CN114283776A - Laser transduction system and laser transduction sound production method - Google Patents
Laser transduction system and laser transduction sound production method Download PDFInfo
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- CN114283776A CN114283776A CN202111591705.1A CN202111591705A CN114283776A CN 114283776 A CN114283776 A CN 114283776A CN 202111591705 A CN202111591705 A CN 202111591705A CN 114283776 A CN114283776 A CN 114283776A
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Abstract
The invention discloses a laser transduction system and a laser transduction sound production method, wherein the system comprises: the laser subsystem is used for generating and outputting a pulse laser signal through a pulse laser; an optical path subsystem for focusing the pulsed laser signal at a bottom surface within the resonant cavity; the sound source subsystem is used for converting the pulse laser signal into a pulse sound wave signal on the bottom surface in the resonant cavity; the laser subsystem is also used for adjusting the repetition frequency of the pulse laser to a proper frequency so as to convert the pulse sound wave signal into a continuous sound wave signal on the bottom surface in the resonant cavity; and the sound source subsystem is also used for outputting continuous sinusoidal sound wave signals with equal positive and negative pressure under the condition that the size of the resonant cavity is adjusted to be a proper size. According to this system, the problem that a continuous sine wave having equal positive and negative pressures cannot be generated can be solved.
Description
Technical Field
The invention relates to the technical field of laser transduction, in particular to a laser transduction system and a laser transduction sound production method.
Background
Laser transducers (Laser transducers) are devices that are capable of converting optical energy into acoustic energy. Laser transducers rely on the photoacoustic effect to generate acoustic waves. Since the laser acoustic technology is rapidly developed, the laser transducer is receiving wide attention by virtue of non-contact property, strong interference resistance and easy miniaturization and arraying.
The existing laser transducer generates pulse sound waves, and the sound waves with unequal positive pressure and negative pressure are generated by the attenuation of shock waves, so that continuous sine waves with equal positive pressure and negative pressure cannot be generated.
Disclosure of Invention
Therefore, the invention provides a laser transduction system and a laser transduction sound production method, and aims to solve the problem that continuous sine waves with equal positive and negative pressures cannot be produced in the prior art.
A first aspect of the present invention provides a laser transduction system, comprising: the laser subsystem, the light path subsystem and the sound source subsystem are sequentially connected, the laser subsystem comprises a pulse laser, and the sound source subsystem is provided with a resonant cavity structure with adjustable size; the laser subsystem is used for generating and outputting a pulse laser signal through a pulse laser; an optical path subsystem for focusing the pulsed laser signal at a bottom surface within the resonant cavity; the sound source subsystem is used for converting the pulse laser signal into a pulse sound wave signal on the bottom surface in the resonant cavity; the laser subsystem is also used for adjusting the repetition frequency of the pulse laser to a proper frequency so as to convert the pulse sound wave signal into a continuous sound wave signal on the bottom surface in the resonant cavity; and the sound source subsystem is also used for outputting continuous sinusoidal sound wave signals with equal positive and negative pressure under the condition that the size of the resonant cavity is adjusted to be a proper size.
In some alternative embodiments, the pulsed laser signal forms a bottom focus at a bottom surface within the resonant cavity, the laser subsystem further comprising: the power adjusting device is used for adjusting the power of the pulse laser according to a power adjusting signal from a preset control device so as to adjust the energy of the single-pulse laser output by the pulse laser; and the sound source subsystem is also used for forming plasma at the bottom focus under the condition that the energy of the single-pulse laser enables the light energy density at the bottom focus to reach a preset energy density threshold value, so that a pulse sound wave signal is generated at the bottom focus through expansion and collapse of the plasma.
In some alternative embodiments, the laser subsystem further comprises: a signal generator for generating and outputting a sine wave signal; the pulse laser is used for generating a pulse laser signal according to the received sine wave signal; and the frequency adjusting device is used for adjusting the repetition frequency of the pulse laser to a proper frequency by adjusting the frequency of the sine wave signal output by the signal generator according to a frequency adjusting signal of a preset control device, so that the plasma generates resonance in the expansion and collapse processes based on the proper frequency, and a continuous sound wave signal is formed at the bottom focus.
In some optional embodiments, the optical path subsystem includes a beam expanding component and a focusing component which are connected in sequence, one end of the resonant cavity is an open end communicated with the focusing component, and the other end of the resonant cavity is a closed end; the beam expanding assembly is used for expanding the pulse laser signals output by the pulse laser; and the focusing assembly is used for transmitting the expanded pulse laser signal into the resonant cavity through the open end of the resonant cavity and focusing the pulse laser signal on the bottom surface of the closed end in the resonant cavity.
In some optional embodiments, the sound source subsystem further comprises: and the position adjusting device is used for adjusting the position of the resonant cavity according to the position adjusting signal from the preset control equipment so as to adjust the focusing position of the pulse laser signal to the central position of the bottom surface in the resonant cavity.
In some optional embodiments, the resonant cavity comprises at least two sleeves which are connected in sequence, and the adjacent sleeves are connected in a nested manner; wherein the at least two sleeves comprise a first sleeve and a second sleeve; the first end of the first sleeve is an open end communicated with the focusing assembly, and the second end of the first sleeve is an open end nested with the next sleeve; the first end of the second sleeve is an open end which is connected with the previous sleeve in a nesting mode, and the second end of the second sleeve is a closed end to serve as a closed end of the resonant cavity.
In some alternative embodiments, the size of the resonant cavity is adjusted in a manner that includes at least one of manual adjustment and automatic adjustment; in the case where the size adjustment mode includes automatic adjustment, the sound source subsystem further includes: and the size adjusting device is used for adjusting the size of the resonant cavity to be the proper size according to the size adjusting signal from the preset control equipment.
The invention provides a laser transduction sound production method in a second aspect, which comprises the following steps: focusing a pulse laser signal output by a pulse laser on the bottom surface in the resonant cavity; converting the pulse laser signal into a pulse acoustic wave signal on the bottom surface in the resonant cavity; adjusting the repetition frequency of the pulsed laser to a suitable frequency to convert the pulsed acoustic signal to a continuous acoustic signal at the bottom surface within the resonant cavity; and under the condition that the size of the resonant cavity is adjusted to be a proper size, outputting a continuous sinusoidal sound wave signal with equal positive and negative pressure.
In some alternative embodiments, the pulsed laser signal is a laser signal generated by a pulsed laser from a sine wave signal generated by a signal generator; converting the pulsed laser signal to a pulsed acoustic wave signal at a bottom surface within the resonant cavity, comprising: adjusting the power of the pulse laser in response to a power adjustment signal of a predetermined control device to adjust the energy of the single-pulse laser output by the pulse laser; and under the condition that the energy of the single-pulse laser enables the light energy density at the bottom focus to reach a preset energy density threshold value, forming plasma at the bottom focus so as to generate a pulse sound wave signal at the bottom focus through expansion and collapse of the plasma.
In some alternative embodiments, adjusting the repetition rate of the pulsed laser to a suitable frequency to convert the pulsed acoustic wave signal to a continuous acoustic wave signal at the bottom surface within the resonant cavity comprises: and adjusting the frequency of the sine wave signal output by the signal generator in response to a frequency adjusting signal of a preset control device so as to adjust the repetition frequency of the pulse laser to a proper frequency, so that the plasma generates resonance in the expansion and collapse processes based on the proper frequency, and a continuous sound wave signal is formed at the bottom focus.
According to the laser transduction system and the laser transduction sound production method, the repetition frequency of the pulse laser is adjusted to be a proper value, so that plasma resonance is realized at the focus of a pulse laser signal, and continuous sound waves are generated in a solid medium; the waveform of the continuous sound wave is further regulated and controlled through the size-adjustable resonant cavity, so that a continuous sound wave signal with an approximate sine waveform is output, and continuous sound waves with the same positive and negative pressure can be output in a time domain.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention.
Fig. 1 is a schematic structural diagram of a laser transduction system according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of a laser transduction system according to another embodiment of the present invention;
FIG. 3 is a schematic structural diagram of a tunable resonant cavity according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a scenario in which sound waves are generated at a bottom surface in an adjustable resonant cavity according to an embodiment of the present invention;
FIG. 5 is a diagram of a time-domain pulsed acoustic signal generated by a single pulsed laser excited resonant cavity with an adjustable length according to an embodiment of the present invention;
FIG. 6 is a graph of a time domain acoustic signal generated by a size-tunable resonator according to an embodiment of the present invention;
FIG. 7 is a graph of a time domain acoustic signal generated by a size-tunable resonator according to another embodiment of the present invention;
FIG. 8 is a flow chart of a method for generating sound by laser transduction according to an embodiment of the present invention;
fig. 9 is a schematic view of a laser transduction system according to an embodiment of the present invention.
In the drawings:
100-laser sound source system; 10-a laser subsystem; 20-an optical path subsystem; 30-a sound source subsystem; 11-a pulsed laser; 12-a signal generator; 13-a power regulating device; 14-frequency adjustment means; 21-a beam expanding assembly; 22-a focusing assembly; 31-a resonant cavity; 32-a position adjustment device; 33-size adjusting means; 301-a pulsed laser beam; 302-open end; 303-an outer layer; 304-inner layer; 305-bottom; 401-bottom metal target in the resonant cavity; 402-a pulsed laser beam; 403-plasma; 404-sound waves; 901-control computer; 902-a signal generator; 903-a pulsed laser; 904-beam expander; 905-focusing lens, 906-length adjustable solid resonator.
Detailed Description
The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present invention and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
In the embodiments of the present invention, in the energy conversion device, a Transducer (Transducer) is a device capable of converting one energy into another energy, and the Transducer may be used for measurement and information transfer, and is generally applied to the fields of electric, electronic components, or electromechanical. For example, a transducer is an element or device, a sensor, etc., that can convert a physical quantity into an electrical signal.
Ultrasonic transducers are one type of transducer that can convert other forms of energy into acoustic energy and are widely used in non-destructive testing and medical diagnostics and therapeutics. The conventional ultrasonic transducer is referred to as a piezoelectric transducer, which is an electrically driven mechanical element capable of converting sound to electricity and electricity to sound based on a piezoelectric effect and an inverse piezoelectric effect of a wafer. Similar to the definition of an ultrasonic transducer, we call a device capable of converting optical energy into acoustic energy a laser transducer.
Laser transducers rely on the photoacoustic effect, which is a very complex process, to generate acoustic waves. The photoacoustic effect can be divided into air, liquid and solid according to different target media; according to different optical power densities, the photoacoustic effect can be subdivided into different principles in different media.
In recent decades, laser acoustic technology has been developed rapidly, and laser transducers have attracted attention of researchers due to the advantages of non-contact, strong interference resistance, and easy miniaturization and arraying. Because the photoacoustic effect in medium water and air is difficult to control, most of the existing laser transducers use laser pulses to excite a solid film to generate shock waves, and the shock waves are propagated and attenuated in the medium to be acoustic waves to realize photoacoustic conversion. Thus, existing laser transducers produce pulsed acoustic waves, and acoustic waves attenuated by the shock wave with unequal positive and negative pressures. However, the ideal transducer generates a continuous sine wave with equal positive and negative pressure, and the existing laser transducer cannot generate the continuous sine wave and is not a true laser transducer.
In some scenarios, in the case of manufacturing acoustic waves by the photoacoustic effect, the related research is mainly to use a shock wave excited by a pulse laser, and the shock wave is attenuated into a pulse acoustic wave in the transmission process, and the positive pressure and the negative pressure of the shock wave are not equal, nor are continuous acoustic waves in the true sense that the positive pressure and the negative pressure are equal.
The embodiment of the invention provides a laser transduction system and a laser transduction sound production method, which can output sound waves which are continuous and have equal positive and negative pressure, and realize a laser transducer in a real sense.
Fig. 1 shows a schematic structural diagram of a laser transduction system according to an embodiment of the present invention. As shown in fig. 1, in some embodiments, the laser transduction system 100 may include a laser subsystem 10, an optical path subsystem 20, and an acoustic source subsystem 30 connected in series, the laser subsystem 10 including a pulsed laser 11, the acoustic source subsystem 30 having a resonator 31 structure with adjustable dimensions.
A laser subsystem 10 for generating and outputting a pulsed laser signal by a pulsed laser 11; an optical path subsystem 20 for focusing the pulsed laser signal at a bottom surface within the resonant cavity 21; a sound source subsystem 30 for converting the pulsed laser signal into a pulsed acoustic signal at the bottom surface within the resonant cavity 31; a laser subsystem 10 for also adjusting the repetition rate of the pulsed laser 11 to a suitable frequency for converting the pulsed acoustic signal to a continuous acoustic signal at the bottom surface within the resonant cavity 31; the sound source subsystem 30 is further configured to output a continuous sinusoidal sound wave signal with equal positive and negative voltages when the size of the resonant cavity 31 is adjusted to a suitable size.
According to the laser transduction system provided by the embodiment of the invention, continuous sound waves are generated in a solid medium at the focus of a pulse laser signal based on plasma resonance by adjusting the repetition frequency of a pulse laser at a proper value, and the waveform of the continuous sound waves is regulated and controlled by a resonant cavity with an adjustable size, so that a continuous sound wave signal with an approximate sine waveform is output; the laser transduction system of the embodiment of the invention can output continuous sound waves with equal positive and negative pressure in the time domain, thereby being a real laser transducer.
Fig. 2 is a schematic structural diagram of a laser transduction system according to another embodiment of the present invention, and the same reference numerals are used for the same or equivalent components in fig. 2 as those in fig. 1. Fig. 3 is a schematic structural diagram of a tunable resonant cavity according to an embodiment of the present invention. A laser transduction system according to another embodiment of the present invention is described below with reference to fig. 2 to 3.
As shown in fig. 2, the laser subsystem 10 in the laser transduction system 100 includes a pulse laser 11, a signal generator 12, a power adjustment device 13, and a frequency adjustment device 14; the optical path subsystem 20 includes: a beam expanding assembly 21 and a focusing assembly 22; the acoustic source subsystem 30 may include: a resonator 31, a position adjusting device 32 and a size adjusting device 33. The invention is not limited to the specific modules described above and shown in fig. 2, and in some embodiments the laser transduction system 100 may comprise only some of the modules, i.e. the laser transduction system 100 comprises a more flexible configuration of modules, as will be described below in connection with specific embodiments.
In some embodiments, the pulsed laser signal forms a bottom focal point at a bottom surface within the resonant cavity 31.
The laser subsystem 100 further includes: a power adjusting means 12 for adjusting the power of the pulse laser 13 in accordance with a power adjustment signal from a predetermined control device to adjust the energy of the single-pulse laser light output by the pulse laser 13; and the sound source subsystem 30 is also used for forming plasma at the bottom focus under the condition that the energy of the single-pulse laser enables the light energy density at the bottom focus to reach a preset energy density threshold value, so that the pulsed sound wave signal is generated at the bottom focus through the expansion and collapse of the plasma.
In some embodiments, the predetermined control devices may include, but are not limited to: computer devices, personal computers, smart phones, tablet computers, personal digital assistants, servers, and the like.
The predetermined control device in the embodiment of the present invention may be referred to as a control computer, for example, by which, on the one hand, the frequency of the output sine wave signal of the signal generator 12 can be changed to adjust the repetition frequency of the pulse laser 11; on the other hand, the control computer can change the working current and working voltage of the pulse laser to adjust the energy of the single pulse laser output by the pulse laser 11.
As an example, the repetition rate of the pulsed laser 11 is adjustable from 1Hz to 200 kHz; the working current of the pulse laser is adjustable from 0A to 60A, and the working voltage is adjustable from 0A to 10V.
In a practical application scenario, the predetermined control device may be an external control device independent of the laser sound source system, and may be a control device arranged inside the laser sound source system. In particular, the predetermined control device may have independent calculation and processing capabilities for implementing the above-described functions of varying the frequency of the output sine wave signal of the signal generator and varying the power of the pulsed laser.
In some embodiments, the laser subsystem further comprises: a signal generator 12 for generating and outputting a sine wave signal; a pulse laser 11 for generating a pulse laser signal from the received sine wave signal; and the frequency adjusting device 13 is used for adjusting the repetition frequency of the pulse laser 11 to a proper frequency by adjusting the frequency of the sine wave signal output by the signal generator 12 according to a frequency adjusting signal of a preset control device, so that the plasma generates resonance in the expansion and collapse processes based on the proper frequency, and a continuous sound wave signal is formed at the bottom focus.
In this embodiment, the suitable frequency of the pulsed laser 11 means that the suitable frequency can make the plasma expansion and collapse process at the bottom focal point of the resonant cavity 31 generate resonance, and form a continuous acoustic wave.
In some embodiments, the signal generator 12 may be a pulsed laser 11 such as Nd: the YAG solid pulse laser provides a sine wave signal to adjust the repetition frequency of the pulse laser 11, and the frequency of the sine wave signal is adjustable from 1Hz to 200 kHz.
In some embodiments, the pulsed laser 11 may be a solid-state pulsed laser. The solid pulse laser has the characteristics of small volume, convenient use, large output power and high repetition frequency.
As an example, the pulse laser 11 may include any one of a neodymium-doped yttrium aluminum garnet (Nd: YAG) laser, a ruby laser, and a neodymium glass laser. In a specific application scenario, the type of the pulse laser used may be selected according to actual needs, and the embodiment of the present invention is not particularly limited.
As an example, the wavelength of the pulsed laser source generated by the pulsed laser 11 is, for example, 300nm to 1064nm, the pulse width is, for example, 1ps to 500ps, the single pulse energy is, for example, 1. mu.J to 500. mu.J, and the repetition frequency is, for example, 1Hz to 500 kHz. Wherein nm is the measurement unit nanometer of the wavelength of the light beam emitted by the pulse laser, ps is the measurement unit picosecond of the pulse laser pulse duration, J is the unit Joule of energy, heat and power, and muJ represents microJoule, namely one thousandth of Joule.
As an example, when the pulse laser 11 is Nd: in the case of YAG pulse laser, Nd: the YAG pulse laser has output laser wavelength of 500-1064 nm, adjustable beam diameter of 1-10 mm, adjustable pulse width of 1-600 ps, adjustable single pulse energy of 1-800 muJ, adjustable repetition frequency of 1Hz-500kHz,
As a specific example, the laser wavelength is, for example, 532nm, the laser beam diameter of the pulsed laser is, for example, 2.5mm, the pulse width is, for example, 15ps, the single pulse energy maximum is, for example, 100 μ J, the repetition frequency is, for example, adjustable from 1Hz to 200kHz, the operating current is, for example, adjustable from 0A to 60A, and the operating voltage is adjustable from 0V to 10V.
In some embodiments, the optical path subsystem 20 includes a beam expanding assembly 21 and a focusing assembly 22 connected in sequence, one end of the resonant cavity 31 is an open end communicated with the focusing assembly 22, and the other end of the resonant cavity 31 is a closed end; the beam expanding assembly 21 is configured to expand a pulse laser signal output by the pulse laser 11; and the focusing assembly 22 is used for transmitting the expanded pulse laser signal into the resonant cavity 31 through the open end of the resonant cavity 31 and focusing the pulse laser signal on the bottom surface of the closed end in the resonant cavity 31.
In this embodiment, the pulse laser signal is expanded and then focused, so that the collimation of the pulse laser signal can be improved, and the focusing effect that the focusing assembly 22 can achieve can be improved.
In some embodiments, the beam expanding assembly 21 may be, for example, a beam expanding lens, and the focusing assembly 22 may be, for example, a focusing lens. As an example, the working wavelength of the beam expanding lens is 532nm, and the magnification is 5 times; the working wavelength of the aspheric focusing lens is 532nm, and the focal length is 100 mm.
In the embodiment of the present invention, the optical path subsystem 21 may be referred to as a beam expanding and focusing optical path, and is used for reducing the diameter of a light spot reaching the surface of the excitation target, and increasing the optical power density at the focus of the surface of the excitation target to be larger than the threshold (107W/cm) of the plasma effect in the photoacoustic effect2) A nearly point-like plasma is formed at the focal point.
In some embodiments, since the bottom surface of the closed end in the resonant cavity 31 may be a metal target surface, the size of a light spot formed on the metal target surface may be expressed by the following expression (1).
Wherein, in the above expression (1), M2The beam quality of the laser is 1.2, for example, the smaller the value is, the better the beam quality of the laser is, theta is the total beam angle of the emergent light, D is the focal spot diameter, theta is0Is the total beam angle of the incident light, D0The incident spot diameter.
In some embodiments, the full beam angle θ of the incident light0And incident spot diameter D0Can be expressed as the following expression (2).
In the above expression (2), λ is a laser wavelength of, for example, 532 nm.
By the above expressions (1) and (2), for example, a focused spot diameter of 8 μm can be calculated.
In some embodiments, the optical power density calculation at the focal point of the metal target surface can be identified by the following expression (3):
in the above expression (3), I is the optical power density of the focal point, and has a unit of W/cm2E is the single pulse energy of the laser, S is the spot area at the focus, and tau is the pulse width of the pulse laser.
In some embodiments, the optical power density at the focal point is ideally about 1.3 × 1010W/cm2The optical power density is larger than the threshold value (10) of the occurrence of the plasmon effect in the photoacoustic effect7W/cm2)。
From the above description of the embodiments, it can be seen that the power of the pulsed laser 11 is adjusted to make the optical power density at the focal spot of the solid medium greater than the optical power density threshold (10) corresponding to the plasma effect7W/cm2) Thereby generating a plasma at the focal spot;the repetition frequency of the pulse laser can be changed subsequently, so that the plasma expansion and collapse process forms resonance, and continuous and approximately sinusoidal sound waves with equal positive and negative pressure are output. That is to say, the power of the pulse laser 11 needs to be adjusted first, so that the energy at the focus reaches the light energy density requirement of the plasma effect, and then the repetition frequency of the pulse laser 11 is adjusted, so that the plasma expansion and collapse process forms resonance, and continuous sound waves are output; further, by changing the size of the tunable cavity 31, the continuous sound wave generated at the bottom in the resonant cavity is adjusted, and when the resonant cavity length is properly adjusted, the continuous sound wave which is approximately sinusoidal is output.
In some embodiments, the acoustic source subsystem 30 further comprises: and a position adjusting device 32 for adjusting the position of the cavity in accordance with a position adjusting signal from a predetermined control device to adjust the focal position of the pulsed laser signal to the bottom surface center position within the cavity.
In this embodiment, after the optical path subsystem 20 is set up in advance, the pulse laser 11 generates a pulse laser beam, the pulse laser beam is transmitted through the beam expander and the focusing lens, the focal position of the beam can be determined, and the pulse laser can be focused on the center position of the bottom metal surface in the resonant cavity by moving the position of the metal resonant cavity, so as to achieve a better focusing effect.
As shown in FIG. 3, in the scenario shown in FIG. 3, there is a pulsed laser beam 301, an open end 302 of the resonant cavity 31, an outer layer 303 of the resonant cavity 31, an inner layer 304 of the resonant cavity 31, and a bottom 305 of the resonant cavity 31. Wherein the bottom 305 of the cavity 31 is closed and the laser beam enters the cavity 31 from the upper open end 302 of the cavity 31, the laser source being generated at the bottom 305 within the cavity 31.
In some embodiments, the resonant cavity 31 includes at least two sleeves connected in sequence and the adjacent sleeves are connected in a nested manner; wherein the at least two sleeves comprise a first sleeve and a second sleeve; the first end of the first sleeve is an open end communicated with the focusing assembly, and the second end of the first sleeve is an open end nested with the next sleeve; the first end of the second sleeve is an open end which is in nested connection with a previous sleeve, e.g. the first sleeve, and the second end of the second sleeve is a closed end to act as a closed end of the resonant cavity 31.
In some alternative embodiments, the resonant cavity 31 may be a cylindrical metal resonant cavity or a resonant cavity with metal walls, the length of which is adjustable and/or the inner diameter of which is adjustable; a cylindrical metal resonator cavity is easy to estimate its resonance frequency. Illustratively, the resonant cavity 31 is composed of a metallic copper material or a composite material including copper.
In the embodiment of the invention, the metal resonant cavity with the adjustable length has the following functions: converting light energy into sound energy at the bottom in the resonant cavity through a plasma mechanism in the photoacoustic effect; and moreover, the output sound wave form can be regulated and controlled by changing the length of the tunable resonant cavity.
In some embodiments, the dimensional parameter for which the resonant cavity can be adjusted includes at least one of a length and an inner diameter. Illustratively, the length-adjustable cylindrical resonant cavity is made of a metal copper material, the length-adjustable range is 100mm-200mm, and the inner diameter of the resonant cavity is adjustable in a range of 20mm-40 mm.
It should be understood that the specific structure of the resonant cavity in the embodiment of the present invention enables the resonant cavity to have a changeable overall length and/or a changeable inner diameter, and the implementation manner of the specific structure may be preset according to actual needs, and the embodiment of the present invention is not particularly limited.
In some embodiments, the size of the resonant cavity 31 is adjusted in a manner that includes at least one of manual adjustment and automatic adjustment; in the case where the size adjustment mode includes automatic adjustment, the sound source subsystem 30 further includes: and a size adjusting means 33 for adjusting the size of the cavity 31 to an appropriate size according to a size adjusting signal from a predetermined control device.
In this embodiment, the proper size of the resonant cavity 31 means that the proper size is a size which can make the output waveform at the bottom focus of the resonant cavity 31 approximate a sine continuous sound wave.
In some embodiments, the size of the resonant cavity 31 can be adjusted by a combination of manual adjustment and automatic adjustment, for example, the size of the resonant cavity 31 is manually adjusted to an empirical size value empirically, and then fine adjustment is automatically performed by the third adjusting device 32 based on the empirical size value according to a size adjusting signal received from a predetermined control device, and when the size (length and/or inner diameter) of the resonant cavity is adjusted to a proper value (a proper length value and/or a proper inner diameter value), a continuous sound wave with approximate sine shape is output.
The working principle of the laser transduction system in the embodiment of the present invention is described below with reference to fig. 4, and fig. 4 is a schematic view of a scene where a sound wave is generated on the bottom surface in the tunable resonant cavity in the embodiment of the present invention.
As shown in fig. 4, a bottom metal target 401 in a resonant cavity is schematically shown in this scenario, a pulsed laser beam 402 is focused at the bottom metal target 401, metal atoms at the bottom metal target 401 absorb energy of the pulsed laser beam 402, multiphoton ionization and avalanche ionization occur, a metal plasma 403 is formed, due to a shielding effect on laser, the plasma 403 can strongly absorb energy of a subsequent pulsed laser beam 402, a local high-temperature and high-pressure environment is formed, then, due to an internal and external pressure difference, the plasma 403 can be violently expanded and collapsed, and output sound waves are coupled into a medium, at this time, a plasma cavity can be approximately regarded as a point sound source. The plasma vacuole excited by the single pulse laser generates a shock wave which is rapidly attenuated into a sound wave 404 (the positive pressure and the negative pressure are not equal) in the transmission process. Therefore, a pulsed acoustic wave attenuated by a shock wave is not a true acoustic wave.
In the embodiment of the invention, each pulse laser can generate a plasma 403 vacuole on the bottom metal surface in the tunable resonant cavity, and then outputs a sound wave by expanding and collapsing. The plasma 403 expands to create a positive pressure, which pushes surrounding material away. After the expansion is complete, the plasma 403 tries to retract, creating a negative pressure. If the repetition frequency of the pulse laser is increased, the plasma 403 is not completely retracted, and the next excitation of the plasma 403 by the laser pulse continues, so that the plasma 403 is expanded more greatly, the corresponding contraction force is increased, and finally a balanced state is achieved, so that the bottom metal target 401 (i.e. the focus) is resonated in the process of expanding and collapsing the plasma 403, and relatively regular sound waves are generated. The sound wave is generated at the bottom in the resonant cavity and interacts with the wall of the resonant cavity in the process of propagation. The waveform of the sound wave generated by the plasma 403 cavitation is regulated by changing the length of the adjustable resonant cavity, so that the plasma cavitation can output a continuous sound wave which is approximate to sine.
FIG. 5 is a diagram of a time-domain pulsed acoustic signal generated by a single pulsed laser excited length-tunable resonator according to an embodiment of the present invention. As shown in fig. 5, the pulsed acoustic wave is attenuated by the shock wave and has a positive pressure greater than a negative pressure, similar to the acoustic wave generated by a conventional laser transducer in a different excitation medium. The data was measured in air with a sound pressure microphone with a sampling rate of 48 kHz. Therefore, the shock wave is rapidly attenuated into the sound wave with unequal positive pressure and negative pressure in the transmission process, and the pulse sound wave attenuated by the shock wave is not the sound wave in the true sense.
FIG. 6 is a graph of time domain acoustic signals produced by a tunable resonator according to an embodiment of the present invention. In fig. 6, when the repetition frequency of the pulse laser is 1kHz, the cavity does not have a plasma resonance effect under excitation of a plurality of continuous pulse lasers. The characteristics are as follows: continuous and good repeatability, and the acoustic waves with unequal positive and negative voltages are attenuated by the shock waves. The data was measured in air with a sound pressure microphone with a sampling rate of 48 kHz.
FIG. 7 is a graph of a time domain acoustic signal produced by a tunable resonator according to another embodiment of the present invention. When the repetition frequency of the pulse laser is 8kHz, the resonant cavity generates a plasma resonance effect at a focal point under the excitation of a plurality of continuous pulse lasers.
And when the whole adjusted length of the resonant cavity is 124.75mm, the acoustic signal is similar to a sine. At this time, it can be clearly seen that the characteristics of the time domain acoustic signal output by the resonant cavity are: the method is continuous, good in repeatability, approximate to sine waves and equal in positive and negative pressure. The data was also measured in air by a sound pressure microphone with a sampling rate of 48 kHz.
As can be seen from the descriptions of fig. 4 to fig. 6, the laser transduction system according to the embodiment of the present invention can generate a continuous sound wave in a solid medium based on plasma resonance at a focal point of a pulse laser signal by adjusting the repetition frequency of the pulse laser at a suitable value, and then adjust and control the waveform of the continuous sound wave through the size-adjustable resonant cavity, so as to output a continuous sound wave signal having an approximately sinusoidal waveform; the laser transduction system of the embodiment of the invention can output continuous sound waves with equal positive and negative pressure in the time domain.
The laser transduction sound production method of the embodiment of the invention is described below with reference to the accompanying drawings. Fig. 8 shows a flow chart of a laser transduction sound generation method of an embodiment of the present invention.
In the embodiment of the invention, the laser transduction sound production method is based on the laser transduction system of the embodiment. As shown in fig. 8, the method for generating sound by laser transduction according to an embodiment of the present invention may include the following steps.
S810, focusing a pulse laser signal output by a pulse laser on the bottom surface in the resonant cavity; s820, converting the pulse laser signal into a pulse sound wave signal on the bottom surface in the resonant cavity; s830, adjusting the repetition frequency of the pulse laser to a proper frequency so as to convert the pulse sound wave signal into a continuous sound wave signal on the bottom surface in the resonant cavity; and S840, outputting continuous sinusoidal sound wave signals with the positive and negative pressures equal to each other under the condition that the size of the resonant cavity is adjusted to be a proper size.
Through the laser transduction sound production method provided by the embodiment of the invention, continuous sound waves can be generated in the length-adjustable resonant cavity based on the plasma resonance effect, and the sound production method can output the sound waves which are continuous and have the same positive and negative pressure.
In some embodiments, step S810 may specifically include: s11, expanding the beam of the pulse laser signal output by the pulse laser by using the beam expanding component; and S12, transmitting the expanded pulse laser signal into the resonant cavity through the open end of the resonant cavity by using the focusing assembly, and focusing the pulse laser signal on the bottom surface of the closed end in the resonant cavity.
In some embodiments, the expanded pulse laser signal is focused at the central position of the bottom surface of the closed end in the resonant cavity by using a focusing component; in this embodiment, after step S12, the method may further include: the position of the cavity is adjusted in accordance with a position adjustment signal from a predetermined control device to adjust the focus position of the pulsed laser signal to a bottom surface center position within the cavity.
In some embodiments, the pulsed laser signal is a laser signal generated by a pulsed laser from a sine wave signal generated by a signal generator.
After this embodiment, step S820 may specifically include: s21, responding to the power adjusting signal of the preset control device, adjusting the power of the pulse laser to adjust the energy of the single pulse laser output by the pulse laser; and S22, forming plasma at the bottom focus under the condition that the energy of the single pulse laser enables the optical energy density at the bottom focus to reach a preset energy density threshold value, so as to generate a pulse sound wave signal at the bottom focus through the expansion and collapse of the plasma.
In some embodiments, step S830 may specifically include: and adjusting the frequency of the sine wave signal output by the signal generator in response to a frequency adjusting signal of a preset control device so as to adjust the repetition frequency of the pulse laser to a proper frequency, so that the plasma generates resonance in the expansion and collapse processes based on the proper frequency, and a continuous sound wave signal is formed at the bottom focus.
The steps of the above methods are divided for clarity, and the implementation may be combined into one step or split some steps, and the steps are divided into multiple steps, so long as the same logical relationship is included, which are all within the protection scope of the present patent; it is within the scope of the patent to add insignificant modifications to the algorithms or processes or to introduce insignificant design changes to the core design without changing the algorithms or processes.
In some embodiments, after S830 and before S840, the method may further comprise: the size of the cavity is adjusted to an appropriate size according to a size adjustment signal from a predetermined control device.
According to the laser transduction sound production method provided by the embodiment of the invention, continuous sound waves are generated in a solid medium at the focus of a pulse laser signal based on plasma resonance by adjusting the repetition frequency of a pulse laser at a proper value, and the waveform of the continuous sound waves is regulated and controlled by a resonant cavity with an adjustable size, so that a continuous sound wave signal with an approximate sine waveform is output, and continuous sound waves with the same positive and negative pressure can be output in a time domain.
A specific workflow of the laser transduction system of the exemplary embodiment of the present invention is described below with reference to fig. 9. Fig. 9 is a schematic view of a laser transduction system according to an embodiment of the present invention.
In the scenario shown in fig. 9, the following are included: a control computer 901, a signal generator 902, a pulse laser 903, a beam expander 904, a focusing lens 905 and a length-adjustable solid resonant cavity 906.
In some embodiments, the signal generator 902 generates and outputs a sine wave signal to the pulse laser 903, the pulse laser 903 generates and outputs a pulse laser according to the sine wave signal, and a laser beam of the pulse laser passes through a focusing optical path formed by the beam expanding of the beam expander 904 and the focusing lens 905 and is focused on a metal surface at the bottom in the solid resonant cavity 906.
In some embodiments, the power of the pulsed laser 903 is adjusted by the control computer 901 to change the energy of the output single-pulse laser, when the single-pulse energy is high enough to make the energy density threshold at the focal point larger than the threshold of the plasma mechanism, the single-pulse laser will generate a plasma point acoustic source on the bottom metal surface in the resonant cavity 906, and generate a shock wave through plasma expansion and collapse, and the shock wave is attenuated into a pulse acoustic wave during propagation.
In some embodiments, the repetition rate of the pulsed laser 903 output pulsed laser light, i.e., the number of times per second that a pulsed acoustic wave is excited, is adjusted by the signal generator 902. When the repetition frequency of the pulse laser 903 is adjusted to a proper frequency value, the plasma at the focal point generates resonance in the processes of expansion and collapse, and continuous sound waves are formed.
In some embodiments, the continuous acoustic wave generated at the bottom of resonant cavity 906 is adjusted by changing the length of tunable cavity 906, and a continuous acoustic wave that is approximately sinusoidal is output when the overall length of resonant cavity 906 is adjusted as appropriate.
By the laser transduction system, based on a plasma mechanism in the photoacoustic effect, plasma resonance at a focus is realized by a simple method for adjusting the repetition frequency of pulse laser, and continuous sound waves with the same positive and negative pressure are generated in a solid medium.
The invention discloses a laser transduction system and a laser transduction sound production method. The method can excite a metal solid to generate sound waves coupled into a medium based on a plasma effect in the photoacoustic effect, then drive the plasma vibration process (expansion and collapse) to form resonance by adjusting the repetition frequency of a pulse laser (for example, the repetition frequency is adjustable from 1Hz to 200 kHz), and adjust the length of a resonant cavity to regulate and control the waveform, so that the laser transducer device outputs the sound waves which are continuous, have equal positive and negative pressures and are approximate to sine. The system and the method realize the functions of the true laser transducer, are simple and easy to operate and have reliable performance.
It is to be understood that the invention is not limited to the particular arrangements and instrumentality described in the above embodiments and shown in the drawings. For convenience and brevity of description, detailed description of a known method is omitted here, and for the specific working processes of the system, the module and the unit described above, reference may be made to corresponding processes in the foregoing method embodiments, which are not described herein again.
It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
Those skilled in the art will appreciate that although some embodiments described herein include some features included in other embodiments instead of others, combinations of features of different embodiments are meant to be within the scope of the embodiments and form different embodiments.
It will be understood that the above embodiments are merely exemplary embodiments taken to illustrate the principles of the present invention, which is not limited thereto. It will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the spirit and substance of the invention, and these modifications and improvements are also considered to be within the scope of the invention.
Claims (10)
1. A laser transduction system, comprising: the laser subsystem, the light path subsystem and the sound source subsystem are sequentially connected, the laser subsystem comprises a pulse laser, and the sound source subsystem is provided with a resonant cavity structure with an adjustable size; wherein the content of the first and second substances,
the laser subsystem is used for generating and outputting a pulse laser signal through the pulse laser;
the optical path subsystem is used for focusing the pulse laser signal on the bottom surface in the resonant cavity;
the sound source subsystem is used for converting the pulse laser signal into a pulse sound wave signal on the bottom surface in the resonant cavity;
the laser subsystem is further used for adjusting the repetition frequency of the pulse laser to a proper frequency so as to convert the pulse sound wave signal into a continuous sound wave signal on the bottom surface in the resonant cavity;
and the sound source subsystem is also used for outputting continuous sinusoidal sound wave signals with equal positive and negative pressure under the condition that the size of the resonant cavity is adjusted to be a proper size.
2. The system of claim 1, wherein the pulsed laser signal forms a bottom focus at a bottom surface within the resonant cavity, the laser subsystem further comprising:
the power adjusting device is used for adjusting the power of the pulse laser according to a power adjusting signal from a preset control device so as to adjust the energy of the single-pulse laser output by the pulse laser;
the sound source subsystem is further used for forming plasma at the bottom focus under the condition that the energy of the single-pulse laser enables the light energy density at the bottom focus to reach a preset energy density threshold value, so that a pulse sound wave signal is generated at the bottom focus through expansion and collapse of the plasma.
3. The system of claim 2, wherein the laser subsystem further comprises:
a signal generator for generating and outputting a sine wave signal;
the pulse laser is used for generating a pulse laser signal according to the received sine wave signal;
and the frequency adjusting device is used for adjusting the repetition frequency of the pulse laser to a proper frequency by adjusting the frequency of the sine wave signal output by the signal generator according to a frequency adjusting signal of a preset control device, so that the plasma generates resonance in the expansion and collapse processes based on the proper frequency, and a continuous sound wave signal is formed at the bottom focus.
4. The system of claim 1, wherein the optical path subsystem comprises a beam expanding component and a focusing component which are connected in sequence, one end of the resonant cavity is an open end communicated with the focusing component, and the other end of the resonant cavity is a closed end; wherein the content of the first and second substances,
the beam expanding assembly is used for expanding the pulse laser signals output by the pulse laser;
and the focusing assembly is used for transmitting the expanded pulse laser signal into the resonant cavity through the open end of the resonant cavity and focusing the pulse laser signal on the bottom surface of the closed end in the resonant cavity.
5. The system of claim 1 or 4, wherein the acoustic source subsystem further comprises:
and the position adjusting device is used for adjusting the position of the resonant cavity according to a position adjusting signal from preset control equipment so as to adjust the focusing position of the pulse laser signal to the central position of the bottom surface in the resonant cavity.
6. The system of claim 4, wherein the resonant cavity comprises at least two sleeves connected in sequence, and the adjacent sleeves are connected in a nested manner; wherein the content of the first and second substances,
the at least two sleeves comprise a first sleeve and a second sleeve;
the first end of the first sleeve is an open end communicated with the focusing assembly, and the second end of the first sleeve is an open end nested with the next sleeve;
the first end of the second sleeve is an open end which is connected with the previous sleeve in a nested mode, and the second end of the second sleeve is a closed end and serves as a closed end of the resonant cavity.
7. The system of claim 2, wherein the resonant cavity is adjustable in size by at least one of manual adjustment and automatic adjustment; in a case where the size adjustment manner includes automatic adjustment, the sound source subsystem further includes:
and the size adjusting device is used for adjusting the size of the resonant cavity to be the proper size according to a size adjusting signal from preset control equipment.
8. A laser transduction sound production method is characterized in that,
focusing a pulse laser signal output by a pulse laser on the bottom surface in the resonant cavity;
converting the pulsed laser signal to a pulsed acoustic wave signal at a bottom surface within the resonant cavity;
adjusting the repetition rate of the pulsed laser to a suitable rate to convert the pulsed acoustic signal to a continuous acoustic signal at the bottom surface within the resonant cavity;
and under the condition that the size of the resonant cavity is adjusted to be a proper size, outputting a continuous sinusoidal sound wave signal with equal positive and negative pressure.
9. The method of claim 8, wherein the pulsed laser signal is a laser signal generated by the pulsed laser from a sine wave signal generated by a signal generator;
the bottom surface within the resonant cavity converts the pulsed laser signal into a pulsed acoustic wave signal, comprising:
adjusting the power of the pulse laser in response to a power adjustment signal of a predetermined control device to adjust the energy of the single-pulse laser output by the pulse laser;
and under the condition that the energy of the single-pulse laser enables the optical energy density at the bottom focus to reach a preset energy density threshold value, forming plasma at the bottom focus so as to generate a pulse acoustic wave signal at the bottom focus through expansion and collapse of the plasma.
10. The method of claim 9, wherein said adjusting the repetition rate of said pulsed laser to a suitable frequency to convert said pulsed acoustic wave signal to a continuous acoustic wave signal at the bottom surface within said resonant cavity comprises:
adjusting the frequency of the sine wave signal output by the signal generator in response to a frequency adjustment signal of the predetermined control device to adjust the repetition frequency of the pulse laser to a suitable frequency, so that the plasma generates resonance in the expansion and collapse process based on the suitable frequency, and a continuous sound wave signal is formed at the bottom focus.
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