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We demonstrate in a numerical manner the intriguing localization-to-delocalization transition of light in frequency-tuned photonic moiré lattices, both in the zero-order and the higher-order regimes of light waves. We present a different technique to realize the composite photonic lattices, by means of two relatively twisted sublattices with different modulated lattice constants. Even though various kinds of photonic patterns including the commensurable and the incommensurable lattices can be well constructed, the observed transition between the localization and the delocalization of light field is moiré angle-independent. This angle-insensitive property was not reported before, and cannot be achieved by those photonic moiré lattices that are all moiré angle-dependent. We reveal that the obtained phase transition of light is robust to the changes of refractive index modulation of the photonic lattices. Moreover, we reveal that the effect of moiré angle-independent transition of light can be extended to the higher-order vortex light field, hence allowing prediction, for the first time to our knowledge, of both the localization and the delocalization of the vortex light field in the photonic lattices.

We demonstrated an eye-safe diamond Raman laser intra-cavity pumped by the 1.3 μm fundamental field for the first time, to the best of our knowledge. The first-Stokes laser at 1634 nm was converted from the 1342 nm fundamental laser, which was produced by an in-band pumped double-end diffusion-bonded a-cut Nd:YVO4 crystal. Under an incident pump power of 21.2 W and an optimal pulse repetition frequency of 25 kHz, the maximum average output power of 2.0 W was obtained with the pulse duration of 5.7 ns and the peak power of 14 kW. The first-Stokes emission was found to be near diffraction limited (M2 ≈ 1.3) and to have a narrow linewidth (∼0.05 nm FWHM; instrument limited).

This paper presents a cross dipole antenna for the fifth generation (5G) sub-6 GHz dual-band applications. The proposed antenna mainly consists of eight copper radiating patches, eight parasitic patches, and a reflector. The proposed antenna can achieve a ±45° polarization characteristic. The overlapped bandwidth is 2.77-5.31GHz, and the corresponding gain varies from 7.6 to 8.4 dBi. The gain increases with increasing operating frequency. Besides, the cross polarization level is less than -28 dB while the port isolation is larger than 26 dB.

We present the first demonstration of an actively Q-switched orthogonally polarized dual-wavelength Nd:YLF/YVO4 Raman laser to our knowledge. The gain competition of the orthogonally polarized dual-wavelength fundamental laser at 1047 and 1053 nm was ultimately avoided by incorporating two Nd:YLF crystals into two laser resonators. By adjusting the gain or loss difference of two resonators, the pulse synchronization of the orthogonally polarized dual-wavelength Raman laser was realized. Benefitting from the efficient thermal stress and energy-transfer upconversion management of Nd:YLF crystal, a maximum dual-wavelength Raman output power of 4.5 W was obtained with M 2 < 1.8, which contained a 2.5 W Raman component at 1155 nm and a 2.0 W Raman component at 1162 nm, under the incident pump power of 46.1 W and pulse repetition frequency of 5 kHz. The corresponding peak powers were as high as 178.6 and 142.9 kW, respectively. As far as we know, we have increased the orthogonally polarized dual-wavelength Raman average output power by six times.

We demonstrated a deep-red laser source by intracavity frequency-doubled crystalline Raman laser for the first time, to the best of our knowledge. The actively Q -switched 1314 nm N d : L i Y F 4 laser was first converted to the eye-safe Raman laser using a K G d ( W O 4 ) 2 (KGW) crystal, which was subsequently frequency-doubled in a bismuth borate crystal. Benefiting from the KGW bi-axial properties, the deep-red laser source was able to lase separately at two different spectral lines at 730 and 745 nm. Under an optimal repetition rate of 4 kHz, the maximum average powers of 1.7 and 2.0 W were attained with good beam quality of M 2 ≈ 1.7 . The corresponding pulse durations were determined to be 3.0 and 2.8 ns with the peak powers up to approximately 140 and 180 kW, respectively.

Optical superoscillation refers to an intriguing phenomenon of a wave packet that can oscillate locally faster than its highest Fourier component, which potentially produces an extremely localized wave in the far field. It provides an alternative way to overcome the diffraction limit, hence improving the resolution of an optical microscopy system. However, the optical superoscillatory waves are inevitably accompanied by strong side lobes, which limits their fields of view and, hence, potential applications. Here, we report both experimentally and theoretically a new superoscillatory wave form, which not only produces significant feature size down to deep subwavelength, but also completely eliminates side lobes in a particular dimension. We demonstrate a new mechanism for achieving such a wave form based on a pair of moonlike sharp-edge apertures. The resultant superoscillatory wave exhibits Bessel-like forms, hence allowing long-distance propagation of subwavelength structures. The result facilitates the study of optical superoscillation and on a fundamental level eliminates the compromise between the superoscillatory feature size and the field of view.

The electronic state and nonlinear optical properties in the Y-shaped quantum dots has been theoretically investigated by adjusting the shape with the applied electric field. Within the effective-mass approximation, the energy levels and the wave functions of the system are obtained by means of the finite difference method. The results show that both the strength or the in-plane orientation of external electric field and the shape of regulable Y-shaped quantum dots have a significant influence on the electronic state, optical absorption coefficients and the refractive index changes.

The vector vortex light beam, which exhibits a space-variant polarization state and is coupled with orbital angular momentum of light, has been drawing much attention due to its fundamental interest and potential applications in a wide range. Here we reveal both theoretically and experimentally that a diffractive structure having cylindrical symmetry is shown to be transparent for the vector vortex state of light with arbitrary topology. We demonstrate such an intriguing phenomenon in the Fresnel diffraction condition, where the vector Helmholtz wave equation can be utilized in the paraxial regime. Our demonstration has implications in control and manipulation of vector vortex light beams in diffractive optics, and hence, it may find potential applications.

Due to the air holes in cladding, it is difficult to process for end faces of ytterbium-doped double-cladding microstructured optical fibers. In this paper, we demonstrate the fabricating method of microlenses on ytterbium-doped double-cladding microstructured optical fibers with a CO2 laser to enhance the coupling efficiency. The theoretical and experimental investigation is carried out to study the effect of minor axis semidiameter and major axis semidiameter of ellipsoidal microlenses on coupling efficiency. The coupling efficiency is up to 88%, which is 14.6% higher than that of the perpendicular flat-end microstructured optical fiber using a free space optical path. These results suggest that the proposed end face processing on microstructured optical fibers provides a straightforward solution for the production of microlenses for laser coupling applications in high-power fiber lasers.

An actively Q-switched eye-safe orthogonally-polarized dual-wavelength intracavity Raman laser was demonstrated for the first time, to the best of our knowledge. The gain balanced dual-wavelength operation at 1314 and 1321 nm within an in-band pumped Nd:YLF laser was realized by slightly titling the cavity mirrors. Owing to the KGW bi-axial properties, two sets of simultaneous orthogonally-polarized dual-wavelength Raman lasers at 1470, 1490 nm and 1461, 1499 nm were achieved by simply rotating the KGW crystal for 90°, respectively. With an incident pump power of 30 W and an optimized pulse repetition frequency of 5 kHz, the maximum dual-wavelength Raman output powers of 2.6 and 2.4 W were obtained with the pulse widths of 5.8 and 6.3 ns, respectively, corresponding to the peak powers up to 89.7 and 76.5 kW.

While there has been various kinds of patterned structures proposed for wave focusing, these patterned structures usually involve complicated lithographic techniques since the element size of the patterned structures should be precisely controlled in microscale or even nanoscale. Here we propose a new and straightforward method for focusing an optical plane wave in free space with a rotationally symmetric sharp-edge aperture. The focusing phenomenon of wave is realized by superposition of a portion of the higher-order symmetric plane waves generated from the sharp edges of the apertures, in contrast to previously focusing techniques which usually depend on a curved phase. We demonstrate both experimentally and theoretically the focusing effect with a series of apertures having different rotational symmetry, and find that the intensity of the hotspots could be controlled by the symmetric strength of the sharp-edge apertures. The presented results would advance the conventional wisdom that light would diffract in all directions and become expanding when it propagates through an aperture. The proposed method is easy to be processed, and might open potential applications in interferometry, image, and superresolution.

We demonstrate a novel theoretical platform to realize geometric control of vector vortex states in an optical coupling system. These complex states are characterized by spatially varying polarizations and coupled with vortex phase profiles. It can be mapped uniquely as a point on a higher-order Poincaré sphere. The geometric theory clearly reveals how a tailored phase mismatch profile, together with a suitable coupling, supports state conversion between these higher-order complex light fields, in analogous to the processes appearing in two-level quantum system as well as three-wave mixing process in nonlinear optics. Specifically, in the phase matching condition, it is shown that these complex states carried by an envelope field exhibit periodic oscillations in the course of state evolution; whereas in the phase mismatching condition the oscillations become detuned, leading to noncyclic state evolution. Intriguingly, when using an adiabatic technique for the phase mismatch, robust state conversion between two arbitrary vector vortex light fields can be realized. Our demonstrations provide a fully control over the vector vortex states on the sphere, and we suggest that it would benefit various potential applications both in the classical and the quantum optics.

A novel mid-infrared (MIR) laser crystal C o / E r : P b F 2 was successfully grown. The use of E r 3 + ion co-doping to sensitize a C o 2 + ion and enhance the 2.1–4.2 µm broadband MIR emission of the C o 2 + ion in a P b F 2 crystal was studied for the first time, to the best of our knowledge. The E r 3 + ion was demonstrated to be an effective sensitizer of the C o 2 + ion, making the C o / E r : P b F 2 crystal propitious to be pumped by commercialized laser diodes. Furthermore, with E r 3 + ion co-doping, the local symmetry of C o 2 + and E r 3 + ions was seriously distorted, thereby enhancing the 2.1–4.2 µm MIR emissions. This study provides a path for designing MIR laser materials with optimal performance.

Single crystal of Ho3+/Yb3+ co-doped PbF2 has been grown successfully by the conventional technique modified Bridgman method. The spectral parameters of Ho3+ were calculated based on the Judd-Ofelt theory. The transition probabilities, radiative lifetime, and branching ratios were also estimated in detail by the J-O parameters obtained. The 2 μm emission characteristic and fluorescence lifetime of the 5 I 7 manifold upon excitation of a conventional 970 nm laser diode were measured and investigated. Fuchtbauer-Ladenburg theory was applied to calculate the absorption, emission, and gain cross sections of 5 I 7 → 5 I 8 transition. Based on examination of spectroscopic parameters evaluated, we suggest Ho3+/Yb3+ co-doped PbF2 crystal is a promising candidate for efficient 2 μm laser.

A transparent Tm:Lu3Al5O12 ceramic is fabricated by solid-state reactive sintering at 1830 °C for 30 h using commercial α-Al2O3 and Lu2O3/Tm2O3 powders and sintering aids - MgO and TEOS. The ceramic belongs to the cubic system and exhibits a close-packed structure (mean grain size: 21 µm). The in-line transmission at ∼1 µm is 82.6%, close to the theoretical limit. The spectroscopic properties of the ceramic are studied in detail. The maximum stimulated-emission cross-section is 2.37×10−21 cm2 at 1749nm and the radiative lifetime of the 3F4 state is about 10 ms. The modified Judd-Ofelt theory accounting for configuration interaction is applied to determine the transition probabilities of Tm3+, yielding the intensity parameters Ω2 = 2.507, Ω4 = 1.236, Ω6 = 1.340 [10−20 cm2] and α = 0.196×10−4 cm. The effect of excited configurations on lower-lying interconnected states with the same J quantum number is discussed. First laser operation is achieved under diode-pumping at 792 nm. A 4 at.% Tm:Lu3Al5O12 ceramic laser generated 3.12 W at 2022-2035nm with a slope efficiency of 60.2%. The ceramic is promising for multi-watt lasers at >2 µm.

Monoclinic (wolframite-type) monotungstate crystals are promising for rare-earth doping. We report polarized room- and low-temperature spectroscopy and efficient high-power laser operation of such a Y b 3 + : M g W O 4 crystal featuring high stimulated emission cross section ( σ S E = 6 . 2 × 10 − 20 c m 2 at 1056.7 nm for light polarization E | | N m ), large Stark splitting of the ground state ( 765 c m − 1 ), large gain bandwidth (26.1 nm for E | | N g ), and strong Raman response (most intense mode at 916 c m − 1 ). A diode-pumped Y b 3 + : M g W O 4 laser generated 18.2 W at ∼ 1056 n m with a slope efficiency of ∼ 89 % and a linearly polarized laser output.

In this Letter, the frequency expansion of an orthogonally polarized dual-wavelength laser, based on the cascaded stimulated Raman scattering, was demonstrated for the first time, to the best of our knowledge. The dual-wavelength fundamental laser generated from two separate Nd:YLF crystals was free of gain competition. Integrating the benefit of the two different orthogonally polarized Raman gain peaks in the KGd(WO4)2 (KGW) crystal, two sets of first-Stokes orthogonally polarized dual-wavelength Raman lasers were first achieved by rotating the Raman crystal for 90°. Furthermore, by simply replacing the Raman output coupler, we attained another two sets of second-Stokes orthogonally polarized dual-wavelength Raman lasers via the cascaded Raman shift. At a pulse repetition frequency of 5 kHz, the maximum first-Stokes and second-Stokes dual-wavelength Raman output powers were 3.12 and 2.09 W, with the combined peak powers of approximately 240 and 290 kW, respectively.

We present a hyper-spectral microscopic imaging system capable of obtaining both transmission- and fluorescence-spectral images for biological measurements. For obtaining high quality images of samples with low self-fluorescence, large aperture optics and low vibration elements were implemented in the system. This study focused on obtaining different types of spectral information, i.e., transmission and fluorescence, to study the structure of the objects and observe the similarities and differences in composition at different positions. By employing this system to investigate bee pollen, we observed a special thin-film structure, which cannot be detected using conventional microscopic systems.

According to the own nature and its related optical characteristics of Nd:YVO4 crystal, a set of compact all-solid-state laser system at 457 nm was designed. At the same time the parameters of the temperature control system and the resonant cavity were also optimized. Based on the realization of Nd:YVO4 laser crystal operation at 914 nm wavelength, 457 nm laser output were obtained by intracavity frequency doubling with LBO and BIBO crystal. The M2 factor was 1.38 and 1.57 by the LBO and BIBO intracavity frequency doubling experiments. Under the pump power of 24.3 W, the output power of 2.34 W and 1.56 W is obtained, respectively, with the same experimental condition. The optical-to-optical efficiency is 9.74% and 6.45%.

A single-longitudinal-mode crystalline Raman laser in the 1.7 µm wave band was reported for the first time, to the best of our knowledge. The Y V O 4 Raman laser, which was intracavity-pumped by an actively Q -switched 1314 nm Nd:YLF laser, demonstrated the cascaded Stokes oscillation at 1715 nm. By inserting an etalon in the fundamental resonator, linewidth narrowing and power scaling of the second-Stokes laser were realized based on the spatial-hole-burning-free Raman gain. With an optimal pulse repetition frequency of 4 kHz, the maximum single-longitudinal-mode average output power of 1.8 W was acquired with the spectrum linewidth of ∼ 340 M H z . Further increasing the incident pump power, the second-Stokes laser transitioned to multimode regime, and the maximum average output power reached 2.7 W with the peak power as high as ∼ 380 k W .

We demonstrated a narrowband eye-safe intracavity Raman laser by incorporating a fused silica etalon into the fundamental resonator. The KGd(WO4)2 (KGW) Raman laser was pumped by an actively Q-switched Nd:YLF laser at 1314 nm. Thanks to the KGW bi-axial properties, two distinct eye-safe Raman lasers operating at 1461 and 1490 nm were obtained separately by rotation of the KGW crystal. At an optimized pulse repetition frequency of 4 kHz, the maximum average output powers of 3.6 and 4.0 W were achieved with the peak powers up to approximately 330 and 480 kW, respectively. The eye-safe Stokes emissions were narrow linewidth (∼0.05 nm FWHM; measurement limited) and near diffraction limited (M 2

Nondiffracting light beams have been attracting considerable attention for their various applications in both classical and quantum optics. Whereas substantial investigations on generation of the nondiffracting beams were made, their lateral dimension is much larger than optical wavelength. Here we present both theoretically and experimentally a study of the generation of nondiffracting light beams at deep-subwavelength scale. The highly localized light field is a result of in-phase interference of high-spatial-frequency waves generated by optical sharp-edge diffraction with a circular thin film. It is shown that the generated beam can maintain its spot size below the optical diffraction limit for a distance of up to considerable Rayleigh range. Moreover, the topological structure of both the phase and polarization of a light beam is found to be preserved when it passes through the diffractive configuration, which enables generating nondiffracting vortex beams as well as transversely polarized vector beams at deep-subwavelength scale. This work opens a new avenue to manipulate higher-order vector vortex beams at subwavelength scale and may find intriguing applications in subwavelength optics, e.g., in superresolution imaging and nanoparticle manipulation.

We report on the frequency expansion of efficient passively Q-switched (PQS) orthogonally-polarized dual-wavelength laser for the first time, to our knowledge. The dynamic of pulse synchronization for the PQS dual-wavelength laser was analyzed theoretically. With two Nd:YLF crystals, the simultaneous PQS orthogonally-polarized dual-wavelength laser at 1047 and 1053 nm was obtained with the maximum output powers of 4.5 and 4.2 W, respectively, resulting in a total optical-to-optical conversion efficiency of 18.7%. The timing jitter between the 1047 nm main pulse and 1053 nm main pulse was 26.6 ns. Furthermore, substituting one of the Nd:YLF crystals for a Nd:YAG crystal, two sets of simultaneous orthogonally-polarized dual-wavelength lasers at 1047, 1064 nm and 1053, 1064 nm were generated with near 6 W of output power.

We demonstrate both experimentally and numerically a new type of hole array structure that exhibits optically diffractive focusing phenomenon. The hole arrays are designed based on the aperiodic Vogel spirals. In contrast to periodic and quasi-periodic hole arrays that contain discrete Bragg peaks in reciprocal space, the Vogel spiral hole arrays have particularly continuous Fourier components with circular symmetry, which enables optical wave focusing into a diffraction-limited hotspot for a wide range of incident wavelengths. We further demonstrate that the diffracted fields contain local orbital angular momentum (OAM) leading to rotations of the diffractive circular rings around the center, although the total OAM is zero.

We report a high average power actively Q-switched (AQS) orthogonal polarization dual-wavelength Nd:YLF laser at 1047 and 1053 nm. The gain-to-loss balance of dual wavelengths was realized via an uncoated quartz etalon. A maximum continuous wave (CW) output power of 14.2 W was obtained under the incident pump power of 41.7 W, corresponding to an optical-to-optical conversion efficiency of 34.1% and a slope efficiency of 38.3%. Active Q-switching was accomplished by inserting an acousto-optic modulator in the cavity. Under the incident pump power of 40 W, this setup delivered a maximum average output power of 10 W at the pulse repetition frequency (PRF) of 30 kHz and the largest pulse energy of 3.4 mJ at the PRF of 1 kHz, respectively. To the best of our knowledge, these are the highest average output powers for both CW and AQS orthogonally polarized dual-wavelength lasers based on laser crystals.

We demonstrate that the spatially diffractive properties of cylindrical vector beams could be controlled via linear interactions with anisotropic crystals. It is the first time to show experimentally that the diffraction of the vector beams can be either suppressed or enhanced significantly during propagation, depending on the sign of anisotropy. Importantly, it is also possible to create a linear non-spreading and shape-preserving vector beam, by vanishing its diffraction during propagation via strong anisotropy in a crystal. The manageable diffractive effect enables manipulating propagation dynamics of the circular Airy vector beams, i.e., their propagation trajectories can be dynamically controlled by weakening or enhancing self-acceleration of the Airy beam. We further demonstrate that the cylindrical vector beams with initially zero orbital angular momentum can be rotated either clockwise or anticlockwise, relying on the sign of the anisotropy.

We observe a nonlinear response of a dual-wavelength Nd:YAG laser when subjected to low-frequency periodic modulations of cavity losses. The modulation frequency is far from the relaxation oscillation frequency. The harmonic resonances of the two laser wavelengths associated with antiphase intensity oscillations are demonstrated and resonances up to the fourth order were observed. For relatively weak modulation, the intensity oscillation frequency of the laser is equal to the modulation frequency. Harmonic resonances occur under a stronger modulation. We find that more harmonic components appear when the modulation frequency is increased. Furthermore, with enhancing the modulation, the dominant frequency of the intensity oscillations of both wavelengths is shifted toward the higher-order harmonic frequency.

We study theoretically and experimentally pulse fluctuations in a passively Q-switched laser caused by the thermal lens effect and design a special thermally insensitive cavity for an end-pumped passively Qswitched laser system with a composite crystal. We show experimentally that using a suitable cavity and maintaining the laser-system operation in the fundamental mode reduce the pulse fluctuations effectively. Under a pump power of 8 W, relative fluctuations of the pulse width and the repetition rate of this system are 2.3% and 3.5%, respectively.

We experimentally demonstrated, the first time to the best of our knowledge, the intracavity Stokes frequency conversion using a Yb:YAG crystal as gain medium and a YVO4 as Raman crystal. At an incident pump power of 9.72 W and a pulse repetition frequency of 39 kHz, the first-Stokes emission at 1157.6 nm with a spectral linewidth of 2.2 nm was observed with respect to the Raman shift of 890 cm $^{-1}$ . The maximum pulse average output power of 750 mW at 1157.6 nm was achieved, with a corresponding incident pump beam to first-Stokes output conversion efficiency of 7.72%.

Well-crystallized and uniform NaGd(MoO4)2 microcrystals with morphologies of bipyramids, truncated bipyramids, quasi-cubes and tetragonal plates were selectively synthesized via a facile hydrothermal method without any additives under mild conditions. The effects of Na2MoO4/Gd(NO3)3 molar ratios and pH values of precursor solutions on the phase and morphology of the as-synthesized microcrystals were systematically investigated. The molar ratios and pH values played key roles in the selective synthesis of pure phase NaGd(MoO4)2 microcrystals with regular morphology. With increasing Na2MoO4/Gd(NO3)3 molar ratios in the appropriate pH range, the morphology of the products changed from bipyramids, truncated bipyramids, quasi-cubes to tetragonal plates, namely, the morphological truncation degree increased gradually. NaGd(MoO4)2 tetragonal microplates could be synthesized at the molar ratio of 9 : 1. A possible morphological formation mechanism of NaGd(MoO4)2 tetragonal microplates was proposed, i.e. nucleation-Ostwald ripening growth process. Color tunable photoluminescence properties of NaGd(MoO4)2:Eu3+,Tb3+ microcrystals were studied in detail. Among the different morphologies of NaGd(MoO4)2:5% Eu3+ microcrystals, tetragonal microplates had a broadened, red-shifted and enhanced charge transfer band in the excitation spectrum. What's more, the full-width at half-maximum for the charge transfer band of the tetragonal plates was highest (58 nm), which favored efficient excitation and absorption in the ultraviolet region. The introduction of a small amount of Tb3+ into NaGd(MoO4)2 microplates doped with Eu3+ would enhance the 5D0 → 7FJ transition of Eu3+ at 616 nm due to the energy transfer process of cross-relaxation from Tb3+ to Eu3+. Multicolor tunable luminescence from deep red, red, orange, yellow to green under 291 nm ultraviolet excitation and from red, reddish orange to pink under 380 nm near-ultraviolet excitation could be obtained in NaGd(MoO4)2 tetragonal microplates by simply adjusting the doping concentrations of Eu3+ and Tb3+, suggesting NaGd(MoO4)2:Eu3+,Tb3+ microcrystals might have practical application in optoelectronic devices, such as light emitting diodes and color display systems. This facile morphology-controlled hydrothermal synthesis strategy was simple, low-cost and environment-friendly, and might be extended to other inorganic materials.

A Tm 3+ /Ho 3+ :NaGd(MoO 4 ) 2 crystal was grown by the Czochralski method. The XRD results matched standard data from JCPDS file, which accorded with scheelite structure with an I41/a space group. Thermal properties of crystal were analyzed by using the TG–DSC curve. The melting point and specific heat are 1182 °C and 0.5 J/g K at 300 K, respectively. The Spectral properties of the Tm 3+ /Ho 3+ :NaGd(MoO 4 ) 2 crystal were investigated, including room temperature absorption spectrum and fluorescence spectrum. The absorption cross-section of Tm 3+ at 796 nm is 4.33 × 10 −20 cm 2 with pertinent full widths at half maximum (FWHM) of 10 nm. The intensity parameters, spontaneous emission probability, fluorescence branching ratios and radiative lifetimes were calculated by Judd–Ofelt theory. The emission cross-sections are 1.47 × 10 −20 cm 2 and 1.36 × 10 −20 cm 2 for Tm 3+ at 1850 nm and Ho 3+ at 2000 nm respectively. The lifetime of 5 I 7 → 5 I 8 (Ho 3+ ) was 4.263 ms.

A stable and compact deep ultraviolet laser system operation at 266 nm with diode-side-pumped and passively Q-switched is reported. The Nd:YAG/Cr4+:YAG/YAG composite crystal is used in realizing fundamental laser output and passively Q-switched modulation and for achieving a high conversion efficiency from 532 nm to 266 nm; a multi-reflected cavity for 532 nm is used in the system. The performances of the average power, pulse width, and pulse repetition rate on pump power are measured. Under the green laser of 13.03 W, the deep ultraviolet laser average output power of 1.27 W is obtained, with a pulse width of 60 ns, the repetition rate of 12.5 kHz, and the corresponding conversion efficiency of 9.74%.

We experimentally investigated the performance of diode-wing-pumped Tm:Y 3 Al 5 O 12 crystalline laser operating at around 2 μm. By systematically making comparisons of laser performance in addition to the laser spectra features between composite and non-composite crystals with two different active segments length, we believed that using diffusion-bonded crystal with shorter Tm 3+ -doped active segment would be a feasible approach for simultaneously up-scaling the output power and slope efficiency in terms of reducing the reabsorption loss and thermal lensing effects.

A side-pumped passively Q-switched 1064 nm laser system by using Nd: YAG/Cr4+: YAG/YAG composite crystal is demonstrated for the first time. Under pump power of 180 W, the maximum average output power of 85.6 W is obtained, with the pulse width of 140 ns and the repetition rate of 14.3 kHz, corresponding single pulse energy of 6.0 mJ and peak power of 42.7 kW. To our knowledge, this is the maximum average power of 1064 nm passively Q-switched laser which has reported.

We demonstrate an 806 nm laser diode end-pumped continuous-wave (CW) and actively Q-switched (AQS) orthogonally-polarized dual-wavelength Nd:YLF laser operating at 1314 and 1321 nm. Benefitting from the small difference of the stimulated emission cross sections at 1314 and 1321 nm in Nd:YLF crystal, the power equalized emissions at both wavelengths were achieved by simply titling the output coupler. A maximum CW output power of 9.2 W was obtained with the incident pump power of 32.5 W, giving an optical-to-optical conversion efficiency of approximately 28% and a slope efficiency of approximately 33%. Furthermore, active Q-switching was realized by inserting a Brewster-cut acousto optic modulator. For an incident pump power of 30 W, this oscillator delivered an average power of 6.5 W at a pulse repetition frequency (PRF) of 20 kHz, and a pulse energy of 2.6 mJ with a peak power of approximately 72 kW at a PRF of 1 kHz.

A diode-side-pumped passively Q-switched laser at 532 nm wavelength by Nd 3+ :YAG/Cr 4+ :YAG/YAG composite crystal is revealed for the first time. The output performances, including the threshold, slope efficiency, average power, pulse width, repetition rate and far field spot of lasers with Cr 4+ :YAG of different initial transmissions are experimentally compared. Under the pump power of 187.5 W, the Q-switched green laser with initial transmission of 85% obtains the maximum average power of 27.2 W and peak power of 7.8 KW. The laser with initial transmission of 65% obtains the pulse width of 59 ns. The initial transmission has significant effects on the output performances of passively Q-switched lasers.

We present a diode-side-pumped Q-switched mode-locked (QML) laser operating at 532 nm for the first time employing a composite crystal Nd:YAG/Cr4+:YAG/YAG and a KTP. The experimental results show that, using a suitable cavity and crystals, one can obtain high-quality QML laser output at 532 nm with a side-pumped system. We measure and analyze the QML performance of the fundamental frequency laser and the green laser. Under a pump power of 127 W, we obtain a QML laser operating at 532 nm with an average power of 4.97 W and a repetition rate of 0.2 GHz for the mode-locked pulses; the corresponding depth of modulation is close to 100%.

The long pulse operation of ultraviolet (UV) laser attributed to multi-reflection is presented on an acousto-optic (AO) Q-switched ultraviolet laser system blocking green light inside a cavity. The ultraviolet laser with the highest average power of 456 mW is obtained with 20 kHz repetition-rate. The numerical simulation of UV pulse broadening was studied using Gaussian curve approximation. The conclusion suggests that the short multi-reflected cavity and high incident pump power will be beneficial to alleviate the width broadening effect. The results, for the first time, would provide the technology for controlling the pulse width of an AO Q-switched DUV laser.

Bi/Ta double doped Gd0.1Y0.9AlO3 (Bi/Ta:GYAP) near-infrared (NIR) laser crystal was successfully grown. The codoping of Ta5+ was demonstrated to effectively enhance the NIR fluorescence emission in Bi/Ta:GYAP crystal for the first time. The introduced Ta5+ ion can induce the change of valence states from Bi3+ to Bi+ based on the charge compensation mechanism, bringing about the enhanced NIR fluorescence emission. The three NIR fluorescence emission peaks centering at 1005, 1195, and 1280 nm were ascribed to three different Bi+ active centers in Bi/Ta:GYAP crystal. These results suggest that the Bi/Ta:GYAP crystal may have potential applications in NIR broadband lasers.

In this paper, the continuous-wave intracavity second harmonic generation of a laser diode side-pumped Nd:YAP laser operating in the 1.3-μm region is demonstrated. A type-I critical phase-matched LiB3O5 (LBO) crystal was used as the frequency doubler. 8.1 W/670.7 nm and 5.1 W/669.6 nm continuous-wave red light outputs were achieved from the 1341.4-nm laser beam polarized along the c crystalline axis and the 1339.2-nm laser beam polarized along the a crystalline axis, respectively. The stability of the 670.7-nm red laser is better than 3% at the output power of 7 W in an hour.

In this paper, a diode-side-pumped acoustooptic Q-switched 1319-nm Nd:YAG laser is described. The output characteristics under the different repetition rates and output couplers have been studied. With a pumping power of 555 W, the average output power decreases from 94 W at 50 kHz to 71 W (slope efficiency 25.2%, optical conversion efficiency 12.8%) at 5 kHz. The highest peak power is up to 95 kW with the pulse duration of 150 ns at the repetition rate of 5 kHz.

We report a completely solid-state continuous-wave (CW) blue laser operating at 447 nm utilizing intracavity frequency tripling of an LD-side-pumped Nd:YAlO3 (Nd:YAP) laser operating at 1341.4 nm. An LBO crystal with type-I critical phase matching and a KTP crystal with type-II critical phase matching (CTM) were used for the second harmonic generation (SHG) and the third harmonic generation (THG), respectively. In view of the analysis of the cavity stability, a four-mirror folded cavity was designed and the output characteristics were theoretically analyzed. Experimental characteristics obtained were shown to be in agreement with the theoretical analysis. The maximum output power of the 447 nm CW blue laser reached 114 mW, which corresponds to a red-to-blue conversion efficiency of 9%.

A diode-side-pumped simultaneous dual-wavelength Q-switched Nd:YAG laser around 1.3 μm is demonstrated. With the pumping power of 480 W, a peak power of 43 kW was obtained at the repetition rate of 5 kHz. The maximum average output power is up to 43 W with the slope efficiency of 20.5%, and the pulse duration is 200 ns. This dual-wavelength Q-switched laser with high peak power has a balanceable and stable proportion of dual-wavelength output.

A high-power CW diode-side-pumped Nd:YAP laser with linearly polarization at 1341 nm has been described. The laser characteristics including thermal lens and stability of flat-flat resonator were studied. By comparing the output powers at different resonator lengths and different output couplers, the c-axis polarized laser working at 1341 nm has been obtained with a maximum output power of 121 W at the pumping power of 555 W. The optical-optical efficiency is 21.8% and the optical slope efficiency is 40%. The a-axis polarized laser at 1339 nm has also been successfully obtained when the c-axis polarized laser had become instable with the increase of pumping power. (c) 2006 Elsevier B.V. All rights reserved.

By using Nd:YAG/Cr:YAG/YAG composite crystal as gain media, a passively Q-switched LD side-pumped laser with high average output power, working at 1064 nm, is set up. The 1064 nm laser output power increases linearly with the pumping light power and the maximum average output power of 83.68 W is observed. With the help of a KTP nonlinear crystal, 532 nm laser pulses with the corresponding pulse width of 210 ns and the repetition rate of 21.2 kHz are obtained under the maximum LD pumping light of 187.5 W. The average output power of 532 nm laser is 27.2 W. The singlepulse energy is 1.28 mJ and the peak power is 6.1 kW. The optical-to-optical conversion efficiency of LD pumping light to 532 nm output light is 14.72%.

This paper reported a passively Q-switched green laser of LD pumped linear cavity structure by using Nd:YAG/Cr 4+ :YAG composite crystal and the type II phase matching KTP crystal. The dependence of average output power, pulse width and pulse repetition rate on pump power at different initial transmissions of Cr 4+ :YAG were measured and analyzed. With Cr 4+ :YAG of 80% initial transmission, under pump power of 13.97 W, the output average power is up to 681 mW, with pulse width of 200 ns and pulse repetition rate of 9.1 kHz. The laser operates in a fundamental mode.

The absorption spectra of Tm3+:KGd(WO4)2 crystal in three mutually perpendicular arbitrary directions at room temperature were measured. Based on Judd–Ofelt theory and TPM method, the intensity parameters Ω t (t=2,4,6) , the radiative lifetimes, the experimental and theoretical oscillation strengths, and the fluorescence branching ratios were obtained. The broad emission spectrum from 1650 to 2000 nm was obtained under 800 nm excitation. Also, the fluorescence spectra at 455 and 665 nm were measured under 360 nm excitation. Their stimulated emission cross-sections were also calculated.

A multi-Watt, multi-GHz laser eye-safe laser was obtained by simultaneously Q-switched Kerr-lens mode-locking and stimulated Raman scattering. The high power fundamental laser at 1342 nm was generated efficiently with a side-pump Nd:YAP laser rod. The fundamental laser was captured by the intra-cavity Raman cavity, and the mode beating of the fundamental laser and the Raman laser was maximized by setting the suitable length relationship between the fundamental cavity and the Raman cavity. The output performance of the Raman lasers with different output coupler were measured and analyzed. The maximum average output power at 1526 nm was 3.5 W, the pulse duration was about 220 ps and the pulse repetition rate was 0.64 GHz.

We demonstrate numerically the ability for directionally releasing the stored ultrashort light pulse from a microcavity by means of two-pulse nonlinear interaction in a cascading Bragg grating structure. The setting is built by a chirped grating segment which is linked through a uniform segment, including a tunable microcavity located at the junction between the two components. Our simulations show that stable trapping of an ultrashort light pulse can be achieved in the setting. The stored light pulse in a microcavity can be possibly released, by nonlinearly interacting with the lateral incident control pulse. Importantly, by breaking the symmetry of potential cavity, the stably trapped light pulse can be successfully released from the microcavity to the expected direction. Owing to the induced optical nonlinearity, the released ultrashort light pulses could preserve their shapes, propagating in a form of Bragg grating solitons through the uniform component, which is in contrast to the extensively studied light pulse trappings in photonic crystal cavities which operate at the linear regime.