grown as the white laser gains [12][13][14][15] and some approaches have been developed for constructing the prerequisite optical feedback "cavity" with the goal of simultaneous RGB or RYGB lasing. [10,11,13,14] However, constrained by the compactness, difficulty in growth or wavelength control, or the environment friendly, the white lasers are still underdeveloped, and the available materials and approaches are still being extensively sought.In recent years, an emerging family of 2D nanomaterials, group of early transition metal carbides and/or carbonitrides labeled MXenes, was developed by selectively etching MAX phases, [16,17] where M represents an early transition metal, A denotes a main group of 3 or 4 elements, and X is either carbon or nitrogen. They have exhibited super chemical, physical, and environmental properties distinguishing from traditional 2D materials, e.g., they possess hydrophilic surface with metallic conductivity, excellent chemical stability, superior electrical conductivity, environmentally friendly characteristics, etc. [18][19][20][21][22] Unfortunately, their intrinsic photoluminescence response is low, which limits their optical and even further biological applications. The formation of quantum dots (QDs) would generally enhance their photoluminescence by means of the quantum confinement and edge effects, which has been recently experimentally realized in Ti 3 C 2 MXene QDs with the wavelength range from about 350 nm (violet) to 600 nm (orange-red). [23,24] Therefore, it can be believed that the 2D MXenes should be excellent white laser gain medium if the gain can be further enhanced especially in the red range and a broadband optical feedback "cavity" can be constructed. Associated with the theory of a finite atomic system, the sensitivity of the electronic states density of the QDs, corresponding to their photoluminescence, is dependent on their sizes due to the Coulomb blockade effect, [25][26][27] which indicated that the MXene quantum systems with fewer atom layers structure should be more susceptible to the same external passivation and should have better passivation effect than those MXenes with more atom layers structure. For MXene materials, their unique structural characteristics determine that they have at least three-atom layered structure, which indicates that the V 2 C MQDs with fewest atom layers should possess enhanced and broadened photoluminescence after passivation. Considering the optical feedback, effective Multicolor photoluminescence over the full visible color spectrum is critical in many modern science and techniques, such as full-color lighting, displays, biological and chemical monitoring, multiband communication, etc., but the ultimate white lasing especially on the nanoscale is still a challenge due to its exacting requirements in the balance of the gain and optical feedback at different wavelengths. Recently, 2D transition metal carbides (MXenes) have emerged, with some superior chemical, physical, and environmental properties distinguishing them from tr...

The mid-infrared spectral range extending from 2 to 6 μm is significant for scientific and technological applications. A promising nonlinear oxide crystal La₃Ga_5.5Nb_0.5O₁₄ (LGN) is proposed and fully characterized for the first time to our knowledge. The transparency range extends between 0.28 and 7.4 μm. The two principal refractive indices were measured and we found that the nonlinear coefficient d11 = 3.0 ± 0.1 pm/V at 0.532 μm. The simultaneous fit of data allowed us to refine the Sellmeier equations of LGN and to calculate the tuning curves for optical parametric generation (OPG) pumped at 1.064 μm. Calculations are consistent with recorded data and also show the generation of a supercontinuum between 1.5 and 3.5 μm when pumped at 0.98 μm by a Ti:Sapphire laser.

Visible light has an important and unique value in research and practical applications, because of its perceptible characteristics by the human eye. Directly pumped bulk visible pulsed lasers are booming in recent years stimulated by the advances of blue laser diodes. As critical components, novel and favorable saturable absorbers in view of distinct nonlinear saturable absorption properties are desired, which can promote the development of ultrafast photonics in the visible range. Over the years, low dimensional materials with the advantages of ultrafast carrier recovery rate and distinct nonlinear saturable absorption have originated a class of innovative applications in photonics and optoelectronics, especially as saturable absorbers in the pulsed lasers. Here, the low dimensional saturable absorbers in the visible range are reviewed, including the fabrication, linear and nonlinear optical response, and applications in the pulsed visible lasers of low dimensional semiconductors and noble metal nanoparticles. The design criteria of the low dimensional saturable absorbers for generating laser pluse by Q‐switching and mode‐locking are proposed and discussed. Finally, some possible development tendency and directions of saturable absorbers for the visible pulsed lasers are proposed in this review by focusing on some potential strengths.

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Sesquioxide crystals were identified as promising gain media for high-power ultrafast lasers, and the broadening of their fluorescence spectra could shorten the achievable laser pulses, corresponding to the enhancement of the peak powers. In this study, we demonstrate the broadening of the fluorescence spectra of the sesquioxides with the electron−phonon coupling effect and ligand engineering associated with the advantages of the Lu 2 O 3 host in the phonon energy and insensitivity to doping concentrations. The Yb:Lu x Y 2−x O 3 (0 ≤ x ≤ 2) sesquioxide crystals were grown and characterized. The introduction of Y 3+ ions broadens the fluorescence spectra by approximately two times those of Yb:Lu 2 O 3 , which could be attributed to the strong electron−phonon coupling effect and octahedral distortion. This work would provide a series of novel laser materials for high-power ultrafast lasers and pave a new route for designing functional materials aimed at the enhancement of the given performance.