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Lattice distortion and amorphization of carbon-doped SUS304 by variation of the laser output were investigated in terms of phase formation and the bonding state. The laser output was changed by 10% in the range of 60% to 100% after covering the SUS304 with carbon paste. A graphite peak and expanded austenite (S-phase) peak were observed in the carbon-doped SUS304, and Rietveld refinement was performed to identify the lattice distortion. The lattice constant of SUS304 was initially 3.612 Å, but expansion lattice distortion occurred in the carbon-doped SUS304 as a result of the S phase formation and carbon doping, and the lattice constant increased to 3.964 Å (100% laser output). X-ray photoelectron spectroscopy analysis for the bonding state of the carbon-doped SUS304 showed that the sp2/sp3 ratio decreased from 3.21 (70% laser output) to 2.52 (100% laser output). The residual stress in the lattice was accumulated due to carbon doping by high thermal energy, which resulted in the formation of amorphous carbon. The bonding environment was represented by the ID/IG ratio using Raman analysis, and it increased from 0.55 (70% laser output) to 1.68 (100% laser output). During microstructure analysis of the carbon-doped SUS304, disordered structures by amorphization were observed in the carbon-doped SUS304 by the greater than 90% laser output. The amorphous carbon filled the lattice grains or voids to lubricate the surface, which improved the friction coefficient and wear rate from 0.23 and 7.63 mm3(Nm)−110−6 to 0.09 and 1.43 mm3(Nm)−110−6, respectively.

Bidirectional output fiber laser oscillators can realize two high-power laser outputs employing only a single-laser resonant cavity and hold the advantages of being low cost and of compact size. However, like other fiber lasers, their power improvement is limited by transverse mode instability (TMI). To achieve higher power output, in this paper, the characteristics and corresponding suppression method of the TMI in bidirectional output fiber laser oscillators were investigated for the first time. Firstly, the TMI threshold was obtained when the fiber laser oscillator was pumped by 976 nm LDs and 981 nm LDs, separately, and the difference between the two pumping conditions was researched in detail. After that, a comparison study between the bidirectional and unidirectional output fiber laser oscillators pumped by 981 nm LDs was carried out. In the experiment, the effect of pump distribution on the TMI threshold was also considered. The results show that the TMI threshold of the bidirectional-output laser pumped by 981 nm LDs is much higher than that pump by 976 nm LDs, which means that the effective TMI suppression methods in the unidirectional output laser are also applicable in the bidirectional output laser. In addition, it is found that the TMI threshold of a bidirectional output fiber laser is much lower than that of a unidirectional output fiber laser.

Output power and beam quality are the two main bottlenecks for semiconductor lasers—the favourite light sources in countless applications because of their compactness, high efficiency and cheapness. Both limitations are due to the fact that it becomes increasingly harder to stabilize a single-mode laser over a broader chip area without multi-mode operations. Here we address this fundamental difficulty with the Dirac-vortex topological cavity1, which offers the optimal single-mode selection in two dimensions. Our topological-cavity surface-emitting laser (TCSEL) exhibits 10 W peak power, sub-1° divergence angle and 60 dB side-mode suppression, among the best-reported performance ever at 1,550 nm—the most important telecommunication and eye-safe wavelength where high-performance surface emitters have always been difficult to make2. We also demonstrate the multi-wavelength capability of two-dimensional TCSEL arrays that are not generally available for commercial lasers2,3. TCSEL, as a new-generation high-brightness surface emitter, can be directly extended to any other wavelength range and is promising for an extremely wide variety of uses.Researchers demonstrate a topological-cavity surface-emitting laser with a 10 W peak power and sub-degree beam divergence at 1,550 nm wavelength. The system is also capable of multiple-wavelength arrays.

In this paper, spatiotemporal dynamics of broad-area lasers with external optical injection is investigated. We demonstrate theoretically that relatively small optical injection suppresses unstable transverse modes and stabilizes laser output. In this paper, the general case of a mismatch in the frequency of the radiation injected and generated by a laser was numerically investigated. It is shown that the frequency mismatch does not destroy the stabilizing effect.

Today, in the face of ever increasing communication traffic, minimizing power consumption in data communication systems has become a challenge. Direct modulation of lasers, a technique as old as lasers themselves, is known for its high energy efficiency and low cost. However, the modulation bandwidth of directly modulated lasers has fallen behind those of external modulators. In this Article, we report wide bandwidths of 65–75 GHz for three directly modulated laser design implementations, by exploiting three bandwidth enhancement effects: detuned loading, photon–photon resonance and in-cavity frequency modulation–amplitude modulation conversion. Substantial reduction of chirp (α < 1.0) as well as isolator-free operation under a reflection of up to 40% are also realized. A fast data transmission of 294.7 Gb s−1 over 15 km of a standard single-mode fibre in the O-band is demonstrated. This was achieved without an optical fibre amplifier due to a high laser output power of 13.6 dBm.Directly modulated semiconductor lasers are shown to be able to operate with bandwidths exceeding 65 GHz thanks to a cavity design that harnesses photon–photon resonances.

Aiming at the problems existing in traditional neodymium-doped yttrium aluminum garnet (Nd: YAG) laser crystals, such as concentration quenching effect, significant thermal effect, insufficient radiation resistance, and limited optical uniformity, the design of doped gradient concentration and doping design was carried out. Nd: YAG laser crystals with different gradient concentrations and Cr-doped Nd: YAG crystals were successfully prepared using the Czochralski method. Their laser output characteristics and performance under high-energy radiation were systematically studied. These research findings provide new gain medium growth technologies for high-energy radiation environments in outer space, holding significant scientific research value and engineering application prospects.

We investigated a dual-wavelength twin-pulse laser with tunable intensity ratio and pulse interval, pumped by an 808 nm laser diode (LD), using Nd: GdVO₄ and Nd: YVO₄ as laser gain media, in conjunction with a Cr⁴⁺:YAG saturable absorber. A new theoretical model of a dual-wavelength twin-pulse laser based on intracavity gain-switched pumping has been established. The findings of the simulation show that it is possible to accomplish dual-wavelength twin-pulse laser output without gain competition. Moreover, the simulation underscores the capability to fine-tune the intensity ratio and the pulse interval between the two wavelengths. In the experiment, theoretical modeling served as a guide for key parameter settings. Ultimately, dual-wavelength twin-pulse laser outputs at 912 nm & 1064 nm were achieved, with a tunable intensity ratio ranging from 0.8 to 1.4 and an adjustable pulse interval from 18 to 6 ns. The experimental results aligned closely with the simulation outcomes.

The temperature dependence of the laser output properties of the Fe:ZnSe single crystal was compared under its excitation by 2.94 μm Q-switched Er:YAG laser radiation and by ∼4.04 μm gain-switched second Fe:ZnSe laser radiation within the same semi-longitudinal configuration. A non-selective laser cavity consisted of a flat highly reflective mirror at ∼4–5 μm and a concave (r = 200 mm) output coupler with a reflectivity of 88% at ∼3.9-5.3 μm. To keep the energy at both excitation wavelengths the same of ∼9.4 mJ, a special filters were used for attenuation of 2.94 μm radiation. The output energy almost doubled since the angle between pumping and generated laser radiation was reduced from ∼20∘ to ∼12∘. The generated laser oscillation wavelength was shifted by ∼100 nm in the case of ∼4.04 μm compared to excitation by 2.94 μm radiation. The maximum laser output energy of ∼1.7 mJ under 2.94 μm excitation was obtained at 78 K. However, at ∼4.04 μm pumping, the maximum of ∼0.5 mJ was obtained at 260 K. The efficiency at 2.94 μm excitation decreased from ∼33% at 78 K to ∼12% at 340 K. At ∼4.04 μm radiation excitation, the efficiency increased from the laser threshold at 120 K to its maximum of ∼9% at 260 K.

Today’s narrowest linewidth lasers are limited by mirror motion in the reference optical resonator used to stabilize the laser’s frequency. Recent proposals suggest that superradiant lasers based on narrow dipole-forbidden transitions in cold alkaline earth atoms could offer a way around this limitation. Such lasers operating on transitions with linewidth of order mHz are predicted to achieve output spectra orders of magnitude narrower than any currently existing laser. As a step towards this goal, we demonstrate and study a laser based on the 7.5-kHz linewidth dipole-forbidden P13 to S01 transition in laser-cooled and tightly confined Sr88 . We can operate this laser in the bad-cavity or superradiant regime, where coherence is primarily stored in the atoms, or continuously tune to the more conventional good-cavity regime, where coherence is primarily stored in the light field. We show that the cold-atom gain medium can be repumped to achieve quasi-steady-state lasing. We also demonstrate up to an order of magnitude suppression in the sensitivity of laser frequency to changes in cavity length, verifying a key feature of the proposed narrow linewidth lasers.

To obtain single-longitudinal-mode (SLM) laser output under high power injection conditions, a theoretical model of multi-mode rate equation based on pre-laser Q-switched and a Fabry–Perot (F-P) etalon group is established in this research. The simulation results show that with the combination of three F-P etalons, not only can the spectral linewidth be initially narrowed, but the transmission loss difference between adjacent longitudinal modes can also be further adjusted. Therefore, the longitudinal mode selection ability of the pre-laser Q-switch under high-power energy injection is effectively enhanced. In the experiment, dynamic modeling is used as a key parameter guide. The final stable output 639.7 nm Pr:YLF SLM laser was obtained. The upper limit of pump absorption was effectively increased by 57%, the single pulse energy was increased by 56%, and the linewidth was compressed to 14 MHz. The experimental results are in good agreement with the simulation results.