CN103983340B - Microvibration measuring system and measuring method based on remote pulse laser speckle - Google Patents

Abstract

The invention discloses a kind of microvibration measuring system based on remote pulse laser speckle, including pulse laser and photo detecting unit, the pulse laser is used to send high-peak power, the pulse laser of high repetition frequency and irradiate measured target, and the photo detecting unit is used to receive the speckle that pulse laser is produced through measured target diffusing reflection.The present invention substitutes continuous wave laser light source using high-peak power and high-repetition-rate pulse LASER Light Source, on the premise of measurement security (low laser average emitted power) is ensured, increase substantially the echo power of measured target return, the microvibration measuring to distant object can be realized, the field such as health detection, safety-protection system, investigation and anti-terrorism, disaster search and rescue in bridge and building has very important actual application value.

Description

Micro-vibration measurement system and measurement method based on long-distance pulsed laser speckle

technical field

The invention relates to the technical field of laser speckle vibration measurement, in particular to a micro-vibration measurement system and measurement method based on long-distance pulsed laser speckle.

Background technique

The non-contact fixed-point measurement of the tiny vibration of long-distance diffuse reflection non-cooperative targets by laser has very important application significance in the fields of bridge and building health detection, security system, detection and anti-terrorism, disaster search and rescue, etc. However, when the measurement distance is long, the laser echo returned from the detection target will be very weak, making it difficult to detect. Although the detection distance can be increased to a certain extent by increasing the laser power, considering the safety and concealment of the measurement, the laser emission power cannot be increased without limit.

Micro-vibration measurement based on laser speckle is a new way of micro-vibration measurement which is different from traditional laser Doppler and interference. The micro-vibration measurement method based on laser speckle has the advantages of simple system, no need for reference beam, and easy operation, which has aroused the interest of many researchers. The general principle of this method is: firstly, the laser is irradiated on the object to be measured, and due to the diffuse reflection characteristics of the surface of the object and the coherence of the laser light source, a randomly distributed speckle field will be formed in the reflection space. Due to the vibration of the target, the spatial speckle field will change correspondingly with the tiny vibration of the target, usually manifested as the translation of the speckle pattern. By detecting the displacement change of the speckle pattern [such as: Zeev Zalevsky, Opt.Express 17, 21566-21580 (2009)], or the flux change of the spatial speckle field [such as: A.A. Veber, Appl Phys B 105:613–617 ( 2011)] can detect and restore the tiny vibration information of the target. The former records the speckle pattern sequence through high-speed imaging, and then obtains the displacement and target vibration information through software processing. This method has very high requirements on the frame rate and sensitivity of the imaging device. At the same time, the amount of data in this method is huge, and post-processing is time-consuming. , it is difficult to achieve real-time measurement. The second method directly measures the change of luminous flux or power passing through the photodetector, but a spatial filter or aperture template with a small aperture must be added at the photodetector end to make the change of luminous flux better reflect the vibration information of the target. However, the addition of a spatial filter or aperture template with a small aperture will inevitably reduce the echo power reaching the photodetector, which will have an adverse effect on the measurement, especially in long-distance measurement or low reflectivity of the target in the case of.

Contents of the invention

The object of the present invention is to provide a micro-vibration measurement system based on long-distance pulsed laser speckle; the present invention also provides a micro-vibration measurement method based on long-distance pulsed laser speckle.

To achieve the above object, the present invention adopts the following technical solutions:

A micro-vibration measurement system based on long-distance pulse laser speckle, including a trigger circuit, a pulse laser, a light detection unit, a sampling and quantization circuit, and a memory, the trigger circuit outputs a trigger signal to the pulse laser, and the pulse laser is used for Send out pulsed laser with high peak power and high repetition rate and irradiate the target to be measured. The light detection unit is composed of a light receiving device, a photodetector and a signal amplification circuit. The light receiving device is used to receive the pulsed laser light through the target The speckle generated by diffuse reflection, the photodetector is optically connected to the light receiving device, the signal input end of the signal amplification circuit is connected to the photodetector, and the signal input end of the sampling and quantization circuit is respectively connected The signal output terminals of the signal amplification circuit and the trigger circuit, and the signal output terminals of the sampling and quantization circuit are connected with the memory.

Preferably, the light receiving device adopts an optical receiving antenna.

Preferably, it also includes a filter circuit, a power amplifier circuit and an audio device serially connected in series, and the signal input terminal of the filter circuit is connected to the signal output terminal of the signal amplifier circuit.

Preferably, it also includes a narrow-band filter, and the narrow-band filter is arranged on the optical path at the front end of the photodetection unit.

A method for measuring micro-vibration based on long-distance pulsed laser speckle, comprising the following steps:

S1. The pulsed laser emits pulsed laser light with high peak power and high repetition rate to irradiate the measured target, and generates pulse echo, which is the speckle generated after the pulsed laser is diffusely reflected by the measured target;

S2. Adjust the pulse echo entering the light receiving device to achieve the best match between the change of luminous flux and the vibration amplitude and frequency of the measured target;

S3. The photodetector detects the change of the luminous flux of the pulse echo passing through the light receiving device, and converts it into a change of photocurrent;

S4. Generate a vibration signal envelope of the measured target according to the change of the photocurrent.

Preferably, the step S2 is realized by the following method: by adjusting the spot size of the pulsed laser irradiating the target to be measured and the receiving aperture of the light receiving device, controlling the number of speckle spots and the luminous flux entering the light receiving device, so that the light entering the light receiving device The change of luminous flux is best matched with the vibration amplitude and frequency of the measured target.

After adopting the technical solution, the present invention has the following advantages compared with the background technology:

1. The present invention adopts high peak power and high repetition rate pulsed laser light source instead of continuous wave laser light source, and under the premise of ensuring measurement safety (low average laser emission power), the echo power returned by the measured target is greatly improved, It can realize the micro-vibration measurement of long-distance targets, and has very important practical application value in the fields of health detection of bridges and buildings, security systems, detection and anti-terrorism, disaster search and rescue, etc.

2. The present invention adopts a light receiving device with a certain receiving aperture to receive laser echoes at a single point without using a spatial filter or a diaphragm template, which avoids a significant drop in echo power caused by a spatial filter or a diaphragm template, This ensures the quality of the measurement.

Description of drawings

Fig. 1 is a schematic structural diagram of the measurement system of the present invention.

Fig. 2 is a schematic flow chart of the measurement method of the present invention.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Embodiment one

Please refer to Figure 1, a micro-vibration measurement system based on long-distance pulse laser speckle, including pulse laser 1, light detection unit 2, narrow-band filter 3, trigger circuit 4, sampling and quantization circuit 5, memory 6, filtering Circuit 7, power amplifier circuit 8 and audio equipment 9, wherein:

The pulsed laser 1 is used to emit pulsed laser with high peak power and high repetition rate to irradiate the measured target A, and the emission wavelength can be visible light wavelength or infrared wavelength. In this embodiment, the pulsed laser 1 is a Q-switched laser.

Referring to Fig. 1, the light detection unit 2 includes a light receiving device 21, a photodetector 22 and a signal amplification circuit 23, wherein:

The light receiving device 21 is used to receive the speckle generated by the diffuse reflection of the pulsed laser light by the measured target A, and has a certain receiving aperture. In this embodiment, the light receiving device 21 adopts an optical receiving antenna, and the optical receiving antenna may be an optical lens.

The photodetector 22 is optically connected to the light receiving device 21, and it can be a photodiode, an avalanche diode or a photomultiplier tube. In this embodiment, the photodetector 22 is a photomultiplier tube.

The signal input terminal of the signal amplification circuit 23 is connected with the photodetector 22 .

Certainly, the light receiving device 21 and the photodetector 22 can also be integrated into one body, and realized directly by using a single-point photodetector.

The narrow-band filter 3 is arranged on the optical path at the front end of the photodetection unit, which can reduce the influence of ambient stray light and improve the signal-to-noise ratio of the measurement system of the present invention.

The trigger circuit 4 outputs a trigger signal to the pulse laser 1 , and the frequency of the trigger signal is the same as the laser pulse frequency emitted by the pulse laser 1 .

The signal input end of described sampling and quantization circuit 5 is respectively connected with the signal output end of described signal amplifying circuit 23 and trigger circuit 4, and the signal output end of described sampling and quantization circuit 5 is connected with memory 6, so just can adopt and laser The peak sampling mode of pulse and frequency is used for synchronous sampling and quantification, so as to realize the real-time digital recording and storage of the micro-vibration of the measured target A. Those skilled in the art should understand that since there is a certain time delay in the laser pulse echo, the sampling trigger signal should be processed with a certain amount of time delay according to the difference in the measurement distance.

The filter circuit 7, the power amplifying circuit 8 and the audio equipment 9 are serially connected in sequence, the signal input end of the filter circuit 7 is connected with the signal output end of the signal amplifying circuit 23, and the audio equipment 9 can be a loudspeaker or an earphone.

Embodiment two

Please refer to Figure 1 and Figure 2, a micro-vibration measurement method based on long-distance pulsed laser speckle, including the following steps:

S1. Pulse laser 1 emits pulsed laser light with high peak power and high repetition frequency to irradiate the target A to be measured and generate pulse echo. The repetition frequency of the pulse laser should be greater than twice the highest vibration frequency of the target A to be measured. The "pulse echo" mentioned here refers to the speckle generated after the pulsed laser is diffusely reflected by the target A under test.

S2. Adjust the pulse echo entering the light receiving device 21 so that the variation of its luminous flux and the vibration amplitude and frequency of the measured target A are optimally matched. This step is specifically implemented by the following methods:

By adjusting the spot size of the pulsed laser 1 irradiating the target A to be measured and the receiving aperture of the light receiving device 21, the number of speckle spots entering the light receiving device 21 and the luminous flux are controlled, so that the change of the luminous flux entering the light receiving device 21 is consistent with the measured target A The vibration amplitude and frequency are optimally matched.

S3. The photodetector 22 detects the change in the luminous flux of the pulse echo passing through the light receiving device 21, and converts it into a change in photocurrent;

S4. Generate a vibration signal envelope of the measured target A according to the change of the photocurrent. This step can be achieved by:

Method 1. Use the peak sampling method with the same frequency as the laser pulse to perform synchronous sampling and quantification to realize real-time digital recording and storage of the micro-vibration of the measured target A.

The second way is to use a high-speed sampling method far exceeding the pulse repetition frequency for sampling and quantification, and then reconstruct the vibration signal envelope through digital filtering or software post-processing.

Method 3: Filter out the high-frequency carrier through the filter circuit 7, reconstruct the envelope of the vibration signal in real time, and then play it in real time through the power amplifier circuit 8 and the audio device 9.

It can be seen from the above description that the present invention can greatly increase the echo power returned by the measured target and increase the distance of micro-vibration measurement under the premise of ensuring the safety of the measurement; The change of luminous flux (power) realizes the real-time measurement and digital recording of the micro-vibration of the long-distance target.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present invention can easily think of changes or Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (5)

1. A micro-vibration measurement system based on long-distance pulse laser speckle, characterized in that: comprising a trigger circuit, a pulse laser, a light detection unit, a sampling and quantization circuit and a memory, the trigger circuit outputs a trigger signal to the pulse laser, The pulse laser is used to emit pulse laser with high peak power and high repetition rate and irradiate the target to be measured. The light detection unit is composed of a light receiving device, a photodetector and a signal amplification circuit. The light receiving device has a certain receiving The aperture receives the speckle generated by the diffuse reflection of the pulsed laser at a single point, the photodetector is optically connected to the light receiving device, and the signal input end of the signal amplification circuit is connected to the photodetector, so The signal input end of the sampling and quantization circuit is respectively connected to the signal output end of the signal amplification circuit and the trigger circuit, and the signal output end of the sampling and quantization circuit is connected to the memory. 2. A micro-vibration measurement system based on long-distance pulsed laser speckle according to claim 1, characterized in that: the optical receiving device adopts an optical receiving antenna. 3. A micro-vibration measurement system based on long-distance pulsed laser speckle as claimed in claim 1, characterized in that: it also includes a filter circuit, a power amplifier circuit and an audio device connected in series in sequence, and the signal of the filter circuit The input end is connected with the signal output end of the signal amplification circuit. 4. A micro-vibration measurement system based on long-distance pulsed laser speckle as claimed in claim 1, characterized in that: it also includes a narrow-band filter, and the narrow-band filter is arranged at the front end of the photodetection unit on the light path. 5. A method utilizing the micro-vibration measurement system according to any one of claims 1-4 to measure micro-vibrations, comprising the following steps: S1. The pulsed laser emits pulsed laser light with high peak power and high repetition rate to irradiate the measured target, and generates pulse echo, which is the speckle generated after the pulsed laser is diffusely reflected by the measured target; S2. Adjust the pulse echo entering the light receiving device to achieve the best match between the luminous flux change and the vibration amplitude and frequency of the measured target, specifically: adjust the spot size of the pulse laser irradiated to the measured target and the receiving aperture of the light receiving device Receive the speckle generated by the diffuse reflection of the measured target with a single point of pulsed laser light, so as to control the number of speckle spots and luminous flux entering the light receiving device; S3. The photodetector detects the change of the luminous flux of the pulse echo passing through the light receiving device, and converts it into a change of photocurrent; S4. Generate a vibration signal envelope of the measured target according to the change of the photocurrent.