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8 pages, 1925 KiB

Open AccessArticle

Investigation of Nonlinear Optical Modulation Characteristics of MXene VCrC for Pulsed Lasers

by Yao Meng, Yizhou Liu, Tao Li, Tianli Feng, Jiacheng Huang, Zheng Ni and Wenchao Qiao

Molecules 2022, 27(3), 759; https://doi.org/10.3390/molecules27030759 - 24 Jan 2022

Cited by 6 | Viewed by 2378

We report the surface morphology and the nonlinear absorption characteristics of MXene VCrC nanosheets prepared by the liquid-phase exfoliation method. The self-made MXene VCrC was applied as a saturable absorber in the Tm:YAP laser experiments, performing excellent Q-switching optical modulation characteristics in infrared [...] Read more.

We report the surface morphology and the nonlinear absorption characteristics of MXene VCrC nanosheets prepared by the liquid-phase exfoliation method. The self-made MXene VCrC was applied as a saturable absorber in the Tm:YAP laser experiments, performing excellent Q-switching optical modulation characteristics in infrared range. With this absorber, a stable passively Q-switched 2 μm laser was achieved. Under an incident pump power of 3.52 W, a maximum output power of 280 mW was obtained with a T = 3% output coupler at a repetition frequency of 49 kHz. The corresponding pulse energy and peak power were 5.7 μJ and 6.6 W, respectively. The shortest pulse duration was 658 ns at the repetition rate of 63 kHz with a T = 1% output coupler. Full article

(This article belongs to the Special Issue Advances in Lasers and Optoelectronics)

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12 pages, 4836 KiB

Open AccessArticle

Passively Mode-Locked Er-Doped Fiber Laser Based on Sb₂S₃-PVA Saturable Absorber

by Qiongyu Hu, Xiaohan Chen, Ming Li, Ping Li, Liwei Xu, Haoxu Zhao, Bin Zhang, Jing Liu and Kejian Yang

Molecules 2022, 27(3), 745; https://doi.org/10.3390/molecules27030745 - 24 Jan 2022

Cited by 5 | Viewed by 2616

Abstract

In this paper, antimony trisulfide (Sb₂S₃) was successfully prepared with the liquid phase exfoliation method and embedded into polyvinyl alcohol (PVA) as a saturable absorber (SA) in a passively mode-locked Er-doped fiber laser for the first time. Based on [...] Read more.

In this paper, antimony trisulfide (Sb₂S₃) was successfully prepared with the liquid phase exfoliation method and embedded into polyvinyl alcohol (PVA) as a saturable absorber (SA) in a passively mode-locked Er-doped fiber laser for the first time. Based on Sb₂S₃-PVA SA with a modulation depth of 4.0% and a saturable intensity of 1.545 GW/cm², a maximum average output power of 3.04 mW and maximum peak power of 325.6 W for the stable mode-locked pulses was achieved with slope a efficiency of 0.87% and maximum single pulse energy of 0.81 nJ at a repetition rate of 3.47 MHz under a pump power of 369 mW. A minimum pulse width value of 2.4 ps with a variation range less than 0.1 ps, and a maximum signal to noise ratio (SNR) of 54.3 dB indicated reliable stability of mode-locking, revealing promising potentials of Sb₂S₃ as a saturable absorber in ultrafast all-fiber lasers. Full article

(This article belongs to the Special Issue Advances in Lasers and Optoelectronics)

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9 pages, 2859 KiB

Open AccessArticle

Experimental and Theoretical Study of an Actively Q-Switched Tm:YLF Laser with an Acousto-Optic Modulator

by Lei Guo, Yaling Yang, Ruihua Wang, Baitao Zhang, Tao Li, Shengzhi Zhao, Jingliang He and Kejian Yang

Molecules 2021, 26(23), 7324; https://doi.org/10.3390/molecules26237324 - 2 Dec 2021

Cited by 4 | Viewed by 2368

Abstract

We report the characteristics of a diode-end-pumped, high-repetition-rate, acoustic-optic (AO) Q-switched Tm:YLF laser operating from 5 kHz to 10 kHz. In the continuous-wave (CW) regime, a maximum average output power of 8.5 W was obtained with a slope efficiency of 30.7%. Under the [...] Read more.

We report the characteristics of a diode-end-pumped, high-repetition-rate, acoustic-optic (AO) Q-switched Tm:YLF laser operating from 5 kHz to 10 kHz. In the continuous-wave (CW) regime, a maximum average output power of 8.5 W was obtained with a slope efficiency of 30.7%. Under the AO Q-switching regime, a maximum output power of 7.32 W was obtained at a repetition frequency of 5 kHz with a pulse width of 68 ns and a pulse energy of 1.4 mJ, corresponding to a peak power of 21.5 kW. A time-dependent rate equation model is introduced to theoretically analyze the results obtained in the experiment, in which the cross-relaxation phenomenon, upconversion losses and ground-state depletion are taken into account. Additionally, the evolution processes of population inversion density and intracavity photon number density with time are also presented. The theoretical results well predict the dependence of laser output characteristics of Tm:YLF crystal on the incident pump powers. Full article

(This article belongs to the Special Issue Advances in Lasers and Optoelectronics)

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8 pages, 2067 KiB

Open AccessArticle

Vacancy-Induced Magnetism in Fluorographene: The Effect of Midgap State

by Daozhi Li, Xiaoyang Ma, Hongwei Chu, Ying Li, Shengzhi Zhao and Dechun Li

Molecules 2021, 26(21), 6666; https://doi.org/10.3390/molecules26216666 - 3 Nov 2021

Cited by 2 | Viewed by 1757

Abstract

Based on density functional theory, we have systematically investigated the geometric, magnetic, and electronic properties of fluorographene with three types of vacancy defects. With uneven sublattice, the partial defect structures are significantly spin-polarized and present midgap electronic states. The magnetic moment is mainly [...] Read more.

Based on density functional theory, we have systematically investigated the geometric, magnetic, and electronic properties of fluorographene with three types of vacancy defects. With uneven sublattice, the partial defect structures are significantly spin-polarized and present midgap electronic states. The magnetic moment is mainly contributed by the adjacent C atoms of vacancy defects. Furthermore, the strain dependence of the bandgap is analyzed and shows a linear trend with applied strain. This defect-induced tunable narrow bandgap material has great potential in electronic devices and spintronics applications. Full article

(This article belongs to the Special Issue Advances in Lasers and Optoelectronics)

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10 pages, 4430 KiB

Open AccessArticle

Highly Stable Passively Q-Switched Erbium-Doped All-Fiber Laser Based on Niobium Diselenide Saturable Absorber

by Ping Hu, Jiajia Mao, Hongkun Nie, Ruihua Wang, Baitao Zhang, Tao Li, Jingliang He and Kejian Yang

Molecules 2021, 26(14), 4303; https://doi.org/10.3390/molecules26144303 - 16 Jul 2021

Cited by 9 | Viewed by 2464

Abstract

A saturable absorber (SA) based on niobium diselenide (NbSe₂), which is a layered transition metal dichalcogenide (TMD) in the VB group, is fabricated by the optically driven deposition method, and the related nonlinear optical properties are characterized. The modulation depth, saturable [...] Read more.

A saturable absorber (SA) based on niobium diselenide (NbSe₂), which is a layered transition metal dichalcogenide (TMD) in the VB group, is fabricated by the optically driven deposition method, and the related nonlinear optical properties are characterized. The modulation depth, saturable intensity, and nonsaturable loss of the as-prepared NbSe₂ nanosheet-based SA are measured to be 16.2%, 0.76 MW/cm², and 14%, respectively. By using the as-fabricated NbSe₂ SA, a highly stable, passively Q-switched, erbium-doped, all-fiber laser is realized. The obtained shortest pulse width is 1.49 μs, with a pulse energy of 48.33 nJ at a center wavelength of 1560.38 nm. As far as we know, this is the shortest pulse duration ever obtained by an NbSe₂ SA in a Q-switched fiber laser. Full article

(This article belongs to the Special Issue Advances in Lasers and Optoelectronics)

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11 pages, 3902 KiB

Open AccessArticle

Fabrication of an Anti-Reflective Microstructure on ZnS by Femtosecond Laser Bessel Beams

by Xun Li, Ming Li, Hongjun Liu and Yan Guo

Molecules 2021, 26(14), 4278; https://doi.org/10.3390/molecules26144278 - 14 Jul 2021

Cited by 16 | Viewed by 3810

Abstract

As an important mid-infrared to far-infrared optical window, ZnS is extremely important to improve spectral transmission performance, especially in the military field. However, on account of the Fresnel reflection at the interface between the air and the high-strength substrate, surface optical loss occurs [...] Read more.

As an important mid-infrared to far-infrared optical window, ZnS is extremely important to improve spectral transmission performance, especially in the military field. However, on account of the Fresnel reflection at the interface between the air and the high-strength substrate, surface optical loss occurs in the ZnS optical window. In this study, the concave antireflective sub-wavelength structures (ASS) on ZnS have been experimentally investigated to obtain high transmittance in the far-infrared spectral range from 6 μm to 10 μm. We proposed a simple method to fabricate microhole array ASS by femtosecond Bessel beam, which further increased the depth of the microholes and suppressed the thermal effects effectively, including the crack and recast layer of the microhole. The influence of different Gaussian and Bessel beam parameters on the microhole morphology were explored, and three ASS structures with different periods were prepared by the optimized Bessel parameters. Ultimately, the average transmittance of the sample with the ASS microhole array period of 2.6 μm increased by 4.1% in the 6 μm to 10 μm waveband, and the transmittance was increased by 5.7% at wavelength of 7.2 μm. Full article

(This article belongs to the Special Issue Advances in Lasers and Optoelectronics)

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9 pages, 2235 KiB

Open AccessFeature PaperArticle

The Investigation on Ultrafast Pulse Formation in a Tm–Ho-Codoped Mode-Locking Fiber Oscillator

by Jingcheng Shang, Yizhou Liu, Shengzhi Zhao, Yuefeng Zhao, Yuzhi Song, Tao Li and Tianli Feng

Molecules 2021, 26(11), 3460; https://doi.org/10.3390/molecules26113460 - 7 Jun 2021

Cited by 6 | Viewed by 3697

Abstract

We experimentally investigate the formation of various pulses from a thulium–holmium (Tm–Ho)-codoped nonlinear polarization rotation (NPR) mode-locking fiber oscillator. The ultrafast fiber oscillator can simultaneously operate in the noise-like and soliton mode-locking regimes with two different emission wavelengths located around 1947 and 2010 [...] Read more.

We experimentally investigate the formation of various pulses from a thulium–holmium (Tm–Ho)-codoped nonlinear polarization rotation (NPR) mode-locking fiber oscillator. The ultrafast fiber oscillator can simultaneously operate in the noise-like and soliton mode-locking regimes with two different emission wavelengths located around 1947 and 2010 nm, which are believed to be induced from the laser transition of Tm³⁺ and Ho³⁺ ions respectively. When the noise-like pulse (NLP) and soliton pulse (SP) co-exist inside the laser oscillator, a maximum output power of 295 mW is achieved with a pulse repetition rate of 19.85-MHz, corresponding to a total single pulse energy of 14.86 nJ. By adjusting the wave plates, the fiber oscillator could also deliver the dual-NLPs or dual-SPs at dual wavelengths, or single NLP and single SP at one wavelength. The highest 61-order harmonic soliton pulse and 33.4-nJ-NLP are also realized respectively with proper design of the fiber cavity. Full article

(This article belongs to the Special Issue Advances in Lasers and Optoelectronics)

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7 pages, 3454 KiB

Open AccessArticle

Tunable and Passively Mode-Locking Nd_0.01:Gd_0.89La_0.1NbO₄ Picosecond Laser

by Shande Liu, Yuqing Zhao, Ke Zhang, Bo Chen, Ning Zhang, Dehua Li, Huiyun Zhang, Yuping Zhang, Lihua Wang, Shoujun Ding and Qingli Zhang

Molecules 2021, 26(11), 3179; https://doi.org/10.3390/molecules26113179 - 26 May 2021

Viewed by 2253

Abstract

A high-quality Nd_0.01:Gd_0.89La_0.1NbO₄ (Nd:GLNO) crystal is grown by the Czochralski method, demonstrating wide absorption and fluorescence spectra and advantage for producing ultrafast laser pulses. In this paper, the tunable and passively mode-locking Nd:GLNO lasers are characterized [...] Read more.

A high-quality Nd_0.01:Gd_0.89La_0.1NbO₄ (Nd:GLNO) crystal is grown by the Czochralski method, demonstrating wide absorption and fluorescence spectra and advantage for producing ultrafast laser pulses. In this paper, the tunable and passively mode-locking Nd:GLNO lasers are characterized for the first time. The tuning coverage is 34.87 nm ranging from 1058.05 to 1092.92 nm with a maximum output power of 4.6 W at 1065.29 nm. A stable continuous-wave (CW) passively mode-locking Nd:GLNO laser is achieved at 1065.26 nm, delivering a pulse width of 9.1 ps and a maximum CW mode-locking output power of 0.27 W. Full article

(This article belongs to the Special Issue Advances in Lasers and Optoelectronics)

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17 pages, 5632 KiB

Open AccessArticle

Femtosecond Laser Drilling of Cylindrical Holes for Carbon Fiber-Reinforced Polymer (CFRP) Composites

by Hao Jiang, Caiwen Ma, Ming Li and Zhiliang Cao

Molecules 2021, 26(10), 2953; https://doi.org/10.3390/molecules26102953 - 16 May 2021

Cited by 38 | Viewed by 5104

Abstract

Ultrafast laser drilling has been proven to effectively reduce the heat-affected zone (HAZ) of carbon fiber-reinforced polymer (CFRP) composites. However, previous research mainly focused on the effects of picosecond laser parameters on CFRP drilling. Compared with a picosecond laser, a femtosecond laser can [...] Read more.

Ultrafast laser drilling has been proven to effectively reduce the heat-affected zone (HAZ) of carbon fiber-reinforced polymer (CFRP) composites. However, previous research mainly focused on the effects of picosecond laser parameters on CFRP drilling. Compared with a picosecond laser, a femtosecond laser can achieve higher quality CFRP drilling due to its smaller pulse width, but there are few studies on the effects of femtosecond laser parameters on CFRP drilling. Moreover, the cross-sectional taper of CFRP produced by laser drilling is very large. This paper introduces the use of the femtosecond laser to drill cylindrical holes in CFRP. The effect of laser power, rotational speed of the laser, and number of spiral passes on HAZ and ablation depth in circular laser drilling and spiral laser drilling mode was studied, respectively. It also analyzed the forming process of the drilling depth in the spiral drilling mode and studied the influence of laser energy and drilling feed depth on the holes’ diameters and the taper. The experimental results show that the cylindrical hole of CFRP with a depth-to-diameter ratio of about 3:1 (taper < 0.32

^{\circ}

, HAZ < 10 m) was obtained by using femtosecond laser and a spiral drilling apparatus. Full article

(This article belongs to the Special Issue Advances in Lasers and Optoelectronics)

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17 pages, 20419 KiB

Open AccessArticle

Inhibitory Effects of Erythrosine/Curcumin Derivatives/Nano-Titanium Dioxide-Mediated Photodynamic Therapy on Candida albicans

by Kasama Kanpittaya, Aroon Teerakapong, Noppawan Phumala Morales, Doosadee Hormdee, Aroonsri Priprem, Wilawan Weera-archakul and Teerasak Damrongrungruang

Molecules 2021, 26(9), 2405; https://doi.org/10.3390/molecules26092405 - 21 Apr 2021

Cited by 13 | Viewed by 3285

Abstract

This study focuses on the role of photosensitizers in photodynamic therapy. The photosensitizers were prepared in combinations of 110/220 µM erythrosine and/or 10/20 µM demethoxy/bisdemethoxy curcumin with/without 10% (w/w) nano-titanium dioxide. Irradiation was performed with a dental blue light in the [...] Read more.

This study focuses on the role of photosensitizers in photodynamic therapy. The photosensitizers were prepared in combinations of 110/220 µM erythrosine and/or 10/20 µM demethoxy/bisdemethoxy curcumin with/without 10% (w/w) nano-titanium dioxide. Irradiation was performed with a dental blue light in the 395–480 nm wavelength range, with a power density of 3200 mW/cm² and yield of 72 J/cm². The production of ROS and hydroxyl radical was investigated using an electron paramagnetic resonance spectrometer for each individual photosensitizer or in photosensitizer combinations. Subsequently, a PrestoBlue^® toxicity test of the gingival fibroblast cells was performed at 6 and 24 h on the eight highest ROS-generating photosensitizers containing curcumin derivatives and erythrosine 220 µM. Finally, the antifungal ability of 22 test photosensitizers, Candida albicans (ATCC 10231), were cultured in biofilm form at 37 °C for 48 h, then the colonies were counted in colony-forming units (CFU/mL) via the drop plate technique, and then the log reduction was calculated. The results showed that at 48 h the test photosensitizers could simultaneously produce both ROS types. All test photosensitizers demonstrated no toxicity on the fibroblast cells. In total, 18 test photosensitizers were able to inhibit Candida albicans similarly to nystatin. Conclusively, 20 µM bisdemethoxy curcumin + 220 µM erythrosine + 10% (w/w) nano-titanium dioxide exerted the highest inhibitory effect on Candida albicans. Full article

(This article belongs to the Special Issue Advances in Lasers and Optoelectronics)

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