CN103954392B - What micro-momentum device was rocked in the measurement of linear frequency modulation multi-beam laser heterodyne rocks micro-impulse measurement method - Google Patents

Abstract

The measurement of linear frequency modulation multi-beam laser heterodyne is rocked the device of micro-momentum and is rocked micro-impulse measurement method based on this device, relates to and rocks micro-impulse measurement technical field.Solve the problem that measuring accuracy that other existing measurement rocks the apparatus and method of micro-momentum is low.The laser action that pulse laser emission goes out produces plasma spraying in working medium target, the effect of regurgitating makes Standard Beam rotate, while Standard Beam rotates, chirped laser device continues to launch chirped laser, chirped laser is incident to flat normal mirror after the first plane mirror and the reflection of the second plane mirror, the front surface of flat normal mirror and rear surface are all reflected chirped laser and are converged on the photosurface of photodetector by convergent lens, electric signal is sent to the pivot angle θ ' that signal processing system obtains Standard Beam by photodetector, micro-momentum I ' that the laser that sends of pulsed laser and the effect of working medium target produce is obtained again according to formula.The present invention is applicable to rock micro-impulse measurement.

Description

What micro-momentum device was rocked in the measurement of linear frequency modulation multi-beam laser heterodyne rocks micro-impulse measurement method

Technical field

The present invention relates to and rock micro-impulse measurement technical field.

Background technology

Laser microthruster has extensive and deep application prospect at microsatellite attitude and orbits controlling field, it has than leaping high, large, the minimum momentum of momentum dynamic range is little, low in energy consumption, energy coupling efficiency is high and be easy to realize, the significant advantage such as lightweight and Digital Control, receive Chinese scholars and pay close attention to widely.And momentum is an important parameter of reflection laser microthruster performance, feature is that magnitude is little, is about 10 ^-7~ 10 ^-5ns.The people such as PhotonicAssociates group Phipps proposed the micro impulse with rocking the generation of systematic survey laser microthruster in 1999, and carried out the test of microthruster performance parameter with it; 2002, the people such as Phipps improved the system of rocking again, and Chinese University of Science and Technology domestic subsequently and equipment Command technical college have also carried out correlative study.From the result of study of report both at home and abroad at present, on the one hand, the precision of the noise meeting influential system of measuring system, in little momentum magnitude, systematic error even reaches 50%; Meanwhile, within power action time, target plane departs from focal plane, and energy coupling efficiency reduces, and this also can affect the measurement of micro-momentum, and therefore conventional little impulse measurement system is difficult to meet measures requirement.

Laser interferance method effectively can solve the above two problems that conventional test system exists, and improves the measuring accuracy of system.The method adopting two corner cubes to form variate replaces original light pointer method measurement to rock the angle of rotation, substantially increases the precision of system; Rock the Push Technology quality of 2010 and be increased to 58g by original 0.2g, overcome out of focus problem.Result of study shows, the introducing of laser interferance method significantly improves the performance of rocking test macro, can meet the test request of laser microthruster micro impulse.But because indirectly measured quantities is more, accidental error is comparatively large, and therefore measuring accuracy also can not be very high.

Summary of the invention

The present invention rocks the low problem of the measuring accuracy of the apparatus and method of micro-momentum to solve existing measurement, proposes the measurement of linear frequency modulation multi-beam laser heterodyne and rocks the device of micro-momentum and rock micro-impulse measurement method based on this device.

The device that micro-momentum is rocked in the measurement of property frequency modulation multi-beam laser heterodyne comprises chirped laser device, the first plane mirror, the second plane mirror, flat normal mirror, Standard Beam, vacuum chamber, pulsed laser, working medium target, convergent lens, photodetector and signal processing system

Described chirped laser device, the first plane mirror, the second plane mirror, flat normal mirror, Standard Beam, pulsed laser, working medium target and convergent lens are all placed in vacuum chamber,

The center of described Standard Beam is fixed with turning axle,

The upper surface at Standard Beam pasted by described working medium target, and the lower surface at Standard Beam pasted by the second plane mirror, and working medium target and the second plane mirror are all positioned at same one end of Standard Beam,

The laser action that pulse laser emission goes out produces plasma spraying in working medium target, the effect of regurgitating makes Standard Beam rotate, while Standard Beam rotates, chirped laser device continues to launch chirped laser, chirped laser is incident to flat normal mirror after the first plane mirror and the reflection of the second plane mirror, the front surface of flat normal mirror and rear surface are all reflected chirped laser and are converged on the photosurface of photodetector by convergent lens, the electrical signal of photodetector is connected with the electric signal input end of signal processing system.

Described signal processing system comprises wave filter, prime amplifier, A/D converter and DSP, the electric signal input end of wave filter is connected with the electrical signal of photodetector as the electric signal input end of signal processing system, the filtering signal output terminal of wave filter is connected with the filtering signal input end of prime amplifier, the amplifying signal output terminal of prime amplifier is connected with the input end of analog signal of A/D converter, and the digital signal output end of A/D converter is connected with the digital signal input end of DSP.

Described vacuum chamber has vacuum window, and described vacuum window is for making the light convergence in vacuum chamber to the photodetector photosurface of vacuum chamber outside.

That rocks the device of micro-momentum based on the measurement of described linear frequency modulation multi-beam laser heterodyne rocks micro-impulse measurement method by following process implementation:

Pulsed laser, chirped laser device, photodetector and signal processing system are switched to duty, the light signal received is converted to electric signal and is sent to signal processing system by photodetector, signal processing system obtains the pivot angle θ ' of Standard Beam according to the continuous print electric signal received

According to:

$I^{\′}=\frac{2J\mathrm{\ω}}{D}\·{\mathrm{\θ}}^{\′}=\frac{4\mathrm{\π}J}{{\mathrm{DT}}^{\′}}\·{\mathrm{\θ}}^{\′}$ (formula one),

The laser that acquisition pulsed laser sends and micro-momentum I ' that the effect of working medium target produces, wherein, J is the moment of inertia of system of rocking, and ω is damped frequency, and T ' is damping period, and D is Standard Beam length, makes k=4 π J/DT ', then:

I '=k θ ' (formula two).

Signal processing system obtains the pivot angle θ ' of Standard Beam by following process implementation according to the continuous print electric signal received:

When chirped laser device continues the chirped laser of transmitting with incidence angle θ ₀when oblique incidence is to flat normal mirror, incident field E (t) of flat normal mirror is:

E (t)=E ₀exp{i (ω ₀t+k ' t ²) (formula three),

Wherein, for the rate of change of modulating bandwidth, T is the frequency modulation cycle, and Δ F is modulating bandwidth, E ₀for incident field amplitude, t is the time, ω ₀for incident field angular frequency, i represents imaginary number,

If the light path that chirped laser arrives flat normal mirror front surface is l, then t-l/c moment chirped laser arrives the reflection light field E of flat normal mirror front surface ₁(t) be:

$E_1\left(t\right)={\mathrm{\α}}_1{E}_0\exp \{i\[{\mathrm{\ω}}_0(t-\frac{l}{c})+k^{\′}{(t-\frac{l}{c})}^2\]\}$ (formula four),

The light of flat normal mirror front surface transmission is not all being carried out multiple reflections and refraction by the front surface of flat normal mirror and rear surface in the same time, and the light field reflecting the reflected light of acquisition is each time:

$\left\{\begin{array}{c}{E}_2\left(t\right)={\mathrm{\α}}_2{E}_0\exp \{i\[{\mathrm{\ω}}_0(t-\frac{l+2ndcos\mathrm{\θ}}{c})+k^{\′}{(t-\frac{l+2ndcos\mathrm{\θ}}{c})}^2+\frac{2{\mathrm{\ω}}_{0}ndcos\mathrm{\θ}}{c}\]\}\\ E_3\left(t\right)={\mathrm{\α}}_3{E}_0\exp \{i\[{\mathrm{\ω}}_0(t-\frac{l+4ndcos\mathrm{\θ}}{c})+k^{\′}{(t-\frac{l+4ndcos\mathrm{\θ}}{c})}^2+\frac{4{\mathrm{\ω}}_{0}ndcos\mathrm{\θ}}{c}\]\}\\ \·\\ \·\\ \·\\ E_m\left(t\right)={\mathrm{\α}}_m{E}_0\exp \{i\[{\mathrm{\ω}}_0(t-\frac{l+2(m-1)nd\cos \mathrm{\θ}}{c})+k^{\′}{(t-\frac{l+2(m-1)nd\cos \mathrm{\θ}}{c})}^2+\frac{2(m-1){\mathrm{\ω}}_{0}ndcos\mathrm{\θ}}{c}\]\}\\ \·\\ \·\\ \·\end{array}\right.$

(formula five),

Wherein, m is nonnegative integer, α ₁=r, α _m=β β ' r ' ^(2m-3)(m>=2), r is the reflectivity of light when injecting flat normal mirror from surrounding medium, β is the transmissivity of light when injecting flat normal mirror from surrounding medium, r ' is the reflectivity of flat normal mirror rear surface, and β ' is transmissivity when light is injected into surrounding medium from flat normal mirror inside, and d is flat normal mirror thickness, θ is refraction angle, n is flat normal mirror refractive index, and c is the light velocity

Photoelectric detector to total light field E ' (t) be:

E ' (t)=E ₁(t)+E ₂(t)+...+E _m(t)+... (formula six),

The photocurrent I that then photodetector exports is:

$I=\frac{\mathrm{\η}e}{hv}\frac{1}{Z}\underset{D}{\∫\∫}\frac{1}{2}\[E_1\left(t\right)+E_2\left(t\right)+...+E_m\left(t\right)+...\]{\[E_1\left(t\right)+E_2\left(t\right)+...+E_m\left(t\right)+...\]}^{*}ds$ (formula seven),

Wherein, e is electron charge, and Z is the intrinsic impedance of photodetector surfaces medium, and η is quantum efficiency, and D is the area of photodetector photosurface, and h is Planck's constant, and v is laser frequency, and No. * represents complex conjugate,

Electric current of intermediate frequency I is obtained according to formula seven _iFfor:

$I_{IF}=\frac{\mathrm{\η}e}{2hv}\frac{1}{Z}\underset{D}{\∫\∫}\underset{p=0}{\overset{m-1}{\Σ}}\underset{j=0}{\overset{m-p}{\Σ}}\left(E_j\right(t\left){E_{j+p}}^{*}\right(t)+{E_j}^{*}(t\left)E_{j+p}\right(t\left)\right)ds$ (formula eight),

Formula four and formula five are substituted in formula eight, arrange:

$I_{IF}=\frac{\mathrm{\η}e}{hv}\frac{\mathrm{\π}}{Z}{E}_0^2\underset{p=0}{\overset{m-1}{\Σ}}\underset{j=0}{\overset{m-p}{\Σ}}{\mathrm{\α}}_{j+p}{\mathrm{\α}}_{j}cos(\frac{4{\mathrm{pk}}^{\′}ndcos\mathrm{\θ}}{c}t-\frac{4{\mathrm{pk}}^{\′}ndcos\mathrm{\θ}(l+ndcos\mathrm{\θ})}{c^2})$ (formula nine),

Fourier transform is carried out to the intermediate frequency item difference on the frequency in formula nine, obtains the frequency f of interference signal _pfor:

$f_p=\frac{2{\mathrm{pk}}^{\′}ndcos\mathrm{\θ}}{\mathrm{\π}c}=K_{p}cos\mathrm{\θ}$ (formula ten),

Thus obtain the value of refraction angle θ, wherein K _pfor scale-up factor, and

According to the known refraction angle θ of refraction law and incidence angle θ ₀pass be:

θ ₀=arcsin (nsin θ) (formula 11),

According to the known incidence angle θ of input path geometric relationship ₀with the pass of the pivot angle θ ' of Standard Beam (3) be:

${\mathrm{\θ}}^{\′}=\frac{{\mathrm{\θ}}_0}{2}=\frac{arcsin\left(nsin\mathrm{\θ}\right)}{2}$ (formula 12),

The value of the pivot angle θ ' of the Standard Beam obtained in formula 12 is substituted in formula two, the laser that acquisition pulsed laser sends and micro-momentum I' that the effect of working medium target produces.

Beneficial effect: what the present invention proposed rocks that micro-impulse measurement method range of linearity is large, resolution is high, the advantage of this angle-measuring method is to rotation sensitive, insensitive to translation, therefore device of the present invention also has comparatively strong anti-interference ability to vibration, particularly low-frequency vibration, working state of system can be returned within a few second, not only reduce measuring error, also reduce the requirement to measuring equipment and experiment bad border.Simultaneously, when rotational angle less (being less than 5 °), the momentum surveyed and incident angle linear, measuring error is less than 0.48%, the requirement of laser microthruster impulse measurement can be met, for the performance assessing laser microthruster provides good measurement means.

Accompanying drawing explanation

Fig. 1 rocks the structural representation of the device of micro-momentum for the linear frequency modulation multi-beam laser heterodyne measurement described in embodiment one and embodiment two;

Fig. 2 is the linear frequency modulation multi-beam laser principle of interference schematic diagram of flat normal mirror;

Fig. 3 is the spectrogram that in different incidence angles situation, micro-impulse measurement is corresponding.

Embodiment

Embodiment one, composition graphs 1 illustrate this embodiment, the device that micro-momentum is rocked in linear frequency modulation multi-beam laser heterodyne measurement described in this embodiment comprises chirped laser device 5, first plane mirror 6, second plane mirror 4, flat normal mirror 7, Standard Beam 3, vacuum chamber 11, pulsed laser 1, working medium target 2, convergent lens 8, photodetector 9 and signal processing system 10

Described chirped laser device 5, first plane mirror 6, second plane mirror 4, flat normal mirror 7, Standard Beam 3, pulsed laser 1, working medium target 2 and convergent lens 8 are all placed in vacuum chamber 11,

The center of described Standard Beam 3 is fixed with turning axle,

The upper surface at Standard Beam 3 pasted by described working medium target 2, and the lower surface at Standard Beam 3 pasted by the second plane mirror 4, and working medium target 2 and the second plane mirror 4 are all positioned at same one end of Standard Beam 3,

The laser action that pulse laser emission goes out produces plasma spraying in working medium target 2, the effect of regurgitating makes Standard Beam 3 rotate, while Standard Beam 3 rotates, chirped laser device 5 continues to launch chirped laser, chirped laser is incident to flat normal mirror 7 after the first plane mirror 6 and the reflection of the second plane mirror 4, the front surface of flat normal mirror 7 and rear surface are all reflected chirped laser and are converged to by convergent lens 8 on the photosurface of photodetector 9, the electrical signal of photodetector 9 is connected with the electric signal input end of signal processing system 10.

Embodiment two, composition graphs 1 illustrates this embodiment, the difference that this embodiment rocks the device of micro-momentum with the linear frequency modulation multi-beam laser heterodyne measurement described in embodiment one is, described signal processing system 10 comprises wave filter 10-1, prime amplifier 10-2, A/D converter 10-3 and DSP10-4, the electric signal input end of wave filter 10-1 is connected with the electrical signal of photodetector 9 as the electric signal input end of signal processing system 10, the filtering signal output terminal of wave filter 10-1 is connected with the filtering signal input end of prime amplifier 10-2, the amplifying signal output terminal of prime amplifier 10-2 is connected with the input end of analog signal of A/D converter 10-3, the digital signal output end of A/D converter 10-3 is connected with the digital signal input end of DSP10-4.

Embodiment three, composition graphs 1 illustrate this embodiment, the difference that this embodiment rocks the device of micro-momentum with the linear frequency modulation multi-beam laser heterodyne measurement described in embodiment one is, described vacuum window is for making the light convergence in vacuum chamber 11 to photodetector 9 photosurface of vacuum chamber 11 outside.

Embodiment four, to rock the device of micro-momentum based on the linear frequency modulation multi-beam laser heterodyne measurement described in embodiment a gang of embodiment two rock micro-impulse measurement method by following process implementation:

Pulsed laser 1, chirped laser device 5, photodetector 9 and signal processing system 10 are switched to duty, the light signal received is converted to electric signal and is sent to signal processing system 10 by photodetector 9, signal processing system 10 obtains the pivot angle θ ' of Standard Beam 3 according to the continuous print electric signal received

According to:

$I^{\′}=\frac{2J\mathrm{\ω}}{D}\·{\mathrm{\θ}}^{\′}=\frac{4\mathrm{\π}J}{{\mathrm{DT}}^{\′}}\·{\mathrm{\θ}}^{\′}$ (formula one),

The laser that acquisition pulsed laser 1 sends and micro-momentum I ' that the effect of working medium target produces, wherein, J is the moment of inertia of system of rocking, and ω is damped frequency, and T ' is damping period, and D is Standard Beam 3 length, makes k=4 π J/DT ', then:

I '=k θ ' (formula two).

Embodiment five, composition graphs 2 illustrate this embodiment, the difference of rocking micro-impulse measurement method of rocking the device of micro-momentum based on measurements of linear frequency modulation multi-beam laser heterodyne described in this embodiment and embodiment four is, signal processing system 10 according to the pivot angle θ ' of the continuous print electric signal acquisition Standard Beam 3 received by following process implementation:

When chirped laser device 5 continues the chirped laser of transmitting with incidence angle θ ₀when oblique incidence is to flat normal mirror 7, incident field E (t) of flat normal mirror 7 is:

E (t)=E ₀exp{i (ω ₀t+k ' t ²) (formula three),

Wherein, for the rate of change of modulating bandwidth, T is the frequency modulation cycle, and Δ F is modulating bandwidth, E ₀for incident field amplitude, t is the time, ω ₀for incident field angular frequency, i represents imaginary number,

If the light path that chirped laser arrives flat normal mirror 7 front surface is l, then t-l/c moment chirped laser arrives the reflection light field E of flat normal mirror 7 front surface ₁(t) be:

$E_1\left(t\right)={\mathrm{\α}}_1{E}_0\exp \{i\[{\mathrm{\ω}}_0(t-\frac{l}{c})+k^{\′}{(t-\frac{l}{c})}^2\]\}$ (formula four),

The light of flat normal mirror 7 front surface transmission is not all being carried out multiple reflections and refraction by the front surface of flat normal mirror 7 and rear surface in the same time, and the light field reflecting the reflected light of acquisition is each time:

$\left\{\begin{array}{c}{E}_2\left(t\right)={\mathrm{\α}}_2{E}_0\exp \{i\[{\mathrm{\ω}}_0(t-\frac{l+2ndcos\mathrm{\θ}}{c})+k^{\′}{(t-\frac{l+2ndcos\mathrm{\θ}}{c})}^2+\frac{2{\mathrm{\ω}}_{0}ndcos\mathrm{\θ}}{c}\]\}\\ E_3\left(t\right)={\mathrm{\α}}_3{E}_0\exp \{i\[{\mathrm{\ω}}_0(t-\frac{l+4ndcos\mathrm{\θ}}{c})+k^{\′}{(t-\frac{l+4ndcos\mathrm{\θ}}{c})}^2+\frac{4{\mathrm{\ω}}_{0}ndcos\mathrm{\θ}}{c}\]\}\\ \·\\ \·\\ \·\\ E_m\left(t\right)={\mathrm{\α}}_m{E}_0\exp \{i\[{\mathrm{\ω}}_0(t-\frac{l+2(m-1)nd\cos \mathrm{\θ}}{c})+k^{\′}{(t-\frac{l+2(m-1)nd\cos \mathrm{\θ}}{c})}^2+\frac{2(m-1){\mathrm{\ω}}_{0}ndcos\mathrm{\θ}}{c}\]\}\\ \·\\ \·\\ \·\end{array}\right.$

(formula five),

Wherein, m is nonnegative integer, α ₁=r, α _m=β β ' r ' ^(2m-3)(m>=2), r is the reflectivity of light when injecting flat normal mirror 7 from surrounding medium, β is the transmissivity of light when injecting flat normal mirror 7 from surrounding medium, r ' is the reflectivity of flat normal mirror 7 rear surface, and β ' is transmissivity light to be injected into surrounding medium during from flat normal mirror 7 inside, and d is flat normal mirror 7 thickness, θ is refraction angle, n is flat normal mirror 7 refractive index, and c is the light velocity

Total light field E ' (t) that photodetector 9 receives is:

E ' (t)=E ₁(t)+E ₂(t)+...+E _m(t)+... (formula six),

The photocurrent I that then photodetector 9 exports is:

$I=\frac{\mathrm{\η}e}{hv}\frac{1}{Z}\underset{D}{\∫\∫}\frac{1}{2}\[E_1\left(t\right)+E_2\left(t\right)+...+E_m\left(t\right)+...\]{\[E_1\left(t\right)+E_2\left(t\right)+...+E_m\left(t\right)+...\]}^{*}ds$ (formula seven),

Wherein, e is electron charge, and Z is the intrinsic impedance of photodetector 9 surface dielectric, and η is quantum efficiency, and D is the area of photodetector 9 photosurface, and h is Planck's constant, and v is laser frequency, and No. * represents complex conjugate,

Electric current of intermediate frequency I is obtained according to formula seven _iFfor:

$I_{IF}=\frac{\mathrm{\η}e}{2hv}\frac{1}{Z}\underset{D}{\∫\∫}\underset{p=0}{\overset{m-1}{\Σ}}\underset{j=0}{\overset{m-p}{\Σ}}\left(E_j\right(t\left){E_{j+p}}^{*}\right(t)+{E_j}^{*}(t\left)E_{j+p}\right(t\left)\right)ds$ (formula eight),

Formula four and formula five are substituted in formula eight, arrange:

$I_{IF}=\frac{\mathrm{\η}e}{hv}\frac{\mathrm{\π}}{Z}{E}_0^2\underset{p=0}{\overset{m-1}{\Σ}}\underset{j=0}{\overset{m-p}{\Σ}}{\mathrm{\α}}_{j+p}{\mathrm{\α}}_{j}cos(\frac{4{\mathrm{pk}}^{\′}ndcos\mathrm{\θ}}{c}t-\frac{4{\mathrm{pk}}^{\′}ndcos\mathrm{\θ}(l+ndcos\mathrm{\θ})}{c^2})$ (formula nine),

Fourier transform is carried out to the intermediate frequency item difference on the frequency in formula nine, obtains the frequency f of interference signal _pfor:

$f_p=\frac{2{\mathrm{pk}}^{\′}ndcos\mathrm{\θ}}{\mathrm{\π}c}=K_{p}cos\mathrm{\θ}$ (formula ten),

Thus obtain the value of refraction angle θ, wherein K _pfor scale-up factor, and $K_p=\frac{2pknd}{\mathrm{\π}c},$

According to the known refraction angle θ of refraction law and incidence angle θ ₀pass be:

θ ₀=arcsin (nsin θ) (formula 11),

According to the known incidence angle θ of input path geometric relationship ₀with the pass of the pivot angle θ ' of Standard Beam 3 be:

${\mathrm{\θ}}^{\′}=\frac{{\mathrm{\θ}}_0}{2}=\frac{arcsin\left(nsin\mathrm{\θ}\right)}{2}$ (formula 12),

Substitute in formula two by the value of the pivot angle θ ' of the Standard Beam 3 obtained in formula 12, the laser that acquisition pulsed laser 1 sends and working medium target 2 act on the micro-momentum I ' produced.

In present embodiment, by measuring the change adding the system cycle before and after Standard Beam 3, calibrating the moment of inertia of system, can Proportional coefficient K be obtained according to calibration result _pvalue.

The device of micro-momentum is rocked in linear frequency modulation multi-beam laser heterodyne measurement shown in Fig. 1, under the condition of work of 10Pa, utilize MATLAB analogue measurement working medium for PVC (Polyvinylchloride)+2%C, thickness is 180 μm, laser initial current is 5A, pulsewidth is 50ms, micro-momentum that laser and working medium interaction produce, and verify the possibility of linear frequency modulation multi-beam laser heterodyne measuring method; get Standard Beam 3 length D=15cm; the refractive index n=1.493983 of flat normal mirror, thickness is 3cm; Chirped laser device wavelength is 1.55 μm, scan period T=1ms, modulation band-width Δ F=5GHz.

Emulation obtains different incidence angles θ ₀in situation, linear frequency modulation multi-beam laser heterodyne measures Fourier transform frequency spectrum corresponding to minute angle as shown in Figure 3, as can be seen from Figure 3, along with incidence angle θ ₀increase, the relative position of frequency spectrum moves, namely along with incidence angle θ to low frequency direction ₀increase, frequency reduce.This is because, at Proportional coefficient K _pwhen constant, due to the frequency f of interference signal _pwith incidence angle θ ₀pass be f _p=K _pcos θ=K _pcos [arcsin (sin θ ₀/ n)], incidence angle θ ₀with the frequency f of interference signal _pbe inversely, work as incidence angle θ ₀during increase, cos θ reduces thereupon, therefore, along with incidence angle θ ₀increase, the relative position of frequency spectrum moves to low frequency direction.

Utilize measuring method of the present invention, continuous coverage eight groups of data, obtain different incidence angles θ ₀the simulated measurement result of the micro-momentum of testing sample in situation, as shown in the table:

The emulation experiment data of table in utilization, calculate the average measurement value of micro-momentum, the maximum relative error of the measured value finally obtained is less than 0.48%, simultaneously, when small angle approximation, the systematic error that environment brings and reading error are negligible in simulations, and the error in emulation experiment is mainly from the trueness error after fast Fourier change and the round-off error in computation process.

Claims (1)

1. what micro-momentum device was rocked in the measurement of linear frequency modulation multi-beam laser heterodyne rocks micro-impulse measurement method, the device that the method relates to comprises chirped laser device (5), the first plane mirror (6), the second plane mirror (4), flat normal mirror (7), Standard Beam (3), vacuum chamber (11), pulsed laser (1), working medium target (2), convergent lens (8), photodetector (9) and signal processing system (10)

Described chirped laser device (5), the first plane mirror (6), the second plane mirror (4), flat normal mirror (7), Standard Beam (3), pulsed laser (1), working medium target (2) and convergent lens (8) are all placed in vacuum chamber (11)

The center of described Standard Beam (3) is fixed with turning axle,

Described working medium target (2) pastes the upper surface in Standard Beam (3), the lower surface in Standard Beam (3) pasted by second plane mirror (4), and working medium target (2) and the second plane mirror (4) are all positioned at same one end of Standard Beam (3)

The laser action that pulse laser emission goes out produces plasma spraying in working medium target (2), the effect of regurgitating makes Standard Beam (3) rotate, while Standard Beam (3) rotates, chirped laser device (5) continues to launch chirped laser, chirped laser is incident to flat normal mirror (7) after the first plane mirror (6) and the second plane mirror (4) reflection, the front surface of flat normal mirror (7) and rear surface are all reflected chirped laser and are converged on the photosurface of photodetector (9) by convergent lens (8), the electrical signal of photodetector (9) is connected with the electric signal input end of signal processing system (10),

Described signal processing system (10) comprises wave filter (10-1), prime amplifier (10-2), A/D converter (10-3) and DSP (10-4), the electric signal input end of wave filter (10-1) is connected with the electrical signal of photodetector (9) as the electric signal input end of signal processing system (10), the filtering signal output terminal of wave filter (10-1) is connected with the filtering signal input end of prime amplifier (10-2), the amplifying signal output terminal of prime amplifier (10-2) is connected with the input end of analog signal of A/D converter (10-3), the digital signal output end of A/D converter (10-3) is connected with the digital signal input end of DSP (10-4),

(11) have vacuum window to described vacuum chamber, and described vacuum window is used for the light in vacuum chamber (11) is assembled to vacuum chamber

(11) on outside photodetector (9) photosurface;

What micro-momentum device was rocked in the measurement of described linear frequency modulation multi-beam laser heterodyne rocks micro-impulse measurement method by following process implementation:

Pulsed laser (1), chirped laser device (5), photodetector (9) and signal processing system (10) are switched to duty, the light signal received is converted to electric signal and is sent to signal processing system (10) by photodetector (9), signal processing system (10) obtains the pivot angle θ ' of Standard Beam (3) according to the continuous print electric signal received

According to:

$I^{\′}=\frac{2J\mathrm{\ω}}{D}\·{\mathrm{\θ}}^{\′}=\frac{4\mathrm{\π}J}{{\mathrm{DT}}^{\′}}\·{\mathrm{\θ}}^{\′}$ (formula one),

The laser that acquisition pulsed laser (1) sends and working medium target (2) act on the micro-momentum I ' produced, and wherein, J is the moment of inertia of system of rocking, ω is damped frequency, and T ' is damping period, and D is Standard Beam (3) length, make k=4 π J/DT ', then:

I '=k θ ' (formula two);

It is characterized in that, signal processing system (10) obtains the pivot angle θ ' of Standard Beam (3) by following process implementation according to the continuous print electric signal received:

When chirped laser device (5) continues the chirped laser of transmitting with incidence angle θ ₀when oblique incidence is to flat normal mirror (7), incident field E (t) of flat normal mirror (7) is:

E (t)=E ₀exp{i (ω ₀t+k ' t ²) (formula three),

Wherein, for the rate of change of modulating bandwidth, T is the frequency modulation cycle, and △ F is modulating bandwidth, E ₀for incident field amplitude, t is the time, ω ₀for incident field angular frequency, i represents imaginary number,

If the light path that chirped laser arrives flat normal mirror (7) front surface is l, then t-l/c moment chirped laser arrives the reflection light field E of flat normal mirror (7) front surface ₁(t) be:

$E_1\left(t\right)={\mathrm{\α}}_1{E}_0\exp \{i\[{\mathrm{\ω}}_0(t-\frac{l}{c})+k^{\′}{\left(t-\frac{l}{c}\right)}^2\]\}$ (formula four),

The light of flat normal mirror (7) front surface transmission is not all being carried out multiple reflections and refraction by the front surface of flat normal mirror (7) and rear surface in the same time, and the light field reflecting the reflected light of acquisition is each time:

$\left\{\begin{array}{c}{E}_2\left(t\right)={\mathrm{\α}}_2{E}_0\exp \{i\[{\mathrm{\ω}}_0(t-\frac{l+2ndcos\mathrm{\θ}}{c})+k^{\′}{\left(t-\frac{l+2ndcos\mathrm{\θ}}{c}\right)}^2+\frac{2{\mathrm{\ω}}_{0}ndcos\mathrm{\θ}}{c}\]\}\\ E_3\left(t\right)={\mathrm{\α}}_3{E}_0\exp \{i\[{\mathrm{\ω}}_0(t-\frac{l+4ndcos\mathrm{\θ}}{c})+k^{\′}{\left(t-\frac{l+2ndcos\mathrm{\θ}}{c}\right)}^2+\frac{4{\mathrm{\ω}}_{0}ndcos\mathrm{\θ}}{c}\]\}\\ \·\\ \·\\ \·\\ E_m\left(t\right)={\mathrm{\α}}_m{E}_0\exp \{i\[{\mathrm{\ω}}_0(t-\frac{l+2(m-1)nd\cos \mathrm{\θ}}{c})+k^{\′}{(t-\frac{l+2(m-1)nd\cos \mathrm{\θ}}{c})}^2+\frac{2(m-1){\mathrm{\ω}}_{0}ndcos\mathrm{\θ}}{c}\]\}\\ \·\\ \·\\ \·\end{array}\right.$

(formula five),

Wherein, m is nonnegative integer, α ₁=r, α _m=β β ' r ' ^(2m-3)(m>=2), r is the reflectivity of light when injecting flat normal mirror (7) from surrounding medium, β is the transmissivity of light when injecting flat normal mirror (7) from surrounding medium, r ' is the reflectivity of flat normal mirror (7) rear surface, β ' is transmissivity light to be injected into surrounding medium during from flat normal mirror (7) inside, d is flat normal mirror (7) thickness, θ is refraction angle, n is flat normal mirror (7) refractive index, c is the light velocity

Total light field E ' (t) that photodetector (9) receives is:

E ' (t)=E ₁(t)+E ₂(t)+...+E _m(t)+... (formula six),

The photocurrent I that then photodetector (9) exports is:

$I=\frac{\mathrm{\η}e}{hv}\frac{1}{Z}\underset{D}{\∫\∫}\frac{1}{2}\[E_1\left(t\right)+E_2\left(t\right)+...+E_m\left(t\right)+...\]{\[E_1\left(t\right)+E_2\left(t\right)+...+E_m\left(t\right)+...\]}^{*}ds$ (formula seven),

Wherein, e is electron charge, and Z is the intrinsic impedance of photodetector (9) surface dielectric, and η is quantum efficiency, and D is the area of photodetector (9) photosurface, and h is Planck's constant, and v is laser frequency, and No. * represents complex conjugate,

Electric current of intermediate frequency I is obtained according to formula seven _iFfor:

$I_{IF}=\frac{\mathrm{\η}e}{2hv}\frac{1}{Z}\underset{D}{\∫\∫}\underset{p=0}{\overset{m-1}{\Σ}}\underset{j=0}{\overset{m-p}{\Σ}}\left(E_j\right(t\left){E_{j+p}}^{*}\right(t)+{E_j}^{*}(t\left)E_{j+p}\right(t\left)\right)ds$ (formula eight),

Formula four and formula five are substituted in formula eight, arrange:

$I_{IF}=\frac{\mathrm{\η}e}{hv}\frac{\mathrm{\π}}{Z}{E}_0^2\underset{p=0}{\overset{m-1}{\mathrm{\Σ}}}\underset{j=0}{\overset{m-p}{\mathrm{\Σ}}}{\mathrm{\α}}_{j+p}{\mathrm{\α}}_j\cos (\frac{4{\mathrm{pk}}^{\′}nd\cos \mathrm{\θ}}{c}t-\frac{4{\mathrm{pk}}^{\′}nd\cos \mathrm{\θ}(l+nd\cos \mathrm{\θ})}{c^2})$ (formula nine),

Fourier transform is carried out to the intermediate frequency item difference on the frequency in formula nine, obtains the frequency f of interference signal _pfor:

$f_p=\frac{2{\mathrm{pk}}^{\′}ndcos\mathrm{\θ}}{\mathrm{\π}c}=K_{p}cos\mathrm{\θ}$ (formula ten),

Thus obtain the value of refraction angle θ, wherein K _pfor scale-up factor, and

According to the known refraction angle θ of refraction law and incidence angle θ ₀pass be:

θ ₀=arcsin (nsin θ) (formula 11),

According to the known incidence angle θ of input path geometric relationship ₀with the pass of the pivot angle θ ' of Standard Beam (3) be:

${\mathrm{\θ}}^{\′}=\frac{{\mathrm{\θ}}_0}{2}=\frac{arcsin\left(nsin\mathrm{\θ}\right)}{2}$ (formula 12),

Substitute in formula two by the value of the pivot angle θ ' of the Standard Beam (3) obtained in formula 12, the laser that acquisition pulsed laser (1) sends and working medium target (2) act on the micro-momentum I ' produced.