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

A device for measuring torsion micro-impulse by linear frequency modulation multi-beam laser heterodyne and a method for measuring torsion micro-impulse based on the device relate to the technical field of torsion micro-impulse measurement. In addition, the problem of low measurement accuracy of the existing device and method for measuring torsion micro-impulse is solved. The laser emitted by the pulsed laser acts on the working fluid target to generate plasma jet, and the backspray effect causes the standard beam to rotate. While the standard beam rotates, the chirp laser continuously emits the chirp laser, and the chirp laser is reflected by the first plane Mirror and the second plane reflector are incident to the plane standard mirror after being reflected, the front surface and the rear surface of the plane standard mirror all reflect the chirp laser and converge it to the photosensitive surface of the photodetector through the converging lens, and the photodetector converts the electric The signal is sent to the signal processing system to obtain the swing angle θ' of the standard beam, and then according to the formula, the micro-pulse I' generated by the interaction between the laser emitted by the pulse laser and the working medium target is obtained. The invention is suitable for torsion micro-impulse measurement.

Description

Method for Measuring Torsional Micro-Impulse of Linear Frequency Modulated Multi-beam Laser Heterodyne Measuring Device of Torsional Micro-impulse

technical field

The invention relates to the technical field of torsion micro-impulse measurement.

Background technique

Laser micro-thrusters have broad and in-depth application prospects in the field of attitude and orbit control of micro-satellites. Significant advantages such as digital control have attracted extensive attention from scholars at home and abroad. The impulse is an important parameter reflecting the performance of the laser microthruster, which is characterized by a small magnitude, about 10 ^-7 ~ 10 ^-5 N·s. In 1999, Phipps et al. of Photonic Associates group proposed to use the torsion pendulum system to measure the micro-impulse generated by the laser micro-thruster, and used it to test the performance parameters of the micro-thruster; in 2002, Phipps et al. improved the torsion system, and then domestic The China University of Science and Technology and the Institute of Equipment Command Technology have also conducted related research. Judging from the research results reported at home and abroad, on the one hand, the noise of the measurement system will affect the accuracy of the system. At the small impulse level, the system error even reaches 50%. Plane, the energy coupling efficiency is reduced, which will also affect the measurement of micro-impulse, so the conventional small-impulse measurement system is difficult to meet the measurement requirements.

Laser interferometry can effectively solve the above two problems existing in conventional test systems and improve the measurement accuracy of the system. Using two corner cubes to form a differential measurement method to replace the original optical pointer method to measure the angle of torsion rotation, greatly improving the accuracy of the system; the mass of the torsion propulsion technology increased from 0.2g to 58g in 2010, which overcomes the problem of separation focus problem. The research results show that the introduction of laser interferometry has greatly improved the performance of the torsion test system, which can meet the test requirements of the small impulse of the laser micro thruster. However, due to the large amount of indirect measurement and the large accidental error, the measurement accuracy will not be very high.

Contents of the invention

In order to solve the problem of low measurement accuracy of existing devices and methods for measuring torsion micro-impulse, the present invention proposes a device for measuring torsion micro-impulse by linear frequency modulation multi-beam laser heterodyne and a method for measuring torsion micro-impulse based on the device.

The device for measuring the torsion micro-impulse by heterodyne frequency-modulated multi-beam laser includes a linear frequency-modulated laser, a first plane mirror, a second plane mirror, a plane standard mirror, a standard beam, a vacuum chamber, a pulse laser, a working medium target, a converging lens, photodetector and signal processing system,

The chirp laser, the first plane reflector, the second plane reflector, the plane standard mirror, the standard beam, the pulse laser, the working medium target and the converging lens are all placed in the vacuum chamber,

The center of the standard beam is fixed with an axis of rotation,

The working fluid target is pasted on the upper surface of the standard beam, the second plane mirror is pasted on the lower surface of the standard beam, and the working fluid target and the second plane mirror are located at the same end of the standard beam,

The laser emitted by the pulsed laser acts on the working fluid target to generate plasma jet, and the backspray effect causes the standard beam to rotate. While the standard beam rotates, the chirp laser continuously emits the chirp laser, and the chirp laser is reflected by the first plane The mirror and the second plane reflector are incident to the plane standard mirror after being reflected, the front surface and the back surface of the plane standard mirror all reflect the chirp laser and converge it to the photosensitive surface of the photodetector through the converging lens, and the electric detector of the photodetector The signal output terminal is connected with the electrical signal input terminal of the signal processing system.

Described signal processing system comprises filter, preamplifier, A/D converter and DSP, and the electrical signal input end of filter is connected with the electrical signal output end of photodetector as the electrical signal input end of signal processing system, and filter The filter signal output end of the preamplifier is connected to the filter signal input end of the preamplifier, the amplified signal output end of the preamplifier is connected to the analog signal input end of the A/D converter, and the digital signal output end of the A/D converter is connected to the DSP Digital signal input connection.

A vacuum window is opened on the vacuum chamber, and the vacuum window is used to converge the light in the vacuum chamber to the photosensitive surface of the photodetector outside the vacuum chamber.

The method of measuring the torsion micro-impulse based on the device for measuring the torsion micro-impulse by linear frequency modulation multi-beam laser heterodyne is realized by the following process:

Switch the pulse laser, chirp laser, photodetector and signal processing system to the working state, the photodetector converts the received optical signal into an electrical signal and sends it to the signal processing system, and the signal processing system receives the continuous electrical signal Obtain the swing angle θ′ of the standard beam,

according to:

$I^{\′}=\frac{2J\mathrm{\ω}}{\mathrm{D.}}\·{\mathrm{\θ}}^{\′}=\frac{4\mathrm{\π}J}{{\mathrm{DT}}^{\′}}\·{\mathrm{\θ}}^{\′}$ (Formula 1),

Obtain the micro-impulse I' generated by the interaction between the laser emitted by the pulsed laser and the working medium target, where J is the moment of inertia of the torsion pendulum system, ω is the damping frequency, T' is the damping period, D is the standard beam length, and k=4πJ/ DT′, then:

I'=k·θ' (Formula 2).

The signal processing system obtains the swing angle θ' of the standard beam according to the received continuous electrical signal through the following process:

When the chirp laser continuously emitted by the chirp laser is obliquely incident on the planar standard mirror at an incident angle θ ₀ , the incident light field E(t) of the planar standard mirror is:

E(t)＝E ₀ exp{i(ω ₀ t+k′t ² )} (Formula 3),

in, is the rate of change of the frequency modulation bandwidth, T is the frequency modulation period, ΔF is the frequency modulation bandwidth, E ₀ is the amplitude of the incident light field, t is time, ω ₀ is the angular frequency of the incident light field, i represents an imaginary number,

Assuming that the optical path of the chirp laser reaching the front surface of the plane standard mirror is l, then the reflected light field E ₁ (t) of the chirp laser reaching the front surface of the plane standard mirror at time tl/c is:

${\mathrm{E.}}_1\left(t\right)={\mathrm{\α}}_1{\mathrm{E.}}_0\exp \{i\[{\mathrm{\ω}}_0(t-\frac{l}{c})+k^{\′}{(t-\frac{l}{c})}^2\]\}$ (Formula 4),

The light transmitted by the front surface of the plane standard mirror is reflected and refracted multiple times by the front surface and the back surface of the plane standard mirror at different times, and the light field of the reflected light obtained by each reflection is:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}^{<span\; class="notranslate">\; \&prime;</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; \}</span>\\ {\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}^{<span\; class="notranslate">\; \&prime;</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; \}</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ {\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}^{<span\; class="notranslate">\; \&prime;</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; \}</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&CenterDot;</span>\end{array}\right.$

(Formula 5),

Among them, m is a non-negative integer, α ₁ = r, α _m = ββ'r' ^(2m-3) (m≥2), r is the reflectivity when light enters the plane standard mirror from the surrounding medium, and β is the light The transmittance when entering the plane standard mirror from the surrounding medium, r' is the reflectivity of the back surface of the plane standard mirror, β' is the transmittance when the light enters the surrounding medium from the inside of the plane standard mirror, and d is the thickness of the plane standard mirror , θ is the angle of refraction, n is the refractive index of the plane standard mirror, c is the speed of light,

The total light field E′(t) received by the photodetector is:

E'(t)=E ₁ (t)+E ₂ (t)+...+E _m (t)+... (Formula 6),

Then the photocurrent I output by the photodetector is:

$I=\frac{\mathrm{\&eta;}e}{hv}\frac{1}{Z}\underset{\mathrm{D.}}{\&Integral;\&Integral;}\frac{1}{2}\&lsqb;{\mathrm{E.}}_1\left(t\right)+{\mathrm{E.}}_2\left(t\right)+...+{\mathrm{E.}}_m\left(t\right)+...\&rsqb;{\&lsqb;{\mathrm{E.}}_1\left(t\right)+{\mathrm{E.}}_2\left(t\right)+...+{\mathrm{E.}}_m\left(t\right)+...\&rsqb;}^{*}d\mathrm{the\; s}$ (Formula 7),

Among them, e is the electron charge, Z is the intrinsic impedance of the surface medium of the photodetector, η is the quantum efficiency, D is the area of the photosensitive surface of the photodetector, h is Planck's constant, v is the laser frequency, and the * sign represents a complex number conjugated,

According to formula 7, the intermediate frequency current I _IF is obtained as:

$I_{If}=\frac{\mathrm{\&eta;}e}{2hv}\frac{1}{Z}\underset{\mathrm{D.}}{\&Integral;\&Integral;}\underset{p=0}{\overset{m-1}{\&Sigma;}}\underset{j=0}{\overset{m-p}{\&Sigma;}}\left({\mathrm{E.}}_j\right(t\left){{\mathrm{E.}}_{j+p}}^{*}\right(t)+{{\mathrm{E.}}_j}^{*}(t\left){\mathrm{E.}}_{j+p}\right(t\left)\right)d\mathrm{the\; s}$ (Equation 8),

Substituting Formula 4 and Formula 5 into Formula 8, we can get:

$I_{If}=\frac{\mathrm{\&eta;}e}{hv}\frac{\mathrm{\&pi;}}{Z}{\mathrm{E.}}_0^2\underset{p=0}{\overset{m-1}{\&Sigma;}}\underset{j=0}{\overset{m-p}{\&Sigma;}}{\mathrm{\&alpha;}}_{j+p}{\mathrm{\&alpha;}}_{j}co\mathrm{the\; s}(\frac{4{\mathrm{pk}}^{\&prime;}\mathrm{no}dco\mathrm{the\; s}\mathrm{\&theta;}}{c}t-\frac{4{\mathrm{pk}}^{\&prime;}\mathrm{no}dco\mathrm{the\; s}\mathrm{\&theta;}(l+\mathrm{no}dco\mathrm{the\; s}\mathrm{\&theta;})}{c^2})$ (Formula 9),

Perform Fourier transform on the frequency difference of the intermediate frequency term in formula 9, and obtain the frequency f _p of the interference signal as:

$f_p=\frac{2{\mathrm{pk}}^{\&prime;}\mathrm{no}dco\mathrm{the\; s}\mathrm{\&theta;}}{\mathrm{\&pi;}c}=K_{p}co\mathrm{the\; s}\mathrm{\&theta;}$ (formula ten),

Thus the value of the refraction angle θ is obtained, where K _p is the proportionality factor, and

According to the law of refraction, the relationship between the refraction angle θ and the incident angle θ ₀ is:

θ ₀ = arcsin(nsinθ) (Formula 11),

According to the geometric relationship of the incident light path, the relationship between the incident angle θ ₀ and the swing angle θ′ of the standard beam (3) is:

${\mathrm{\&theta;}}^{\&prime;}=\frac{{\mathrm{\&theta;}}_0}{2}=\frac{arc\mathrm{the\; s}i\mathrm{no}\left(\mathrm{no}\mathrm{the\; s}i\mathrm{no}\mathrm{\&theta;}\right)}{2}$ (Formula 12),

Substituting the value of the swing angle θ' of the standard beam obtained in Formula 12 into Formula 2, the micro-impulse I' generated by the interaction between the laser light emitted by the pulse laser and the working medium target is obtained.

Beneficial effects: the torsional micro-impulse measurement method proposed by the present invention has a large linear range and high resolution. The advantage of this angle measurement method is that it is sensitive to rotation and insensitive to translation, so the device of the present invention also has strong anti-interference to vibration Capability, especially low-frequency vibration, can be restored to the working state of the system within a few seconds, which not only reduces the measurement error, but also reduces the requirements for the measurement equipment and the experimental environment. At the same time, when the rotation angle is small (less than 5°), the measured impulse has a linear relationship with the incident angle, and the measurement error is less than 0.48%, which can meet the requirements of laser microthruster impulse measurement. Provides a good means of measurement.

Description of drawings

Fig. 1 is a structural schematic diagram of the device for measuring torsional micro-impulse by chirped multi-beam laser heterodyne described in Embodiment 1 and Embodiment 2;

Fig. 2 is a schematic diagram of the chirp multi-beam laser interference principle of the planar standard mirror;

Fig. 3 is the spectrum diagram corresponding to the micro-impulse measurement under different incident angles.

detailed description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 1. This specific embodiment is described in conjunction with FIG. 1. The device for measuring the torsion micro-impulse by chirping multi-beam laser heterodyne described in this specific embodiment includes a chirp laser 5, a first plane mirror 6, a second plane Mirror 4, plane standard mirror 7, standard beam 3, vacuum chamber 11, pulse laser 1, working medium target 2, converging lens 8, photodetector 9 and signal processing system 10,

The chirp laser 5, the first plane reflector 6, the second plane reflector 4, the plane standard mirror 7, the standard beam 3, the pulsed laser 1, the working medium target 2 and the converging lens 8 are all placed in the vacuum chamber 11,

The center of the standard beam 3 is fixed with a rotating shaft,

The working fluid target 2 is pasted on the upper surface of the standard beam 3, the second plane mirror 4 is pasted on the lower surface of the standard beam 3, and the working fluid target 2 and the second plane mirror 4 are both located on the standard beam 3 same end,

The laser emitted by the pulsed laser acts on the working medium target 2 to generate plasma spray, and the backspray effect causes the standard beam 3 to rotate. While the standard beam 3 rotates, the chirp laser 5 continuously emits the chirp laser, and the chirp laser passes through The first plane reflector 6 and the second plane reflector 4 are incident to the plane standard mirror 7 after reflection, the front surface and the rear surface of the plane standard mirror 7 all reflect the chirp laser and converge to the photodetector 9 through the converging lens 8 On the photosensitive surface, the electrical signal output end of the photodetector 9 is connected to the electrical signal input end of the signal processing system 10 .

Specific Embodiment 2. This specific embodiment is described in conjunction with FIG. 1. The difference between this specific embodiment and the device for measuring torsion micro-impulse by chirp multi-beam laser heterodyne described in specific embodiment 1 is that the signal processing system 10 includes Filter 10-1, preamplifier 10-2, A/D converter 10-3 and DSP10-4, the electrical signal input terminal of filter 10-1 is used as the electrical signal input terminal of signal processing system 10 and photodetector The electrical signal output end of 9 is connected, the filter signal output end of filter 10-1 is connected with the filter signal input end of preamplifier 10-2, the amplified signal output end of preamplifier 10-2 is connected with A/D converter 10 The analog signal input end of -3 is connected, and the digital signal output end of A/D converter 10-3 is connected with the digital signal input end of DSP10-4.

Specific Embodiment 3. This specific embodiment is described in conjunction with FIG. 1. The difference between this specific embodiment and the device for measuring torsion micro-impulse by chirp multi-beam laser heterodyne described in specific embodiment 1 is that the vacuum window is used to use The light in the vacuum chamber 11 converges to the photosensitive surface of the photodetector 9 outside the vacuum chamber 11 .

Embodiment 4. The method for measuring the micro-impulse torsion of the device for measuring the micro-impulse torsion by heterodyning the linear frequency-modulated multi-beam laser described in the second embodiment is realized by the following process:

Switch the pulse laser 1, the chirp laser 5, the photodetector 9 and the signal processing system 10 to the working state, the photodetector 9 converts the received optical signal into an electrical signal and sends it to the signal processing system 10, and the signal processing system 10 according to The received continuous electrical signal obtains the swing angle θ' of the standard beam 3,

according to:

$I^{\&prime;}=\frac{2J\mathrm{\&omega;}}{\mathrm{D.}}\&Center\; Dot;{\mathrm{\&theta;}}^{\&prime;}=\frac{4\mathrm{\&pi;}J}{{\mathrm{DT}}^{\&prime;}}\&Center\; Dot;{\mathrm{\&theta;}}^{\&prime;}$ (Formula 1),

Obtain the micro-impulse I' generated by the action of the laser light emitted by the pulsed laser 1 and the working medium target, wherein J is the moment of inertia of the torsional pendulum system, ω is the damping frequency, T' is the damping period, D is the length of the standard beam 3, and k= 4πJ/DT′, then:

I'=k·θ' (Formula 2).

Embodiment 5. This embodiment is described in conjunction with FIG. 2. The difference between this embodiment and the method for measuring the torsion micro-impulse based on the device for measuring the torsion micro-impulse based on chirp multi-beam laser heterodyne described in Embodiment 4 is that, The acquisition of the swing angle θ' of the standard beam 3 by the signal processing system 10 according to the received continuous electrical signal is realized by the following process:

When the chirp laser continuously emitted by the chirp laser 5 is obliquely incident on the plane standard mirror 7 at an incident angle θ ₀ , the incident light field E(t) of the plane standard mirror 7 is:

E(t)＝E ₀ exp{i(ω ₀ t+k′t ² )} (Formula 3),

in, is the rate of change of the frequency modulation bandwidth, T is the frequency modulation period, ΔF is the frequency modulation bandwidth, E ₀ is the amplitude of the incident light field, t is time, ω ₀ is the angular frequency of the incident light field, i represents an imaginary number,

Let the optical path of the chirp laser reach the front surface of the plane standard mirror 7 be l, then the reflected light field E ₁ (t) of the chirp laser reaching the front surface of the plane standard mirror 7 at time t1/c is:

${\mathrm{E.}}_1\left(t\right)={\mathrm{\&alpha;}}_1{\mathrm{E.}}_0\exp \{i\&lsqb;{\mathrm{\&omega;}}_0(t-\frac{l}{c})+k^{\&prime;}{(t-\frac{l}{c})}^2\&rsqb;\}$ (Formula 4),

The light transmitted by the front surface of the plane standard mirror 7 is reflected and refracted multiple times by the front surface and the rear surface of the plane standard mirror 7 at different times, and the light field of the reflected light obtained by each reflection is:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}^{<span\; class="notranslate">\; \&prime;</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; \}</span>\\ {\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}^{<span\; class="notranslate">\; \&prime;</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; \}</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ {\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}^{<span\; class="notranslate">\; \&prime;</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; \}</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\end{array}\right.$

(Formula 5),

Among them, m is a non-negative integer, α ₁ =r, α _m =ββ'r' ^(2m-3) (m≥2), r is the reflectivity when light enters the plane standard mirror 7 from the surrounding medium, and β is The transmittance when light enters the plane standard mirror 7 from the surrounding medium, r' is the reflectivity of the rear surface of the plane standard mirror 7, and β' is the transmittance when the light enters the surrounding medium from the inside of the plane standard mirror 7, and d is The thickness of the plane standard mirror 7, θ is the refraction angle, n is the refractive index of the plane standard mirror 7, c is the speed of light,

The total light field E'(t) received by the photodetector 9 is:

E'(t)=E ₁ (t)+E ₂ (t)+...+E _m (t)+... (Formula 6),

Then the photoelectric current I of photodetector 9 output is:

$I=\frac{\mathrm{\&eta;}e}{hv}\frac{1}{Z}\underset{\mathrm{D.}}{\&Integral;\&Integral;}\frac{1}{2}\&lsqb;{\mathrm{E.}}_1\left(t\right)+{\mathrm{E.}}_2\left(t\right)+...+{\mathrm{E.}}_m\left(t\right)+...\&rsqb;{\&lsqb;{\mathrm{E.}}_1\left(t\right)+{\mathrm{E.}}_2\left(t\right)+...+{\mathrm{E.}}_m\left(t\right)+...\&rsqb;}^{*}d\mathrm{the\; s}$ (Formula 7),

Wherein, e is electron charge, Z is the intrinsic impedance of photodetector 9 surface medium, η is quantum efficiency, D is the area of 9 photosensitive surfaces of photodetector, h is Planck's constant, v is laser frequency, * sign represents the complex conjugate,

According to formula 7, the intermediate frequency current I _IF is obtained as:

$I_{If}=\frac{\mathrm{\&eta;}e}{2hv}\frac{1}{Z}\underset{\mathrm{D.}}{\&Integral;\&Integral;}\underset{p=0}{\overset{m-1}{\&Sigma;}}\underset{j=0}{\overset{m-p}{\&Sigma;}}\left({\mathrm{E.}}_j\right(t\left){{\mathrm{E.}}_{j+p}}^{*}\right(t)+{{\mathrm{E.}}_j}^{*}(t\left){\mathrm{E.}}_{j+p}\right(t\left)\right)d\mathrm{the\; s}$ (Equation 8),

Substituting Formula 4 and Formula 5 into Formula 8, we can get:

$I_{If}=\frac{\mathrm{\&eta;}e}{hv}\frac{\mathrm{\&pi;}}{Z}{\mathrm{E.}}_0^2\underset{p=0}{\overset{m-1}{\&Sigma;}}\underset{j=0}{\overset{m-p}{\&Sigma;}}{\mathrm{\&alpha;}}_{j+p}{\mathrm{\&alpha;}}_{j}co\mathrm{the\; s}(\frac{4{\mathrm{pk}}^{\&prime;}\mathrm{no}dco\mathrm{the\; s}\mathrm{\&theta;}}{c}t-\frac{4{\mathrm{pk}}^{\&prime;}\mathrm{no}dco\mathrm{the\; s}\mathrm{\&theta;}(l+\mathrm{no}dco\mathrm{the\; s}\mathrm{\&theta;})}{c^2})$ (Formula 9),

Perform Fourier transform on the frequency difference of the intermediate frequency term in formula 9, and obtain the frequency f _p of the interference signal as:

$f_p=\frac{2{\mathrm{pk}}^{\&prime;}\mathrm{no}dco\mathrm{the\; s}\mathrm{\&theta;}}{\mathrm{\&pi;}c}=K_{p}co\mathrm{the\; s}\mathrm{\&theta;}$ (formula ten),

Thus the value of the refraction angle θ is obtained, where K _p is the proportionality factor, and $K_p=\frac{2pk\mathrm{no}d}{\mathrm{\&pi;}c},$

According to the law of refraction, the relationship between the refraction angle θ and the incident angle θ ₀ is:

θ ₀ = arcsin(nsinθ) (Formula 11),

According to the geometric relationship of the incident light path, the relationship between the incident angle θ ₀ and the swing angle θ′ of the standard beam 3 is:

${\mathrm{\&theta;}}^{\&prime;}=\frac{{\mathrm{\&theta;}}_0}{2}=\frac{arc\mathrm{the\; s}i\mathrm{no}\left(\mathrm{no}\mathrm{the\; s}i\mathrm{no}\mathrm{\&theta;}\right)}{2}$ (Formula 12),

Substituting the value of the swing angle θ' of the standard beam 3 obtained in Formula 12 into Formula 2, the micro-impulse I' generated by the interaction between the laser light emitted by the pulse laser 1 and the working medium target 2 is obtained.

In this embodiment, the moment of inertia of the system is calibrated by measuring the change of the system period before and after adding the standard beam 3, and the value of the proportional coefficient _Kp can be obtained according to the calibration result.

The device for measuring torsion micro-impulse by linear frequency modulation multi-beam laser heterodyne shown in Figure 1, under the working condition of 10Pa, using MATLAB to simulate and measure the working medium is PVC (polyvinyl chloride) + 2% C, the thickness is 180μm, the laser initial The current is 5A, the pulse width is 50ms, the micro-pulse generated by the interaction between the laser and the working medium, and the possibility of the linear frequency modulation multi-beam laser heterodyne measurement method is verified. The length of the standard beam 3 is D = 15cm, and the refractive index of the plane standard mirror n=1.493983, the thickness is 3cm; the wavelength of the chirp laser is 1.55μm, the scan period T=1ms, and the modulation bandwidth ΔF=5GHz.

In the case of different incident angles θ ₀ , the Fourier transform spectrum corresponding to the small angle measured by chirped multi-beam laser heterodyne is shown in Fig. 3. It can be seen from Fig. 3 that with the increase of incident angle θ ₀ , the relative position of the spectrum moves to the low frequency direction, that is, as the incident angle θ ₀ increases, the frequency decreases. This is because, when the proportionality coefficient K _p is constant, the relationship between the frequency f _p of the interference signal and the incident angle θ ₀ is f _p =K _p cosθ=K _p cos[arcsin(sinθ ₀ /n)], The incident angle θ ₀ and the frequency f _p of the interference signal are inversely proportional to each other. When the incident angle θ ₀ increases, cosθ decreases accordingly. Therefore, as the incident angle θ ₀ increases, the relative position of the spectrum moves to the low frequency direction .

Utilize measuring method described in the present invention, measure eight groups of data continuously, obtain the simulated measurement result of micro-impulse of sample to be measured under the situation of different incident angles θ ₀ , as shown in the following table:

Using the simulation experiment data in the table above, the average measurement value of the micro-impulse is calculated, and the maximum relative error of the final measurement value is less than 0.48%. At the same time, in the case of small angle approximation, the system error and reading error caused by the environment are in It can be ignored in the simulation, and the error in the simulation experiment mainly comes from the precision error after the fast Fourier transformation and the rounding error in the calculation process.

Claims (1)

1. A torsional pendulum micro impulse measuring method of a linear frequency modulation multi-beam laser heterodyne torsional pendulum micro impulse measuring device relates to a device comprising a linear frequency modulation laser (5), a first plane reflector (6), a second plane reflector (4), a plane standard mirror (7), a standard beam (3), a vacuum chamber (11), a pulse laser (1), a working medium target (2), a converging lens (8), a photoelectric detector (9) and a signal processing system (10),

the linear frequency modulation laser (5), the first plane reflector (6), the second plane reflector (4), the plane standard mirror (7), the standard beam (3), the pulse laser (1), the working medium target (2) and the convergent lens (8) are all arranged in a vacuum chamber (11),

a rotating shaft is fixed at the center of the standard beam (3),

the working medium target (2) is pasted on the upper surface of the standard beam (3), the second plane reflector (4) is pasted on the lower surface of the standard beam (3), the working medium target (2) and the second plane reflector (4) are both positioned at the same end of the standard beam (3),

the laser emitted by the pulse laser acts on the working medium target (2) to generate plasma jet, the standard beam (3) rotates under the action of back spray, the linear frequency modulation laser (5) continuously emits linear frequency modulation laser while the standard beam (3) rotates, the linear frequency modulation laser is reflected by the first plane reflecting mirror (6) and the second plane reflecting mirror (4) and then enters the plane standard mirror (7), the front surface and the rear surface of the plane standard mirror (7) reflect the linear frequency modulation laser and converge the linear frequency modulation laser on the photosensitive surface of the photoelectric detector (9) through the converging lens (8), and the electric signal output end of the photoelectric detector (9) is connected with the electric signal input end of the signal processing system (10);

the signal processing system (10) comprises a filter (10-1), a preamplifier (10-2), an A/D converter (10-3) and a DSP (10-4), wherein an electric signal input end of the filter (10-1) is connected with an electric signal output end of a photoelectric detector (9) as an electric signal input end of the signal processing system (10), a filtering signal output end of the filter (10-1) is connected with a filtering signal input end of the preamplifier (10-2), an amplifying signal output end of the preamplifier (10-2) is connected with an analog signal input end of the A/D converter (10-3), and a digital signal output end of the A/D converter (10-3) is connected with a digital signal input end of the DSP (10-4);

the vacuum chamber (11) is provided with a vacuum window for converging the light in the vacuum chamber (11) to the vacuum chamber

(11) The external photoelectric detector (9) is arranged on the photosensitive surface;

the torsional pendulum micro-impulse measuring method of the linear frequency modulation multi-beam laser heterodyne torsional pendulum micro-impulse measuring device is realized by the following processes:

the pulse laser (1), the linear frequency modulation laser (5), the photoelectric detector (9) and the signal processing system (10) are switched to a working state, the photoelectric detector (9) converts received optical signals into electric signals and sends the electric signals to the signal processing system (10), the signal processing system (10) obtains the swing angle theta' of the standard beam (3) according to the received continuous electric signals,

according to the following steps:

$I^{\&prime;}=\frac{2J\mathrm{\&omega;}}{D}\&CenterDot;{\mathrm{\&theta;}}^{\&prime;}=\frac{4\mathrm{\&pi;}J}{{\mathrm{DT}}^{\&prime;}}\&CenterDot;{\mathrm{\&theta;}}^{\&prime;}$ (formula one),

obtaining micro impulse I ' generated by the action of laser emitted by a pulse laser (1) and a working medium target (2), wherein J is the rotational inertia of a torsional pendulum system, omega is damping frequency, T ' is damping period, D is the length of a standard beam (3), and k is 4 pi J/DT ':

i '═ k · θ' (equation two);

the method is characterized in that the signal processing system (10) obtains the swing angle theta' of the standard beam (3) according to the received continuous electric signals by the following steps:

when the linear frequency modulation laser (5) continuously emits linear frequency modulation laser at an incidence angle theta₀When the light is obliquely incident to the plane standard mirror (7), the incident light field E (t) of the plane standard mirror (7) is as follows:

E(t)＝E₀exp{i(ω₀t+k′t²) A (formula three) is calculated,

wherein,for the rate of change of the bandwidth of the modulation, T is the period of the modulation, △ F isBandwidth of modulation, E₀For the amplitude of the incident light field, t is time, omega₀For the incident field angle frequency, i represents an imaginary number,

setting the optical path of the linear frequency modulation laser reaching the front surface of the plane standard mirror (7) as l, and then the linear frequency modulation laser reaches the reflected light field E of the front surface of the plane standard mirror (7) at the time of t-l/c₁(t) is:

$E_1\left(t\right)={\mathrm{\&alpha;}}_1{E}_0\exp \{i\&lsqb;{\mathrm{\&omega;}}_0(t-\frac{l}{c})+k^{\&prime;}{\left(t-\frac{l}{c}\right)}^2\&rsqb;\}$ (formula four) of the reaction solution,

the light transmitted by the front surface of the plane standard mirror (7) is reflected and refracted for multiple times by the front surface and the back surface of the plane standard mirror (7) at different times, and the light field of the reflected light obtained by each reflection is as follows:

$\left\{\begin{array}{c}{E}_2\left(t\right)={\mathrm{\&alpha;}}_2{E}_0\exp \{i\&lsqb;{\mathrm{\&omega;}}_0(t-\frac{l+2ndcos\mathrm{\&theta;}}{c})+k^{\&prime;}{\left(t-\frac{l+2ndcos\mathrm{\&theta;}}{c}\right)}^2+\frac{2{\mathrm{\&omega;}}_{0}ndcos\mathrm{\&theta;}}{c}\&rsqb;\}\\ E_3\left(t\right)={\mathrm{\&alpha;}}_3{E}_0\exp \{i\&lsqb;{\mathrm{\&omega;}}_0(t-\frac{l+4ndcos\mathrm{\&theta;}}{c})+k^{\&prime;}{\left(t-\frac{l+2ndcos\mathrm{\&theta;}}{c}\right)}^2+\frac{4{\mathrm{\&omega;}}_{0}ndcos\mathrm{\&theta;}}{c}\&rsqb;\}\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ E_m\left(t\right)={\mathrm{\&alpha;}}_m{E}_0\exp \{i\&lsqb;{\mathrm{\&omega;}}_0(t-\frac{l+2(m-1)nd\cos \mathrm{\&theta;}}{c})+k^{\&prime;}{(t-\frac{l+2(m-1)nd\cos \mathrm{\&theta;}}{c})}^2+\frac{2(m-1){\mathrm{\&omega;}}_{0}ndcos\mathrm{\&theta;}}{c}\&rsqb;\}\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\end{array}\right.$

(formula five) of the reaction solution,

wherein m is a non-negative integer α₁＝r，α_m＝ββ′r′^(2m-3)(m is not less than 2), r is the reflectance when light enters the planar standard mirror (7) from the surrounding medium, β is the transmittance when light enters the planar standard mirror (7) from the surrounding medium, r 'is the reflectance of the rear surface of the planar standard mirror (7), β' is the transmittance when light enters the surrounding medium from the inside of the planar standard mirror (7), d is the thickness of the planar standard mirror (7), theta is the refraction angle, n is the refraction index of the planar standard mirror (7), c is the speed of light,

the total light field E' (t) received by the photodetector (9) is:

E′(t)＝E₁(t)+E₂(t)+...+E_m(t) +. - (equation six),

the photocurrent I output by the photodetector (9) is then:

$I=\frac{\mathrm{\&eta;}e}{hv}\frac{1}{Z}\underset{D}{\&Integral;\&Integral;}\frac{1}{2}\&lsqb;E_1\left(t\right)+E_2\left(t\right)+...+E_m\left(t\right)+...\&rsqb;{\&lsqb;E_1\left(t\right)+E_2\left(t\right)+...+E_m\left(t\right)+...\&rsqb;}^{*}ds$ (formula seven) of the reaction mixture,

wherein e is the electron electric quantity, Z is the intrinsic impedance of the surface medium of the photoelectric detector (9), eta is the quantum efficiency, D is the area of the photosensitive surface of the photoelectric detector (9), h is the Planck constant, v is the laser frequency, and the sign indicates complex conjugate,

obtaining the intermediate frequency current I according to the formula_IFComprises the following steps:

$I_{IF}=\frac{\mathrm{\&eta;}e}{2hv}\frac{1}{Z}\underset{D}{\&Integral;\&Integral;}\underset{p=0}{\overset{m-1}{\&Sigma;}}\underset{j=0}{\overset{m-p}{\&Sigma;}}\left(E_j\right(t\left){E_{j+p}}^{*}\right(t)+{E_j}^{*}(t\left)E_{j+p}\right(t\left)\right)ds$ (the eighth formula),

substituting the formula four and the formula five into the formula eight, and arranging to obtain:

$I_{IF}=\frac{\mathrm{\&eta;}e}{hv}\frac{\mathrm{\&pi;}}{Z}{E}_0^2\underset{p=0}{\overset{m-1}{\mathrm{\&Sigma;}}}\underset{j=0}{\overset{m-p}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_{j+p}{\mathrm{\&alpha;}}_j\cos (\frac{4{\mathrm{pk}}^{\&prime;}nd\cos \mathrm{\&theta;}}{c}t-\frac{4{\mathrm{pk}}^{\&prime;}nd\cos \mathrm{\&theta;}(l+nd\cos \mathrm{\&theta;})}{c^2})$ (the ninth formula),

fourier transform is carried out on the frequency difference of the intermediate frequency term in the formula nine to obtain the frequency f of the interference signal_pComprises the following steps:

$f_p=\frac{2{\mathrm{pk}}^{\&prime;}ndcos\mathrm{\&theta;}}{\mathrm{\&pi;}c}=K_{p}cos\mathrm{\&theta;}$ (formula ten) of the above-mentioned formula,

thereby obtaining a value of angle of refraction θ, where K_pIs a proportionality coefficient, and

the refraction angle theta and the incidence angle theta can be known according to the law of refraction₀The relationship of (1) is:

θ₀arcsin (nsin θ) (formula eleven),

the incident angle theta can be known according to the geometrical relation of the incident light path₀The relationship of the swing angle theta' with the standard beam (3) is as follows:

${\mathrm{\&theta;}}^{\&prime;}=\frac{{\mathrm{\&theta;}}_0}{2}=\frac{arcsin\left(nsin\mathrm{\&theta;}\right)}{2}$ (formula twelve),

and substituting the value of the swing angle theta 'of the standard beam (3) obtained in the formula twelve into the formula two to obtain the micro impulse I' generated by the action of the laser emitted by the pulse laser (1) and the working medium target (2).