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  • Hu, Cong  (6)
  • 1
    Online Resource
    Online Resource
    Laguerre-Gaussian mode expansion for arbitrary optical fields using a subspace projection method
    Optica Publishing Group ; 2019
    In:  Optics Letters Vol. 44, No. 7 ( 2019-04-01), p. 1615-
    Details
    In: Optics Letters, Optica Publishing Group, Vol. 44, No. 7 ( 2019-04-01), p. 1615-
    Type of Medium: Online Resource
    ISSN: 0146-9592 , 1539-4794
    URL: Article
    DOI: 10.1364/OL.44.001615
    Language: English
    Publisher: Optica Publishing Group
    Publication Date: 2019
    detail.hit.zdb_id: 243290-0
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  • 2
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    Analysis of crosstalk in spectral beam combining of diode laser bar
    Optica Publishing Group ; 2022
    In:  Applied Optics Vol. 61, No. 12 ( 2022-04-20), p. 3390-
    Details
    In: Applied Optics, Optica Publishing Group, Vol. 61, No. 12 ( 2022-04-20), p. 3390-
    Abstract: Spectral beam combining (SBC) of laser diodes has been proven to be an effective method to improve beam brightness. The crosstalk between different emitters in the SBC system will significantly affect the beam-combining efficiency and output beam properties without effective control. The interfering factors of the crosstalk beam intensity in semiconductor laser SBC have been theoretically analyzed, and experiments have been built to carry out the SBC of a semiconductor laser bar with a high filling factor of 80%. It is found that by adding an inverted Kepler telescope, reducing the focal length of the transmission lens or increasing the spacing of the grating and the output coupling mirror, the crosstalk can be suppressed. In an experiment of beam combining with five emitters, the ratio of the first-order crosstalk peak energy to that of the central beam spot is about 0.34 when the spacing of the grating and the output coupling mirror is 50 mm and the focal length of the transmission lens is 200 mm. The ratio decreases to 0.035 when the spacing of the grating and the output coupling mirror is 200 mm. With the addition of an inverted Kepler telescope with a magnification of 2, the ratio decreases to 0.085. In addition, the ratio decreases to 0.07 when the focal length of the transmission lens is 80 mm.
    Type of Medium: Online Resource
    ISSN: 1559-128X , 2155-3165
    URL: Article
    DOI: 10.1364/AO.456640
    Language: English
    Publisher: Optica Publishing Group
    Publication Date: 2022
    detail.hit.zdb_id: 207387-0
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  • 3
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    Mode analysis and measurement of single-emitter blue diode lasers
    Optica Publishing Group ; 2023
    In:  Applied Optics Vol. 62, No. 23 ( 2023-08-10), p. 6264-
    Details
    In: Applied Optics, Optica Publishing Group, Vol. 62, No. 23 ( 2023-08-10), p. 6264-
    Abstract: Recent developments in blue diode lasers have been hindered by the challenge of balancing high power with beam quality. Typically, high-power blue diode lasers exhibit low beam quality due to the output of multiple longitudinal and lateral modes. A promising solution to this problem is to control and shape the blue beam mode output from a single emitter. To achieve this, it is key to have full knowledge of the properties of the output mode under various conditions. In this paper, we explore the mode characteristics of an InGaN single-emitter laser diode that has a typical wavelength of 447 nm (wavelength range: 440–455 nm). We measure and analyze the near-field mode using the box model, finding that the near-field mode excited by the blue diode laser overlapped near the threshold current of 0.32 A. The p =2 order lateral mode of longitudinal mode groups 3 and 4 overlapped with the p =4 order mode of adjacent longitudinal mode groups. Through a Fourier transform of the near-field mode, we obtain the far-field mode and reveal a spatial law of mode distribution that is similar to the near-field mode. As the current is gradually increased and approaches the rated current of the laser diode, the near-field mode continuously has new longitudinal mode groups added to the long-wavelength side of the starting group. We observe an increase in the number of longitudinal mode groups and high-order lateral modes, leading to more mode overlaps. Additionally, we observe a gradual shift in the peak energy of the modes to the long-wavelength side. This study reveals the mode characteristics of broad-area blue diode lasers, providing crucial information to achieve high-quality laser beams in such systems.
    Type of Medium: Online Resource
    ISSN: 1559-128X , 2155-3165
    URL: Article
    DOI: 10.1364/AO.495355
    Language: English
    Publisher: Optica Publishing Group
    Publication Date: 2023
    detail.hit.zdb_id: 207387-0
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  • 4
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    Theoretical and experimental research on crosstalk in spectral beam combining of a laser diode bar with a high fill factor
    Optica Publishing Group ; 2021
    In:  Applied Optics Vol. 60, No. 26 ( 2021-09-10), p. 8213-
    Details
    In: Applied Optics, Optica Publishing Group, Vol. 60, No. 26 ( 2021-09-10), p. 8213-
    Abstract: Spectral beam combining is an important way to improve the brightness of semiconductor laser beams. For a spectral beam combining system, crosstalk between different emitters would cause the deterioration of beam quality and the reduction of beam combining efficiency, especially for the laser diode bar with a high fill factor. In this paper, an analysis model of the spectral beam combining system with crosstalk is established. The most important advantage of this model is that it can analyze the spectral distribution of the combined beam and also give a relatively good estimation for the beam quality parameters, such as beam size and far-field divergence angle. This model is verified by the experimental results. Furthermore, based on the theoretical model, a method for eliminating crosstalk is developed. By introducing a spatial filter inside the grating external cavity, the crosstalk between different emitters is blocked in the far field, and the beam quality is improved. In the experiment of beam combining of five emitters, after crosstalk is eliminated, the divergence angle of the combined laser beam is reduced from 10.09 to 4.73 mrad, the beam parameter product is reduced from 2.95 to 0.91 mm ⋅ mrad, and the power of the main lobe is improved from 1.77 to 2 W.
    Type of Medium: Online Resource
    ISSN: 1559-128X , 2155-3165
    URL: Article
    DOI: 10.1364/AO.438280
    Language: English
    Publisher: Optica Publishing Group
    Publication Date: 2021
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  • 5
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    Optimization of brightness in a Nd:YAG laser by maximizing the single-mode power factor with an intra-cavity spatial light modulator
    Optica Publishing Group ; 2022
    In:  Applied Optics Vol. 61, No. 6 ( 2022-02-20), p. 1482-
    Details
    In: Applied Optics, Optica Publishing Group, Vol. 61, No. 6 ( 2022-02-20), p. 1482-
    Abstract: We report a simple and effective approach for designing resonators with high brightness and high mode discrimination based on optimizing the single-mode power factor of the fundamental mode, which represents the total power extracted by the fundamental mode from the gain medium. By optimizing the single-mode power factor of the fundamental mode, the cavity can be designed to operate in mono-mode, increasing mode purity and improving brightness significantly. Our method is verified on a digital laser with a spatial light modulator as the rear mirror, and the loaded phase profile is acquired by a simulated annealing algorithm. As a result, the optimized resonator with a Fresnel number of 7.2 operates in a single fundamental mode, and the brightness of the output beam yields 240% and 276% improvement, compared with conventional plane–plane and plane–concave resonators, respectively. This approach is ready to be applied to more sophisticated mode selection and may serve as a general method for designing cavities with high efficiency and high brightness.
    Type of Medium: Online Resource
    ISSN: 1559-128X , 2155-3165
    URL: Article
    DOI: 10.1364/AO.451538
    Language: English
    Publisher: Optica Publishing Group
    Publication Date: 2022
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  • 6
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    Generation of arbitrary complex fields with high efficiency and high fidelity by cascaded phase-only modulation method
    Optica Publishing Group ; 2023
    In:  Optics Express Vol. 31, No. 4 ( 2023-02-13), p. 6675-
    Details
    In: Optics Express, Optica Publishing Group, Vol. 31, No. 4 ( 2023-02-13), p. 6675-
    Abstract: Independent or joint control over the amplitude and phase of the complex field by phase-only modulation element is crucial in numerous applications. Existing modulation methods can realize high levels of accuracy but are accompanied by noticeable losses in light-usage efficiency. Here a cascaded modulation method is proposed for the generation of arbitrary complex fields with high efficiency and high fidelity. This approach is based on a gradient descent optimization algorithm that minimizes a customized cost function. The major advantage of our approach over existing modulation methods is that the efficiency is significantly enhanced while ensuring high modulation accuracy. For the generation of Laguerre-Gaussian mode (LG 01 ), with similar high accuracy, the efficiency by our approach can reach 79.5%, which is enhanced by 192% compared with the theoretical maximum efficiency of 41.5% [ Opt. Express 25 , 11692 ( 2017 ) 10.1364/OE.25.011692 ]. Furthermore, the efficiency of existing modulation methods deteriorates rapidly as the target field turns more intricate, whereas in our approach it maintains at a relatively high level. The field generation fidelity and energy efficiency of the proposed cascaded modulation method are compared with that of several different single-pass modulation methods in generating a series of typical Hermite-Gaussian and Laguerre-Gaussian modes and an amplitude-only "OSA" pattern. Our proposed method features both high efficiency and high accuracy in the simulation and experiment, which may be of growing interest to applications such as optical manipulation or quantum communication.
    Type of Medium: Online Resource
    ISSN: 1094-4087
    URL: Article
    DOI: 10.1364/OE.483686
    Language: English
    Publisher: Optica Publishing Group
    Publication Date: 2023
    detail.hit.zdb_id: 1491859-6
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