wide band and the ultra-large view field is characterized by comprising a Michelson interferometer with the ultra-wide band and the ultra-large view field, a sealing cavity and an air pressure tuning mechanism;
The Michelson interferometer with the ultra-wide band and the ultra-large view field comprises a glass arm compensation reflector, a mixing arm gap block and a beam splitting prism; the glass arm compensation reflector is directly bonded with the beam splitting prism, and the mixing arm compensation reflector is bonded with the beam splitting prism through two mixing arm gap blocks; the external light beam is divided into two beams after entering from one side of the beam splitting prism, and the two beams are reflected by the glass arm compensation mirror and the mixed arm compensation mirror respectively and then are combined to interfere through the beam splitting prism again; the interference light beam has two paths, one path returns to be called a reflection channel, and the other path is turned by 90 degrees to be emitted to be called a transmission channel;
The sealing cavity is communicated with the air pressure tuning mechanism, and the Michelson interferometer with ultra-wide wave band and ultra-large visual field is arranged in the sealing cavity and isolated from the external environment; when the air pressure tuning mechanism operates, the air pressure in the sealing cavity changes, so that the refractive index of air in the sealing cavity changes, and further the interference optical path difference and the center frequency of the whole Michelson interference frequency discrimination device are changed, and tuning is realized.
2. The michelson interference frequency discrimination device with ultra-wide band and ultra-large view field according to claim 1, wherein the coated wave bands of the glass arm compensating mirror, the mixed arm gap block and the beam splitting prism are the same, and the optical elements are bonded by adopting an optical cement or ultraviolet gluing mode.
3. The michelson interference frequency discrimination device with ultra-wide band and ultra-large view field according to claim 1, wherein the material of said glass arm compensation reflector is optical glass, marked as G 1, refractive index is n 1, thickness is d 1, inner and outer surfaces are parallel, and outer surface is coated with high-reflection film;
The material of the mixing arm compensation reflector is optical glass, G 3 is marked, the refractive index is n 3, the thickness is d 3, and the inner surface and the outer surface are parallel; the inner surface is plated with an antireflection film, the outer surface is plated with a high-reflection film, and the reflectivity of the high-reflection film is the same as that of the glass arm compensation reflector;
The thickness of the mixing arm gap block is d 2, and the two bonding surfaces are parallel;
The material of the light-splitting prism substrate is optical glass, G 4 is marked, and the light-splitting ratio is 50:50.
4. The michelson interference frequency discrimination apparatus of ultra-wide band and ultra-large field of view according to claim 3, wherein when G 4 is the same as G 1, an interface of said beam-splitting prism and glass arm compensation mirror is not coated with a film; when G 4 is different from G 1, an anti-reflection film is plated on the bonding interface of the beam splitting prism and the glass arm compensation reflector; the other 3 optical surfaces of the beam-splitting prism are plated with antireflection films.
5. The michelson interference frequency discrimination apparatus of ultra-wide band and ultra-large field of view according to claim 3, wherein said optical glass G 1、G3 satisfies the following requirements:
；
Where λ 1 and λ 2 are design reference wavelengths, and λ min < λ1 < λ2 < λmax,λmin and λ max are minimum and maximum wavelengths, respectively.
6. A michelson interference frequency discrimination apparatus with ultra wide band and ultra large field of view according to claim 3, wherein said thickness parameter d 1、d2、d3 satisfies the following requirements:
；
Wherein lambda 0 is the design center wavelength, lambda min < λ1 ≤ λ0 ≤ λ2 < λmax,θ1 and theta 2 are the 1-order and 2-order field broadening angles of the Michelson interferometer respectively, FSR is the free spectrum range of the Michelson interference frequency discrimination device, and c is the light speed; θ 1、θ2 and FSR are set as required.
7. The michelson interference frequency discrimination device with the ultra-wide band and ultra-large view field according to claim 1, wherein window sheets are arranged at the incidence port and the emergence port of the michelson interference frequency discrimination device in the sealing cavity, the optical axis of the window sheets coincides with the optical axis of the michelson interferometer, and an antireflection film is plated on the surface of the window sheets.
8. The michelson interference frequency discriminator of ultra-wide band ultra-large field of view according to claim 1, wherein said air pressure tuning mechanism has at least two operation modes of scanning and stepping, the absolute air pressure in the sealed cavity continuously changes within the range of 1±Δp/2 atm during scanning operation, the maximum air pressure change Δp satisfies Δp > λ/4 χd 2, where d 2 is the thickness of the hybrid arm gap block, χ is the refractive index-air pressure slope, and the calculation formula is as follows, regarding wavelength λ and temperature T:
；
Wherein n air is the refractive index of air, and P is the air pressure.
9. The Michelson interference frequency discrimination method of the ultra-wide band ultra-large view field is characterized by comprising a processing and adjusting method of the Michelson interference frequency discrimination device, a single-channel multi-wavelength time-sharing detection method based on pulse synchronization and a multi-channel multi-wavelength scanning detection method based on a dichroic mirror, wherein the Michelson interference frequency discrimination device of the ultra-wide band ultra-large view field is used in any one of claims 1-8;
the processing and adjusting method of the Michelson interference frequency discrimination device comprises the following steps:
(1-1) completing the design of each parameter of the Michelson interference frequency discrimination device according to the requirement, wherein the design comprises the steps of determining a free spectral range FSR of the Michelson interference frequency discrimination device, selecting optical glass G 1 of a glass arm compensation reflector, selecting optical glass G 3 of a mixed arm compensation reflector, determining the thickness d 1 of the glass arm compensation reflector, determining the thickness d 2 of a mixed arm gap block and determining the thickness d 3 of the mixed arm compensation reflector;
(1-2) finishing the shape processing and polishing of the beam splitting prism, the mixing arm compensating mirror and the mixing arm gap block;
(1-3) measuring the actual thickness d 2'、d3 'of the hybrid arm gap block and the hybrid arm compensation reflector, calculating the corrected thickness d 1' of the glass arm compensation reflector, carrying out shape processing and polishing on the glass arm compensation reflector according to d 1 ', and calculating the actual FSR';
(1-4) plating all the antireflection films and bonding all the optical elements;
(1-5) measuring the relative wavefront error delta W of the Michelson interferometer, and performing secondary polishing and finishing on the outer surface of the glass arm compensation reflector according to the measurement result until the wavefront error converges;
(1-6) plating all high-reflection films, and connecting and assembling the Michelson interferometer with a sealing cavity and an air pressure tuning mechanism;
the single-channel time-sharing detection method based on pulse synchronization comprises the following steps:
(2-1) respectively starting a light source of the multi-wavelength HSRL system, wherein N corresponding wavelengths are lambda c1、λc2, …, λcN respectively, aligning a telescope to a standard reference object, setting an air pressure tuning mechanism as a scanning mode, obtaining a transmission light intensity curve of a Michelson interference frequency discrimination device, and recording an optimal working point P c1, Pc2, …, PcN of each central wavelength; the optimal working point P c1, Pc2, …, PcN is the position of the light intensity minimum value on the transmission light intensity curve with the wavelength lambda c1、λc2, …, λcN;
(2-2) simultaneously starting a light source of the multi-wavelength HSRL system, aligning the telescope to a test target area, and adjusting pulse laser parameters to ensure that the repetition frequencies f of pulses with different wavelengths are consistent, wherein the time interval is deltat; the time interval Deltat satisfies Deltat < 1/Nf;
(2-3) setting an air pressure tuning mechanism to be in a stepping mode, setting a stepping time interval to be delta t, and setting a stepping signal to be synchronous with laser pulses; after synchronization is completed, the telescope is aligned to the target area for detection; after the acquisition of k periods is completed, a multi-wavelength frequency discrimination detection DATA matrix DATA and DATA sequences I 1, I2, …, IN of N wavelengths lambda c1、λc2, …, λcN are obtained for subsequent processing;
；
The multichannel scanning detection method based on the dichroic mirror comprises the following steps:
(3-1) setting N-1 dichroic mirrors and detectors with corresponding wavelengths at the exit port of the Michelson interference frequency discrimination device with ultra wide band and ultra large field of view for a HSRL system with lambda c1、λc2, …, λcN and total N wavelengths, thereby constructing N detection channels with different wavelengths; n-1 dichroic mirrors separate light beams having wavelengths of lambda c1 and lambda c2,…,λc(N-1) and lambda cN, respectively;
(3-2) setting an air pressure tuning mechanism as a scanning mode, and collecting m data points in one scanning period; simultaneously, a light source of the multi-wavelength HSRL system is started, and the telescope is aimed at the target area for detection; after the data acquisition of k periods is completed, respectively obtaining a scanning detection data sequence I 1', I2', …, IN' of a lambda c1、λc2, …, λcN channel for subsequent processing; wherein the m data points of each period form a sine curve with period T and length lT, and l is more than 0.5 to ensure that the data has a minimum value.
10. The michelson interference frequency discrimination method of ultra-wideband ultra-large field of view according to claim 9, wherein in step (1-3), said actual thickness is measured by a micrometer gauge, and the corrected thickness d 1 'and the actual FSR' are determined by the following expressions:
；
；
Wherein c is the speed of light; lambda 0 is the design center wavelength, theta 1 and theta 2 are the 1-order and 2-order field broadening angles of the Michelson interferometer, theta 1、θ2 and FSR are set according to requirements, n 1 is the refractive index of the glass arm compensation mirror, and n 3 is the refractive index of the hybrid arm compensation mirror.
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