Deep learning enabled robust wavefront sensing for active beam smoothing with a continuous phase modulator
Yamin Zheng, Yifan Zhang, Liquan Guo, Pei Li, Zichao Wang, Yongchen Zhuang, Shibing Lin, Qiao Xue, Deen Wang, and Lei Huang
In laser systems requiring a flat-top distribution of beam intensity, beam smoothing is a critical technology for enhancing laser energy deposition onto the focal spot. The continuous phase modulator (CPM) is a key component in beam smoothing, as it introduces high-frequency continuous phase modulation across the laser beam profile. However, the presence of the CPM makes it challenging to measure and correct the wavefront aberration of the input laser beam effectively, leading to unwanted beam intensity distribution and bringing difficulty to the design of the CPM. To address this issue, we propose a deep learning enabled robust wavefront sensing (DLWS) method to achieve effective wavefront measurement and active aberration correction, thereby facilitating active beam smoothing using the CPM. The experimental results show that the average wavefront reconstruction error of the DLWS method is 0.04 μm in the root mean square, while the Shack–Hartmann wavefront sensor reconstruction error is 0.17 μm.In laser systems requiring a flat-top distribution of beam intensity, beam smoothing is a critical technology for enhancing laser energy deposition onto the focal spot. The continuous phase modulator (CPM) is a key component in beam smoothing, as it introduces high-frequency continuous phase modulation across the laser beam profile. However, the presence of the CPM makes it challenging to measure and correct the wavefront aberration of the input laser beam effectively, leading to unwanted beam intensity distribution and bringing difficulty to the design of the CPM. To address this issue, we propose a deep learning enabled robust wavefront sensing (DLWS) method to achieve effective wavefront measurement and active aberration correction, thereby facilitating active beam smoothing using the CPM. The experimental results show that the average wavefront reconstruction error of the DLWS method is 0.04 μm in the root mean square, while the Shack–Hartmann wavefront sensor reconstruction error is 0.17 μm.
- Apr. 18, 2025
- High Power Laser Science and Engineering
- Vol. 13, Issue 2, 02000e19 (2025)
- DOI：10.1017/hpl.2025.6
Thermal-lens-free active-mirror ytterbium-doped yttrium aluminum garnet amplifier
Grigory Kurnikov, Mikhail Volkov, Anton Gorokhov, Ivan Kuznetsov, Evgeny Perevezentsev, and Ivan Mukhin
A new method is developed for suppressing thermally induced wavefront distortions of the radiation in the active element of disk geometry. The method is based on controlling radial temperature gradients in the active element using a profiled heatsink. An active element with a zero thermal lens developed on the basis of numerical simulation was experimentally demonstrated in a disk laser head. Higher-order phase aberrations in the active element with a profiled heatsink were weaker than in the element with a flat heatsink. Using this method, a thermal-lens-free active-mirror ytterbium-doped yttrium aluminum garnet amplifier with an output energy of 54 mJ at an average pump power of 100 W and a repetition rate of 106 Hz was implemented.A new method is developed for suppressing thermally induced wavefront distortions of the radiation in the active element of disk geometry. The method is based on controlling radial temperature gradients in the active element using a profiled heatsink. An active element with a zero thermal lens developed on the basis of numerical simulation was experimentally demonstrated in a disk laser head. Higher-order phase aberrations in the active element with a profiled heatsink were weaker than in the element with a flat heatsink. Using this method, a thermal-lens-free active-mirror ytterbium-doped yttrium aluminum garnet amplifier with an output energy of 54 mJ at an average pump power of 100 W and a repetition rate of 106 Hz was implemented.
- Apr. 18, 2025
- High Power Laser Science and Engineering
- Vol. 13, Issue 2, 02000e20 (2025)
- DOI：10.1017/hpl.2025.2
A 5.32 mJ and 47.5 kW cavity-dumped Pr3+:LiYF4 pulsed laser at 639 nm
Wei Yuan, Shaoqiang Zheng, Zheng Zhang, Yongkang Yao, Huiying Xu, and Zhiping Cai
In this work, we confirm a Pr3+:LiYF4 pulsed laser with high power and high energy at 639 nm based on the acousto-optic cavity dumping technique. The maximum average output power, narrowest pulse width, highest pulse energy and peak power of the pulsed laser at a repetition rate of 0.1 kHz are 532 mW, 112 ns, 5.32 mJ and 47.5 kW, respectively. A 639 nm pulsed laser with such high pulse energy and peak power has not been reported previously. Furthermore, we obtain a widely tunable range of repetition rates from 0.1 to 5000 kHz. The diffracted beam quality factors M2 are 2.18 (in the x direction) and 2.04 (in the y direction). To the best of our knowledge, this is the first time that a cavity-dumped all-solid-state pulsed laser in the visible band has been reported. This work provides a promising method for obtaining high-performance pulsed lasers.In this work, we confirm a Pr3+:LiYF4 pulsed laser with high power and high energy at 639 nm based on the acousto-optic cavity dumping technique. The maximum average output power, narrowest pulse width, highest pulse energy and peak power of the pulsed laser at a repetition rate of 0.1 kHz are 532 mW, 112 ns, 5.32 mJ and 47.5 kW, respectively. A 639 nm pulsed laser with such high pulse energy and peak power has not been reported previously. Furthermore, we obtain a widely tunable range of repetition rates from 0.1 to 5000 kHz. The diffracted beam quality factors M2 are 2.18 (in the x direction) and 2.04 (in the y direction). To the best of our knowledge, this is the first time that a cavity-dumped all-solid-state pulsed laser in the visible band has been reported. This work provides a promising method for obtaining high-performance pulsed lasers.
- Apr. 18, 2025
- High Power Laser Science and Engineering
- Vol. 13, Issue 2, 02000e18 (2025)
- DOI：10.1017/hpl.2025.1
Bending-switchable terahertz metamaterial with a single layer based on laser-induced graphene
Abdul Jalal, Yan Dong, Bowen Deng, Muhammad Qasim, Mojtaba Moghaddasi, Ubaid Ur Rahman Qureshi, Zongyuan Wang, Xudong Wu, Chenjie Xiong, and Bin Hu
We propose a fast-printable and function-switchable metamaterial based on laser-induced graphene for terahertz (THz) wave modulation in the reflection mode. The design can modulate the linear polarization of the incoming wave fronts to its cross-polarization from 0.27 to 0.41 THz and linear polarization to circular polarization from 0.48 to 0.62 THz. The function of the device can also be switched from a polarization converter to an absorber by bending it with an angle of 57°. Experimental results showed a good agreement with those of the simulation. The proposed polarization converter may find its application in THz polarization control systems and sensing.We propose a fast-printable and function-switchable metamaterial based on laser-induced graphene for terahertz (THz) wave modulation in the reflection mode. The design can modulate the linear polarization of the incoming wave fronts to its cross-polarization from 0.27 to 0.41 THz and linear polarization to circular polarization from 0.48 to 0.62 THz. The function of the device can also be switched from a polarization converter to an absorber by bending it with an angle of 57°. Experimental results showed a good agreement with those of the simulation. The proposed polarization converter may find its application in THz polarization control systems and sensing.
- Apr. 18, 2025
- Chinese Optics Letters
- Vol. 23, Issue 4, 043603 (2025)
- DOI：10.3788/COL202523.043603
Nonlinear Cherenkov radiation in rotatory nonlinear optics
Zhongmian Zhang, Dazhi Lu, Haohai Yu, Huaijin Zhang, and Yicheng Wu
Nonlinear Cherenkov radiation is a phenomenon of light first observed in 1970 that can be manipulated by phase matching conditions. However, under a rotatory symmetry, the nonlinear Cherenkov radiation was still untouched, where the rotation parameters in optics would introduce an additional phase to the beam, change the phase velocity of the electromagnetic wave, and lead to novel optical phenomena. Here, we introduce rotation as a new freedom and study the nonlinear Cherenkov radiation in optically rotatory crystals in theory. With a quartz crystal as the representative, we derive theoretical variations, which show that the phase velocity of the crystal-coupled wave is found to be accelerated or decelerated by the rotational angular velocity, corresponding to the change of the Cherenkov radiation angle. In addition, the variation on the effective nonlinear coefficient of quartz crystals with rotational polarization direction is analyzed theoretically and used to simulate the Cherenkov ring distribution in rotatory nonlinear optics. This work introduces the rotation parameter into the non-collinear phase matching process and may inspire the development of modern photonics and physics in rotatory frames.Nonlinear Cherenkov radiation is a phenomenon of light first observed in 1970 that can be manipulated by phase matching conditions. However, under a rotatory symmetry, the nonlinear Cherenkov radiation was still untouched, where the rotation parameters in optics would introduce an additional phase to the beam, change the phase velocity of the electromagnetic wave, and lead to novel optical phenomena. Here, we introduce rotation as a new freedom and study the nonlinear Cherenkov radiation in optically rotatory crystals in theory. With a quartz crystal as the representative, we derive theoretical variations, which show that the phase velocity of the crystal-coupled wave is found to be accelerated or decelerated by the rotational angular velocity, corresponding to the change of the Cherenkov radiation angle. In addition, the variation on the effective nonlinear coefficient of quartz crystals with rotational polarization direction is analyzed theoretically and used to simulate the Cherenkov ring distribution in rotatory nonlinear optics. This work introduces the rotation parameter into the non-collinear phase matching process and may inspire the development of modern photonics and physics in rotatory frames.
- Apr. 18, 2025
- Chinese Optics Letters
- Vol. 23, Issue 4, 041901 (2025)
- DOI：10.3788/COL202523.041901
280 W near-diffraction-limited picosecond amplifier system with two-segmented doped Nd:YVO4 crystals
Yiwen Jin, Zhibin Ye, Xiang Zhang, Yang Liu, Xiaoyan Qiu, Yuhong Shen, Yichao Peng, Miao Hu, Chong Liu, and Dong Liu
A multistage amplifier system based on high-power end-pumped two-segmented Nd:YVO4 is developed, which realizes the effective beam quality management in high-power lasers. Because of the severe thermal effect caused by high-power end pumping, both the appropriate crystal and beam filling factor (the ratio of the laser beam radius to the pump beam radius) are important in the amplifier. The multisegmented doped crystal is controlled in cooperation with the beam filling factor to realize high output power and maintain good beam quality. To study the thermal effect in the end-pumped crystal, the temperature distributions of end-pumped single-segmented and two-segmented Nd:YVO4 are theoretically calculated. In the experiment, a probe laser is employed to measure the spherical aberration coefficient and the beam quality of the laser at the rear end of the two end-pumped crystals, respectively, and the experimental results are in good agreement with the theoretical results. In the power amplification, a seed laser is employed in the experiment. The appropriate gain medium and beam filling factor are determined by considering the spherical aberration coefficient, beam quality, and power extraction efficiency. Based on the reasonable layout of the power amplification for each stage amplifier, the multistage amplifier system outputs a 280.2 W picosecond laser with the beam quality factors of Mx2 = 1.28 and My2 = 1.32.A multistage amplifier system based on high-power end-pumped two-segmented Nd:YVO4 is developed, which realizes the effective beam quality management in high-power lasers. Because of the severe thermal effect caused by high-power end pumping, both the appropriate crystal and beam filling factor (the ratio of the laser beam radius to the pump beam radius) are important in the amplifier. The multisegmented doped crystal is controlled in cooperation with the beam filling factor to realize high output power and maintain good beam quality. To study the thermal effect in the end-pumped crystal, the temperature distributions of end-pumped single-segmented and two-segmented Nd:YVO4 are theoretically calculated. In the experiment, a probe laser is employed to measure the spherical aberration coefficient and the beam quality of the laser at the rear end of the two end-pumped crystals, respectively, and the experimental results are in good agreement with the theoretical results. In the power amplification, a seed laser is employed in the experiment. The appropriate gain medium and beam filling factor are determined by considering the spherical aberration coefficient, beam quality, and power extraction efficiency. Based on the reasonable layout of the power amplification for each stage amplifier, the multistage amplifier system outputs a 280.2 W picosecond laser with the beam quality factors of Mx2 = 1.28 and My2 = 1.32.
- Apr. 18, 2025
- Chinese Optics Letters
- Vol. 23, Issue 4, 041403 (2025)
- DOI：10.3788/COL202523.041403
High-resolution single-pixel holography for biological specimens
Zhiyong Wang, Yazhen Wang, Yuecheng Shen, Dalong Qi, Yunhua Yao, Lianzhong Deng, Zhenrong Sun, and Shian Zhang
Single-pixel imaging (SPI) is a computational imaging technique that is able to reconstruct high-resolution images using a single-pixel detector. However, most SPI demonstrations have been mainly focused on macroscopic scenes, so their applications to biological specimens are generally limited by constraints in space-bandwidth-time product and spatial resolution. In this work, we further enhance SPI’s imaging capabilities for biological specimens by developing a high-resolution holographic system based on heterodyne holography. Our SPI system achieves a space-bandwidth-time product of 41,667 pixel/s and a lateral resolution of 4–5 μm, which represent state-of-the-art technical indices among reported SPI systems. Importantly, our SPI system enables detailed amplitude imaging with high contrast for stained specimens such as epithelial and esophageal cancer samples, while providing complementary phase imaging for unstained specimens including molecular diagnostic samples and mouse brain tissue slices, revealing subtle refractive index variations. These results highlight SPI’s versatility and establish its potential as a powerful tool for advanced biomedical imaging applications.Single-pixel imaging (SPI) is a computational imaging technique that is able to reconstruct high-resolution images using a single-pixel detector. However, most SPI demonstrations have been mainly focused on macroscopic scenes, so their applications to biological specimens are generally limited by constraints in space-bandwidth-time product and spatial resolution. In this work, we further enhance SPI’s imaging capabilities for biological specimens by developing a high-resolution holographic system based on heterodyne holography. Our SPI system achieves a space-bandwidth-time product of 41,667 pixel/s and a lateral resolution of 4–5
- Apr. 18, 2025
- Chinese Optics Letters
- Vol. 23, Issue 4, 041103 (2025)
- DOI：10.3788/COL202523.041103
Phong shading approximation of computer-generated holography based on fully analytical triangle meshes
Xi Zou, Qingyang Fu, Yan Liu, Min Yang, Pin Wang, Yaping Zhang, and Ting-Chung Poon
We propose a Phong shading approximation, which gives the amplitude of each point inside the triangle through linear interpolation within the framework of self-similarity segmentation and affine transformation in polygon-based computer-generated holography. Shading is important as it reflects the geometric properties of the objects. To accurately represent the geometric properties of objects in three-dimensional space, the method involves calculating the amplitude distribution on each triangle and maintaining a complete analytical framework, with the edges of the reconstructed polygons nearly unobservable. Numerical simulations and optical reconstructions demonstrate that the proposed method successfully addresses the issue of edge discontinuity on polygonal surfaces.We propose a Phong shading approximation, which gives the amplitude of each point inside the triangle through linear interpolation within the framework of self-similarity segmentation and affine transformation in polygon-based computer-generated holography. Shading is important as it reflects the geometric properties of the objects. To accurately represent the geometric properties of objects in three-dimensional space, the method involves calculating the amplitude distribution on each triangle and maintaining a complete analytical framework, with the edges of the reconstructed polygons nearly unobservable. Numerical simulations and optical reconstructions demonstrate that the proposed method successfully addresses the issue of edge discontinuity on polygonal surfaces.
- Apr. 18, 2025
- Chinese Optics Letters
- Vol. 23, Issue 4, 040501 (2025)
- DOI：10.3788/COL202523.040501
Comments on high-speed mesoscale light-field microscopy
Euiheon Chung, Youngseung Yoo, Christine H. Hwang, and Ki Hean Kim
- Apr. 18, 2025
- Advanced Imaging
- Vol. 2, Issue 2, 023001 (2025)
- DOI：10.3788/AI.2025.30002
Recent advances in femtosecond laser direct writing of three-dimensional periodic photonic structures in transparent materials
Bin Zhang, Wenchao Yan, and Feng Chen
The femtosecond laser direct writing technique is a highly precise processing method that enables the rapid fabrication of three-dimensional (3D) micro- and nanoscale photonic structures in transparent materials. By focusing ultrashort laser pulses into transparent optical materials, such as crystals and glasses, it is possible to efficiently modify specific optical properties, including refractive indices and ferroelectric domains, at the laser focus. By carefully designing and optimizing the movement trajectory of the femtosecond laser, one can achieve periodic modulation of the optical features of these materials in 3D space. The resulting changes in material properties are closely linked to both the processing parameters of the femtosecond laser and the types of materials used. Through ongoing optimization of these parameters, desired periodic photonic structures can be created in specific transparent optical materials, leading to the development of 3D nonlinear photonic crystals (NPCs) and 3D waveguide arrays. Femtosecond laser direct writing breaks through the limitations of traditional techniques to fabricate 3D NPCs [e.g., 3D lithium niobate (LiNbO3) NPCs] and complex waveguide arrays (e.g., 3D helical waveguide arrays), realizing a paradigm shift in the fabrication of complex periodic photonic structures. To date, femtosecond-laser-written 3D NPCs and waveguide arrays have found extensive applications in integrated photonics, nonlinear optics, quantum optics, and topological photonics. We highlight recent advancements in femtosecond-laser-written 3D NPCs and waveguide arrays, such as pivotal breakthroughs in the fabrication of nanoscale-resolution 3D NPCs in LiNbO3. Finally, several potential research directions, such as the formation mechanism of domain wall and inducing millimeter-scale domain inversion with femtosecond Bessel beam, have been proposed at the end of this article.The femtosecond laser direct writing technique is a highly precise processing method that enables the rapid fabrication of three-dimensional (3D) micro- and nanoscale photonic structures in transparent materials. By focusing ultrashort laser pulses into transparent optical materials, such as crystals and glasses, it is possible to efficiently modify specific optical properties, including refractive indices and ferroelectric domains, at the laser focus. By carefully designing and optimizing the movement trajectory of the femtosecond laser, one can achieve periodic modulation of the optical features of these materials in 3D space. The resulting changes in material properties are closely linked to both the processing parameters of the femtosecond laser and the types of materials used. Through ongoing optimization of these parameters, desired periodic photonic structures can be created in specific transparent optical materials, leading to the development of 3D nonlinear photonic crystals (NPCs) and 3D waveguide arrays. Femtosecond laser direct writing breaks through the limitations of traditional techniques to fabricate 3D NPCs [e.g., 3D lithium niobate (LiNbO3) NPCs] and complex waveguide arrays (e.g., 3D helical waveguide arrays), realizing a paradigm shift in the fabrication of complex periodic photonic structures. To date, femtosecond-laser-written 3D NPCs and waveguide arrays have found extensive applications in integrated photonics, nonlinear optics, quantum optics, and topological photonics. We highlight recent advancements in femtosecond-laser-written 3D NPCs and waveguide arrays, such as pivotal breakthroughs in the fabrication of nanoscale-resolution 3D NPCs in LiNbO3. Finally, several potential research directions, such as the formation mechanism of domain wall and inducing millimeter-scale domain inversion with femtosecond Bessel beam, have been proposed at the end of this article.
- Apr. 16, 2025
- Advanced Photonics
- Vol. 7, Issue 3, 034002 (2025)
- DOI：10.1117/1.AP.7.3.034002
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