Abstract ：

Traditional top-emitting vertical-cavity surface-emitting lasers (VCSELs) exhibit a long distance between the source region and heat sink, and internal heat conduction of the device is difficult, resulting in limited output power of both single-tube and array devices. To address these limitations, this study proposes a top-emitting VCSEL with a heat dissipation hole on the substrate. This hole is located directly below the countertop and is filled with high-thermal-conductivity materials, enabling rapid heat transfer from within the device. This design ensures mechanical support for the entire structure while improving the heat dissipation capacity. Simulation results indicate that the thermal flip power of the VCSEL device with a heat dissipation hole is 9. 54 mW, representing a 36. 4% increase compared to VCSEL devices without a heat dissipation hole. VCSEL devices with an oxidation aperture of 12 μm are prepared and tested under a duty cycle of 0. 6%. The peak power of the VCSEL with a heat dissipation hole reaches 9. 59 mW, which is 31% higher than that of the VCSEL without a heat dissipation hole. © 2025 Universitat zu Koln. All rights reserved.

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high temperature vertical cavity surface emitting laser substrate heat dissipation top emitting

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A laser diode (LD) corner-pumped Nd∶YAG electro-optical Q-switched laser with high efficiency and high stability that generates a 1.06- μm pulse laser output is designed and experimentally verified. Amplified spontaneous emission and parasitic oscillation are suppressed by using a low-doped Nd∶YAG crystal as a gain medium and a bonding Sm∶YAG crystal on both sides. The angular pump direct pumping method is used to increase the pump absorption optical path and thus increase the pump absorption efficiency of the gain crystal, and a zig-zag structure is used to improve the thermal effect. Under the conditions of a pump pulse energy of 383 mJ, repetition frequency of 20 Hz, and pump pulse width of 230 μs, laser output with a single pulse energy of 97.5 mJ and pulse width of 7 ns is obtained. The dynamic-to-static ratio of the output energy is 95.3%, the optical-to-optical conversion efficiency is 25.43%, the beam quality factors in two directions are M2x = 4.31 and M2y = 4.67, the change in Q-switched output energy within 140 s is less than 2%, and the energy instability of three consecutive working cycles is also less than 2%. The individual output energy attenuations are 1.59% and 2.11%, and the total output energy attenuation is 3.67%. © 2025 Universitat zu Koln. All rights reserved.

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high stability laser zig-zag structure electro-optical Q-switching high efficiency

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Objective A vertical- external- cavity surface- emitting laser (VECSEL) offers unique advantages such as high power, good beam quality, and designable emitting wavelength. Additionally, the external- cavity structure allows for the convenient insertion of other optical components, thus enabling the VECSEL to operate in mode- locking, single- frequency running, or wavelength- tuning mode. These characteristics render the VESCEL a desirable candidate for various applications not realizable by conventional lasers (e. g., solid- state lasers, gas lasers, fiber lasers, or laser diodes). In particular, the peak power pulses generated by a mode- locked VECSEL can be used in diverse fields such as multiphoton imaging, high- resolution time- domain terahertz spectroscopy, and supercontinuum generation. However, obtaining high peak- power pulses from a mode- locked VECSEL is not trivial. To increase the peak power of mode- locked pulses, one can increase the average output power of the laser, reduce the pulse time width, or reduce the pulse repetition rate. However, these three methods are mutually restrictive; thus, the pulse peak power in a mode- locked VECSEL can only be improved to a certain extent. In particular, the carrier lifetime of the semiconductor gain media used in a VECSEL is short, i. e., in the nanosecond level, which significantly limits the further reduction of the repetition rate of mode- locked laser pulses. Consequently, the increase in the peak power of pulses generated from the mode- locked VECSEL is restricted considerably. Methods In this study, a custom- designed saturable Bragg reflector (SBR) was used as a saturable absorber, where a moderate saturation fluence can effectively balance between the cycling power and multi- pulse generation in the resonant cavity, thereby maintaining a sufficiently high average output power at low repetition rates and significantly improving the peak power of the mode-locked laser pulses. The epitaxial structure of the gain chip used in the experiment (Fig. 1) is a reverse- order structure of the active region, followed by a distributed Bragg reflector (DBR). First, an Al0.86GaAs etching stop layer was deposited on the GaAs substrate. Subsequently, a GaAs protective layer, a high-barrier Al0.6GaAl window layer, an active region, and a DBR were deposited. Finally, the entire structure was terminated with an oxygen-resistant GaAs layer. Unlike gain chips achieved via reverse growth, the SBR exhibits an epitaxial structure (Fig. 1) that is consistent with the normal order of a DBR followed by an absorption region. The saturable absorber is a single InGaAs quantum well located in the final quarter-wavelength layer of the DBR, with a thickness of 10 nm. The quantum well is intentionally set at the peak position away from the laser standing wave to obtain a large saturation fluence. Additionally, because the saturation fluence of the SBR should not be excessively high, we implemented a single quantum well with a commonly used thickness of 10 nm. The laser resonant cavity used in the experiment (Fig. 2) comprises six mirror cavities, including a DBR each at the bottom of both the gain chip and SBR. Except for the output coupler, which presents a certain transmittance at the laser wavelength, all other mirrors demonstrate high reflectivity at the laser wavelength. Results and Discussions Based on the experimental result, the temporal waveform of the pulses exhibits double or triple pulses connected to each other (Fig. 3). We believe that this may be due to the low intensity of the intra-cavity pulses (corresponding to a relatively high saturation fluence of the SBR) and the inadequateness of one pulse in fully saturating the SBR. Therefore, before the SBR is fully recovered, absorption continues to occur on one or two following pulses, thus resulting in double or triple pulses. Stable continuous-wave (CW) fundamental mode-locked pulse trains, steady second-harmonic mode-locked pulses, and higher-order unstable harmonic mode-locked pulses are obtained (Fig. 5). In our opinion, the high-order harmonics occurred because as the pump power increases, the pulse intensity inside the cavity increases, thus resulting in a low saturation fluence of the SBR. After a pulse saturates the SBR, owing to the long resonant cavity length, the SBR has sufficient time to recover. Therefore, one or more subsequent pulses can saturate the SBR again, thus resulting in multiple pulses in the cavity, which eventually evolve into higher-order harmonic mode locking. The interconnected double or triple pulses mentioned above, as well as the occurrence of high-order harmonic mode locking can be described by numerically solving the delay differential equations for passive mode locking, and the evolution of intra-cavity pulses over time can be obtained (Fig. 4). The measured fundamental CW mode-locked pulse has a period of approximately 14.92 ns, a repetition rate of 67 MHz, and a pulse width of 2.08 ps (Fig. 6). When the absorbed pump power increases to 18.9 W, an output power of 0.325 W can be obtained. When the absorbed pump power exceeds 21.7 W, the maximum output power of the second harmonic mode locking is 0.836 W. The maximum output power of the fourth-harmonic mode locking is 0.683 W (Fig. 7). Under fundamental, second- and fourth-harmonic mode locking, the maximum peak powers of the pulses are 2.33, 3.00, and 1.23 kW, respectively. Conclusions The short carrier lifetime (of nanosecond level) of a VECSEL significantly limits the further reduction of the pulse repetition rate under passive mode locking, thereby limiting the improvement to the pulse peak power. For saturable absorbers used to commence mode locking, a relatively high saturation fluence may generate interconnected double or triple pulses, whereas a relatively low saturation fluence may result in multiple pulses in the resonant cavity. This study utilizes a custom-designed SBR with a moderate saturation fluence to achieve both low repetition rates and high average output power levels in a passive mode-locked VECSEL. We experimentally achieved a repetition rate of 67 MHz. In the case of fundamental, second- and fourth-harmonic mode locking, the corresponding peak powers of the pulses are 2.33, 3.00, and 1.23 kW, respectively, which demonstrate a passive mode-locked VECSEL with a repetition rate below 100 MHz and a peak power above 1 kW simultaneously. © 2025 Science Press. All rights reserved.

Keyword ：

vertical external-cavity surface-emitting laser repetition rate passive mode locking peak power

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Objective The blue waveband is the window for underwater wireless optical communication, and high-performance blue lasers are the ideal light source for underwater wireless optical communication. Pulsed blue lasers have high peak power than that of continuouswave laser, experience less attenuation during underwater transmission and have better communication performance. As an important technique for obtaining pulsed lasers, Q-switching has been widely used in solid-state lasers. However, for semiconductor lasers, it is difficult to obtain large pulse energy or high peak power due to the nanosecond short lifetime of the carriers. But in the other hand, Q-switched semiconductor lasers can produce pulse trains with higher repetition rates because of their shorter carrier lifetime, and combined with their flexible and designable emitting wavelengths, their application range can also be expanded. Methods In the gain chip of a semiconductor disk laser (SDL), there exists the nonlinear Kerr effect in the semiconductor multiple quantum wells of the active region, where the refractive index in the region is proportional to the light intensity, i.e. n=n2I, where n is the refractive index of the material, I is the incident light intensity, and n2 is the Kerr coefficient. For the semiconductor multiple quantum wells materials, the above n2 is negative. The nonlinear Kerr effect in the active region leads to an equivalent lens depending on the intensity of light, causing the pulsed laser to experience a higher refractive index, while the continuous-wave laser suffers to a lower refractive index. When there is an aperture in the resonant cavity or a so-called soft aperture composed of pump spot on the gain chip, the equivalent lens mentioned above will cause the pulsed laser to experience less loss in the resonant cavity, start the pulse operation of the laser, and maintain stable pulse train output. If the effect of the Kerr equivalent lens is weak, SDL will operate in a Q-switching state, producing Q-switching pulse train with a pulse width on the order of nanosecond, which is called self Q-switching. If the Kerr equivalent lens has a stronger effect, SDL may operate in a mode-locked state, generating shorter picosecond pulses. This article utilizes the above-mentioned Kerr equivalent lens to achieve stable self Q-switching in the SDL. Then, while maintaining the Q-switched operation of the laser, a self Q-switched frequency-doubled blue laser is obtained by inserting a LiB3O5 (LBO) nonlinear crystal into the resonant cavity. Finally, pulsed blue laser is used as the light source for an underwater wireless optical communication, and the communication performance of the pulsed blue laser and the continuous-wave blue laser is compared. Results and Discussions In a Z-type resonant cavity composed of the bottom distributed Bragg reflector (DBR) in the gain chip, the high-reflectivity mirror M1, the frequency-doubling output mirror M2, and the planar high-reflectivity mirror M3, when the absorbed pump power is 29.4 W, the maximum output power of the 982 nm fundamental laser is 4.22 W. After the nonlinear crystal LBO is placed in the resonant cavity and the absorbed pump power is 28 W, the maximum average output power of the self Q-switched blue laser is 702 mW, with a pulse width of 8 ns and a period of 16.1 ns, corresponding to a pulse repetition rate of 61.9 MHz. The repetition rate of the output pulses of the self Q-switched blue SDL increases with the increase of the absorbed pump power, but the width of the pulse decreases with the increase of the absorbed pump power. In the underwater wireless optical communication system constructed using the above-mentioned self Q-switched pulse blue laser as the light source, the bit error rate of the pulse optical communication is at least one order of magnitude lower than that of the continuous-wave optical communication under the same water type, data rate, and link length. The reason is that the self Q-switched laser pulses can be regarded as a high-frequency modulated light waves, which have smaller scattering attenuation than that of the continuous-wave laser. Therefore, the pulsed laser power obtained by the receiver will be significantly greater than that of the continuous-wave laser, thereby increasing the signal intensity, improving the signal-to-noise ratio, and reducing the bit error rate. Conclusions Based on the nonlinear Kerr effect of the semiconductor medium in the active region of the SDL gain chip, stable self Q-switching of the SDL with an emission wavelength of 982 nm is achieved in a Z-type resonant cavity. After placing an LBO crystal at the smallest waist of the beam inside the cavity, 491 nm pulsed blue laser output is obtained. When the absorbed pump power is 28 W, the maximum average output power of the Q-switched blue laser pulse is 702 mW, the pulse width is 8 ns, and the repetition rate is 61.9 MHz. In the underwater wireless optical communication system constructed using the above-mentioned self Q-switched pulsed blue laser, under the same conditions (input optical power, Maalox solution mass concentration, communication link length, and data rate), the communication performance of the self Q-switched blue SDL is significantly better than that of the continuouswave blue SDL. When the data rate is 10 Mbit/s and the link length is 18 m, the bit error rate of the self Q-switched blue SDL communication is reduced by about one order of magnitude compared to that of the continuous-wave blue SDL communication. © 2025 Science Press. All rights reserved.

Keyword ：

self-Q-switching frequency-doubling underwater wireless optical communications semiconductor disk laser

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高峰值功率、高光束质量的1550 nm波段激光在生物医学、材料加工和环境监测等领域具有广泛应用.本文报道了一种基于主振荡功率放大器(MOPA)结构的人眼安全脉冲光纤激光器,成功实现了 12.2 kW的峰值功率,光光转换效率达到17.7％,中心波长为1549.884 nm,3 dB谱线宽为1.182 nm,重复频率为50 kHz,脉冲宽度为6.146 ns,光束质量达到1.11.此外,本文对人眼安全脉冲光纤激光器进行了工程化设计,以增强其对环境变化的耐受性,从而进一步提高其应用潜力.

Keyword ：

人眼安全激光 高峰值功率 高光束质量 环境变化耐受性 光纤激光器

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垂直外腔面发射激光器(VECSEL)具有高功率、高光束质量、波长可根据实际需要进行设计等独特优点,应用场景十分丰富.锁模VECSEL产生的高峰值功率脉冲能应用于多光子成像、高分辨率时域太赫兹光谱、超连续谱产生等多个重要领域.但是,半导体增益介质纳秒量级的载流子寿命,极大地限制了锁模VECSEL重复频率的降低和峰值功率的提高.使用特殊设计的可饱和布拉格反射镜(SBR)作为可饱和吸收体,其中等适度的饱和通量可以有效地平衡谐振腔内的循环功率和多脉冲的产生,从而在较低的重复频率下保持足够高的平均输出功率,显著提高脉冲的峰值功率.SBR被动锁模VECSEL的脉冲重复频率被降低到67 MHz,激光器在基波、二次谐波和四次谐波锁模状态下的脉冲峰值功率分别为2.33、3.00、1.23 kW,被动锁模VECSEL在低于100 MHz的重复频率下获得了kW量级脉冲峰值功率.另外,结合实验结果,对SBR锁模VECSEL中多脉冲的产生及谐波锁模过程的演化进行了定性的分析讨论.

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垂直外腔面发射激光器 被动锁模 峰值功率 重复频率

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蓝光波段是水下无线光通信的窗口,高性能的蓝光激光器是水下无线光通信的理想光源.利用半导体碟片激光器增益芯片中的Kerr效应,在半导体碟片激光器中实现了稳定的自调Q输出,激光波长为982 nm.利用5 mm长的三硼酸锂(LBO)晶体进行腔内倍频,实现了脉冲宽度为8 ns、重复频率为61.9 MHz、平均输出功率为702 mW的高功率自调Q蓝光输出.基于上述脉冲蓝光激光器,搭建了水下无线光通信系统,并在不同数据传输速率和不同Maalox溶液浓度下,比较了自调Q脉冲蓝光与连续蓝光的通信性能.实验表明,在相同条件下,自调Q脉冲蓝光通信的误码率比连续蓝光的误码率降低了约一个数量级.

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半导体碟片激光器 倍频 水下无线光通信 自调Q

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钬固体激光器因其高效、安全和适用性广泛,成为肾结石手术中最常用的激光器之一,然而钬激光在碎石手术中还存在碎石不充分、热效应大等问题.2 μm超快掺铥光纤激光器以其覆盖水吸收峰的发射波长、高效的转化效率、良好的光束质量以及结构稳定等特点,有望在激光碎石领域解决以上问题.并且由于其高峰值功率、低脉冲能量的性质,有望在提高碎石效率的同时,降低周围软组织的热损伤.以线形腔SESAM锁模光纤激光器作为种子源,采用MOPA结构放大的方式实现了波长1962nm,脉宽～50 ps,峰值功率大于20 kW的高峰值功率皮秒脉冲激光输出,并进行了体外碎石研究.研究结果表明:在固定光斑直径下,当激光功率提高2.4倍时,结石质量损失最大可提升12.9倍;在固定激光功率下,当光斑直径减小2倍时,碎石质量损失最大可提升1.8倍.其中,在光斑直径200 μm,激光功率12 W时,获得了最大的结石质量损失为(75.2±9.1)mg.2 μm皮秒激光碎石的主要机理为光热效应,其中光热烧蚀和液体微爆两种作用同时存在.

Keyword ：

掺铥光纤激光器 激光碎石 皮秒激光器 激光碎石机制

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设计并通过实验验证了一种激光二极管角侧泵浦Nd∶YAG电光调Q激光器,实现了高效率、高稳定性的1.06 μm脉冲激光输出.通过采用低掺杂的Nd∶YAG晶体作为增益介质及在其两侧键合Sm∶YAG晶体来抑制放大自发辐射和寄生振荡;采用角泵浦直接抽运的方式,增大泵浦吸收光程来提高增益晶体的泵浦吸收效率,采用Z字形结构改善热效应.在泵浦脉冲能量为383 mJ、重复频率为20 Hz、泵浦脉冲宽度为230 μs的条件下,获得了单脉冲能量为97.5 mJ、脉冲宽度为7 ns的激光输出,输出能量的动静比为95.3%,光-光转换效率为25.43%,两个方向的光束质量因子M2x=4.31,M2y=4.67,持续工作140 s时间内调Q输出能量变化小于2%,连续3个工作循环的能量不稳定度同样小于2%,每次输出能量衰减分别为1.59%、2.11%,输出能量总衰减为3.67%.

Keyword ：

激光器 高稳定性 Z字形结构 电光调Q 高效率

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为了获得光谱更宽、功率更高以及结构简单的白光超连续谱输出,通过光纤中的受激布里渊散射(SBS)和瑞利散射(RS)机制,探索了自调Q技术在产生高功率白光超连续谱中的应用.通过实验构建了一个半开腔结构,利用掺镱光纤、光子晶体光纤和高反射率光栅,无外部脉冲调制的条件下,当泵浦功率达到 97.4 W时,成功获得了光谱覆盖410～1 700 nm、输出功率为 24 W、重复频率为 188.7 kHz的高功率白光超连续谱.该白光输出的光-光转换效率为24.6%.实验结果表明,基于SBS自调Q机制的白光超连续谱光纤激光器作为一种新型光源,具有结构简单、光谱范围广、平坦度较好等优点,为高功率白光超连续谱光源的研发提供了新方案.

Keyword ：

白光超连续谱 受激布里渊散射 光纤激光器 被动调Q

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