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Open AccessArticle

Modeling for Spatial Overlap Effect of End-Pumped Passively Q-Switched Nd:YVO₄/Cr⁴⁺:YAG Laser and Its Experimental Verification

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Appl. Sci. 2022, 12(3), 1338; https://doi.org/10.3390/app12031338 - 27 Jan 2022

Cited by 1 | Viewed by 1339

Abstract

In this work, the spatial effects of the pumping and lasing were considered into the coupled rate equations of passively Q-switched lasers for the condition of no saturation in the gain medium. A transcendental equation of energy utilization was derived, and the solution [...] Read more.

In this work, the spatial effects of the pumping and lasing were considered into the coupled rate equations of passively Q-switched lasers for the condition of no saturation in the gain medium. A transcendental equation of energy utilization was derived, and the solution to the equation was approximated by an analytic model developed in previous work. The reflection factor of output coupler with low reflectivity was modified for more accurate output energy evaluations. Experimentally, an end-pumped Nd:YVO₄/Cr⁴⁺:YAG laser in a concave-plano cavity with output coupling reflectivity ranging from 10% to 92% was demonstrated, and two different pumping spot sizes of laser diode were adopted for validating the developed spatial model. The experimental results showed good agreements with the theoretical calculations. Full article

(This article belongs to the Special Issue Optoelectronics for Lasers: Latest Advances and Prospects)

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Open AccessArticle

Investigating the Threshold Conditions of Air Breakdown with Mode-Locked Q-Switched Laser Pulses, and the Temporal Dynamics of Induced Plasma with Self-Scattering Phenomenon

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Appl. Sci. 2022, 12(1), 41; https://doi.org/10.3390/app12010041 - 21 Dec 2021

Cited by 1 | Viewed by 1770

Abstract

A Q-switched Nd:YAG laser with mode-locked modulations is utilized to explore the laser-induced air breakdown. The various modulation depths of the mode-locking within the Q-switched pulse can be utilized to investigate the threshold conditions. With the GHz high-speed detectors to accurately measure the [...] Read more.

A Q-switched Nd:YAG laser with mode-locked modulations is utilized to explore the laser-induced air breakdown. The various modulation depths of the mode-locking within the Q-switched pulse can be utilized to investigate the threshold conditions. With the GHz high-speed detectors to accurately measure the temporal pulse shape pulse by pulse, it is verified that the air breakdown threshold is crucially determined by the peak-power density instead of the energy density from the statistic results, especially for mode-locked Q-switched lasers. The stability of the system for laser-induced breakdown can be evaluated by threshold width through fitting the statistical result. Otherwise, by measuring the temporal characteristics of the excitation pulse and the induced plasma, it is further found that the plasma radiation displays a few-nanoseconds time delay to the excitation pulse and shows a decaying tail to be 10 times longer than the plasma build-up time. Moreover, the incident laser pulse is observed to be self-scattered by the air breakdown, and a rapidly modulated scattering rate is found with a slight delay time to the excitation mode-locked subpulse modulations. Full article

(This article belongs to the Special Issue Optoelectronics for Lasers: Latest Advances and Prospects)

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Open AccessArticle

Comparison between Self-Raman Nd:YVO₄ Lasers and NdYVO₄/KGW Raman Lasers at Lime and Orange Wavelengths

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Appl. Sci. 2021, 11(22), 11068; https://doi.org/10.3390/app112211068 - 22 Nov 2021

Cited by 4 | Viewed by 960

Abstract

The comparison of output powers between self-Raman Nd:YVO₄ lasers and Nd:YVO₄/KGW Raman lasers operating at lime and orange wavelengths is presented. We exploit the LBO crystal with cutting angle θ = 90° and φ = 8° for the lime wavelengths, [...] Read more.

The comparison of output powers between self-Raman Nd:YVO₄ lasers and Nd:YVO₄/KGW Raman lasers operating at lime and orange wavelengths is presented. We exploit the LBO crystal with cutting angle θ = 90° and φ = 8° for the lime wavelengths, and then we change the angle to θ = 90° and φ = 3.9° for the orange wavelengths. In self-Raman Nd:YVO₄ lasers, experimental results reveal that thermal loading can impact on the output performances, especially at the high pump power. However, by using a KGW crystal as Raman medium can remarkably share the thermal loading from gain medium. Besides, the designed coating for high reflectively at the Stokes field on the surface of KGW also improved the beam quality and reduced the lasing threshold. For self-Raman Nd:YVO₄ lasers, we have achieved the output powers of 6.54 W and 5.12 W at 559 nm and 588 nm, respectively. For Nd:YVO₄/KGW Raman lasers, the output powers at 559 nm and 589 nm have been increased to 9.1 W and 7.54 W, respectively. All lasers operate at a quasi-CW regime with the repetition rate 50 Hz and the duty cycle 50%. Full article

(This article belongs to the Special Issue Optoelectronics for Lasers: Latest Advances and Prospects)

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Open AccessArticle

SESAM Mode-Locked Yb:Ca₃Gd₂(BO₃)₄ Femtosecond Laser

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Appl. Sci. 2021, 11(20), 9464; https://doi.org/10.3390/app11209464 - 12 Oct 2021

Cited by 4 | Viewed by 941

Abstract

We report on the first passively mode-locked femtosecond-laser operation of a disordered Yb:Ca₃Gd₂(BO₃)₄ crystal using a SEmiconductor Saturable Absorber Mirror (SESAM). Pumping with a single-transverse mode fiber-coupled laser diode at 976 nm, nearly Fourier-transform-limited pulses as [...] Read more.

We report on the first passively mode-locked femtosecond-laser operation of a disordered Yb:Ca₃Gd₂(BO₃)₄ crystal using a SEmiconductor Saturable Absorber Mirror (SESAM). Pumping with a single-transverse mode fiber-coupled laser diode at 976 nm, nearly Fourier-transform-limited pulses as short as 96 fs are generated at 1045 nm with an average output power of 205 mW and a pulse repetition rate of ~67.3 MHz. In the continuous-wave regime, high slope efficiency up to 59.2% and low laser thresholds down to 25 mW are obtained. Continuous wavelength tuning between 1006–1074 nm (a tuning range of 68 nm) is demonstrated. Yb:Ca₃Gd₂(BO₃)₄ crystals are promising for the development of ultrafast lasers at ~1 μm. Full article

(This article belongs to the Special Issue Optoelectronics for Lasers: Latest Advances and Prospects)

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Open AccessArticle

Systematically Investigating the Structural Variety of Crystalline and Kaleidoscopic Vortex Lattices by Using Laser Beam Arrays

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Appl. Sci. 2021, 11(17), 8018; https://doi.org/10.3390/app11178018 - 30 Aug 2021

Viewed by 681

Abstract

We theoretically demonstrate that a family of vortex-lattice structures can be flexibly generated using a multi-beam interference approach. Numerical calculation presents a variety of crystalline and kaleidoscopic patterns. Based on the numerical analysis, we experimentally realized these structure beams by combining an amplitude [...] Read more.

We theoretically demonstrate that a family of vortex-lattice structures can be flexibly generated using a multi-beam interference approach. Numerical calculation presents a variety of crystalline and kaleidoscopic patterns. Based on the numerical analysis, we experimentally realized these structure beams by combining an amplitude mask with multiple apertures and a spiral phase plate. The excellent agreement between the experimental and theoretical results not only validates the presented method, but also manifests the structure of vortex lattices. Full article

(This article belongs to the Special Issue Optoelectronics for Lasers: Latest Advances and Prospects)

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Open AccessArticle

Passively Q-Switched KTA Cascaded Raman Laser with 234 and 671 cm⁻¹ Shifts

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Appl. Sci. 2021, 11(15), 6895; https://doi.org/10.3390/app11156895 - 27 Jul 2021

Cited by 2 | Viewed by 945

Abstract

A compact KTA cascaded Raman system driven by a passively Q-switched Nd:YAG/Cr⁴⁺:YAG laser at 1064 nm was demonstrated for the first time. The output spectra with different cavity lengths were measured. Two strong lines with similar intensity were achieved with a [...] Read more.

A compact KTA cascaded Raman system driven by a passively Q-switched Nd:YAG/Cr⁴⁺:YAG laser at 1064 nm was demonstrated for the first time. The output spectra with different cavity lengths were measured. Two strong lines with similar intensity were achieved with a 9 cm length cavity. One is the first-Stokes at 1146.8 nm with a Raman shift of 671 cm⁻¹, and the other is the Stokes at 1178.2 nm with mixed Raman shifts of 234 cm⁻¹ and 671 cm⁻¹. At the shorter cavity length of 5 cm, the output Stokes lines with high intensity were still at 1146.8 nm and 1178.2 nm, but the intensity of 1178.2 nm was higher than that of 1146.8 nm. The maximum average output power of 540 mW was obtained at the incident pump power of 10.5 W with the pulse repetition frequency of 14.5 kHz and the pulse width around 1.1 ns. This compact passively Q-switched KTA cascaded Raman laser can yield multi-Stokes waves, which enrich laser output spectra and hold potential applications for remote sensing and terahertz generation. Full article

(This article belongs to the Special Issue Optoelectronics for Lasers: Latest Advances and Prospects)

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Review

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Open AccessReview

Review of the Yb³⁺:ScBO₃ Laser Crystal Growth, Characterization, and Laser Applications

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Appl. Sci. 2021, 11(22), 10879; https://doi.org/10.3390/app112210879 - 17 Nov 2021

Viewed by 946

Abstract

Passive Q-switching is an effective approach for generating pulsed lasers, owing to its compact and additional modulation-free design. However, to compare favorably with active Q-switching and multi-stage amplification, the output energy needs to be enhanced for practical applications. Kramers Ytterbium ion (Yb³⁺ [...] Read more.

Passive Q-switching is an effective approach for generating pulsed lasers, owing to its compact and additional modulation-free design. However, to compare favorably with active Q-switching and multi-stage amplification, the output energy needs to be enhanced for practical applications. Kramers Ytterbium ion (Yb³⁺)-doped borate crystals, with their excellent energy storage capacity, have been proven to be high-potential laser gain mediums for achieving pulsed lasers with moderate and high output energy using passive Q-switching technology. In this study, the growth, characterization, and laser generation of one Yb³⁺-doped borate crystal, the Yb³⁺:ScBO₃ crystal, are systematically reviewed. The continuous-wave and passive Q-switching laser characteristics are presented in detail, and the self-pulsations derived from intrinsic ground-state reabsorption are also demonstrated. The specific characteristics and experiments confirm the potential of the Yb³⁺:ScBO₃ crystal for future pulsed laser applications with moderate or even high energy output. Full article

(This article belongs to the Special Issue Optoelectronics for Lasers: Latest Advances and Prospects)

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Open AccessReview

Laser Transverse Modes with Ray-Wave Duality: A Review

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Appl. Sci. 2021, 11(19), 8913; https://doi.org/10.3390/app11198913 - 24 Sep 2021

Cited by 3 | Viewed by 1067

Abstract

We present a systematic overview on laser transverse modes with ray-wave duality. We start from the spectrum of eigenfrequencies in ideal spherical cavities to display the critical role of degeneracy for unifying the Hermite–Gaussian eigenmodes and planar geometric modes. We subsequently review the [...] Read more.

We present a systematic overview on laser transverse modes with ray-wave duality. We start from the spectrum of eigenfrequencies in ideal spherical cavities to display the critical role of degeneracy for unifying the Hermite–Gaussian eigenmodes and planar geometric modes. We subsequently review the wave representation for the elliptical modes that generally carry the orbital angular momentum. Next, we manifest the fine structures of eigenfrequencies in a spherical cavity with astigmatism to derive the wave-packet representation for Lissajous geometric modes. Finally, the damping effect on the formation of transverse modes is generally reviewed. The present overview is believed to provide important insights into the ray-wave correspondence in mesoscopic optics and laser physics. Full article

(This article belongs to the Special Issue Optoelectronics for Lasers: Latest Advances and Prospects)

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