A method for generating sound waves in air using pulsed laser

Abstract

The present invention discloses a method for generating sound waves in the air using a pulsed laser. The device for generating sound waves is composed of a pulsed laser and an optical modulation system. The pulsed laser is emitted by a pulsed laser and then acts on water vapor in the air after passing through the optical modulation system. The water vapor absorbs the heat energy of the pulsed laser. After the pulsed laser passes through, the water vapor temperature instantly rises and expands, thereby generating pressure waves in the area of ​​action, that is, generating sound waves through the photoacoustic effect. In addition, a three-color visible light laser is used to illuminate the area of ​​action for imaging. The structure of the method for generating sound waves in the air using laser pulses proposed by the present invention is simple. Since water vapor can still be generated even in air with low relative humidity, the effect can be achieved by only following the above steps. The method has research value in the manipulation of microparticles, biological imaging, space imaging, sound communication, and naked-eye three-dimensional display.

Description

Technical Field

[0001] The present invention relates to a method for realizing the generation of sound waves by the interaction of pulsed laser with water vapor in air, and in particular to acoustic tweezers and sound wave communication generated in air by modulating the emission frequency and scanning frequency of pulsed laser and the photoacoustic effect of water vapor. Background Art

[0002] Lasers interacting with matter generate acoustic waves. The principle is that the laser energy is transferred to the medium, generating pressure waves that vibrate and generate acoustic waves. Lasers interact with solids, liquids, and gases, with applications in fields such as medicine, imaging, and particle manipulation. Currently, applications based on the photoacoustic effect are common, with laser-generated acoustic tweezers for particle manipulation being a hot topic. Acoustic tweezers are used to manipulate the position and motion of very small objects using sound waves. However, the application of laser-generated acoustic tweezers is relatively limited. Strictly speaking, only configurations based on a single beam can be called acoustic tweezers. However, the broad concept of acoustic tweezers encompasses two types of beam configurations: single beam and standing wave. This technique works by controlling the location of acoustic pressure nodes, which attract objects to specific locations in a fixed acoustic field. The target object must be significantly smaller than the wavelength of the sound being used. This technique is commonly used to manipulate microscopic particles. Laser acoustic signal communication is also a hot topic, currently primarily used for underwater communication and signal propagation within organisms. Research in air is relatively limited.

[0003] Acoustic tweezers primarily rely on standing waves generated by ultrasonic generators. Professor Bruce Drinkwater of the University of Bristol, UK, has achieved manipulation of particles at the micron and even centimeter scale by studying standing waves generated by ultrasonic generators. However, since standing waves require two sound waves propagating in opposite directions, this limits some applications of acoustic tweezers. Furthermore, laser-based methods for generating acoustic tweezers are currently relatively rare.

[0004] Research into laser acoustic communication is increasingly focused on methods for transmitting sound signals by embedding them in light. While this method can propagate at speeds far greater than that of sound waves, research into how to transmit sound signals directly through light interacting with matter is still ongoing. Summary of the Invention

[0005] Technical problem: The present invention provides a method for generating sound waves in the air using a pulsed laser: a device for generating sound waves is composed of a pulsed laser and an optical modulation system, wherein a pulsed laser is used to emit a pulsed laser which passes through the optical modulation system and then reacts with water vapor in the air. The water vapor absorbs the heat energy of the pulsed laser. After the pulsed laser passes through, the temperature of the water vapor instantly rises and expands, thereby generating a pressure wave in the action area, that is, generating sound waves through the photoacoustic effect.

[0006] The device for generating sound waves composed of a pulse laser and an optical modulation system is a device for generating sound waves composed of a first pulse laser and a first optical modulation system, and its frequency is adjustable. Each time a pulse laser is emitted, a sound wave is generated, and then the sound waves continuously resonate and superimpose. The pulse emission frequency determines the number of times the sound wave resonance is generated, the propagation phase and the period. Various sound waves are modulated by modulating the resonance, and standing waves and traveling waves are realized.

[0007] The device for generating sound waves composed of a pulse laser and an optical modulation system is a device for generating sound waves composed of a second pulse laser and a second optical modulation system. The second optical modulation system outputs a scanning laser that converges and moves the pulse laser emitted by the second pulse laser. The scanning frequency is adjustable. By adjusting the scanning frequency, the lateral resonance frequency of the sound wave is controlled to achieve a superposition effect of sound waves in space, thereby generating different sound wave signals.

[0008] The first pulse laser and the first optical modulation system each have two devices constituting two groups of sound wave generation. The emission directions of the two pulse lasers form an acute angle, so that the two laser beams coincide at the convergence position, i.e., the focal point position of the two first optical modulation systems. By controlling the emission frequency of the two pulse lasers, the resonance effect of the sound wave is controlled to generate two superimposed traveling waves of acoustic tweezers.

[0009] The second pulse laser and the second optical modulation system each have two devices constituting two groups of sound wave generating devices. The emission directions of the two scanning pulse lasers form an acute angle. The scanning frequencies of the pulse laser beams are modulated respectively by the two second optical modulation systems. The change of the scanning frequency controls the resonance superposition of the sound waves to generate an enhanced sound wave signal.

[0010] The two first pulse lasers are placed opposite to each other, that is, the emission directions of the two lasers are opposite; the two pulse lasers are respectively used to make the convergence points of the laser pulses coincide with each other through the first optical modulation system, and sound waves propagating in opposite directions are generated based on the photoacoustic effect. The sound waves propagating in opposite directions are superimposed to generate standing waves, and the resonance frequency of the sound waves is controlled by controlling the emission frequencies of the two pulse lasers, thereby generating standing wave acoustic tweezers.

[0011] The two second pulse lasers are placed opposite to each other, that is, the emission directions of the two lasers are opposite; the two second optical modulation systems respectively modulate the scanning frequency of the two laser pulses in the relative propagation directions in space, and the change in the scanning frequency causes the resonance superposition of the sound waves in the direction perpendicular to the laser generation direction, thereby enhancing the generation of the sound wave signal.

[0012] The pulse laser has a laser wavelength of about 1400nm or 1900nm and operates in a pulse wave mode. Light near these two wavelengths can be largely absorbed by water vapor in the air, making it easier to generate sound waves based on the photoacoustic effect.

[0013] The energy of a single pulse of the first pulse laser or the second pulse laser is at least in the order of millijoules.

[0014] The method for generating sound waves adopts adding an air humidifying device to increase and control the humidity of the surrounding air.

[0015] In addition, the laser pulse passes through the optical modulation system and modulates the laser pulse frequency to generate different sound signals, which is completely different from the traditional method.

[0016] Beneficial Effects: This method, for the first time, proposes the use of pulses interacting with water vapor in the air to generate superposition effects of acoustic waves for applications in acoustic tweezers and acoustic communication. Using a pulsed laser and an optical modulation system, acoustic waves can be generated in the air. A single pulsed laser can generate superposition by varying the frequency of its pulses, while two laser pulses can be superimposed to generate enhanced acoustic waves, such as traveling and standing waves. Furthermore, unlike traditional acoustic wave generation methods, this method is easy to operate and has a simple structure, providing new insights into the manipulation of microparticles, bioimaging, and acoustic communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a system schematic diagram of Example 1;

[0018] Figure 2 This is a system schematic diagram of Example 2;

[0019] Figure 3 This is a system schematic diagram of Example 3;

[0020] Figure 4 This is a system schematic diagram of Example 4;

[0021] Figure 5 This is a system schematic diagram of Example 5;

[0022] Figure 6 This is a system schematic diagram of Example 6;

[0023] The figure includes: a first pulse laser 1, a first optical modulation system 2, a second pulse laser 3, and a second optical modulation system 4. DETAILED DESCRIPTION

[0024] The present invention provides a method for realizing the generation of sound waves by the interaction of a pulsed laser with water vapor in the air, which mainly comprises a first pulsed laser 1 and a first optical modulation system 2 to form a device for generating sound waves. The first pulsed laser 1 is used to emit a laser pulse which passes through the first optical modulation system 2 and then interacts with water vapor in the air. The water vapor absorbs the heat energy of the laser pulse. Therefore, after the laser pulse passes, the temperature of the water vapor instantly rises and expands, and then a pressure wave is generated in the action area, that is, sound waves are generated by the principle of photoacoustic effect. The pulse emission frequency determines the number of times the sound wave resonance is generated, the propagation phase and the period, that is, the modulation of various sound waves can be achieved by modulating the resonance. For the superposition of sound waves propagating in the same direction, a traveling wave can be realized. The principle formula for generating traveling waves based on the superposition of sound waves is as follows:

[0025]

[0026] Formula (1) shows that when two sound waves propagating in the same direction resonate and superimpose to produce a traveling wave, the multiple pulses used in the present invention generate multiple sound waves propagating in the +y direction. When the phase of the sound waves propagating in the same direction is 2kπ (k is a positive integer), the sound wave resonance is enhanced. When the phase of the sound waves propagating in the same direction is (2k+1)π, the sound wave resonance cancels out. Therefore, the addition of multiple sound waves produces a traveling wave acoustic tweezers.

[0027] A second optical modulation system 4 modulates the spatial scanning frequency of the laser pulses emitted by the second pulsed laser 3. This change in scanning frequency controls the resonance of the acoustic waves, generating different acoustic wave signals based on the photoacoustic effect. Based on the generation of traveling waves, the present invention allows the pulses to generate more superimposed acoustic waves within the pulse scanning area, achieving a stronger resonance effect.

[0028] The two first pulsed lasers 1 emit lasers at an acute angle, allowing the two laser beams to overlap at their convergence point (i.e., the convergence point of the first optical modulation system 2). By controlling the emission frequencies of the two pulsed lasers, the resonance of the acoustic waves is controlled, generating acoustic tweezers. Based on formula (1), the two traveling waves generated by the two laser pulses produce superimposed resonance at an acute angle. When the two acoustic waves are at a phase of 2kπ, a resonance enhancement effect is generated, while at a phase of (2k+1)π, a resonance cancellation effect occurs. This results in a more powerful acoustic tweezer.

[0029] The two second pulsed lasers 3 emit lasers at an acute angle. The two second optical modulation systems 4 modulate the scanning frequencies of the pulsed laser beams. The changes in scanning frequency control the resonance of the acoustic waves, generating acoustic signals. This method allows the two acoustic waves at an acute angle to overlap in the horizontal direction, achieving a resonant and superimposed amplification of the acoustic signal.

[0030] The two first pulse lasers 1 are placed opposite to each other, i.e., the emission directions of the two lasers are opposite. The laser pulses are passed through the two first optical modulation systems 2 to make the focal points of the laser pulses coincide with each other. Based on the principle of the photoacoustic effect, sound waves propagating in opposite directions are generated. The superposition of the sound waves propagating in opposite directions can generate a standing wave. By controlling the emission frequency of the two pulse lasers, the resonance of the sound waves is controlled, thus generating a standing wave acoustic tweezers system. The superposition formula of two sound waves propagating in opposite directions is:

[0031] y(x,t)=y m sin(kx-ωt)+y m sin(kx+ωt)=2y m According to formula (2), when two acoustic waves with equal amplitude, frequency, and wavelength propagate in opposite directions, the acoustic resonance is enhanced when the phase of the acoustic waves propagating in opposite directions is 2kπ (k is a positive integer). When the phase of the acoustic waves propagating in opposite directions is (2k+1)π, the acoustic resonance cancels out. This generates a standing wave. The present invention utilizes two identical acoustic wave-generating devices placed opposite each other to generate standing wave acoustic tweezers.

[0032] The two second pulsed lasers 3 are positioned opposite each other, i.e., they emit in opposite directions. Two second optical modulation systems 4 modulate the scanning frequencies of the two laser pulses in the perpendicular directions of their relative propagation in space. Variations in the scanning frequencies control the resonance of the acoustic waves, thereby enhancing the effect of acoustic wave superposition. This method also employs the principle of generating standing waves, simultaneously utilizing laser pulse scanning in the lateral active area to achieve the effect of acoustic wave resonance superposition.

[0033] The laser wavelength of the first pulse laser 1 is around 1400nm or 1900nm, and the working mode is pulse wave; light near these two wavelengths can be largely absorbed by water vapor in the air, making it easier to generate sound waves based on the photoacoustic effect.

[0034] The energy of a single pulse of the first pulse laser 1 and the second pulse laser 3 is at least in the order of millijoules.

[0035] The method for generating sound waves adopts adding an air humidifying device to increase and control the humidity of the surrounding air.

[0036] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0037] Example 1:

[0038] like Figure 1 As shown, an embodiment of the present invention discloses a method for generating sound waves in air using laser pulses, comprising the following specific steps:

[0039] 1) Equipment layout: according to Figure 1 The first pulse laser 1 and the first optical modulation system 2 are arranged in sequence.

[0040] 2) The position of the focal point of the acoustic wave to be generated is adjusted by the first optical modulation system 2. Based on the principle of photoacoustic effect, a single laser pulse interacting with water vapor will generate an acoustic wave along the +y direction, and emitting multiple laser pulses will generate multiple acoustic waves superimposed.

[0041] 3) During the aforementioned superposition of acoustic waves, the superposition frequency of the ultrasound waves is related to the frequency of the pulses, modulating the emission frequency of the pulsed laser to generate multiple acoustic waves of varying frequencies along the +y direction. Based on the principle that acoustic waves propagate in the same direction, adjusting the emission frequency of the pulsed laser can adjust the phase of the superimposed ultrasound waves. This superposition of multiple acoustic waves propagating in the same direction can generate traveling-wave acoustic tweezers.

[0042] Example 2:

[0043] like Figure 2 As shown, an embodiment of the present invention discloses a method for generating sound waves in air using laser pulses, comprising the following specific steps:

[0044] 1) Equipment layout: according to Figure 1 The second pulse laser 3 and the second optical modulation system 4 are arranged in sequence.

[0045] 2) The second optical modulation system 4 is used to modulate the scanning frequency of the pulsed laser beam of the second pulsed laser 3, so that the laser pulse scans back and forth in the vertical laser emission direction within the active area. Based on the principle of photoacoustic effect, the pulsed light beam generates an acoustic wave signal in the scanned area. The spatial frequency of the laser pulse is modulated by the first optical modulation system, and the acoustic wave generates a resonant superposition in the active area.

[0046] 3) During the aforementioned acoustic signal superposition process, the superposition frequency of the ultrasonic waves is related to the pulse generation frequency and the scanning modulation frequency of the second optical modulation system 4. By modulating the emission frequency and scanning frequency of the laser pulses, acoustic signals of varying intensities are generated in the active area based on the principle of acoustic wave superposition. The intensity of the generated acoustic wave is then adjusted by the intensity of the air disturbance. This allows for applications such as laser acoustic communication.

[0047] Example 3:

[0048] like Figure 3 As shown, an embodiment of the present invention discloses a method for generating sound waves in air using laser pulses, comprising the following specific steps:

[0049] 1) Equipment layout: according to Figure 3 The two first pulse lasers 1 and the two first optical modulation systems 2 are arranged in sequence so that the convergence positions of the light beams generated by the two first pulse lasers 1 overlap.

[0050] 2) A first pulsed laser 1 and a first optical modulation system 2 generate acoustic waves at the convergence point of the optical modulation system. Simultaneously, another first pulsed laser 1 and a first optical modulation system 2 also generate acoustic waves at the convergence point of the optical modulation system. At this point, the two acoustic waves, propagating at an acute angle, will superimpose and resonate in real time.

[0051] 3) In the region where the two ultrasonic beams overlap, the pulsed laser's emission frequency is modulated. A stronger superimposed acoustic wave is generated at the intersection of the two ultrasonic beams, i.e., the optical modulation system. The superposition of the two ultrasonic beams along the y-direction produces a stronger superposition effect, thus creating a stronger acoustic tweezers system in this region.

[0052] Example 4:

[0053] like Figure 4 As shown, an embodiment of the present invention discloses a method for generating sound waves in air using laser pulses, comprising the following specific steps:

[0054] 1) Equipment layout: according to Figure 4 The two second pulse lasers 3 and the two second optical modulation systems 4 are arranged in sequence so that the emission directions of the two second pulse lasers 3 form an acute angle, and the scanning frequencies of the two second optical modulation systems 4 are modulated respectively.

[0055] 2) A second optical modulation system 4 modulates the scanning frequency of the pulse beam of the second pulsed laser 3 to generate an acoustic signal in the active area. Simultaneously, another second optical modulation system 4 modulates the pulse beam of the second pulsed laser 3 using the same scanning frequency to generate an acoustic signal in the active area. At this point, the acoustic signals generated by the two scanning pulse beams continuously intersect and resonate within the common active area, causing the generated acoustic signals to resonate and be amplified.

[0056] 3) In the region where the two ultrasonic beams overlap, the laser pulse emission and scanning frequencies are modulated. Multiple sound waves continuously overlap and resonate, generating stronger superimposed sound waves. This produces sound signals of varying intensities, which is beneficial for the further development of laser acoustic communication.

[0057] Example 5:

[0058] like Figure 5 As shown, an embodiment of the present invention discloses a method for generating sound waves in air using laser pulses, comprising the following specific steps:

[0059] 1) Equipment layout: according to Figure 5 The two first pulse lasers 1 and the two first optical modulation systems 2 are arranged in sequence, and the emission directions of the two first pulse lasers 1 are placed opposite to each other, so that the convergence positions of the two first optical modulation systems 2 coincide, that is, the focusing positions of the two laser pulses coincide.

[0060] 2) The first pulsed laser 1, under the action of the first optical modulation system 2, generates ultrasonic waves propagating in the +y direction near the focal point. Simultaneously, another set of first pulsed lasers 1, under the action of the first optical modulation system 2, also generates acoustic waves propagating in the -y direction at the focal point. At this point, the two acoustic waves propagating in opposite directions will resonate and superimpose in real time.

[0061] 3) In the region where the two acoustic beams overlap, the pulsed laser's emission frequency is modulated. The two acoustic waves propagating in opposite directions produce a stronger superimposed acoustic wave at the focal point of the optical modulation system. Based on the principle of superposition of two acoustic beams propagating in opposite directions, a standing wave is generated, thus creating a standing wave-like acoustic tweezer system.

[0062] Example 6:

[0063] like Figure 6 As shown, an embodiment of the present invention discloses a method for generating sound waves in air using laser pulses, comprising the following specific steps:

[0064] 1) Equipment layout: according to Figure 6 The two second pulse lasers 3 and the two second optical modulation systems 4 are arranged in sequence, and the emission directions of the two second pulse lasers 3 are placed opposite to each other. The spatial scanning frequencies of the two second optical modulation systems 4 are modulated so that the pulses of the two pulse lasers overlap at the focus point.

[0065] 2) The second optical modulation system 4 performs scanning frequency modulation on the laser pulses of the second pulsed laser 3 in the direction perpendicular to the pulse emission direction. Simultaneously, another second optical modulation system 4 performs scanning frequency modulation on the pulsed laser beams of another second pulsed laser 3 in the direction perpendicular to the pulse emission direction. At this point, multiple acoustic waves are superimposed in real time.

[0066] 3) In the above-mentioned acoustic wave superposition area, the emission frequency and scanning frequency of the laser pulse are modulated. The resonance superposition of multiple pulses will produce a stronger acoustic wave signal, which is conducive to further research on laser acoustic wave communication.

[0067] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for generating sound waves in air using a pulsed laser, characterized in that: The device for generating sound waves is composed of a pulsed laser and an optical modulation system. The pulsed laser is emitted by a pulsed laser and then interacts with water vapor in the air after passing through the optical modulation system. The water vapor absorbs the heat energy of the pulsed laser. After the pulsed laser passes through, the water vapor temperature rises instantly and expands, thereby generating a pressure wave in the area of ​​action, that is, generating sound waves through the photoacoustic effect. The device for generating sound waves composed of a pulse laser and an optical modulation system is a device for generating sound waves composed of a first pulse laser (1) and a first optical modulation system (2). The frequency of the first pulse laser (1) is adjustable. Each time a pulse laser is emitted, a sound wave is generated, and then the sound waves are continuously resonated and superimposed. The pulse emission frequency determines the number of times the sound wave resonance is generated, the propagation phase and the period. Various sound waves are modulated by modulating the resonance, and standing waves and traveling waves are respectively realized.

2. The method for generating sound waves in air using pulsed laser according to claim 1, characterized in that: The device for generating sound waves composed of a pulse laser and an optical modulation system is a device for generating sound waves composed of a second pulse laser (3) and a second optical modulation system (4). The second optical modulation system (4) outputs a scanning laser to converge and move the pulse laser emitted by the second pulse laser (3). The scanning frequency is adjustable. By adjusting the scanning frequency, the resonance frequency of the sound wave in the lateral direction is controlled to achieve a superposition effect of sound waves in space, thereby generating different sound wave signals.

3. The method for generating sound waves in air using pulsed laser according to claim 1, wherein: The first pulse laser (1) and the first optical modulation system (2) each have two devices constituting two groups of acoustic wave generation devices. The emission directions of the two pulse lasers form an acute angle, so that the two laser beams coincide at a convergence position, i.e., the focal point position of the two first optical modulation systems (2). By controlling the emission frequency of the two pulse lasers to control the resonance effect of the acoustic wave, two traveling wave superposition acoustic tweezers are generated.

4. The method for generating sound waves in air using pulsed laser according to claim 2, characterized in that: The second pulse laser (3) and the second optical modulation system (4) each have two devices constituting two groups of sound wave generating devices. The emission directions of the two scanning pulse lasers form an acute angle. The scanning frequencies of the pulse laser beams are modulated respectively by the two second optical modulation systems (4). The change of the scanning frequencies controls the resonance superposition of the sound waves, thereby generating an enhanced sound wave signal.

5. The method for generating sound waves in air using pulsed laser according to claim 1, characterized in that: There are two first pulse lasers (1) and they are placed opposite to each other, that is, the emission directions of the two lasers are opposite; the two pulse lasers are respectively used to make the convergence points of the laser pulses coincide with each other through the first optical modulation system (2), and sound waves propagating in opposite directions are generated based on the photoacoustic effect. The sound waves propagating in opposite directions are superimposed to generate standing waves, and the resonance frequency of the sound waves is controlled by controlling the emission frequencies of the two pulse lasers, thereby generating standing wave acoustic tweezers.

6. The method for generating sound waves in air using pulsed laser according to claim 2, characterized in that: The two second pulse lasers (3) are placed opposite to each other, that is, the emission directions of the two lasers are opposite to each other; the two second optical modulation systems (4) respectively modulate the scanning frequencies of the two laser pulses in the relative propagation directions in space, and the change of the scanning frequencies causes the resonance superposition of the sound waves in the direction perpendicular to the laser generation direction, thereby enhancing the generated sound wave signal.

7. The method for generating sound waves in air using pulsed laser according to claim 1, characterized in that: The pulse laser has a laser wavelength of about 1400nm or 1900nm and operates in a pulse wave mode. Light near these two wavelengths is largely absorbed by water vapor in the air, making it easier to generate sound waves based on the photoacoustic effect.

8. The method for generating sound waves in air using pulsed laser according to claim 1, characterized in that: The energy of a single pulse of the first pulse laser (1) or the second pulse laser (3) is at least in the order of millijoules.

9. The method for generating sound waves in air using pulsed laser according to claim 1, characterized in that: The method for generating sound waves adopts adding an air humidifying device to increase and control the humidity of the surrounding air.

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