A pulse width adjustable pulse cluster laser generation device and method

Abstract

This invention discloses a pulse width-adjustable pulse cluster laser generation device and method, belonging to the field of laser technology. It includes: a long-pulse laser, a waveplate and a rotating device, and a polarization beam splitter and combiner. The long-pulse laser is used to output linearly polarized long-pulse laser light. The waveplate and rotating device are used to rotate the half-waveplate to convert the long-pulse laser light into linearly polarized laser light with periodically changing polarization. The polarization beam splitter and combiner is used to split the periodically polarized linearly polarized laser light into a first sub-beam and a second sub-beam with orthogonal polarization states. The first sub-beam is guided by a reflecting element, and the second sub-beam is delayed by an optical delay device before being combined to output a pulse cluster. This invention can achieve a wide range of pulse width and repetition frequency adjustment and peak power multiplication with a simple structure and low cost, and can be widely used in materials processing, biomedicine, lidar, and optical waveguide microwave technology.

Description

Technical Field

[0001] This invention belongs to the field of laser technology, specifically relating to a pulse cluster laser generation device and method with adjustable pulse width. Background Technology

[0002] Burst-mode lasers emit laser energy in the form of a series of high-frequency, short-interval micropulses (i.e., "clusters"), rather than traditional single long pulses or continuous waves. This unique output mode gives it greater time-domain adjustability and extreme thermal management capabilities, enabling stronger controllability and superior performance. It has irreplaceable advantages and application value in fields such as precision machining and advanced manufacturing, medical and biomedical fields, scientific research and sensing, and optical waveguide microwave technology.

[0003] Currently, traditional methods for realizing pulsed cluster lasers include seed light modulation and amplification, intracavity modulation, gain switching, and nonlinear frequency conversion combined with modulation. Among these, seed light modulation and amplification based on a master oscillator power amplifier (MOPA) structure can independently and precisely control the duration of the pulse cluster, the repetition frequency of micropulses within the cluster, and the width and shape of individual micropulses. Combined with a laser amplifier, it can achieve output power or energy far exceeding that of the seed source, thus becoming the mainstream solution in industrial applications (such as precision cutting and welding) and scientific research applications requiring high power, high precision, and high flexibility. For example, patent document CN107579427A provides a method and laser for generating different laser pulse widths. It generates mode-locked lasers or continuous lasers through an oscillator, and uses a pulse selector to select the pulses of the mode-locked laser to output ultrafast pulse clusters, and modulates the continuous laser to output long-pulse-width lasers, realizing the time-division multiplexing of lasers with different temporal domain forms from the same laser. However, MOPA lasers based on seed light modulation typically use a high-voltage driving source during electro-optic modulation, which leads to problems such as system complexity and high cost. Furthermore, they face issues such as severe pulse envelope distortion caused by gain saturation during amplification, becoming key obstacles restricting their wider application.

[0004] For example, patent document CN114512889A also provides a cluster pulse generator and a high-power narrow-pulse-width ultrashort pulse laser. It outputs a high-repetition-rate femtosecond pulse sequence through a seed source, which is then divided into cluster pulses by an acousto-optic modulator, injected into a Mamyshev oscillator for amplification, and finally outputs high-energy cluster pulses. However, this solution is relatively complex, lacks flexibility in adjusting the number of pulses and envelope shape within the cluster, and relies on seed source injection locking, requiring high stability and making it difficult to meet the needs of rapid switching and low-cost integration in industrial settings.

[0005] Therefore, there is an urgent need to develop a new technology that can realize high-energy pulsed cluster lasers. This technology should be simple in structure, low in cost, and easy to integrate, so as to promote the large-scale application of pulsed cluster lasers in precision manufacturing, biomedicine, remote sensing and other fields. Summary of the Invention

[0006] In view of the above, the purpose of this invention is to provide a pulse width adjustable pulse cluster laser generation device and method, which adopts a mechanical polarization control scheme of rotating half-wave plate combined with polarization beam splitting and adjustable delay beam combining, to achieve high-energy, high-peak-power sinusoidal waveform pulse cluster output with simple structure and low cost. Moreover, the pulse width and repetition frequency can be adjusted over a wide range, and the peak power can be multiplied. It can be widely used in materials processing, biomedicine, lidar and optical waveguide microwave technology and other fields.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: In a first aspect, an embodiment of the present invention provides a pulse width adjustable pulse cluster laser generating device, comprising: a long pulse laser, a waveplate and a rotation device, and a polarization beam splitter and beam combiner. The long-pulse laser is used to output long-pulse lasers in a linearly polarized state; The waveplate and rotating device are used to rotate the half-waveplate to convert long-pulse laser into linearly polarized laser with periodically changing polarization state. The polarization beam splitter and combiner is used to split a linearly polarized laser with periodically changing polarization state into a first sub-beam and a second sub-beam with orthogonal polarization states. The first sub-beam is guided by a reflective element, and the second sub-beam is delayed by an optical delay device. The two sub-beams are then combined to output a pulse cluster.

[0008] Preferably, the long-pulse laser output by the long-pulse laser must be linearly polarized; otherwise, its polarization state cannot be effectively adjusted by a waveplate. Its pulse width is on the order of nanoseconds, microseconds, or milliseconds. If it is too narrow (e.g., below picoseconds), it will be difficult to form a clear polarization period modulation by rotating the waveplate; if it is too wide (e.g., on the order of seconds), it will result in low energy utilization. Furthermore, to cover the requirements of current major application scenarios, the repetition frequency is designed to be 10Hz–100kHz, and the wavelength is greater than 200nm, thereby ensuring the long-term stable operation of the device.

[0009] Preferably, the waveplate and rotating device include a half-wave plate and a rotating mechanism for driving the half-wave plate. The rotating mechanism is driven by a high-speed motor and its rotational speed is amplified by a multi-stage gear set, which can achieve a higher half-wave plate rotational speed under limited motor speed. To modulate laser micropulses with higher repetition frequency and narrower pulse width, the rotational speed n of the high-speed motor is adjustable from 10krpm to 500krpm, and the transmission ratio R of the multi-stage gear set is no higher than 1:100. Obviously, the rotational period of the half-wave plate is 60R / n, and the oscillation period of the micropulse is 15R / n.

[0010] Preferably, the high-speed motor includes a brushless DC motor, an AC induction motor, or a magnetic levitation motor, which can be flexibly selected according to the specific application.

[0011] Preferably, the polarization beam splitting and combining device includes a first polarizer, a second polarizer, a first reflective element, a second reflective element, and an optical delayer; the first polarizer is used to split the linearly polarized laser with periodically changing polarization state into a first reflected sub-beam and a second transmitted sub-beam; the first reflective element and the second reflective element are used to guide the first sub-beam to the reflection output of the second polarizer; the optical delayer is used to delay and adjust the second sub-beam before transmitting it to the transmission output of the second polarizer; and the second polarizer is used to combine the two sub-beams in the time domain and output them.

[0012] Preferably, the first polarizer and the second polarizer are identical thin-film polarizers, square or circular in shape, with a transmittance of more than 99% for P-polarized lasers and a reflectance of more than 99% for S-polarized lasers, and an operating angle of 40° to 60° (typically 45° or 55.6°) to ensure good polarization performance, i.e., high transmittance for P-light and high reflectance for S-light.

[0013] Preferably, the first and second reflective elements are the same laser reflective elements, which are square or circular in shape and have a reflectivity of more than 99% for the first sub-beam. The working angles of the first and second reflective elements are consistent with the working angles of the first and second polarizers, respectively, to ensure that the two sub-beams are combined on the second polarizer 3.

[0014] Preferably, the delay of the second sub-bundle by the optical delayer is freely adjustable, with a maximum adjustment range not less than half of the micropulse oscillation period in the pulse cluster, i.e., 15R / 2n. Furthermore, when the delay δ satisfies δ=π / 2+nπ, the pulse cluster intensity of the combined output of the two sub-bundles reaches its peak value, where n=0,1,2,3… If the optical delay is less than half of the micropulse oscillation period, the time-domain adjustment range is insufficient, and the pulse peaks of the two sub-bundles cannot overlap.

[0015] Preferably, the optical retarder includes a Babinette compensator, an electro-optic retarder, an acousto-optic retarder, or a magneto-optic retarder, which can be flexibly selected according to the cost and speed requirements of the actual application.

[0016] Secondly, the present invention provides a pulse width-adjustable pulse cluster laser generation method, implemented based on the aforementioned pulse width-adjustable pulse cluster laser generation device, comprising the following steps: S1, activate the long-pulse laser, outputting a linearly polarized long-pulse laser; S2, by rotating the half-wave plate through the wave plate and the rotating device, the long pulse laser is converted into a linearly polarized laser with a periodically changing polarization state; S3 uses a polarization beam splitter and combiner to split a linearly polarized laser with periodically changing polarization state into a first sub-beam and a second sub-beam with orthogonal polarization states. The first sub-beam is guided by a reflective element, and the second sub-beam is delayed by an optical delay device. The two sub-beams are then combined to output a pulse cluster. S4 controls the relative position of the two sub-beams in the time domain by adjusting the delay of the optical retarder, thereby adjusting the pulse width and peak power of the output pulse cluster.

[0017] Compared with the prior art, the beneficial effects of the present invention include at least the following: (1) This invention implements mechanical polarization control on long pulse lasers and uses common half-wave plates and polarizers as modulation components. It has an extremely high anti-laser damage threshold and can achieve the modulation and generation of high-energy, high-peak-power laser pulse clusters with a simple structure and low cost. Furthermore, the time-domain waveform of the laser micropulse is a standard sine wave, and the laser repetition frequency and pulse width can be adjusted in a wide range according to the requirements.

[0018] (2) In this invention, since both sub-beam pulses are sinusoidal waves with the same period, precise timing control is achieved through an adjustable optical delay device, enabling the two sub-beams to be synthesized in the time domain, thus doubling the peak power of the micro-pulse. This invention effectively reduces the structure and cost of existing high-energy pulse cluster lasers and is suitable for applications requiring high energy, high peak power, and adjustable pulse width, such as materials processing, biomedicine, lidar, and optical waveguide microwave technology. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1This is a schematic diagram of a pulse width adjustable pulse cluster laser generating device provided in an embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of the deflection of the polarization state of a long pulse laser after it has been rotated by a half-wave plate, as provided in an embodiment of the present invention.

[0022] Figure 3 This is a schematic diagram of the sinusoidal light field distribution of P-beams and S-beams provided in an embodiment of the present invention.

[0023] Figure 4 This is a schematic diagram of the pulse cluster output provided by an embodiment of the present invention, which is the superposition of two beams after phase delay.

[0024] Figure 5 This is a schematic flowchart of a pulse width adjustable pulse cluster laser generation method provided in an embodiment of the present invention.

[0025] The specific reference numerals in the attached drawings are as follows: 1. Long pulse laser; 2. Waveplate and rotating device; 2-1. Half-waveplate; 2-2. Rotating mechanism; 3. Polarization beam splitting and combining device; 3-1. First polarizer; 3-2. First reflecting element; 3-3. Second reflecting element; 3-4. Optical delay device; 3-5. Second polarizer. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of this invention.

[0027] The inventive concept of this invention is as follows: In view of the problems of complex high-voltage drive systems and high costs in existing pulse cluster laser generation schemes, the embodiments of this invention provide a pulse cluster laser generation device and method with adjustable pulse width. By using a high-speed rotating half-wave plate to convert long pulse laser into linearly polarized laser with periodically changing polarization state, and after beam splitting, reflection guidance and adjustable delay, the beam is combined to directly generate pulse clusters with a wide range of continuously adjustable pulse widths. There is no need for complex electro-optic modulation and amplification stages, thus achieving high-energy and high-peak-power pulse cluster output with a simple structure and low cost.

[0028] Figure 1 This is a schematic diagram of a pulse-width-adjustable pulse cluster laser generation device provided in an embodiment of the present invention. Figure 1As shown, the embodiment provides a pulse width adjustable pulse cluster laser generating device, including: a long pulse laser 1, a waveplate and rotation device 2 (including a half-waveplate 2-1 and a rotation mechanism 2-2), and a polarization beam splitting and combining device 3 (including a first polarizer 3-1, a first reflective element 3-2, a second reflective element 3-3, an optical delayer 3-4, and a second polarizer 3-5).

[0029] In this embodiment, the long-pulse laser 1 is an LD-pumped quasi-continuous-pumped Nd:YAG laser with an output wavelength of 1064 nm, a single-pulse energy of 400 mJ, a pulse width of 200 μs, a repetition frequency of 500 Hz, and a linear polarization state. The waveplate and rotating device 2 are driven by a brushless DC motor with a speed of 60,000 RPM. The waveplate is a 1-inch diameter circular half-wave plate with a working wavelength of 1064 nm, mounted on a dedicated frame with gears on the outer ring. The brushless motor drives the half-wave plate to rotate at high speed through a multi-stage gear set with a transmission ratio of 1:1000 (i.e., a speed increase factor of 1000). Clearly, when the motor speed is 60,000 RPM, the rotational speed of the half-wave plate reaches 6 × 10⁻⁶ RPM. 7 RPM corresponds to a half-wave plate rotation period of 1μs.

[0030] In this embodiment, the linearly polarized long-pulse laser output from the long-pulse laser 1 enters the waveplate and rotating device 2. Due to the high-speed rotation of the half-wave plate 2-1, the polarization direction of the laser rotates periodically with a rotation period of 1 μs. Figure 2 As shown, the red arrow indicates the transmission direction of the long-pulse laser. The rotation of half-wave plate 2-1 causes its fast axis to change linearly with time at an angle θ relative to the polarization direction of the incident long-pulse laser (θ=ωt, where ω is the angular velocity, ω=2π / (1μs)). Half-wave plate 2-1 rotates the polarization direction of the output laser by 2θ (i.e., the effective polarization angle φ=2ωt). When the laser passes through the first polarizer 3-1, according to Malus's law, the transmitted (P-polarized) and reflected (S-polarized) light intensities are Ip and Iv, respectively. t =I0cos 2 (φ) = I0cos 2 (2ωt) and I r =I0sin 2 (φ)=I0sin 2 (2ωt), where I0 is the incident light intensity. This causes the two sub-beams (the first sub-beam is S-polarized reflected light, and the second sub-beam is P-polarized transmitted light) to exhibit a sinusoidal intensity distribution: the intensity of the first sub-beam changes sin with time. 2 The second sub-bundle intensity follows the (2ωt) form (phase conjugation) and is cosine-independent. 2 The two polarizations are orthogonal and their phases are complementary, and they are in the form of (2ωt).

[0031] Subsequently, the second sub-beam (P-polarized) is introduced with a fixed phase delay δ (e.g., π / 2) via optical retarder 3-4 to compensate for the phase difference between the two sub-beams. The first sub-beam (S-polarized) is transmitted directly via the first reflecting element 3-2 and the second reflecting element 3-3. The two sub-beams are re-superimposed at the second polarizer 3-5. Due to the orthogonal polarization, the intensity of the superimposed optical field is I. total =I0[sin 2 (2ωt)+cos 2 (2ωt+δ)]. When δ=π / 2+nπ, n=0,1,2,3……, intensity modulation is achieved, forming a pulse cluster output; specifically, the superposition process generates periodic intensity peaks, forming a pulse cluster every 0.25μs (i.e. 1 / 4 of the waveplate rotation period), and the cluster contains multiple sub-pulses, with the pulse width and interval determined by ω and δ.

[0032] For example, within one rotation of the waveplate (1 μs), the intensity distribution undergoes four complete cycles (period T). mod =π / (2ω)=0.25μs), corresponding to the sinusoidal optical field distribution of the P-beam and S-beam. The output pulse cluster is achieved by superimposing the two beams after phase delay. The repetition frequency of the output pulse cluster is 4 MHz (1 / 0.25μs), suitable for high-power laser processing or optical communication applications.

[0033] To further illustrate this process, such as Figure 3 The time-domain intensity distribution curves shown are plotted with time t (in μs) on the horizontal axis and normalized intensity (0-1) on the vertical axis. The dashed curve represents the intensity distribution of the first sub-beam (S-polarized), exhibiting a sin... 2 The phase is conjugate to the solid line curve in the form of (2ωt), with peak values ​​at t = 0.125, 0.375, 0.625... μs. The solid line curve represents the intensity distribution of the second sub-beam (P-polarized), exhibiting a cosine similarity. 2 The curve is in the form of (2ωt), sinusoidal, with a period of 0.25 μs and peaks at t = 0, 0.25, 0.5... μs. The two curves are complementary and their sum is a constant 1, demonstrating phase conjugation.

[0034] like Figure 4 The temporal domain composite intensity distribution curves are shown, with the horizontal axis representing time t (in μs) and the vertical axis representing normalized light intensity (0-2). The solid curve represents the distribution of the second sub-beam (P-polarized) before delay; the dashed curve represents the distribution of the first sub-beam (S-polarized); and the dotted-dash curve represents the superposition result of the two sub-beams after a delay δ=T / 4=π / 2+nπ, n=0,1,2,3… (here taken as 0.125μs). After superposition, the peak intensity reaches 2 (twice the original peak value), forming a series of high-frequency bursts with a repetition frequency of 4MHz (corresponding to 4 times the rotation period). Figure 4The delay is marked as δ=π / 2+nπ, n=0,1,2,3…… (0.125μs here), and the peak power multiplication effect is shown: the peak power of the original sub-bundle is P0, and the combined peak power is 2P0. The overall pulse cluster envelope is still 200μs, which reflects the temporal synthesis and incoherent superposition.

[0035] Experiments have verified that, under the parameter settings of this device, the envelope width of the output pulse cluster remains at 200 μs, the repetition frequency of the micropulses within the cluster is 4 MHz, and each micropulse exhibits a tall sine wave with a corresponding pulse width of 125 ns. This device cleverly achieves time-domain transformation from long pulses to pulse clusters and multiplication of pulse peak power by combining mechanical rotation with passive optical delay.

[0036] Based on the same inventive concept, such as Figure 5 As shown, this embodiment of the invention also provides a method for generating pulsed cluster lasers with adjustable pulse width, comprising the following steps: S1, activate the long-pulse laser, outputting a linearly polarized long-pulse laser; S2, by rotating the half-wave plate through the wave plate and the rotating device, the long pulse laser is converted into a linearly polarized laser with a periodically changing polarization state; S3 uses a polarization beam splitter and combiner to split a linearly polarized laser with periodically changing polarization state into a first sub-beam and a second sub-beam with orthogonal polarization states. The first sub-beam is guided by a reflective element, and the second sub-beam is delayed by an optical delay device. The two sub-beams are then combined to output a pulse cluster. S4 controls the relative position of the two sub-beams in the time domain by adjusting the delay of the optical retarder, thereby adjusting the pulse width and peak power of the output pulse cluster.

[0037] It should be noted that the pulse width adjustable pulse cluster laser generation method provided in the above embodiments belongs to the same inventive concept as the pulse width adjustable pulse cluster laser generation device. For details of its specific implementation process, please refer to the embodiment of the pulse width adjustable pulse cluster laser generation device, which will not be repeated here.

[0038] The specific embodiments described above illustrate the technical solution and beneficial effects of the present invention in detail. It should be understood that the above description is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A pulse-width adjustable pulse cluster laser generating device, characterized in that, include: Long-pulse lasers, waveplates and rotating devices, polarization beam splitters and combiners; The long-pulse laser is used to output long-pulse lasers in a linearly polarized state; The waveplate and rotating device are used to rotate the half-waveplate to convert long-pulse laser into linearly polarized laser with periodically changing polarization state. The polarization beam splitter and combiner is used to split a linearly polarized laser with periodically changing polarization state into a first sub-beam and a second sub-beam with orthogonal polarization states. The first sub-beam is guided by a reflective element, and the second sub-beam is delayed by an optical delay device. The two sub-beams are then combined to output a pulse cluster. The maximum adjustment range of the delay of the second sub-beam by the optical delay device is not less than half of the micropulse oscillation period in the pulse cluster.

2. The pulse width adjustable pulse cluster laser generating device according to claim 1, characterized in that, The long-pulse laser output by the long-pulse laser has a pulse width on the order of nanoseconds, microseconds, or milliseconds, a repetition frequency of 10Hz to 100kHz, and a wavelength greater than 200nm.

3. The pulse width adjustable pulse cluster laser generating device according to claim 1, characterized in that, The waveplate and rotating device include a half-waveplate and a rotating mechanism that drives the half-waveplate to rotate. The rotating mechanism is driven by a high-speed motor and the rotation speed is amplified by a multi-stage gear set. The speed adjustment range of the high-speed motor is 10krpm to 500krpm, and the transmission ratio of the multi-stage gear set is not higher than 1:

100.

4. The pulse width adjustable pulse cluster laser generating device according to claim 3, characterized in that, The high-speed motor includes a brushless DC motor, an AC induction motor, or a magnetic levitation motor.

5. The pulse width adjustable pulse cluster laser generating device according to claim 1, characterized in that, The polarization beam splitting and combining device includes a first polarizer, a second polarizer, a first reflecting element, a second reflecting element, and an optical delayer. The first polarizer is used to split a linearly polarized laser with a periodically changing polarization state into a first reflected sub-beam and a second transmitted sub-beam. The first reflecting element and the second reflecting element are used to guide the first sub-beam to the reflection output of the second polarizer. The optical delayer is used to delay the second sub-beam and then transmit it to the transmission output of the second polarizer. The second polarizer is used to combine the two sub-beams in the time domain and then output them.

6. The pulse width adjustable pulse cluster laser generating device according to claim 5, characterized in that, The first polarizer and the second polarizer are the same thin-film polarizers, with a transmittance of more than 99% for P-polarized lasers and a reflectance of more than 99% for S-polarized lasers, and a working angle of 40° to 60°.

7. The pulse width adjustable pulse cluster laser generating device according to claim 6, characterized in that, The first reflective element and the second reflective element are the same laser reflective element, with a reflectivity of more than 99% for the first sub-beam, and the working angles of the first reflective element and the second reflective element are consistent with the working angles of the first polarizer and the second polarizer, respectively.

8. The pulse width adjustable pulse cluster laser generating device according to claim 1, characterized in that, When the delay δ satisfies δ=π / 2+nπ, the pulse cluster intensity of the combined output of the two sub-beams reaches its peak value, where n=0,1,2,3…….

9. The pulse width adjustable pulse cluster laser generating device according to claim 1, characterized in that, The optical retarder includes a Barbigue compensator, an electro-optic retarder, an acousto-optic retarder, or a magneto-optic retarder.

10. A method for generating pulsed cluster laser with adjustable pulse width, implemented using the pulsed cluster laser generating apparatus according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1, activate the long-pulse laser, outputting a linearly polarized long-pulse laser; S2, by rotating the half-wave plate through the wave plate and the rotating device, the long pulse laser is converted into a linearly polarized laser with a periodically changing polarization state; S3 uses a polarization beam splitter and combiner to split a linearly polarized laser with periodically changing polarization state into a first sub-beam and a second sub-beam with orthogonal polarization states. The first sub-beam is guided by a reflective element, and the second sub-beam is delayed by an optical delay device. The two sub-beams are then combined to output a pulse cluster. S4 controls the relative position of the two sub-beams in the time domain by adjusting the delay of the optical retarder, thereby adjusting the pulse width and peak power of the output pulse cluster.

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