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The exploitation of multicomponent nanocomposites with suitable hierarchical heterostructures is an attractive strategy to obtain high performance microwave absorption materials. In this work, a versatile strategy is proposed for synthesizing 1D hierarchical core-shell structure with Co-ZIF arrays derived carbon nanotubes (CNTs) coupled on cotton fiber (CF)-supported MXene shell (Co/CNTs-MXene@CF). The advantages of Co-ZIF arrays derived CNTs and MXene dielectric layer can be efficiently integrated to realize multiple electron transfer paths by the construction of the well-designed hierarchical structure. The designed heterogeneous composites consist of the interlayer MXene and CNTs grow sequentially from the outermost Co-ZIF nanosheet arrays with appropriate conductivity and abundant heterointerfaces, which can improve the conduction loss and interfacial polarization response. As expected, the elaborate 1D Co/CNTs-MXene@CF heterostructures exhibit the optimal reflection loss of −61.41 dB at 2.52 mm and effective absorption bandwidth reaches 5.04 GHz with a thickness of only 1.5 mm. The experimental results demonstrate that the optimized structure dramatically improves the electromagnetic wave attenuation behavior. This work illuminates a new design strategy for the preparation of multicomponent composites with reasonable hierarchical structure that enables high-performance microwave absorption materials.

Low-loss depressed cladding waveguide architecture is highly attractive for improving the laser performance of waveguide lasers. We report on the design and fabrication of the “ear-like” waveguide structures formed by a set of parallel tracks in neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal via femtosecond laser writing. The obtained “ear-like” waveguides are with more symmetric mode profiles and lower losses by systematically comparing the guiding properties of two kinds of normal cladding waveguide. Efficient waveguide lasers are realized based on the designed structure in both continuous wave and pulsed regimes. Combined the high-gain from cladding waveguide and special “ear-like” structure, a passively fundamentally Q-switched laser with the narrow pulse width and the high repetition rate has been obtained by using tin diselenide (SnSe2) as saturable absorber., National Natural Science Foundation of China (12074223, 61775120); China Postdoctoral Science Foundation (2020M682155); Qilu Young Scholar Program; Taishan Scholar Foundation of Shandong Province; Consejería de Educación, Junta de Castilla y León (SA287P18, SA136P20); Ministerio de Economía y Competitividad (FIS2017-87970R).

Room-temperature pulsed and continuous-wave (cw) operation of a tunable external cavity (EC) quantum cascade laser (QCL) at an emitting wavelength of $$4.7\,\upmu \hbox {m}$$ was presented. The effect of different external cavity lengths and grating angles of the EC–QCL system were analyzed numerically. A wide tuning range greater than $$131\,\hbox {cm}^{-1}$$ was obtained in pulsed mode at room temperature. Without the anti-reflection coating procedure, single-mode cw operation with a side-mode suppression ratio (SMSR) above 20 dB and a wide tuning range greater than $$116\, \hbox {cm}^{-1}$$ were achieved. Near the center region, SMSR about 30 dB was also realized through designing the external cavity length. Strain-compensation combined with two-phonon resonance in an active region design and the high-reflection coating promised low threshold current density. A record low threshold current density of $$0.901\,\hbox {kA/cm}^{2}$$ for an EC–QCL operated in cw mode was realized.

A passively Q-switched and mode-locked Nd:LuVO4 laser with V:YAG at 1.34 μm was successfully demonstrated. Comparisons between c-cut and a-cut Nd:LuVO4 lasers were experimentally made. The maximum average output power of 170 mW, the highest Q-switched pulse energy of 4.5 μJ were obtained in c-cut Nd:LuVO4 laser. The duration of mode-locked pulse was estimated to be less than 540 ps with repetition rate of 110 MHz.

A novel nonlinear frequency conversion process was demonstrated to realize the synchronized dual-wavelength emissions at 1534 and 1572 nm by the mixed optical parametric oscillation (OPO) conversion in gray-tracking-resistance KTP (GTR-KTP) and KTA crystals. Both the two crystals were inserted into the diode-pumped Nd:YAG/Cr4+:YAG fundamental resonator, with their Y axes perpendicular to each other. This could eliminate the competition of the two OPO processes in fundamental radiation. Furthermore, the ratio between the length of GTR-KTP and KTA has also been specially designed to satisfy the same OPO thresholds. The synchronized dual-wavelength lasing with the power ratio of 1:1 between 1534 and 1572 nm was successfully realized. At an incident LD pump power of 7 W, the maximum total output power of 460 mW was achieved, with the corresponding pulse width and repetition rate measured to be 3.9 ns and 5.5 kHz, respectively. This mixed conversion opens a new door for the multi-wavelength lasing.

This paper reported a broadband tuning intracavity optical parametric oscillator (IOPO), based on the multiple grating periodical poled lithium niobate (PPLN) pumped by a acoustic-optical (AO) Q-switched Nd:YVO4 laser. The widely tunable OPO output signal wavelength range from 1390 to 1605 nm, which was obtained by changing PPLN poling period from 27.8 to 31.6 μm at a certain temperature of 46°C, while the continuous tuning range was measured from 1475 to 1592 nm with the PPLN poling period of 30 μm by varying the temperature of nonlinear crystal PPLN from 50 to 120°C. The maximum output power of 0.92 W at 1534 nm with the minimum pulse width of 5.17 ns was generated under the incident pump power of 9.6 W at 808 nm. The corresponding peak power and single pulse energy were calculated to be 5.94 kW and 30.7 μJ, respectively. The M2-factor was measured to be 2.01 at the signal power of 0.4 W.

The efficient dual-wavelength oscillation at 1064 and 1342 nm in the passively Q-switched laser based on Nd:YVO4/V3+:YAG is successfully obtained, as demonstrated in this paper. A total average output power of 2.2 W is obtained with 1.3 W for 1064 nm and 0.9 W for 1342 nm under the incident pump power of 7.7 W, corresponding to a total optical-optical conversion efficiency of 28.2%. The pulse widths are 58 and 54 ns for 1064 and 1342 nm, respectively, with the repetition rate of 89 kHz. Moreover, a rate equation model considering the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density is presented to characterize the dual-wavelength passive Q-switching operation.

We report a passively mode-locked Yb:Y2Ca3(BO3)4 (Yb:CYB) laser with a partially reflective semiconductor saturable-absorber mirror. The minimum pulse duration of 244-fs with a repetition rate of ~ 55 MHz has been obtained at the central wavelength of 1044.7 nm (8.1 nm full width at half maximum (FWHM)). The measured average output power amounts to 261 mW under the absorbed pump power of 7.0 W. To our best knowledge, this is the first demonstration of a femtosecond Yb:CYB laser.

A simultaneous dual-wavelength eye-safe laser at around 1.9 and 1.7 μm based on only a single KTiOAsO4 (KTA) intracavity optical parametric oscillator (IOPO) is firstly reported. The dual-wavelength-IOPO is driven by an acousto-optic (AO) Q-switched Nd:YAG laser, which is simultaneously oscillated at the radiations of 1.3 and 1.06 μm. Within the KTA-IOPO cavity, the signal output waves of IOPO at the wavelength of 1.9 and 1.7 μm are pumped by the 1.3 and 1.06 μm radiations from Nd:YAG laser, respectively. With the laser diode pumped power of 100 W and the pulse repetition rate of 4 kHz, the maximum average output power of 1.3 W at 1895 nm with the pulse duration of 30 ns and that of 0.9 W at 1715 nm with the pulse duration of 18 ns are obtained. With different diode pump power, the central wavelength of IOPO signal light at 1.9 μm is tunable from 1850 to 1895 nm, while the other signal wave at 1.7 μm is from 1650 to 1715 nm.

The character of a diode-pumped passively Q-switched Nd:GdVO4/V3+:YAG 912 nm laser was demonstrated for the first time to our knowledge. With an absorbed pump power of 7.4 W, an average output power of 360 mW with a Q-switched pulse width of 328 ns at a pulse repetition rate of 163 kHz was obtained. The Q-switching efficiency was found to be 32.7%. Our work further indicated V3+:YAG could be an effective fast passive Q-switch for 0.9 μm radiation.

We report on the generation of continuous wave lasers at a wavelength of ∼1064 nm in a Nd:YAG ceramic waveguide at room temperature. The waveguide was fabricated by using 6 MeV carbon ion implantation at a fluence of 3×1014 ions/cm2. Laser operation has been realized with a slope efficiency as high as ∼11%. The pump threshold of an 808-nm laser beam for the waveguide laser oscillation is 19.5 mW.

The continuous wave (CW) and passively Q-switched Nd:Gd3AlxGa5-xO12 (Nd:GAGG) laser operation at 938 nm have been realized for the first time. The maximum CW output power of 0.44 W was obtained under the absorbed pump power of 8.54 W, corresponding to the slope efficiency of 7.8% and optical-to-optical efficiency of 5.2% respectively. A V3+:YAG saturable absorber crystal with the initial transmission of 97% was used for the passive Q-switching regime. The maximum average output power of 0.19 W was achieved with the minimum pulse width of 358 ns and Q-switched repetition rate of 116 kHz. The corresponding single pulse energy and pulse peak power were determined to be 1.6 μJ and 4.6 W, respectively.

A diode-pumped passively Q-switched Nd:LuVO4 1.34 μm laser using Co:LMA saturable absorber was successfully demonstrated. The average output power, pulse width, repetition rate of a-cut and c-cut Nd:LuVO4 lasers were studied with different output couplers. The maximum average output power of 164 mW was obtained at the pump power of 10.3 W and the narrowest pulse width of 168 ns was achieved at repetition rate of 457 kHz under pump power of 8.59 W in a-cut Nd:LuVO4 laser with T = 8%.

A simple and compact diode-pumped acousto-optically Q-switched intracavity frequency-doubled Nd:LuVO4/KTP green laser were demonstrated successfully for the first time. At an incident pump power of 6.5 W, an average output power of 663 mW, a pulse width of 26 ns were obtained with a PRF of 10 kHz. The pulse energy and peak power of the green light were determined to be 66.3 μJ and 2.55 kW, respectively.

We report an intracavity optical parametric oscillator at 1.57 μm based on non-critically nonlinear crystal KTP driven by an end-pumped acousto-optically Q-switched Nd:LuVO4 crystal. The output characteristics of 1.57 μm were studied with different pulse repetition frequency. The pulse width of 5ns, the maximum peak power and pulse energy of 4.8 kW and 24 μJ were obtained, respectively, with pulse repetition frequency of 5 kHz. The compression ration of pulse width was six times for 1.06 μm to 1.57 μm.

The performance of a diode-end-pumped cont- inuous wave (CW) and passively Q-switched Nd:(Lu0.1Gd0.9)3Ga5O12 (Nd:LGGG) laser at 1330 nm were realized for the first time. The maximum CW output power of 0.93 W was obtained under the absorbed pump power of 11 W, corresponding to the slope efficiency of 10.4. By using V3+:YAG crystal as an absorber for passively Q-switching operation, the maximum average output power of 167 mW was generated with the minimum pulsewidth of 15.6 ns and the maximum repetition rate of 10 kHz. The corresponding signal pulse energy and pulse peak power were calculated to be 16.7 μJ and 1.1 kW, respectively.

It has been demonstrated that shared cavity optical parametric oscillator (OPO) could improve power stability in comparison with that of coupled cavity OPO. By theoretically calculating the spectral transmissions induced by the etalon effect, it has been found that the shared cavity OPO had much wider transmission bandwidth than that of coupled OPO. The corresponding experimental results agreed with the theoretical analysis. Furthermore, the OPO and fundamental laser resonator have nearly the same longitudinal mode spacing in the shared cavity configuration. The above two factors can account for the improved performance of the shared OPO operation.

We demonstrated the 1.33 microm laser performance with Nd:Gd(3)Al(x)Ga(5-x)O(12) (x = 0.94) (Nd:GAGG) laser crystals for the first time. Continuous-wave (cw) output power of 2.45 W was obtained with the optical-optical conversion efficiency of 21.8% and slope efficiency of 23.3%. In the passive Q-switching regime, the highest output power, the shortest pulse width, largest pulse energy and highest peak power were achieved to be 326 mW 18.2 ns, 36.3 microJ and 2.0 kW, respectively, with V(3+):YAG crystal as the saturable absorber.

We report a diode-pumped passively Q-switched Nd:LuVO4 laserat 1.34 microm using V3+:YAG as saturable absorber. The characteristics of a-cut and c-cut Nd:LuVO4 passive Q-switching operation were studied. The average output power of 1.02 W was obtained under the pump power of 12.88 W, corresponding to the optical conversion efficiency of 8% and slope efficiency of 10% in c-cut Nd:LuVO4 laser. The maximum pulse energy of 17.6 microJ and the highest peak power of 820 W were obtained at pulse width of 21 ns and pulse repetition rate of 22.4 kHz in a-cut Nd:LuVO4 laser.

A high-gain optical waveguide amplifier has been realized in a channel waveguide platform of Nd:YAG ceramic produced by swift carbon ion irradiation with metal masking. The waveguide is single mode at wavelength of 810 and 1064 nm, and with the enhanced fluorescence intensity at around 1064 nm due to the Nd(3+) ion emissions. In conjunction with the low propagation loss of the waveguide, about 26.3 dB/cm of the small signal gain at 1064 nm is achieved with an 18 ns pulse laser as the seeder under the 810-nm laser excitation. This work suggests the carbon ion irradiated Nd:YAG waveguides could serve as efficient integrated amplifiers for the signal amplification.

Continuous-wave operation of a distributed-feedback quantum cascade laser emitting at around 4.6 µm grown by solid source molecular beam epitaxy combined with metal organic vapour phase epitaxy is presented. These devices display an ultra-low threshold current density of 0.85 kA/cm2 at 30 °C. The low threshold characteristics resulted in continuous-wave operating temperature up to 100 °C for thermoelectrically cooled devices and room-temperature continuous-wave output power in excess of 8.5 mW for uncooled devices.

The singlemode operation of a distributed feedback terahertz quantum cascade laser with complex-coupled metallic relief gratings emitting at 3.09 THz (λ=97.07 µm) is reported. The side-mode suppression ratio is about 20 dB at all operating temperatures. The highest working temperature of up to 88 K is obtained, with the optical power of 10 mW at 10 K and 1 mW at 88 K.

A tapered distributed feedback quantum cascade laser emitting at lambda similar to 8.1 mu m is reported. utilising a tapered waveguide structure with a surface metal grating, the device exhibited singlemode operation over the temperature range of 100 to 214 k, with sidemode suppression ratio > 20 db and a nearly diffraction limited far-field beam divergence angle of 5.4 degrees.

Electrically pumped, edge-emitting, singlemode operation of a two-dimensional photonic crystal distributed feedback (PCDFB) quantum cascade laser emitting at similar to 7.8 mu m is demonstrated. The two-beam holographic technique combined with wet-etching process is successfully used to de. ne a square-lattice PCDFB structure on the top grating layer of the laser. This simple PC fabrication method may open exciting opportunities for the wide application of PCDFB lasers.

A sample grating distributed feedback quantum cascade laser array aim at broad tunability and enhanced side mode suppression ratios is presented. Utilizing a sample grating dependence on emission wavelength and epitaxial side down bonding technique, the array of laser ridges exhibited three separated single mode emissions centered at 4.760, 4.721, and 4.711 μm respectively, in continuous wave at room temperature. Side mode suppression ratios of >35 dB and continuous wave output powers of >10 mW per laser ridge were obtained.