LU500859B1 - Device and method for measuring refractive index of middle and upper atmosphere - Google Patents
Device and method for measuring refractive index of middle and upper atmosphere Download PDFInfo
- Publication number
- LU500859B1 LU500859B1 LU500859A LU500859A LU500859B1 LU 500859 B1 LU500859 B1 LU 500859B1 LU 500859 A LU500859 A LU 500859A LU 500859 A LU500859 A LU 500859A LU 500859 B1 LU500859 B1 LU 500859B1
- Authority
- LU
- Luxembourg
- Prior art keywords
- laser light
- light
- frequency difference
- measurement
- refractive index
- Prior art date
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/21—Polarisation-affecting properties
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
Abstract
A device and a method for measuring a refractive index of middle and upper atmosphere, comprising: a laser device, comprising a gain tube where two ends are sealed with a fixed cavity mirror and an anti-reflection window, respectively; a polarizing beam splitter, arranged at an outer side of the anti-reflection window; a first independent cavity mirror, arranged at a reflection end of the splitter; a second independent cavity mirror, arranged at a transmission end of the splitter; a high vacuum tube, arranged between the splitter and the first independent cavity mirror; a detection tube cavity, arranged between the splitter and the second independent cavity mirror; a polarizer, arranged at an outer side of the fixed cavity mirror; a frequency difference detector; a frequency meter, connected with the frequency difference detector to record a detected value of the frequency difference; and a data processing system, connected with the frequency meter.
Description
TECHNICAL FIELD The present application relates to the technical field of optical measurement, and in particular, to a device and a method for measuring a refractive index of middle and upper atmosphere.
BACKGROUND ART The middle and upper atmosphere (generally above 20km-200km) is an important part of near-Earth space environment, and physical processes, chemical processes and radiative processes therein are key links that affects changes of sun-earth space environment, global space climate and ground ecological environment. More and more detectors and aircrafts have entered the middle and upper atmosphere with space-air-ground integrated development, and therefore, it is important to research on physical characteristics and environmental changes of the middle and upper atmosphere.
Among characteristic parameters of the middle and upper atmosphere, density and temperature are key parameters for research of space physics and space weather forecast, and therefore, continuous measurements of density field and temperature field of the middle and upper area are critical to basically research on atmospheric climate, atmospheric dynamics, content of atmospheric molecules and the like. It is conducive to understanding interaction between upper atmospheric layer and lower atmospheric layer and constructing more accurate space weather forecast model. At the same time, the density, the temperature and the like of the middle and upper atmosphere have definite quantitative relationships with refractive index and may be obtained by measuring the refractive index and based on numerical models such as a Rüeger formula, a Barrell & Sears formula, and the like.
The density, the temperature and the like of the middle and upper atmosphere may be measured through technologies such as a laser radar, a meteor radar, an
Intermediate Frequency (IF)/Very High Frequency (VHF) radar, sounding rocket an&U500859 balloon carrying, satellite limb sounding, and the like. For example, a laser device emits a light beam of a specific wavelength into the atmosphere, and the light beam reacts with specific components in to-be-measured atmosphere to generate scattered and reflected light signals. Intensity, Doppler shift or broadening and the like of the scattered and reflected light signals are measured to invert density, temperature, wind speed and the like of the middle and upper atmosphere. A LEO (low earth orbit) satellite carries a high-precision accelerometer to measure acceleration changes generated when non-conservative force such as density damping, solar radiation light pressure, earthshine and outward radiation of the atmosphere acts on the satellite during operation. As a result, atmospheric density may be obtained through inversion after calibration and coordinate transformation. These detection methods generally have complex systems, are poor in linear response, have many intermediate error factors, and are difficult to compare with each other. As a result, the way of directly measuring the temperature and the density of the middle and upper atmosphere cannot obtain an ideal measurement result as a result of big measuring difficulty and small measuring height.
As mentioned above, the density and the temperature of the atmosphere may be inverted from the refractive index of the atmosphere. Therefore, it is particularly important to measure the refractive index of the middle and upper atmosphere. Various methods taking laser light as a medium to detect the middle and upper atmosphere include detecting based on changes of light intensity (such as a scattering laser radar and the like) and detecting based on frequency changes (such as a Doppler wind lidar, a Doppler broadening temperature-measuring radar and the like). As an excellent light source for outputting light with high power and a special wavelength, the laser device only can receive a weak echo light signal by adopting a large-caliber optical telescope, a narrow-line-width light filter, a high-sensitivity photoelectric detector and the like. Besides, these methods cannot directly measure the important optical index, namely the refractive index of the middle and upper atmosphere to further obtain information such as the density, the temperature and the like as a result of low matter density in the middle and upper atmosphere.
SUMMARY LU500859 To overcome the defects in the prior art, the present application aims to provide a device and a method for measuring a refractive index of middle and upper atmosphere, which are simple in structure and high in measuring precision.
To achieve the purpose, the present application adopts following technical solutions.
One aspect of the present application provides a device for measuring a refractive index of middle and upper atmosphere, comprising: a laser device, which is of a half-external cavity structure, and comprises a gain tube, where two ends of the grain tube are sealed with a fixed cavity mirror and an anti-reflection window, respectively, and the anti-reflection window is positioned at a light emitting end of the gain tube; a polarizing beam splitter, arranged at an outer side of the anti-reflection window and forms an angle with an emitted light, where the emitted light of the gain tube is reflected into a reference laser light and transmitted into a measurement laser light through the polarizing beam splitter, and polarization directions of the reference laser light and the measurement laser light are orthogonal to each other; a first independent cavity mirror, arranged at a reflection end of the polarizing beam splitter and forms a reference resonant cavity with the gain tube; a second independent cavity mirror, arranged at a transmission end of the polarizing beam splitter and forms a measurement resonant cavity with the gain tube; a high vacuum tube, arranged between the polarizing beam splitter and the first independent cavity mirror in the reference resonant cavity; a detection tube cavity, arranged between the polarizing beam splitter and the second independent cavity mirror in the measurement resonant cavity, where a length of the detection tube cavity is equal to a length of the high vacuum tube, and the detection tube cavity comprises an opening end which can be introduced into to-be-measured middle and upper atmosphere; a polarizer, arranged at an outer side of the fixed cavity mirror; a frequency difference detector, arranged at a polarized side of the laser device to detect a frequency difference between the reference laser light and the measuremerk/500859 laser light; a frequency meter, connected with the frequency difference detector to record a detected value of the frequency difference; and a data processing system, connected with the frequency meter and configured to calculate the refractive index of the middle and upper atmosphere based on the frequency difference.
In some embodiments of the present application, the device further comprises: a beam splitter, arranged between the polarizer and the fixed cavity mirror, and forms an angle of 45 degrees with a light transmission direction of the fixed cavity mirror, where the polarizer is positioned on a light transmission path of the beam splitter; a Wollaston prism, arranged on a light reflection path of the beam splitter, where reflected light of the beam splitter is split into a first polarized light and a second polarized light by the Wollaston prism according to two orthogonal polarized states; a first photoelectric detector, arranged on a light path of the first polarized light and configured to acquire light intensity of the first polarized light; a second photoelectric detector, arranged on a light path of the second polarized light and configured to acquire light intensity of the second polarized light; a data processing system, connected to the first photoelectric detector and the second photoelectric detector, and configured to record the light intensity of the first polarized light and the light intensity of the second polarized light and generate a first drive signal based on a difference value between the light intensity of the first polarized light and the light intensity of the second polarized light; a temperature control mechanism, connected with the data processing system and a heating wire on a surface of the gain tube, and configured to receive the first drive signal to control the heating wire to work, so as to compensate telescopic deformation of the gain tube caused by an environmental factor; and a piezoelectric ceramic actuator, connected with the data processing system and the first independent cavity mirror and configured to receive a second drive signal to drive the first independent cavity mirror.
In some embodiments of the present application, the frequency difference detector/500859 is a PIN diode or an avalanche photodiode.
In some embodiments of the present application, the data processing system is configured to calculate the refractive index of the middle and upper atmosphere according to following method: calculating the refractive index of the middle and upper atmosphere based on the frequency difference between the reference laser light in the reference resonant cavity and the measurement laser light in the measurement resonant cavity;
A A n=—|1-—|+1 2/ A
AAA 2 > wherein, 7 is the refractive index of the middle and upper atmosphere, A, is a first frequency difference between the measurement laser light at a descending edge and the reference laser light, A, is a second frequency difference between the measurement laser light at an ascending edge and the reference laser light, A is a longitudinal mode spacing of the measurement laser light, 4 is a wavelength of the measurement laser light and / is a length, in a direction of the laser beam, of the detection tube cavity.
Another aspect of the present application provides a method for measuring a refractive index of middle and upper atmosphere, using any one of the aforementioned device, wherein the method comprises following steps: step 1: introducing to-be-measured atmosphere into the detection tube cavity; step 2: detecting a first frequency difference between a reference laser light and a measurement laser light by the frequency difference detector and the frequency meter when the measurement laser light is at a descending edge, and detecting a second frequency difference between the reference laser light and the measurement laser light by the frequency difference detector and the frequency meter when the measurement laser light is at an ascending edge; and step 3: calculating the refractive index of the middle and upper atmosphere based on the first frequency difference and the second frequency difference through the datä/500859 processing system.
In some embodiments of the present application, the step 2 further comprises following steps: adjusting the temperature control mechanism and the heating wire according to light intensities of the first photoelectric detector and the second photoelectric detector, to make the measurement laser light at the descending edge and be equal to the reference laser light in light intensity to reach a first equal-light intensity point, and detecting the first frequency difference between the reference laser light and the measurement laser light by the frequency difference detector and the frequency meter; continue to adjust the temperature control mechanism and the heating wire by changing temperature, to make the measurement laser light at the ascending edge and be equal to the reference laser light in light intensity to reach a second equal-light intensity point, and detecting the second frequency difference between the reference laser light and the measurement laser light by the frequency difference detector and the frequency meter.
In some embodiments of the present application, the method further comprises following steps: vacuumizing the detection tube cavity firstly before performing the step 1, recording a third frequency difference A, when the reference laser light and the measurement laser light reach a first equal-light intensity point and a fourth frequency difference A, when the reference laser light and the measurement laser light reach a second equal-light intensity point; calculating an initial equivalent refractive index difference Am: An _ À An — A, "21 A0 +A, after the refractive index of the middle and upper atmosphere is calculated according to the step 3, compensating the initial equivalent refractive index difference An, in the calculated refractive index.
In some embodiments of the present application, a method for calculating the refractive index in the step 3 is as follows: LUS500859
A A n=—|1-—|+1 2/ A
AAA 2 > wherein, 7 is the refractive index of the middle and upper atmosphere, A, is the first frequency difference between the measurement laser light at the descending edge and the reference laser light, A, is the second frequency difference between the measurement laser light at the ascending edge and the reference laser light, A is a longitudinal mode spacing of the measurement laser, / is a wavelength of the measurement laser light and / is a length, in a direction of the laser beam, of the detection tube cavity.
Compared with the prior art, the present application has the following advantages and positive effects: (1) The to-be-measured atmosphere is introduced into the detection tube cavity; and the refractive index of the atmosphere is transformed into changes of laser frequency through cooperation of the gain tube, the high vacuum tube and the detection tube cavity, such that detection flexibility of the device is improved, and the middle and upper atmosphere with a very small refractive index can be measured.
(2) The laser light is split into two independent oscillating channels through the polarizing beam splitter based on s light and p light for respectively allowing gas disturbed and undisturbed by the atmosphere to pass through; and the two channels are separately designed, such that relative changes, caused by the changes of the refractive index of the atmosphere, of the length of the detection cavity may be sensitively responded.
(3) The detection system of the laser device does not need other frequency reference, and the laser device only may be directly used for detection, such that the light paths are simple, and the device is compact in structure, small in size, weight and power loss, and more suitable for a high-altitude platform that carriers a satellite or a balloon.
(4) The changes of the cavity length of a common part of a gain region of the laser device may be compensated through temperature compensation, so as to reduce thé/500859 influences of cavity length drift caused by environmental factors such as temperature on the measurement result and improve the measurement accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of laser resonant frequency; FIG. 2 is a principle diagram of measuring an atmospheric refractive index by a bifurcated cavity laser device; FIG. 3 is a schematic diagram showing an interval between two orthogonal polarization frequencies of a laser device at a first equal-light intensity point; FIG. 4 is a schematic diagram showing an interval between two orthogonal polarization frequencies of the laser device at a second equal-light intensity point; and FIG. 5 is a schematic diagram showing cavity lengths of a reference resonant cavity and a measurement resonant cavity of the laser device.
In the figures: 1-laser device; 101-laser gain tube; 102-fixed cavity mirror; 103-anti-reflection window; 2-polarizing beam splitter; 3-first independent cavity mirror, 4-second independent cavity mirror; 5-high vacuum tube; 6-detection tube cavity; 7-polarizer; 8-frequency difference detector; 9-frequency meter; 10-data processing system; 11-beam splitter; 12-Wollaston prism; 13-photoelectric detectors; 1301-first photoelectric detector; 1302-second photoelectric detector; 14-temperature control mechanism; 15-heating wire; and 16- piezoelectric ceramic actuator.
DETAILED DESCRIPTION OF EMBODIMENTS Hereinafter, the present application will be described in detail through exemplary embodiments. However, it should be understood that without further description, elements, structures, and features in one embodiment may also be beneficially combined into other embodiments.
In the description of the present application, it is to be understood that orientation or position relationships indicated by terms "upper", "lower", "front", "back" and the like ar&/500859 orientation or position relationships shown in the drawings, merely for describing the present application and simplifying the description rather than indicating or implying that the specified apparatus or element must have a particular orientation or be constructed and operated in a particular orientation, so the terms should not be interpreted as limitations to the present application.
It should be noted that when referred to as being "disposed on",or "fixed to" another element, an element may be directly on the other element or indirectly on the other element. When referred to as being "connected to" another element, one element may be directly connected to the other element or indirectly connected to the other element. In addition, the terms "first" and "second" are only used for the descriptive purpose, and cannot be understood as indicating or implying relative importance.
Embodiment 1 The first embodiment of the present application provides a device for measuring a refractive index of middle and upper atmosphere, which can be carried on high-altitude operation platforms.
The present application adopts the following design principle.
Among characteristic parameters of output laser light, light intensity is limited by stability of a pump source, a gain medium, and the like, and it is difficult to improve measurement accuracy. Frequency and phase are related together to meet the following self-consistent conditions: y =q—— 1 q Toni, ( ) 27 Aß=— 2nl, =q: 27 (g=1,2,3:-%) (2) Wherein, Vv, is oscillation frequency of a laser light, A¢ is total phase delay of the laser light going back and forth in a resonant cavity, À is wavelength of the laser light, L, is a cavity length of the resonant cavity, # is an equivalent refractive index in the resonant cavity, ¢ is light speed in vacuum and 4 is a positive integer. Since the frequency of the laser light is very big, reaching an order of 10", a value of 4 in a gas laser device is very big, generally reaching an order of 10° to 108. A frequency spectrum distribution of equally spaced resonant frequencies (namely longitudinal modes of th&U500859 laser light) of the laser device is shown in FIG. 1. Among them, fluorescence spectrum lines matched to gain medium and frequency selections Vv, and Vv,., of the resonant cavity and other limited modes can be formed to oscillate.
According to the formulas (1) and (2), the oscillation frequency is determined by equivalent physical cavity length L =nl, of the laser device. When the refractive index n in the resonant cavity changes slightly (such as a disturbance in middle and upper atmospheric), the big number 4 may cause significant changes in the oscillation frequency. At present, time and frequency are the most accurate basic physical quantities to be measured in the measurement field, which has achieved quantum standards, and reached measurement accuracy with an order of 10-15. Therefore, when thin middle and upper atmosphere is introduced into the resonant cavity, density and temperature changes cause equivalent refractive index to produce a small disturbance, and a precise measurement of frequency shift of the laser light caused thereby can achieve high-sensitivity detection on the refractive index of the middle and upper atmosphere.
Refer to FIG. 2, a first implementation structure of the device for measuring the refractive index of the middle and upper atmosphere comprises: a laser device 1 which is of a half-external cavity structure, and comprises a gain tube 101, where two ends of the grain tube 101 are sealed with a fixed cavity mirror 102 and an anti-reflection window 103, respectively, and the anti-reflection window 103 is positioned at a light emitting end of the gain tube 101; a polarizing beam splitter 2 which is arranged at an outer side of the anti-reflection window 103 and forms an angle with an emitted light, where the emitted light of the gain tube 101 is reflected into a reference laser light and transmitted into a measurement laser light through the polarizing beam splitter 2, and polarization directions of the reference laser light and the measurement laser light are orthogonal to each other; specifically, the laser light is partially reflected by the polarizing beam splitter 2 to form a reflected light , and is partially transmitted through the polarizing beam splitter 2 to form a transmitted light; a resonant cavity is split into two independent oscillation channels through the polarizing beam splitter 2 based on s light (marked as a perpendicular polarization state, namely reflected light) and p light (marked as a horizontal polarization state, namely transmitted light); LUS500859 a first independent cavity mirror 3 which is arranged at a reflection end of the polarizing beam splitter 2 and forms a reference resonant cavity with the gain tube 101; a second independent cavity mirror 4 which is arranged at a transmission end of the polarizing beam splitter 2 and forms a measurement resonant cavity with the gain tube 101; a high vacuum tube 5 which is arranged between the polarizing beam splitter 2 and the first independent cavity mirror 3 in the reference resonant cavity, i.e., positioned on a reflection light path of the polarizing beam splitter 2, and arranged on a light path of light with the perpendicular polarization state, where a cavity length of the high vacuum tube is L, and does not change because it is not affected by external atmospheric environment; in addition, the higher the vacuum degree of the high vacuum tube 5, the better; preferably, an air pressure in the high vacuum tube 5 is less than 10-7 Pa: a detection tube cavity 6 which is arranged between the polarizing beam splitter 2 and the second independent cavity mirror 4 in the measurement resonant cavity, where a length of the detection tube cavity 6 is equal to the cavity length of the high vacuum tube 5, and the detection tube cavity 6 comprises an opening end which can be introduced into to-be-measured middle and upper atmosphere; a polarizer 7 which is arranged at an outer side of the fixed cavity mirror 102; a frequency difference detector 8 which is arranged at a polarized side of the laser device 1 to detect a frequency difference between two orthogonal polarized laser lights, i.e., the reference laser light and the measurement laser light, where the frequency difference detector 8 may adopt a PIN diode or an avalanche photodiode; a frequency meter 9 which is connected with the frequency difference detector 8 to record a detected value of the frequency difference, where the frequency difference refers to a frequency difference between the reference laser light and the measurement laser light; and a data processing system 10 which is connected with the frequency meter 9 and configured to calculate the refractive index of the middle and upper atmosphere based on the frequency difference of the two orthogonal polarized laser lights.
In transmission processes on the light paths, s light is reflected to the first independent cavity mirror 3 by the polarizing beam splitter 2, and is further reflected té/500859 pass through the high vacuum tube 5 and form a resonant channel of a longitudinal mode Vv, of the reference laser light with the fixed cavity mirror 102; p light is completely transmitted through the polarizing beam splitter 2, and comes into the second independent cavity mirror 4 after passing through middle and upper atmospheric substance introduced through an external channel, to form a resonant channel of a longitudinal mode Vol of the measurement laser light with the fixed cavity mirror 102.
The longitudinal mode Vv, of the reference laser light is in a vacuum environment and is not disturbed by atmosphere, such that frequency of the reference laser light will not change; whereas, the longitudinal mode Vol of the measurement laser light is in the middle and upper atmospheric environment and is affected by factors such as density, temperature of the atmosphere and the like, the refractive index changes to cause frequency shift with offset Av as shown in FIG. 3.
After being emitted from an output end of the laser device 1, the two orthogonal polarized laser lights form an optical beat after passing through the polarizer 7; photoelectric detectors receive a beat frequency signal, i.e., the frequency difference of the two laser lights, and frequency offset between the s light and the p light is read by the frequency meter 9.
The present application further provides a second implementation structure of the device, refer to FIG. 2.
Since unstable factors of the laser device 1 are mainly concentrated in the gain medium and the pump source, that is, in the light path from the polarizing beam splitter 2 to the fixed cavity mirror 102, changes of the laser cavity lengths when changes occur are the same for the two oscillation channels, such that the mode Vv, and the mode Vol translate in a same direction on a frequency axis without changing the frequency difference, which belongs to common mode noise. In such a manner, the two laser modes may be at an "equal-light intensity point" by adjusting the fixed cavity mirror 102, such that non-linear errors of the measuring system are further reduced.
Specifically, in order to solve influences of space temperature changes on the resonant cavity and further influences on the measurement result, in somé&U500859 embodiments of the present application, based on the first implementation structure, the device further comprises: a beam splitter 11 which is arranged between the polarizer 7 and the fixed cavity mirror 102, and forms an angle of 45 degrees with a light transmission direction of the fixed cavity mirror 102, where the polarizer 7 is positioned on a light transmission path of the beam splitter 11; a Wollaston prism 12 which is arranged on a light reflection path of the beam splitter 11, where reflected light of the beam splitter 11 is split into a first polarized light and a second polarized light by the Wollaston prism 12; photoelectric detectors 13 comprising a first photoelectric detector 1301 arranged on a light path of the first polarized light and configured to acquire light intensity of the first polarized light, and a second photoelectric detector 1302 arranged on a light path of the second polarized light and configured to acquire light intensity of the second polarized light; a data processing system 10 which is connected to the first photoelectric detector 1301 and the second photoelectric detector 1302 and configured to generate a first drive signal based on a difference value between the light intensity of the first polarized light and the light intensity of the second polarized light; a temperature control mechanism 14 which is connected with the data processing system 10 and a heating wire 15 on a surface of the gain tube 101, and configured to receive the first drive signal to control the heating wire 15 to work, so as to compensate telescopic deformation, caused by an environmental factor, of the gain tube 101; and a piezoelectric ceramic actuator 16 which is connected with the data processing system 10 and the first independent cavity mirror 5 and configured to receive a second drive signal to drive the first independent cavity mirror 3.
Light output by the laser device 1 from one side of the fixed cavity mirror 102 is split into two light beams after passing through the beam splitter 11, and the light intensities of the two polarized lights split from one light beam are received by the two photoelectric detectors 13, respectively; the other light beam forms the optical beat after passing through the polarizer 7, the frequency difference between the mode v, of the reference
. , Co L laser light and the mode y, of the measurement laser light is measured through the 7500859 frequency difference detector 8, and is input to the frequency meter 9 to read out. When the gain tube 101 has telescopic deformation due to disturbances such as environmental temperature, vibration and the like, modes Vv, and Vol will shift in the same direction and be located at different positions on a gain curve, and thus nonlinear errors are introduced. The first photoelectric detector 1301 and the second photoelectric detector 1302 receive the light intensities of the two modes, and the first drive signal is generated after the data processing system 10 compares the light intensities; the heating wire 15 on the gain tube 101 is fed back and controlled to compensate the telescopic deformation of the gain tube 101, so that the modes Vv, and Vol are always at the "equal-light intensity point”. As shown in FIG. 3 and FIG. 4, measurement precision of the frequency difference is improved.
In the first implementation structure and the second implementation structure, the data processing system 10 is configured to calculate the refractive index of the middle and upper atmosphere based on the frequency difference between the reference laser light in the reference resonant cavity and the measurement laser light in the measurement resonant cavity according to the following method: calculating the refractive index of the middle and upper atmosphere based on the frequency difference between the reference laser light in the reference resonant cavity and the measurement laser light in the measurement resonant cavity;
A A n=—|1-—|+1 2/ A A +A, . . Co : As , Wherein, ” is the refractive index of the middle and upper atmosphere, A, is a first frequency difference between the measurement laser light at a descending edge and the reference laser light, A, is a second frequency difference between the measurement laser light at an ascending edge and the reference laser light, A is a longitudinal mode spacing of the measurement laser light, 1 is a wavelength of the measurement laser light and / is a length, in a direction of the laser beam, of the detection tube cavity 8.
The refractive index adopts the following calculating principle. LU500859 According to the measuring device as shown in FIG. 2, the longitudinal mode Vv, in the reference resonant cavity is a perpendicular polarization mode, the longitudinal mode Vol in the measurement resonant cavity is a horizontal polarization mode, and the two modes respectively meet the self-consistent condition, and the two orthogonal polarization modes are shown on a frequency spectrogram in FIG. 3, an envelope curve corresponds to gain curve width of the laser medium, and a central frequency is 4. The heating wire 15 of the gain tube 101 is adjusted in the device for measuring the refractive index of the middle and upper atmosphere, such that the perpendicular polarization mode Vv, in the reference resonant cavity and the horizontal polarization mode Vol in the measurement resonant cavity translate in the positive direction to reach a “first equal-light intensity point” position. Wherein, Vv, is at the ascending edge of the gain curve and Vol is at the descending edge of the gain curve. Before the measurement starts, the detection tube cavity 6 in the measurement resonant cavity is firstly vacuumized into a high vacuum degree, which is the same with that of the high vacuum tube 5. At this time, the light path of the measuring device is as shown in FIG. 5; equivalent physical cavity lengths between the fixed cavity mirror 102 of the gain tube 101 and the first independent cavity mirror 3 in the reference resonant cavity and between the fixed cavity mirror 102 and second independent cavity mirror 4 in the measurement resonant cavity are adjusted to be equal, which are L. At the same time, geometric lengths of the high vacuum tube 5 in the reference resonant cavity and the detection tube cavity 6 in the measurement resonant cavity are /. According to formula (1), the frequency of the reference laser light is as follows:
C V =q— 3 a by; (3) After reaching a detection position, the middle and upper atmosphere is introduced into the detection tube cavity 8 in the measurement resonant cavity via the opening end, the cavity length is changed to be L' =L+(n—1)/ based on changes of the gas refractive index, where the frequency of the oscillating laser is as follows: , C Yan (d+1) 57 (4)
The first frequency difference between the two oscillation modes is as follows: | LU500859 oe ,el'=1) A ST Tor ©) The length of the laser gain tube 101 is changed by further adjusting the temperature of the heating wire 15, such that the mode Vol of the measurement laser light moves out of a gain bandwidth; and meanwhile, a next-stage longitudinal mode Vu moves into the gain bandwidth to reach “a second equal-light intensity point”, as shown in FIG. 4. According to the above analysis, the second frequency difference between Vv, and Vu is as follows: , c c(L'-L) A,=v,— =—+4—" 6 2 Va Via 27! q 2LL! ( ) According to the frequency differences A, and A, measured at the equal-light intensity points twice, the frequency offset Av of Vu and Vol as well as longitudinal mode spacing A of adjacent stages, caused by introduction of the middle and upper atmosphere can be obtained from the above formulas (5) and (6): Ay = A, —A _g FL) 2 2LL (7) Ae A +A € 2 21" The refractive index of the middle and upper atmosphere may be obtained by calculating the cavity length Z’ in combination with formula (2):
A A n=—|1+— |+1 (8) 2/ A Embodiment 2 A second embodiment of the present application provides a method for measuring a refractive index of middle and upper atmosphere, using the device as described in Embodiment 1, wherein the method comprises the following steps: S1: to-be-measured atmosphere is introduced into the detection tube cavity 6 via an opening of the detection tube cavity 6.
S2: a first frequency difference between a reference laser light and a measuremert/500859 laser light is detected by the frequency difference detector 8 and the frequency meter 9 when the measurement laser light is at a descending edge of a gain curve, and a second frequency difference between the reference laser light and the measurement laser light is detected by the frequency difference detector 8 and the frequency meter 9 when the measurement laser light is at an ascending edge of the gain curve.
In some embodiments of the present application, the temperature control mechanism 14 and the heating wire 15 may be adjusted according to light intensity values of the first photoelectric detector 1301 and the second photoelectric detector 1302, to make the measurement laser light at the descending edge and be equal to the reference laser light in light intensity to reach a first equal-light intensity point, and the first frequency difference between the reference laser light and the measurement laser light is detected by the frequency difference detector 8 and the frequency meter 9.
The temperature control mechanism 14 and the heating wire 15 are adjusted by changing the temperature, to make the measurement laser light at the ascending edge and be equal to the reference laser light in light intensity and reach a second equal-light intensity point, and the second frequency difference between the reference laser light and the measurement laser light is detected by the frequency difference detector 8 and the frequency meter 9.
S3: the refractive index of the middle and upper atmosphere is calculated based on the frequency differences between the reference laser light and the measurement laser light measured twice through the data processing system 10. The calculating method is as follows.
n= ZA} ARTE , Wherein, ” is the refractive index of the middle and upper atmosphere, À, is the first frequency difference between the measurement laser light at a descending edge and the reference laser light, A, is the second frequency difference between the measurement laser light at an ascending edge and the reference laser light, A is a longitudinal mode spacing of the measurement laser, 4 is a wavelength of the measurement laser light and / is a length, in a direction of the laser beam, of the detection tube cavity 6. LUS500859 The physical cavity length of the reference resonant cavity is not equal to that of the measurement resonant cavity anymore as optical elements such as the anti-reflection window 103, the polarizing beam splitter 2, the high vacuum tube 5, the detection tube cavity 6 and the like in the laser resonant cavity have small anisotropy, for example, stress birefringence.
In some embodiments of the present application, the refractive index may be calibrated before measurement.
Before the to-be-measured atmosphere is introduced into the detection tube cavity 6, the detection tube cavity 6 is firstly vacuumized, and light intensity may be adjusted according to step S2. Frequency differences A, and A, when the reference laser light and the measurement laser light reach the first equal-light intensity point and the second equal-light intensity point are recorded; and in a follow-up measuring process, the light intensities of the reference laser light and the measurement laser light are not equal anymore, which may be caused by anisotropy in the cavity. According to formula (8), initial cavity length difference introduced based on anisotropy of elements may be equivalent as refractive index difference An, according to the following calculating formula: An, _ À An — A, (9) 21 Ay + An wherein, À, is a third frequency difference between the measurement laser light and the reference laser light when the detection tube cavity 6 is in a vacuum state and the reference laser light and the measurement laser light reach the first equal-light intensity point; A,, is a fourth frequency difference between the measurement laser light and the reference laser light when the detection tube cavity 6 is in a vacuum state and the reference laser light and the measurement laser light reach the second equal-light intensity point.
After the middle and upper atmosphere is introduced to measure the refractive index, the refractive index difference An, is subtracted from measurement result # of the refractive index to accomplish correction of the measurement result.
According to the device and the method for measuring the refractive index of the middle and upper atmosphere provided in the present application, no other frequenc/500859 reference is required, and the laser device only can be directly used for detection, the measurement result is high in accuracy; and the light paths are simple, and the device is compact in structure, small in size, weight and power loss, and more suitable for a high-altitude platform that carriers a satellite or a balloon.
Claims (8)
1. A device for measuring a refractive index of middle and upper atmosphere, comprising: a laser device, which is of a half-external cavity structure, and comprises a gain tube, where two ends of the grain tube are sealed with a fixed cavity mirror and an anti-reflection window, respectively, and the anti-reflection window is positioned at a light emitting end of the gain tube; a polarizing beam splitter, arranged at an outer side of the anti-reflection window and forms an angle with an emitted light, where the emitted light of the gain tube is reflected into a reference laser light and transmitted into a measurement laser light through the polarizing beam splitter, and polarization directions of the reference laser light and the measurement laser light are orthogonal to each other; a first independent cavity mirror, arranged at a reflection end of the polarizing beam splitter and forms a reference resonant cavity with the gain tube; a second independent cavity mirror, arranged at a transmission end of the polarizing beam splitter and forms a measurement resonant cavity with the gain tube; a high vacuum tube, arranged between the polarizing beam splitter and the first independent cavity mirror in the reference resonant cavity; a detection tube cavity, arranged between the polarizing beam splitter and the second independent cavity mirror in the measurement resonant cavity, where a length of the detection tube cavity is equal to a length of the high vacuum tube, and the detection tube cavity comprises an opening end which can be introduced into to-be-measured middle and upper atmosphere; a polarizer, arranged at an outer side of the fixed cavity mirror; a frequency difference detector, arranged at a polarized side of the laser device to detect a frequency difference between the reference laser light and the measurement laser light; a frequency meter, connected with the frequency difference detector to record a detected value of the frequency difference; and a data processing system, connected with the frequency meter and configured to calculate the refractive index of the middle and upper atmosphere based on thé&U500859 frequency difference.
2. The device according to claim 1, wherein, further comprises: a beam splitter, arranged between the polarizer and the fixed cavity mirror, and forms an angle of 45 degrees with a light transmission direction of the fixed cavity mirror, where the polarizer is positioned on a light transmission path of the beam splitter; a Wollaston prism, arranged on a light reflection path of the beam splitter, where reflected light of the beam splitter is split into a first polarized light and a second polarized light by the Wollaston prism according to two orthogonal polarized states; a first photoelectric detector, arranged on a light path of the first polarized light and configured to acquire light intensity of the first polarized light; a second photoelectric detector, arranged on a light path of the second polarized light and configured to acquire light intensity of the second polarized light; a data processing system, connected to the first photoelectric detector and the second photoelectric detector, and configured to record the light intensity of the first polarized light and the light intensity of the second polarized light and generate a first drive signal based on a difference value between the light intensity of the first polarized light and the light intensity of the second polarized light; a temperature control mechanism, connected with the data processing system and a heating wire on a surface of the gain tube, and configured to receive the first drive signal to control the heating wire to work, so as to compensate telescopic deformation of the gain tube caused by an environmental factor; and a piezoelectric ceramic actuator, connected with the data processing system and the first independent cavity mirror and configured to receive a second drive signal to drive the first independent cavity mirror.
3. The device according to claim 1, wherein, the frequency difference detector is a PIN diode or an avalanche photodiode.
4. The device according to claim 1, wherein, the data processing system is configured to calculate the refractive index of the middle and upper atmosphere according to following method:
calculating the refractive index of the middle and upper atmosphere based on th&U500859 frequency difference between the reference laser light in the reference resonant cavity and the measurement laser light in the measurement resonant cavity;
A A n=—|1-—|+1 2/ A
AAA 2 > wherein, 7 is the refractive index of the middle and upper atmosphere, A, is a first frequency difference between the measurement laser light at a descending edge and the reference laser light, A, is a second frequency difference between the measurement laser light at an ascending edge and the reference laser light, A is a longitudinal mode spacing of the measurement laser light, 4 is a wavelength of the measurement laser light and / is a length, in a direction of the laser beam, of the detection tube cavity.
5. A method for measuring a refractive index of middle and upper atmosphere, using the device according to any one of claims 1-4, wherein the method comprises following steps: step 1: introducing to-be-measured atmosphere into the detection tube cavity; step 2: detecting a first frequency difference between a reference laser light and a measurement laser light by the frequency difference detector and the frequency meter when the measurement laser light is at a descending edge, and detecting a second frequency difference between the reference laser light and the measurement laser light by the frequency difference detector and the frequency meter when the measurement laser light is at an ascending edge; and step 3: calculating the refractive index of the middle and upper atmosphere based on the first frequency difference and the second frequency difference through the data processing system.
6. The method according to claim 5, wherein, the step 2 further comprises following steps: adjusting the temperature control mechanism and the heating wire according to light intensities of the first photoelectric detector and the second photoelectric detector /500859 to make the measurement laser light at the descending edge and be equal to the reference laser light in light intensity to reach a first equal-light intensity point, and detecting the first frequency difference between the reference laser light and the measurement laser light by the frequency difference detector and the frequency meter; continue to adjust the temperature control mechanism and the heating wire by changing temperature, to make the measurement laser light at the ascending edge and be equal to the reference laser light in light intensity to reach a second equal-light intensity point, and detecting the second frequency difference between the reference laser light and the measurement laser light by the frequency difference detector and the frequency meter.
7. The method according to claim 5, wherein, further comprises following steps: vacuumizing the detection tube cavity firstly before performing the step 1, recording a third frequency difference A, when the reference laser light and the measurement laser light reach a first equal-light intensity point and a fourth frequency difference A, when the reference laser light and the measurement laser light reach a second equal-light intensity point; calculating an initial equivalent refractive index difference Am: An _ À An An "21 A0 +A, after the refractive index of the middle and upper atmosphere is calculated according to the step 3, compensating the initial equivalent refractive index difference An, in the calculated refractive index.
8. The method according to any one of claims 5-7, wherein, a method for calculating the refractive index in the step 3 is as follows:
A A n=—|1-—|+1 2/ A
AAA 2 > wherein, 7 is the refractive index of the middle and upper atmosphere, A, is th&U500859 first frequency difference between the measurement laser light at the descending edge and the reference laser light, A, is the second frequency difference between the measurement laser light at the ascending edge and the reference laser light, A is a longitudinal mode spacing of the measurement laser, / is a wavelength of the measurement laser light and / is a length, in a direction of the laser beam, of the detection tube cavity.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110504149.3A CN113092385B (en) | 2021-05-10 | 2021-05-10 | Middle and high-rise atmospheric refractive index measuring device and method |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| LU500859B1 true LU500859B1 (en) | 2022-05-17 |
Family
ID=76665171
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| LU500859A LU500859B1 (en) | 2021-05-10 | 2021-11-16 | Device and method for measuring refractive index of middle and upper atmosphere |
Country Status (2)
| Country | Link |
|---|---|
| CN (1) | CN113092385B (en) |
| LU (1) | LU500859B1 (en) |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5838485A (en) * | 1996-08-20 | 1998-11-17 | Zygo Corporation | Superheterodyne interferometer and method for compensating the refractive index of air using electronic frequency multiplication |
| AU2829499A (en) * | 1998-01-23 | 1999-08-09 | Torsana Biosensor A/S | Detection of a substance by refractive index change |
| KR101214850B1 (en) * | 2010-06-29 | 2012-12-24 | 서강대학교산학협력단 | polarization diversity interferometer, and microscope using this |
| CN102033053B (en) * | 2010-11-12 | 2012-06-20 | 浙江理工大学 | Method and device for measuring refractive index of air based on laser synthetic wavelength interferometry |
| CN102507450A (en) * | 2011-11-02 | 2012-06-20 | 中国人民解放军国防科学技术大学 | Method and device for measuring refractive index of transparent medium based on Y-shaped-cavity orthogonal polarization laser |
| US8902425B2 (en) * | 2012-04-08 | 2014-12-02 | University Of Zagreb | Temperature-stable incoherent light source |
| CN102735646B (en) * | 2012-06-20 | 2014-08-27 | 清华大学 | Measuring apparatus and measuring method for refractive index of transparent medium |
| CN104237164B (en) * | 2014-08-28 | 2017-08-25 | 华北水利水电大学 | Measurement apparatus and method of the nonlinear optical crystal in terahertz wave band refractive index |
| WO2019097024A1 (en) * | 2017-11-16 | 2019-05-23 | Consiglio Nazionale Delle Ricerche - Cnr | Method to measure the refractive index of a sample using surface plasmon polaritons |
-
2021
- 2021-05-10 CN CN202110504149.3A patent/CN113092385B/en active Active
- 2021-11-16 LU LU500859A patent/LU500859B1/en active IP Right Grant
Also Published As
| Publication number | Publication date |
|---|---|
| CN113092385B (en) | 2022-03-22 |
| CN113092385A (en) | 2021-07-09 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Spiers et al. | Atmospheric CO 2 measurements with a 2 μm airborne laser absorption spectrometer employing coherent detection | |
| Sommargren | A new laser measurement system for precision metrology | |
| CN101923162B (en) | Raman lidar calibration device and calibration method thereof | |
| CN100507478C (en) | Device and method for trace to the source for measuring any wave plate retardation | |
| CN110441792B (en) | Rayleigh scattering laser radar system capable of measuring wind and temperature simultaneously and related calibration method | |
| CN110411650B (en) | Vacuum measurement method based on optical frequency comb | |
| Eggins et al. | Laser-Doppler velocity measurements in an under-expanded free jet | |
| CN112731353B (en) | High-precision optical calibration device and method for large-range distance measurement | |
| Sonnenfroh et al. | In-situ sensing of tropospheric water vapor using an airborne near-IR diode laser hygrometer | |
| Downs et al. | Bi-directional fringe counting interference refractometer | |
| CN112433221B (en) | Absolute distance measuring device based on polarization modulation | |
| CN109579820B (en) | Method for improving scale factor performance of optical fiber gyroscope | |
| LU500859B1 (en) | Device and method for measuring refractive index of middle and upper atmosphere | |
| Vali et al. | Laser interferometer for earth strain measurements | |
| CN110702090A (en) | High-precision lock-zone-free laser gyro device and method | |
| Ledsham et al. | Dispersive reflection spectroscopy in the far infrared using a polarising interferometer | |
| CN102564613A (en) | Wavelength tracker | |
| JP2021189094A (en) | Light source device for fiber optic gyroscope | |
| Shen et al. | Fabry–Perot etalon-based ultraviolet high-spectral-resolution lidar for tropospheric temperature and aerosol measurement | |
| Huggett et al. | Precision electromagnetic distance-measuring instrument for determining secular strain and fault movement | |
| CN214201777U (en) | Absolute distance measuring device based on polarization modulation | |
| US6034773A (en) | Length measuring machine and method using laser beams | |
| Wen et al. | Vibration correction system toward dynamic absolute gravimetry | |
| US5233176A (en) | Precision laser surveying instrument using atmospheric turbulence compensation by determining the absolute displacement between two laser beam components | |
| Owens | The use of atmospheric dispersion in optical distance measurement |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FG | Patent granted |
Effective date: 20220517 |