Photonics

Research

8 pages, 4410 KiB

Open AccessCommunication

Research on the Thermal Effect of Micro-Channel Cooled Thin-Slab Tm:YAP Lasers

by Jianhua Shang, Xiaojin Cheng, Qixin Li and Xiangnan Wu

Photonics 2023, 10(6), 680; https://doi.org/10.3390/photonics10060680 - 12 Jun 2023

Viewed by 774

Using the finite element method and the heat conduction equation, the temperature, stress, and end-face deformation in Tm:YAP crystal under high pump power were analyzed. Combined with gradient doping technology, an effective way to improve the internal heat distribution of the crystal was [...] Read more.

Using the finite element method and the heat conduction equation, the temperature, stress, and end-face deformation in Tm:YAP crystal under high pump power were analyzed. Combined with gradient doping technology, an effective way to improve the internal heat distribution of the crystal was studied. The results showed that when the total pump power was 200 W, under the same cooling conditions, the maximum temperature difference inside Tm:YAP decreased from 58 K to 25 K after gradient doping. The thermal stress and end-face thermal deformation were also significantly improved. In addition, a reasonable micro-channel structure also effectively removed the heat generated inside the crystal. Full article

(This article belongs to the Special Issue High Power Laser: Theory and Applications)

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12 pages, 3729 KiB

Open AccessArticle

Influence of Large-Aperture Output Wavefront Distribution on Focal Spot in High-Power Laser Facility

by Jiamei Li, Hui Yu, Dawei Li, Li Wang, Junyong Zhang, Qiong Zhou, Fengnian Lv and Xingqiang Lu

Photonics 2023, 10(3), 270; https://doi.org/10.3390/photonics10030270 - 3 Mar 2023

Cited by 1 | Viewed by 959

Abstract

To improve the focal spot quality, the output wavefront of the Shenguang-II Upgrade facility is divided into four types based on the spatial frequency and division band of power spectral density. The influence of each on the focal spot was quantitatively studied, and [...] Read more.

To improve the focal spot quality, the output wavefront of the Shenguang-II Upgrade facility is divided into four types based on the spatial frequency and division band of power spectral density. The influence of each on the focal spot was quantitatively studied, and the results indicate that the spatial profile, energy concentration, and peak intensity of the focal spot are mainly affected by low-spatial-frequency, and the relative intensity of the sidelobes is greatly affected by both the low- and mid-spatial counterparts. The peak-to-valley value of the wavefront of the Shenguang-II Upgrade should not exceed 2.27λ under the requirement that 50% of the energy is enclosed within 3 times the diffraction limit (DL), and it should be less than 2.45λ under the requirement that 95% is within 10DL. Meanwhile, the Strehl ratio dropped to within 0.2 under these conditions. These results can be applied to focal quality improvement in designing an adaptive optical system, optical element processing, as well as focal spot prediction in high-power laser facilities. Full article

(This article belongs to the Special Issue High Power Laser: Theory and Applications)

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8 pages, 2836 KiB

Open AccessCommunication

Ultra-Broadband NPE-Based Femtosecond Fiber Laser

by Sergei I. Abdrakhmanov, Vladislav D. Efremov, Alexey G. Kuznetsov, Denis S. Kharenko and Sergey A. Babin

Photonics 2023, 10(1), 85; https://doi.org/10.3390/photonics10010085 - 12 Jan 2023

Viewed by 1609

Abstract

A dissipative soliton mode-locked Yb-doped fiber laser is investigated experimentally and numerically from the point of view of generating ultra-broadband ultrashort pulses. An energy up to 2.2 nJ and a spectral bandwidth over 60 nm (at the −10 dB level) were obtained experimentally [...] Read more.

A dissipative soliton mode-locked Yb-doped fiber laser is investigated experimentally and numerically from the point of view of generating ultra-broadband ultrashort pulses. An energy up to 2.2 nJ and a spectral bandwidth over 60 nm (at the −10 dB level) were obtained experimentally without dispersion compensation in the cavity. Almost a 100-fold compression coefficient has been achieved, so the resulting pulse duration was 149 fs. The numerical simulation has shown that a further scaling up to 3.5 nJ and a 100 nm spectral bandwidth is possible by reducing the low power transmission coefficient of the NPE-based SAM and increasing the amplification. At the same time, the tolerance of the SAM to a low power radiation is responsible for the transition to a multi-pulse operation regime. Full article

(This article belongs to the Special Issue High Power Laser: Theory and Applications)

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23 pages, 5166 KiB

Open AccessArticle

Numerical Simulations of the Influence on the Temperature Fields of Large-Sized Nd-Glass Slab with Designed Edge-Cladding Materials, Methods, and Structures

by Jixi Xu, Weichang Li, Xin Wang, Jingping Tang, Wei Chen, Shubin Chen and Lili Hu

Photonics 2022, 9(12), 931; https://doi.org/10.3390/photonics9120931 - 2 Dec 2022

Cited by 1 | Viewed by 1222

Abstract

The good cladding of a large-sized Nd-doped phosphate glass slab as a laser amplifier requires not only the amplified spontaneous emission and parasitic oscillation to be fully absorbed, to hold up the small signal gain coefficient of the Nd ions, but also the [...] Read more.

The good cladding of a large-sized Nd-doped phosphate glass slab as a laser amplifier requires not only the amplified spontaneous emission and parasitic oscillation to be fully absorbed, to hold up the small signal gain coefficient of the Nd ions, but also the absorbed heat energy to be appropriately dissipated to extend a uniform temperature field for the larger laser beam aperture of the edge-cladded Nd–glass slab. In the present work, numerical simulations were performed based on the developed feasible edge-cladding designs for a 786 × 436 × 40 mm³ Nd–glass slab, including the following alterations: optical absorptivity, quantum-dot absorption centers, ceramics with higher thermal diffusivity, glasses with lower and higher specific heat values, 3D printing edge-cladding methods, double-deck edge-cladding structure with transparent strips as a buffer layer, and thickening of the edge-cladding. All of these designed edge-cladding materials, methods, and structures satisfy both requirements of sufficiently absorbing and precisely matching with the refractive index, as emphasized by the edge-cladding for the Nd–glass. Some of the designed edge-claddings resulted in a much more uniform temperature field than the composite polymer–glass edge-cladding as the standard for comparison, which could be utilized to extend the effective laser aperture of the Nd–glass slab, thus being beneficial to the laser beam size and laser energy in the optics recycle loop strategy. Full article

(This article belongs to the Special Issue High Power Laser: Theory and Applications)

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12 pages, 4723 KiB

Open AccessArticle

Research on High Power Laser Damage Resistant Optically Addressable Spatial Light Modulator

by Tongyao Du, Dajie Huang, He Cheng, Wei Fan, Zhibo Xing, Jianqiang Zhu and Wen Liu

Photonics 2022, 9(11), 811; https://doi.org/10.3390/photonics9110811 - 28 Oct 2022

Viewed by 1805

Abstract

Liquid crystal spatial light modulators (LC-SLMs) are devices that can accurately adjust the parameters of beam amplitude, phase, wavefront and polarization. However, due to the limitation of laser damage resistance of component materials, LC-SLMs still have difficulty meeting the application and development needs [...] Read more.

Liquid crystal spatial light modulators (LC-SLMs) are devices that can accurately adjust the parameters of beam amplitude, phase, wavefront and polarization. However, due to the limitation of laser damage resistance of component materials, LC-SLMs still have difficulty meeting the application and development needs of a high-average power laser system. Here, we proposed an optically addressable spatial light modulator (OASLM) based on a sapphire substrate. Due to the good thermal conductivity of sapphire, the laser damage resistance of the device was greatly improved. The thermal distribution of OASLM based on the sapphire substrate and the K9 substrate is analyzed by a laser-induced temperature rise model. The experimental results also show the excellent performance of sapphire OASLM under high-power CW laser irradiation, its laser power density is increased from 10 W/cm² to 75 W/cm², and the working time is more than 30 min. By bonding sapphire to the other side, the laser power density can be increased to 100 W/cm², and these are completed without active heat dissipation. This method provides a feasible path for high-average-power SLMs. Full article

(This article belongs to the Special Issue High Power Laser: Theory and Applications)

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9 pages, 2811 KiB

Open AccessCommunication

Laser Method for Studying Temperature Distribution within Yb:YAG Active Elements

by Gleb V. Kuptsov, Alyona O. Konovalova, Vladimir A. Petrov, Alexey V. Laptev, Victor V. Atuchin and Victor V. Petrov

Photonics 2022, 9(11), 805; https://doi.org/10.3390/photonics9110805 - 27 Oct 2022

Cited by 5 | Viewed by 1389

Abstract

Currently, laser systems based on active elements doped with Yb³⁺ with simultaneously high pulse repetition rates and high peak power are in demand for many applications. High thermal load of active elements is the primary limiting factor for average power scaling. Experimental [...] Read more.

Currently, laser systems based on active elements doped with Yb³⁺ with simultaneously high pulse repetition rates and high peak power are in demand for many applications. High thermal load of active elements is the primary limiting factor for average power scaling. Experimental investigation of temperature distribution in active elements is of particular importance for estimation of cooling efficiency and for thermal processes’ monitoring. In the present work, the method of dynamic laser thermometry is proposed for temperature distribution investigation within cryogenically cooled Yb³⁺-doped active elements. The method is based on the dependence of the Yb³⁺ ion absorption cross-section on temperature at a wavelength of 1030 nm. The method was tested to study the 2D temperature map of the Yb:YAG active element of the high-power, diode-pumped, cryogenically cooled laser amplifier. The best measurement accuracy ±3 K is achieved at the maximal temperature 176 K. The results of numerical simulation are in good agreement with the experimental data. On the basis of the investigation, the quality of the cooling system is evaluated. The advantages and other possible applications of the method are discussed. Full article

(This article belongs to the Special Issue High Power Laser: Theory and Applications)

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9 pages, 2180 KiB

Open AccessCommunication

First Demonstration and Comparison of 5 kW Monolithic Fiber Laser Oscillator Pumped by 915 nm and 981 nm LDs

by Yujun Wen, Peng Wang, Baolai Yang, Hanwei Zhang, Xiaoming Xi, Xiaolin Wang and Xiaojun Xu

Photonics 2022, 9(10), 716; https://doi.org/10.3390/photonics9100716 - 30 Sep 2022

Cited by 2 | Viewed by 1311

Abstract

Fiber laser performances including transverse mode instability (TMI), stimulated Raman scattering (SRS) and optical-to-optical efficiency are in connection with the pump wavelength. Here we studied the output characteristics of a 5-kW ytterbium-doped fiber laser oscillator pumped with two different pump sources, i.e., 915 [...] Read more.

Fiber laser performances including transverse mode instability (TMI), stimulated Raman scattering (SRS) and optical-to-optical efficiency are in connection with the pump wavelength. Here we studied the output characteristics of a 5-kW ytterbium-doped fiber laser oscillator pumped with two different pump sources, i.e., 915 nm and 981 nm laser diodes (LDs). The output characteristics of fiber laser oscillators pumped by 915 nm and 981 nm have been compared strictly and directly with the same structure in a high-power situation. Experimental results show that both pump wavelengths can scale the power up to more than 5 kW by suppressing the TMI effect. While in the case of pumping by the 981 nm LDs, the laser oscillator has an optical-to-optical efficiency of 87%, which is 13% higher than that of the 915 nm pumped scheme. In addition, due to the higher backward pumping ratio and lower total pump power, the laser oscillator has a better SRS suppression ratio when pumped at 981 nm. Thus, it reveals a great potential to balance the limitations of TMI and SRS for scaling up to an even higher output while pumping at 981 nm. All the devices of the oscillator are commercial, and it will be helpful for the commercialization of high-power fiber laser oscillators. Full article

(This article belongs to the Special Issue High Power Laser: Theory and Applications)

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13 pages, 2913 KiB

Open AccessArticle

Specific Phase Modulation with Dynamic Variable Spectral Width of Nanosecond Optical Pulse in High-Power Lasers

by Xinlei Qian, Xiaochao Wang, Shouying Xu, Zhuli Xiao, Yue Wang, Shenlei Zhou and Wei Fan

Photonics 2022, 9(8), 586; https://doi.org/10.3390/photonics9080586 - 18 Aug 2022

Viewed by 1380

Abstract

High-power laser pulse transmitted by phase modulation with certain spectrum distribution can suppress the buildup of transverse stimulated Brillouin scattering (TSBS) in large aperture laser optics and smooth the speckle pattern illuminating the target by spectral smoothing dispersion (SSD). In this paper, based [...] Read more.

High-power laser pulse transmitted by phase modulation with certain spectrum distribution can suppress the buildup of transverse stimulated Brillouin scattering (TSBS) in large aperture laser optics and smooth the speckle pattern illuminating the target by spectral smoothing dispersion (SSD). In this paper, based on the requirements of the double-cone ignition scheme including simultaneously realizing that the focal spot is variable at different times in size and the spatial intensity distribution is uniform, we propose a novel phase modulation technology with a rapid variable modulation index in the nanosecond scale instead of utilizing conventional constant amplitude sinusoidal curve. The relevant simulation results indicate that the proposed technology can realize the dynamic nanosecond spectral distribution and the trend correlates with the variety of modulation index. Particularly, we indirectly measure this rapid changeable spectral distribution based on the mapping relationship between frequency and time domain. We believe that the new technology is expected to meet the requirements of SSD and the dynamic focus simultaneously. Full article

(This article belongs to the Special Issue High Power Laser: Theory and Applications)

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