Laser transducer system and laser transducer sound generation method

Abstract

The present invention discloses a laser transducer system and a method for generating sound using a laser transducer. The system includes: a laser subsystem for generating and outputting a pulsed laser signal through a pulsed laser; an optical path subsystem for focusing the pulsed laser signal on the bottom surface inside the resonant cavity; a sound source subsystem for converting the pulsed laser signal into a pulsed acoustic signal on the bottom surface inside the resonant cavity; the laser subsystem is further configured to adjust the repetition frequency of the pulsed laser to a suitable frequency so as to convert the pulsed acoustic signal into a continuous acoustic signal on the bottom surface inside the resonant cavity; the sound source subsystem is further configured to output a continuous sinusoidal acoustic signal with equal positive and negative pressures when the size of the resonant cavity is adjusted to a suitable size. According to this system, the problem of being unable to generate a continuous sinusoidal wave with equal positive and negative pressures can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of laser transducers, and in particular to a laser transducer system and a laser transducer sound generation method. Background Art

[0002] A laser transducer is a device that can convert light energy into sound energy. The laser transducer relies on the photoacoustic effect to generate sound waves. Due to the rapid development of laser acoustic technology, the laser transducer has received extensive attention due to its advantages of non-contact, strong anti-interference, easy miniaturization, and array formation.

[0003] The existing laser transducers generate pulsed sound waves, and the sound waves with unequal positive and negative pressures attenuated from shock waves, rather than continuous sine waves with equal positive and negative pressures. Summary of the Invention

[0004] Therefore, the present invention provides a laser transducer system and a laser transducer sound generation method to solve the problem in the prior art that continuous sine waves with equal positive and negative pressures cannot be generated.

[0005] In a first aspect of the present invention, a laser transducer system is provided, including: a laser subsystem, an optical path subsystem, and a sound source subsystem connected in sequence. The laser subsystem includes a pulsed laser. The sound source subsystem has a resonant cavity structure with adjustable size. Among them, the laser subsystem is used to generate and output a pulsed laser signal through the pulsed laser. The optical path subsystem is used to focus the pulsed laser signal on the bottom surface in the resonant cavity. The sound source subsystem is used to convert the pulsed laser signal into a pulsed sound wave signal on the bottom surface in the resonant cavity. The laser subsystem is further used to adjust the repetition frequency of the pulsed laser to a suitable frequency to convert the pulsed sound wave signal into a continuous sound wave signal on the bottom surface in the resonant cavity. The sound source subsystem is further used to output a continuous sine sound wave signal with equal positive and negative pressures when the size of the resonant cavity is adjusted to a suitable size.

[0006] In some optional embodiments, the pulsed laser signal forms a bottom focus on the bottom surface in the resonant cavity. The laser subsystem further includes: a power adjustment device, which is used to adjust the power of the pulsed laser according to a power adjustment signal from a predetermined control device to adjust the energy of a single pulsed laser output by the pulsed laser. The sound source subsystem is further used to form a plasma at the bottom focus when the energy of the single pulsed laser makes the light energy density at the bottom focus reach a predetermined energy density threshold, so as to generate a pulsed sound wave signal at the bottom focus through the expansion and collapse of the plasma.

[0007] In some alternative embodiments, the laser subsystem further includes: a signal generator for generating and outputting a sine wave signal; a pulsed laser for generating a pulsed laser signal according to the received sine wave signal; and a frequency adjustment device for adjusting the repetition frequency of the pulsed laser to a suitable frequency by adjusting the frequency of the sine wave signal output by the signal generator according to a frequency adjustment signal from a predetermined control device, so that the plasma generates resonance during the expansion and collapse process based on the suitable frequency, thereby forming a continuous acoustic wave signal at the bottom focus.

[0008] In some alternative embodiments, the optical path subsystem includes a beam expanding component and a focusing component connected in sequence. One end of the resonant cavity is an open end communicating with the focusing component, and the other end is a closed end; wherein, the beam expanding component is used for expanding the pulsed laser signal output by the pulsed laser; the focusing component is used for transmitting the expanded pulsed laser signal into the resonant cavity through the open end of the resonant cavity and focusing it on the bottom surface of the closed end in the resonant cavity.

[0009] In some alternative embodiments, the sound source subsystem further includes: a position adjustment device for adjusting the position of the resonant cavity according to a position adjustment signal from a predetermined control device to adjust the focusing position of the pulsed laser signal to the center position of the bottom surface in the resonant cavity.

[0010] In some alternative embodiments, the resonant cavity includes at least two sleeves connected in sequence and the adjacent sleeves are nested; wherein, the at least two sleeves include a first sleeve and a second sleeve; the first end of the first sleeve is an open end communicating with the focusing component, 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 nested with the previous sleeve, and the second end of the second sleeve is a closed end to serve as the closed end of the resonant cavity.

[0011] In some alternative embodiments, the size adjustment method of the resonant cavity includes at least one of manual adjustment and automatic adjustment; in the case where the size adjustment method includes automatic adjustment, the sound source subsystem further includes: a size adjustment device for adjusting the size of the resonant cavity to a suitable size according to a size adjustment signal from a predetermined control device.

[0012] The second aspect of the present invention provides a laser energy conversion sound generation method, which includes: focusing the pulsed laser signal output by the pulsed laser on the bottom surface in the resonant cavity; converting the pulsed laser signal into a pulsed 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 wave signal into a continuous acoustic wave signal on the bottom surface in the resonant cavity; and outputting a continuous sine acoustic wave signal with equal positive and negative pressures when the size of the resonant cavity is adjusted to a suitable size.

[0013] In some alternative embodiments, the pulsed laser signal is a laser signal generated by a pulsed laser according to a sine wave signal generated by a signal generator; converting the pulsed laser signal into a pulsed acoustic wave signal on the bottom surface in the resonant cavity includes: in response to a power adjustment signal of a predetermined control device, adjusting the power of the pulsed laser to adjust the energy of a single pulsed laser output by the pulsed laser; when the energy of the single pulsed laser enables the light energy density at the bottom focal point to reach a predetermined energy density threshold, forming a plasma at the bottom focal point, so as to generate a pulsed acoustic wave signal at the bottom focal point through the expansion and collapse of the plasma.

[0014] In some alternative embodiments, adjusting the repetition frequency of the pulsed laser to a suitable frequency to convert the pulsed acoustic wave signal into a continuous acoustic wave signal on the bottom surface in the resonant cavity includes: in response to a frequency adjustment signal of a predetermined control device, adjusting the frequency of the sine wave signal output by the signal generator to adjust the repetition frequency of the pulsed laser to a suitable frequency, so that the plasma resonates during the expansion and collapse process based on the suitable frequency, and then a continuous acoustic wave signal is formed at the bottom focal point.

[0015] According to the laser transducer system and the laser transducer sound generation method of the embodiments of the present invention, by adjusting the repetition frequency of the pulsed laser to a suitable value, plasma resonance is achieved at the focal point of the pulsed laser signal, so as to generate continuous acoustic waves in a solid medium; subsequently, the waveform of the continuous acoustic waves is further regulated by a resonant cavity with adjustable dimensions, so as to output a continuous acoustic wave signal with an approximate sine waveform, realizing the output of continuous acoustic waves with equal positive and negative pressures in the time domain. Description of the Drawings

[0016] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification, and are used to explain the present invention together with the following specific embodiments, but do not constitute a limitation to the present invention.

[0017] Figure 1 It is a schematic structural diagram of a laser transducer system provided by an embodiment of the present invention;

[0018] Figure 2 It is a schematic structural diagram of a laser transducer system provided by another embodiment of the present invention;

[0019] Figure 3 It is a schematic structural diagram of an adjustable resonant cavity provided by an embodiment of the present invention;

[0020] Figure 4 It is a schematic diagram of the scenario where acoustic waves are generated on the bottom surface of the adjustable resonant cavity according to an embodiment of the present invention;

[0021] Figure 5 It is a time-domain pulsed acoustic signal diagram generated by a single pulsed laser exciting a resonant cavity with adjustable length according to an embodiment of the present invention;

[0022] Figure 6 Time-domain acoustic signal diagram generated by the size-adjustable resonant cavity provided by an embodiment of the present invention;

[0023] Figure 7 Time-domain acoustic signal diagram generated by the size-adjustable resonant cavity provided by another embodiment of the present invention;

[0024] Figure 8 Flow chart showing the laser transducer sound generation method provided by the embodiment of the present invention;

[0025] Figure 9 Scene schematic diagram of the laser transducer system provided by the embodiment of the present invention.

[0026] In the drawings:

[0027] 100 - Laser transducer system; 10 - Laser subsystem; 20 - Optical path subsystem; 30 - Sound source subsystem; 11 - Pulse laser; 12 - Signal generator; 13 - Power adjustment device; 14 - Frequency adjustment device; 21 - Beam expansion assembly; 22 - Focusing assembly; 31 - Resonant cavity; 32 - Position adjustment device; 33 - Size adjustment device; 301 - Pulse laser beam; 302 - Open end; 303 - Outer layer; 304 - Inner layer; 305 - Bottom; 401 - Metal target; 403 - Plasma; 404 - Sound wave; 901 - Control computer; 904 - Beam expander; 905 - Focusing lens. Detailed implementation manners

[0028] The following will describe in detail the specific implementation manners of the present invention with reference to the accompanying drawings. It should be understood that the specific implementation manners described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0029] As used in the present invention, the term "and / or" includes any and all combinations of one or more related listed items. The terms used in the present invention are only used to describe specific embodiments and are not intended to limit the present invention. As used in the present invention, the singular forms "a" and "the" are also intended to include the plural forms unless the context clearly indicates otherwise.

[0030] Unless otherwise defined, the meanings of all terms (including technical and scientific terms) used in the present invention are the same as those commonly understood by those of ordinary skill in the art. It will also be understood that terms such as those defined in common dictionaries should be interpreted as having a meaning consistent with their meaning in the relevant art and the context of the present invention, and will not be interpreted as having an idealized or overly formal meaning unless the present invention is clearly defined as such.

[0031] In the embodiments of the present invention, in an energy conversion device, a transducer is a device that can convert one form of energy into another. Transducers can be used for measurement and information transmission, and are usually applied in the fields of electrical, electronic components or electromechanical. For example, a transducer is a component or device, such as a sensor, that can convert a physical quantity into an electrical signal.

[0032] An ultrasonic transducer is a type of transducer that can convert other forms of energy into sound energy and is widely used in non-destructive testing and medical diagnosis and treatment. A traditional ultrasonic transducer refers to a piezoelectric transducer, which is an electrically driven mechanical component that can achieve the conversion between sound and electricity and between electricity and sound based on the piezoelectric effect and inverse piezoelectric effect of the wafer. Similar to the definition of an ultrasonic transducer, a device that can convert light energy into sound energy is called a laser transducer.

[0033] A laser transducer generates sound waves relying on the photoacoustic effect, and the photoacoustic effect is a very complex process. According to different target media, it can be divided into photoacoustic effects in air, liquid, and solid; according to different light power densities, in different media, it can be further divided into photoacoustic effects with different principles.

[0034] In recent decades, laser acoustics technology has developed rapidly. Laser transducers have attracted the attention of researchers due to their advantages of non-contact, strong anti-interference, easy miniaturization, and array formation. Since the photoacoustic effects in media such as water and air are difficult to control, most existing laser transducers use laser pulses to excite solid films to generate shock waves, and the shock waves propagate and attenuate into sound waves in the medium to achieve photoacoustic conversion. Therefore, the existing laser transducers generate pulsed sound waves, and the sound waves with unequal positive and negative pressures are attenuated from shock waves. However, an ideal transducer generates continuous sound waves with equal positive and negative pressures. The existing laser transducers cannot achieve this and are not real laser transducers in the true sense.

[0035] In some scenarios, when manufacturing sound waves through the photoacoustic effect, the current related research mainly uses shock waves excited by pulsed lasers. The shock waves attenuate into pulsed sound waves during transmission, and their positive and negative pressures are not equal, nor are they continuous and truly equal positive and negative pressure sound waves in the true sense.

[0036] The embodiments of the present invention provide a laser transducer system and a laser transducer sound generation method, which can output sound waves that are continuous and have equal positive and negative pressures, realizing a real laser transducer in the true sense.

[0037] Figure 1 The structural schematic diagram of a laser transducer system according to an embodiment of the present invention is shown. As Figure 1As shown, in some embodiments, the laser transducer system 100 may include a laser subsystem 10, an optical path subsystem 20, and a sound source subsystem 30 connected in sequence. The laser subsystem 10 includes a pulsed laser 11, and the sound source subsystem 30 has a resonant cavity 31 structure with adjustable dimensions.

[0038] The laser subsystem 10 is configured to generate and output a pulsed laser signal through the pulsed laser 11; the optical path subsystem 20 is configured to focus the pulsed laser signal on the bottom surface within the resonant cavity 31; the sound source subsystem 30 is configured to convert the pulsed laser signal into a pulsed acoustic signal on the bottom surface within the resonant cavity 31; the laser subsystem 10 is further configured to adjust the repetition frequency of the pulsed laser 11 to a suitable frequency to convert the pulsed acoustic signal into a continuous acoustic signal on the bottom surface within the resonant cavity 31; the sound source subsystem 30 is further configured to output a continuous sinusoidal acoustic signal with equal positive and negative pressures when the dimensions of the resonant cavity 31 are adjusted to suitable dimensions.

[0039] According to the laser transducer system of an embodiment of the present invention, by adjusting the repetition frequency of the pulsed laser to a suitable value, a continuous acoustic wave is generated in a solid medium based on plasma resonance at the focus of the pulsed laser signal. Subsequently, the waveform of the continuous acoustic wave is regulated by a resonant cavity with adjustable dimensions, thereby outputting a continuous acoustic wave signal with an approximate sinusoidal waveform. The laser transducer system of the embodiment of the present invention can output continuous acoustic waves with equal positive and negative pressures in the time domain, so it is a true laser transducer.

[0040] Figure 2 is a schematic structural diagram of a laser transducer system according to another embodiment of the present invention. Figure 2 and Figure 1 identical or equivalent components are denoted by the same reference numerals. Figure 3 is a schematic structural diagram of an adjustable resonant cavity according to an embodiment of the present invention. The following will describe a laser transducer system according to another embodiment of the present invention in conjunction with Figures 2-3 .

[0041] As Figure 2 shown, the laser subsystem 10 in the laser transducer system 100 includes a pulsed 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 expander assembly 21 and a focusing assembly 22; the sound source subsystem 30 may include: a resonant cavity 31, a position adjustment device 32, and a size adjustment device 33. However, the present invention is not limited to the specific modules described above and shown in Figure 2 . In some embodiments, the laser transducer system 100 may only include some of the modules, that is, the laser transducer system 100 has a more flexible module configuration, which will be described in conjunction with specific embodiments below.

[0042] In some embodiments, the pulsed laser signal forms a bottom focus on the bottom surface within the resonant cavity 31.

[0043] The laser subsystem 10 further includes: a power adjustment device 13 for adjusting the power of the pulsed laser 11 according to a power adjustment signal from a predetermined control device, so as to adjust the energy of the single-pulse laser output by the pulsed laser 11; and a sound source subsystem 30 for forming a plasma at the bottom focus when the energy of the single-pulse laser enables the optical energy density at the bottom focus to reach a predetermined energy density threshold, so as to generate a pulsed acoustic wave signal at the bottom focus through the expansion and collapse of the plasma.

[0044] In some embodiments, the predetermined control device may include, but is not limited to, computer devices, personal computers, smart phones, tablet computers, personal digital assistants, servers, etc.

[0045] In the embodiments of the present invention, the predetermined control device can be referred to as a control computer for example. On the one hand, the frequency of the output sine wave signal of the signal generator 12 can be changed through the control computer to adjust the repetition frequency of the pulsed laser 11; on the other hand, the operating current and operating voltage of the pulsed laser can be changed through the control computer to adjust the energy of the single-pulse laser output by the pulsed laser 11.

[0046] As an example, the repetition frequency of the pulsed laser 11 is adjustable from 1 Hz to 200 kHz; the operating current of the pulsed laser is adjustable from 0 A to 60 A, and the operating voltage is adjustable from 0 A to 10 V.

[0047] In an actual application scenario, the predetermined control device can be an external control device independent of the laser transducer system or a control device arranged inside the laser transducer system. Specifically, the predetermined control device can have independent computing and processing capabilities to implement the functions of changing the frequency of the output sine wave signal of the signal generator and changing the power of the pulsed laser as described above.

[0048] In some embodiments, the laser subsystem further includes: a signal generator 12 for generating and outputting a sine wave signal; a pulsed laser 11 for generating a pulsed laser signal according to the received sine wave signal; and a frequency adjustment device 14 for adjusting the repetition frequency of the pulsed laser 11 to a suitable frequency by adjusting the frequency of the sine wave signal output by the signal generator 12 according to a frequency adjustment signal from a predetermined control device, so that the plasma resonates during the expansion and collapse process based on the suitable frequency, and then a continuous acoustic wave signal is formed at the bottom focus.

[0049] In this embodiment, the suitable frequency of the pulsed laser 11 means that the suitable frequency can enable the plasma expansion and collapse process at the bottom focus of the resonant cavity 31 to resonate and form continuous acoustic waves.

[0050] In some embodiments, the signal generator 12 may provide a sine wave signal for the pulsed laser 11, such as a Nd:YAG solid pulsed laser, to adjust the repetition frequency of the pulsed laser 11. The frequency of the sine wave signal is adjustable from 1 Hz to 200 kHz.

[0051] In some embodiments, the pulsed laser 11 may be a solid pulsed laser. The solid pulsed laser has the characteristics of small volume, convenient use, high output power, and high repetition frequency.

[0052] As an example, the pulsed 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 pulsed laser to be used can be selected according to actual needs, and the embodiments of the present invention do not make specific limitations.

[0053] As an example, the wavelength of the pulsed laser source generated by the pulsed laser 11 is, for example, 300 nm to 1064 nm, the pulse width is, for example, 1 ps to 500 ps, the single-pulse energy is, for example, 1 μJ to 500 μJ, and the repetition frequency is, for example, 1 Hz to 500 kHz. Among them, nm is the unit of measurement for the wavelength of the light beam emitted by the pulsed laser, which is nanometer, ps is the unit of measurement for the pulse duration of the pulsed laser, which is picosecond, J is the unit of energy, heat, and work, and μJ represents microjoule, which is one thousandth of a joule.

[0054] As an example, when the pulsed laser 11 is a Nd:YAG pulsed laser, the laser wavelength output by the Nd:YAG pulsed laser is adjustable from 500 nm to 1064 nm, the beam diameter is adjustable from 1 mm to 10 mm, the pulse width is adjustable from 1 ps to 600 ps, the single-pulse energy is adjustable from 1 μJ to 800 μJ, and the repetition frequency is adjustable from 1 Hz to 500 kHz.

[0055] As a specific example, the laser wavelength is, for example, 532 nm, the laser beam diameter of the pulsed laser is, for example, 2.5 mm, the pulse width is, for example, 15 ps, the maximum value of the single-pulse energy is, for example, 100 μJ, the repetition frequency is, for example, adjustable from 1 Hz to 200 kHz, the operating current is, for example, adjustable from 0 A to 60 A, and the operating voltage is adjustable from 0 V to 10 V.

[0056] In some embodiments, the optical path subsystem 20 includes a beam expander assembly 21 and a focusing assembly 22 connected in sequence. One end of the resonant cavity 31 is an open end communicating with the focusing assembly 22, and the other end of the resonant cavity 31 is a closed end; wherein, the beam expander assembly 21 is configured to expand the pulsed laser signal output by the pulsed laser 11; the focusing assembly 22 is configured to transmit the expanded pulsed laser signal into the resonant cavity 31 through the open end of the resonant cavity 31 and focus it on the bottom surface of the closed end in the resonant cavity 31.

[0057] In this embodiment, expanding the pulsed laser signal first and then focusing it can improve the collimation of the pulsed laser signal, which is beneficial to improving the focusing effect that the focusing assembly 22 can achieve.

[0058] In some embodiments, the beam expander assembly 21 can be, for example, a beam expander lens, and the focusing assembly 22 can be, for example, a focusing lens. As an example, the operating wavelength of the beam expander lens is 532 nm and the magnification is 5 times; the operating wavelength of the aspherical focusing lens is 532 nm and the focal length is 100 mm.

[0059] In the embodiments of the present invention, the optical path subsystem 20 can be referred to as an expanding and focusing optical path, and its function is to reduce the diameter of the light spot reaching the surface of the excitation target, increase the optical power density at the focal point on the surface of the excitation target, making it greater than the threshold value (107 W / cm 2 ) at which the plasma effect occurs in the photoacoustic effect, and form a plasma approximately in the shape of a point at the focal point.

[0060] In some embodiments, since the bottom surface of the closed end in the resonant cavity 31 can be the surface of a metal target, the size of the light spot formed on the surface of the metal target can be expressed by the following expression (1).

[0061]

[0062] Wherein, in the above expression (1), M 2 is the beam quality of the laser. For example, the beam quality of the laser is 1.2, and the smaller the value, the better the beam quality of the laser. θ is the full beam angle of the outgoing light, D is the focal spot diameter, θ0 is the full beam angle of the incident light, and D0 is the incident light spot diameter.

[0063] In some embodiments, the full beam angle θ0 of the incident light and the incident light spot diameter D0 can be expressed by the following expression (2).

[0064]

[0065] In the above expression (2), λ is the laser wavelength, such as 532 nm.

[0066] Through the above expressions (1) and (2), for example, the focal spot diameter can be calculated to be 8 μm.

[0067] In some embodiments, the calculation of the optical power density at the focus on the surface of the metal target can be denoted by the following expression (3):

[0068]

[0069] In the above expression (3), I is the optical power density at the focus, with the unit of W / cm 2 , E is the single-pulse energy of the laser, S is the spot area at the focus, and τ is the pulse width of the pulsed laser.

[0070] In some embodiments, ideally, the optical power density at the focus is approximately 1.3×10 10 W / cm 2 , and this optical power density is greater than the threshold (10 7 W / cm 2 ) at which the plasma effect occurs in the photoacoustic effect.

[0071] From the content of the above embodiments, it can be seen that by adjusting the power of the pulsed laser 11, the optical power density at the focal spot of the solid medium is made greater than the optical power density threshold corresponding to the plasma effect (10 7 W / cm 2 ), thereby generating plasma at the focal spot; subsequently, by changing the repetition frequency of the pulsed laser, the process of plasma expansion and collapse can form resonance, and continuous sound waves with equal positive and negative pressures and approximately sinusoidal waveforms can be output. That is to say, first, the power of the pulsed laser 11 needs to be adjusted so that the energy at the focus meets the requirements of the optical energy density of the plasma effect, and then the repetition frequency of the pulsed laser 11 is adjusted to make the process of plasma expansion and collapse form resonance and output continuous sound waves; further, by changing the size of the adjustable resonant cavity 31, the continuous sound waves generated at the bottom of the resonant cavity are adjusted. When the length of the resonant cavity is adjusted appropriately, continuous sound waves approximately in the shape of a sine wave are output.

[0072] In some embodiments, the sound source subsystem 30 further includes: a position adjustment device 32 for adjusting the position of the resonant cavity according to a position adjustment signal from a predetermined control device to adjust the focusing position of the pulsed laser signal to the center position of the bottom surface inside the resonant cavity.

[0073] In this embodiment, after the optical path subsystem 20 is pre-built, the pulsed laser 11 generates a pulsed laser beam. After the pulsed laser beam is transmitted through the beam expander and the focusing lens, the focal position of the beam can be determined. By moving the position of the metal resonant cavity, the pulsed laser can be focused on the center position of the metal surface at the bottom inside the resonant cavity to achieve a better focusing effect.

[0074] As Figure 3 shown, in Figure 3In the shown scenario, it includes a pulsed laser beam 301, an open end 302 of the resonator 31, an outer layer 303 of the resonator 31, an inner layer 304 of the resonator 31, and a bottom 305 of the resonator 31. Among them, the bottom 305 of the resonator 31 is closed, the laser beam enters the resonator 31 from the upper open end 302 of the resonator 31, and the laser sound source is generated at the bottom 305 inside the resonator 31.

[0075] In some embodiments, the resonator 31 includes at least two sleeves connected in sequence and the adjacent sleeves are nested; among them, the at least two sleeves include a first sleeve and a second sleeve; the first end of the first sleeve is an open end communicating with the focusing component, 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 nested with the previous sleeve, for example, the first sleeve, and the second end of the second sleeve is a closed end to serve as the closed end of the resonator 31.

[0076] In some alternative embodiments, the resonator 31 can be a cylindrical metal resonator with adjustable length and / or adjustable inner diameter or a resonator with a metal wall surface; the cylindrical metal resonator is easy to estimate its resonance frequency. Exemplarily, the resonator 31 is made of metal copper material or made of a composite material containing copper.

[0077] In the embodiments of the present invention, the metal resonator with adjustable length has the following functions: converting light energy into sound energy at the bottom inside the resonator through the plasma mechanism in the photoacoustic effect; and can adjust the output sound wave waveform by changing the length of the adjustable resonator.

[0078] In some embodiments, the adjustable size parameters of the resonator include at least one of length and inner diameter. Exemplarily, the length-adjustable cylindrical resonator is made of metal copper material, the adjustable range of the length is 100 mm - 200 mm, and the adjustable range of the inner diameter of the resonator is 20 mm - 40 mm.

[0079] It should be understood that the specific structure of the resonator in the embodiments of the present invention can enable the resonator to have a changeable overall length and / or a changeable inner diameter, and the more specific structural implementation manner can be preset according to actual needs, and the embodiments of the present invention do not make specific limitations.

[0080] In some embodiments, the size adjustment method of the resonator 31 includes at least one of manual adjustment and automatic adjustment; in the case where the size adjustment method includes automatic adjustment, the sound source subsystem 30 further includes: a size adjustment device 33 for adjusting the size of the resonator 31 to a suitable size according to the size adjustment signal from a predetermined control device.

[0081] In this embodiment, the appropriate size of the resonant cavity 31 means that the appropriate size can enable the output waveform at the bottom focus of the resonant cavity 31 to be an approximate sine continuous acoustic wave.

[0082] In some embodiments, the size of the resonant cavity 31 can be adjusted by a combination of manual adjustment and automatic adjustment. For example, first manually adjust the size of the resonant cavity 31 to a size empirical value according to experience, and then, according to the received size adjustment signal from a predetermined control device, automatically fine-tune on the basis of this size empirical value through the size adjustment device 33. When the size of the resonant cavity (length and / or inner diameter) is adjusted to an appropriate value (appropriate length value and / or appropriate inner diameter value), an approximate sine continuous acoustic wave is output.

[0083] The following combines Figure 4 to describe the working principle of the laser transducer system in the embodiments of the present invention. Figure 4 It is a schematic diagram of the scenario where acoustic waves are generated on the bottom surface inside the adjustable resonant cavity of the embodiment of the present invention.

[0084] As Figure 4 shown, the metal target 401 at the bottom inside the resonant cavity is schematically shown in this scenario. The pulsed laser beam 301 is focused at the bottom metal target 401. The metal atoms at the bottom metal target 401 absorb the energy of the pulsed laser beam 301, undergo multi-photon ionization and avalanche ionization, and form a metal plasma 403. Due to the shielding effect on the laser, the plasma 403 will strongly absorb the energy of the subsequent pulsed laser beam 301, forming a locally high-temperature and high-pressure environment. Then, due to the internal and external pressure difference, the plasma 403 will expand and collapse violently to output acoustic waves coupled into the medium. At this time, the plasma bubble can be approximately regarded as a point sound source. The single-pulse laser excitation of the plasma bubble generates a shock wave, and the shock wave rapidly decays into an acoustic wave 404 (the positive pressure and negative pressure are not equal) during transmission. Therefore, the pulsed acoustic wave decayed from the shock wave is not an acoustic wave in the true sense.

[0085] In an embodiment of the present invention, each pulsed laser can generate a plasma 403 bubble on the bottom metal surface inside the tunable resonant cavity, and then output sound waves through expansion and collapse. The expansion of the plasma 403 generates a positive pressure, and the surrounding substances are pushed away during the expansion process. After the expansion ends, the plasma 403 tries to shrink back, forming a negative pressure. If the repetition frequency of the pulsed laser is increased, before the plasma 403 bubble has completely shrunk back, the excitation of the next laser pulse on the plasma 403 arrives continuously, resulting in a larger expansion of the plasma 403 bubble, and the corresponding contraction force will increase. Eventually, a balanced state is reached, causing the expansion and collapse processes of the plasma 403 at the bottom metal target 401 (i.e., the focal point) to resonate, generating relatively regular sound waves. The sound waves are generated at the bottom of the resonant cavity and will interact with the inner wall of the resonant cavity during the propagation process. By changing the length of the tunable resonant cavity, the waveform of the sound waves generated by the plasma 403 bubble can be regulated to output approximately sinusoidal continuous sound waves.

[0086] Figure 5 This is the time-domain pulse sound signal diagram generated by a single pulsed laser exciting a length-tunable resonant cavity according to an embodiment of the present invention. As Figure 5 shown, similar to the sound waves generated by traditional laser transducers in different excitation media, this pulsed sound wave is attenuated from a shock wave and the positive pressure is greater than the negative pressure. This data was measured by a sound pressure microphone with a sampling rate of 48 kHz in air. It can be seen that the shock wave rapidly attenuates into a sound wave with unequal positive and negative pressures during the transmission process, and the pulsed sound wave attenuated from the shock wave is not a true sound wave in the real sense.

[0087] Figure 6 This is the time-domain sound signal diagram generated by a size-tunable resonant cavity according to an embodiment of the present invention. In Figure 6 , when the repetition frequency of the pulsed laser is 1 kHz, no plasma resonance effect occurs in this resonant cavity under the excitation of multiple consecutive pulsed lasers. Its characteristics are: continuous, highly repetitive, and a sound wave with unequal positive and negative pressures attenuated from a shock wave. This data was measured by a sound pressure microphone with a sampling rate of 48 kHz in air.

[0088] Figure 7 This is the time-domain sound signal diagram generated by a size-tunable resonant cavity according to another embodiment of the present invention. When the repetition frequency of the pulsed laser is 8 kHz, a plasma resonance effect occurs at the focal point in this resonant cavity under the excitation of multiple consecutive pulsed lasers.

[0089] Moreover, when the overall length of the resonant cavity after adjustment is 124.75 mm, the sound signal is approximately sinusoidal. At this time, it can be clearly seen that the characteristics of the time-domain sound signal output by the resonant cavity are: continuous, relatively repetitive, approximately sinusoidal wave, and equal positive and negative pressures. This data was also measured by a sound pressure microphone with a sampling rate of 48 kHz in air.

[0090] From the above Figures 4-6 description, it can be known that according to the laser transducer system of the embodiment of the present invention, by adjusting the repetition frequency of the pulsed laser to an appropriate value, continuous acoustic waves can be generated in the solid medium based on plasma resonance at the focus of the pulsed laser signal. Subsequently, the waveform of the continuous acoustic waves can be regulated by a resonator with adjustable size, so as to output a continuous acoustic wave signal with an approximate sine waveform; the laser transducer system of the embodiment of the present invention can output continuous acoustic waves with equal positive and negative pressures in the time domain.

[0091] Next, in conjunction with the accompanying drawings, the laser transducer sound generation method of the embodiment of the present invention will be introduced. Figure 8 The flowchart showing the laser transducer sound generation method of the embodiment of the present invention is shown.

[0092] In the embodiment of the present invention, the laser transducer sound generation method is based on the laser transducer system of the above embodiment. As Figure 8 shown, the laser transducer sound generation method of the embodiment of the present invention may include the following steps.

[0093] S810, focusing the pulsed laser signal output by the pulsed laser on the bottom surface in the resonator; S820, converting the pulsed laser signal into a pulsed acoustic wave signal on the bottom surface in the resonator; S830, adjusting the repetition frequency of the pulsed laser to an appropriate frequency to convert the pulsed acoustic wave signal into a continuous acoustic wave signal on the bottom surface in the resonator; S840, when the size of the resonator is adjusted to an appropriate size, outputting a continuous sine acoustic wave signal with equal positive and negative pressures.

[0094] Through the laser transducer sound generation method of the embodiment of the present invention, continuous acoustic waves can be generated in a resonator with adjustable length based on the plasma resonance effect, and the sound wave output by this sound generation method can be continuous and have equal positive and negative pressures.

[0095] In some embodiments, step S810 may specifically include: S11, expanding the pulsed laser signal output by the pulsed laser using a beam expanding component; S12, using a focusing component to transmit the expanded pulsed laser signal through the open end of the resonator into the resonator and focusing it on the bottom surface of the closed end in the resonator.

[0096] In some embodiments, the expanded pulsed laser signal is focused on the center position of the bottom surface of the closed end in the resonator; in this embodiment, after step S12, the method may further include: adjusting the position of the resonator according to the position adjustment signal from a predetermined control device to adjust the focusing position of the pulsed laser signal to the center position of the bottom surface in the resonator.

[0097] In some embodiments, the pulsed laser signal is a laser signal generated by a pulsed laser according to a sine wave signal generated by a signal generator.

[0098] In this embodiment, step S820 may specifically include: S21, in response to a power adjustment signal of a predetermined control device, adjusting the power of the pulsed laser to adjust the energy of a single pulsed laser output by the pulsed laser; S22, when the energy of the single pulsed laser enables the optical energy density at the bottom focus to reach a predetermined energy density threshold, forming a plasma at the bottom focus, so as to generate a pulsed acoustic wave signal at the bottom focus through the expansion and collapse of the plasma.

[0099] In some embodiments, step S830 may specifically include: in response to a frequency adjustment signal of a predetermined control device, adjusting the frequency of the sine wave signal output by the signal generator to adjust the repetition frequency of the pulsed laser to an appropriate frequency, so that the plasma generates resonance during the expansion and collapse process based on the appropriate frequency, and further forming a continuous acoustic wave signal at the bottom focus.

[0100] The step division of the above various methods is only for clear description. When implemented, they can be combined into one step or some steps can be split into multiple steps. As long as the same logical relationship is included, they are all within the protection scope of this patent; adding insignificant modifications to the algorithm or process or introducing insignificant designs, but not changing the core design of its algorithm and process are all within the protection scope of this patent.

[0101] In some embodiments, after S830 and before S840, the method may further include: adjusting the size of the resonant cavity to an appropriate size according to a size adjustment signal from a predetermined control device.

[0102] According to the laser energy conversion and sound generation method of the embodiments of the present invention, by adjusting the repetition frequency of the pulsed laser to an appropriate value, a continuous acoustic wave is generated in a solid medium at the focus of the pulsed laser signal based on plasma resonance. Subsequently, the waveform of the continuous acoustic wave is regulated by a resonant cavity with an adjustable size, so as to output a continuous acoustic wave signal with an approximate sine waveform, realizing the output of a continuous acoustic wave with equal positive and negative pressures in the time domain.

[0103] The following combines Figure 9 Describe the specific working process of the laser energy conversion system according to the exemplary embodiments of the present invention. Figure 9 It is a schematic diagram of the scenario of the laser energy conversion system provided by the embodiments of the present invention.

[0104] In Figure 9 The shown scenario includes: a control computer 901, a signal generator 12, a pulsed laser 11, a beam expander 904, a focusing lens 905, and a solid resonant cavity 31 with an adjustable length.

[0105] In some embodiments, the signal generator 12 generates and outputs a sine wave signal to the pulsed laser 11. The pulsed laser 11 generates and outputs pulsed laser light according to the sine wave signal. The laser beam of the pulsed laser light passes through the focusing optical path composed of the beam expander 904 and the focusing lens 905, and is focused on the metal surface at the bottom inside the solid resonator 31.

[0106] In some embodiments, the power of the pulsed laser 11 is adjusted by the control computer 901 to change the energy of the output single-pulse laser light. When the single-pulse energy is high enough so that the energy density threshold at the focus is greater than the threshold of the plasma mechanism, a single-pulse laser light will generate a plasma point sound source on the metal surface at the bottom inside the resonator 31. Through the expansion, collapse, and production of the plasma, a shock wave is generated. The shock wave attenuates into a pulsed sound wave during propagation.

[0107] In some embodiments, the signal generator 12 is used to adjust the repetition frequency of the pulsed laser 11 outputting pulsed laser light, that is, the number of times the pulsed sound wave is excited per second. When the repetition frequency of the pulsed laser 11 is adjusted to an appropriate frequency value, resonance occurs during the expansion and collapse process of the plasma at the focus, forming continuous sound waves.

[0108] In some embodiments, by changing the length of the tunable resonator 31, the continuous sound waves generated at the bottom inside the resonator 31 are adjusted. When the overall length of the resonator 31 is adjusted appropriately, continuous sound waves approximating a sine wave are output.

[0109] Through the laser energy conversion system of the embodiments of the present invention, based on the plasma mechanism in the photoacoustic effect, by using a simple method of adjusting the repetition frequency of pulsed laser light, plasma resonance at the focus is achieved, and continuous sound waves with equal positive and negative pressures are generated in the solid medium.

[0110] The laser energy conversion system and the laser energy conversion sound generation method of the present invention can excite a metal solid based on the plasma effect in the photoacoustic effect to generate sound waves coupled into the medium. Then, by adjusting the repetition frequency of the pulsed laser (for example, adjustable from 1 Hz to 200 kHz), the plasma vibration process (expansion, collapse) is driven to form resonance, and then the length of the resonator is adjusted to control the waveform, so that the sound waves output by the laser energy conversion device are continuous, have equal positive and negative pressures, and approximate a sine wave. This system and method achieve the function of a true laser energy converter, and are simple, easy to implement, and reliable in performance.

[0111] It should be clear that the present invention is not limited to the specific configurations and processes described in the above embodiments and shown in the figures. For the convenience and brevity of description, the detailed description of known methods is omitted here, and the specific working processes of the systems, modules, and units described above can refer to the corresponding processes in the foregoing method embodiments, and will not be elaborated here.

[0112] It should be noted that, in this document, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising one..." does not exclude the presence of additional identical elements in the process, method, article or device comprising that element.

[0113] Those skilled in the art can understand that, although some of the embodiments described herein include certain features included in other embodiments rather than other features, the combination of features of different embodiments means that it is within the scope of this embodiment and forms different embodiments.

[0114] It can be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principles of the present invention. However, the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also regarded as the protection scope of the present invention.

Claims

1. A laser energy conversion system, characterized in that, Comprising: A laser subsystem, an optical path subsystem, and a sound source subsystem connected in sequence. The laser subsystem includes a pulsed laser, and the sound source subsystem has a resonant cavity structure with adjustable size; wherein, The laser subsystem is configured to generate and output a pulsed laser signal through the pulsed laser; The optical path subsystem is configured to focus the pulsed laser signal on the bottom surface within the resonant cavity; The sound source subsystem is configured to convert the pulsed laser signal into a pulsed acoustic signal on the bottom surface within the resonant cavity; The laser subsystem is further configured to adjust the repetition frequency of the pulsed laser to a suitable frequency to convert the pulsed acoustic signal into a continuous acoustic signal on the bottom surface within the resonant cavity; The sound source subsystem is further configured to output a continuous sinusoidal acoustic signal with equal positive and negative pressures when the size of the resonant cavity is adjusted to a suitable size; The optical path subsystem includes a focusing component. One end of the resonant cavity is an open end communicating with the focusing component, and the other end is a closed end; The resonant cavity includes at least two sleeves connected in sequence, and adjacent sleeves are nested; wherein, The at least two sleeves include a first sleeve and a second sleeve; The first end of the first sleeve is an open end communicating with the focusing component, 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 nested with the previous sleeve, and the second end of the second sleeve is a closed end to serve as the closed end of the resonant cavity.

2. The system according to claim 1, characterized in that, The pulsed laser signal forms a bottom focus on the bottom surface within the resonant cavity. The laser subsystem further includes: A power adjustment device configured to adjust the power of the pulsed laser according to a power adjustment signal from a predetermined control device to adjust the energy of a single-pulse laser output by the pulsed laser; The sound source subsystem is further configured to form a plasma at the bottom focus when the energy of the single-pulse laser makes the optical energy density at the bottom focus reach a predetermined energy density threshold, and generate a pulsed acoustic signal at the bottom focus through the expansion and collapse of the plasma.

3. The system according to claim 2, wherein The laser subsystem further includes: A signal generator configured to generate and output a sine wave signal; The pulsed laser is configured to generate a pulsed laser signal according to the received sine wave signal; A frequency adjustment device configured to adjust the repetition frequency of the pulsed laser to a suitable frequency by adjusting the frequency of the sine wave signal output by the signal generator according to a frequency adjustment signal from a predetermined control device, such that the plasma resonates during the expansion and collapse process based on the suitable frequency, and further forms a continuous acoustic signal at the bottom focus.

4. The system according to claim 1, wherein The optical path subsystem further includes a beam expander component connected to the focusing component; wherein, The beam expander component is configured to expand the pulsed laser signal output by the pulsed laser; The focusing component is configured to transmit the expanded pulsed laser signal through the open end of the resonant cavity into the resonant cavity and focus it on the bottom surface of the closed end within the resonant cavity.

5. The system according to claim 1 or 4, characterized in that, The sound source subsystem further includes: A position adjusting device, configured to adjust the position of the resonant cavity according to a position adjusting signal from a predetermined control device, so as to adjust the focusing position of the pulsed laser signal to the center position of the bottom surface inside the resonant cavity.

6. The system according to claim 2, wherein The size adjustment mode of the resonant cavity includes at least one of manual adjustment and automatic adjustment; when the size adjustment mode includes automatic adjustment, the sound source subsystem further includes: A size adjusting device, configured to adjust the size of the resonant cavity to the appropriate size according to a size adjusting signal from a predetermined control device.

7. A laser transducer sound generation method, characterized in that Focus the pulsed laser signal output by a pulsed laser on the bottom surface inside the resonant cavity; Convert the pulsed laser signal into a pulsed acoustic wave signal on the bottom surface inside the resonant cavity; Adjust the repetition frequency of the pulsed laser to an appropriate frequency, so as to convert the pulsed acoustic wave signal into a continuous acoustic wave signal on the bottom surface inside the resonant cavity; Output a continuous sinusoidal acoustic wave signal with equal positive and negative pressures when the size of the resonant cavity is adjusted to the appropriate size; Wherein, the optical path subsystem includes a focusing component, one end of the resonant cavity is an open end communicating with the focusing component, and the other end is a closed end; The resonant cavity includes at least two sleeves connected in sequence, and the adjacent sleeves are nested; wherein, The at least two sleeves include a first sleeve and a second sleeve; The first end of the first sleeve is an open end communicating with the focusing component, 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 nested with the previous sleeve, and the second end of the second sleeve is a closed end to serve as the closed end of the resonant cavity.

8. The method according to claim 7, wherein The pulsed laser signal is a laser signal generated by the pulsed laser according to a sine wave signal generated by a signal generator; The converting the pulsed laser signal into a pulsed acoustic wave signal on the bottom surface inside the resonant cavity includes: Responding to a power adjustment signal from a predetermined control device, adjusting the power of the pulsed laser to adjust the energy of a single-pulse laser output by the pulsed laser; When the energy of the single-pulse laser makes the optical energy density at the bottom focus reach a predetermined energy density threshold, forming a plasma at the bottom focus, so as to generate a pulsed acoustic wave signal at the bottom focus through the expansion and collapse of the plasma.

9. The method according to claim 8, wherein The adjusting the repetition frequency of the pulsed laser to an appropriate frequency to convert the pulsed acoustic wave signal into a continuous acoustic wave signal on the bottom surface inside the resonant cavity includes: Responding to the frequency adjustment signal from the predetermined control device, adjusting the frequency of the sine wave signal output by the signal generator to adjust the repetition frequency of the pulsed laser to an appropriate frequency, so that the plasma resonates during the expansion and collapse process based on the appropriate frequency, and then a continuous acoustic wave signal is formed at the bottom focus.

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