Publications by authors named "Huaijin Zhang"

137 Publications

Self-mode-locked alexandrite femtosecond lasers with multi-GHz repetition rates.

Opt Lett 2021 Apr;46(8):1979-1982

We report the laser-diode pumped multi-gigahertz (GHz) self-mode-locked alexandrite femtosecond (fs) lasers for the first time, to the best of our knowledge. Using a simple linear cavity, stable mode-locked laser was achieved with a repetition rate of 3.6 GHz and a pulse width of 237 fs. Additionally, the second-harmonic mode-locked pulse was realized with a repetition rate of 7.5 GHz and a pulse width of 201 fs based on the Fabry-Perot effect generated in the laser cavity. It was observed that this laser possesses advantages of high repetition rate and short pulse width that enable the development of promising applications in modern ultrafast photonics.
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http://dx.doi.org/10.1364/OL.423249DOI Listing
April 2021

Mid-infrared pulsed nanosecond difference frequency generation of oxide LGN crystal up to 5.7 µm.

Opt Lett 2021 Feb;46(4):785-788

We demonstrate the tunable difference frequency generation (DFG) of an oxide (LGN) crystal pumped by near-infrared lasers with nanosecond pulses for the first time to our knowledge. The type I and II phase-matching conditions of DFG were calculated in the mid-infrared region. With the processed LGN crystals, tunable lasers in the wavelength range from 4.4 to 5.7 µm and 4.56 to 5.6 µm were achieved under type II and I phase-matching conditions, respectively, with the maximum output energy of 13.1 µJ, which agreed well with the theoretical calculation. This work provides the kind of promising mid-infrared nonlinear crystals for the pumping of nanosecond pulsed lasers as well as a tunable mid-infrared laser source at a wavelength over 5 µm in further photonic applications.
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http://dx.doi.org/10.1364/OL.418215DOI Listing
February 2021

Three-dimensional nonlinear photonic crystal in naturally grown potassium-tantalate-niobate perovskite ferroelectrics.

Light Sci Appl 2020 Nov 24;9(1):193. Epub 2020 Nov 24.

State Key Laboratory of Crystal Materials and Institute of Crystal Materials, Shandong University, Jinan, 250100, China.

Since quasi-phase-matching of nonlinear optics was proposed in 1962, nonlinear photonic crystals were rapidly developed by ferroelectric domain inversion induced by electric or light poling. The three-dimensional (3D) periodical rotation of ferroelectric domains may add feasible modulation to the nonlinear coefficients and break the rigid requirements for the incident light and polarization direction in traditional quasi-phase-matching media. However, 3D rotating ferroelectric domains are difficult to fabricate by the direct external poling technique. Here, we show a natural potassium-tantalate-niobate (KTN) perovskite nonlinear photonic crystal with spontaneous Rubik's cube-like domain structures near the Curie temperature of 40 °C. The KTN crystal contains 3D ferroelectric polarization distributions corresponding to the reconfigured second-order susceptibilities, which can provide rich reciprocal vectors to compensate for the phase mismatch along an arbitrary direction and polarization of incident light. Bragg diffraction and broadband second-harmonic generation are also presented. This natural nonlinear photonic crystal directly meets the 3D quasi-phase-matching condition without external poling and establishes a promising platform for all-optical nonlinear beam shaping and enables new optoelectronic applications for perovskite ferroelectrics.
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http://dx.doi.org/10.1038/s41377-020-00427-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7687908PMC
November 2020

Few-cycle pulses tunable from 3 to 7  µm via intrapulse difference-frequency generation in oxide LGN crystals.

Opt Lett 2020 Oct;45(20):5728-5731

An ultrashort mid-infrared (IR) source beyond 5 µm is crucial for a plethora of existing and emerging applications in spectroscopy, medical diagnostics, and high-field physics. Nonlinear generation of such sources from well-developed near-IR lasers, however, remains a challenge due to the limitation of mid-IR crystals. Based on oxide (LGN) crystals, here we report the generation of femtosecond pulses tunable from 3 to 7 µm by intrapulse difference-frequency generation of 7.5 fs, 800 nm pulses. The efficiency and bandwidth dependences on pump polarization and crystal length are studied for both Type-I and Type-II phase-matching configurations. Maximum pulse energy of ∼10 is generated at 5.2 µm with a conversion efficiency of ∼0.14. Because of the few-cycle pump pulse duration, the generated mid-IR pulses are as short as about three cycles. These results, to the best of our knowledge, represent the first experimental demonstration of LGN in generating mid-IR ultrashort pulses.
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http://dx.doi.org/10.1364/OL.406025DOI Listing
October 2020

High-efficiency Er-doped yttrium gallium garnet laser resonantly pumped by a laser diode at 1.47  µm.

Opt Lett 2020 Aug;45(15):4361-4364

The spectroscopic and laser properties of an -doped yttrium gallium garnet crystal, (YGG), are studied. The stimulated emission cross section is 1.4×10 at 1.65 µm. A continuous-wave laser resonantly pumped by a laser diode at 1.47 µm is demonstrated, delivering a maximum output power of 3.34 W. Benefiting from the low phonon energy of the YGG host, the corresponding slope efficiency is as high as ∼42. To the best of our knowledge, this is the highest slope efficiency from the laser-diode resonantly pumped Er lasers at room temperature in the 1.6 µm spectral range.
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http://dx.doi.org/10.1364/OL.401155DOI Listing
August 2020

Pushing periodic-disorder-induced phase matching into the deep-ultraviolet spectral region: theory and demonstration.

Light Sci Appl 2020 18;9:45. Epub 2020 Mar 18.

State Key Laboratory of Crystal Materials and Institute of Crystal Materials, Shandong University, Jinan, 250100 China.

Nonlinear frequency conversion is a ubiquitous technique that is used to obtain broad-range lasers and supercontinuum coherent sources. The phase-matching condition (momentum conservation relation) is the key criterion but a challenging bottleneck in highly efficient conversion. Birefringent phase matching (BPM) and quasi-phase matching (QPM) are two feasible routes but are strongly limited in natural anisotropic crystals or ferroelectric crystals. Therefore, it is in urgent demand for a general technique that can compensate for the phase mismatching in universal nonlinear materials and in broad wavelength ranges. Here, an additional periodic phase (APP) from order/disorder alignment is proposed to meet the phase-matching condition in arbitrary nonlinear crystals and demonstrated from the visible region to the deep-ultraviolet region (e.g., LiNbO and quartz). Remarkably, pioneering 177.3-nm coherent output is first obtained in commercial quartz crystal with an unprecedented conversion efficiency above 1‰. This study not only opens a new roadmap to resuscitate those long-neglected nonlinear optical crystals for wavelength extension, but also may revolutionize next-generation nonlinear photonics and their further applications.
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http://dx.doi.org/10.1038/s41377-020-0281-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7078200PMC
March 2020

Highly Efficient Super-Continuum Generation on an Epsilon-Near-Zero Surface.

ACS Omega 2020 Feb 30;5(5):2458-2464. Epub 2020 Jan 30.

State Key Laboratory of Crystal Materials and Institute of Crystal Materials, Shandong University, Jinan 250100, China.

The efficient super-continuum (SC) generation on a surface via a high-order photo-electron interaction is a great challenge for integrated optics because the surficial nonlinear optical efficiency is usually limited by finite light-matter interaction length and electric field intensity. Nowadays, epsilon-near-zero (ENZ) materials, showing infinite enhanced electronic field in theory, provide a kind of new platform to obtain a giant nonlinear response on the surface. Here, under the irradiation of a multiwavelength laser, an exotic and efficient SC generation from 406 to 1100 nm on the ENZ aluminum-doped zinc oxide surface was experimentally demonstrated by diversified nonlinear processes, including second harmonic generation, third harmonic generation, four wavelength mixing, and cascading stimulated Raman scattering. Particularly, an unprecedented nonlinear conversion efficiency of 3.94% W, 16 orders of magnitude higher than the common surface case (about 10% W), was presented.
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http://dx.doi.org/10.1021/acsomega.9b04026DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7017490PMC
February 2020

Defect Engineering of MoS for Room-Temperature Terahertz Photodetection.

ACS Appl Mater Interfaces 2020 Feb 28;12(6):7351-7357. Epub 2020 Jan 28.

State Key Laboratory of Crystal Materials and Institute of Crystal Materials , Shandong University , Jinan 250100 , China.

Two-dimensional (2D) materials have exotic intrinsic electronic band structures and are considered as revolutionary foundations for novel nanodevices. Band engineering of 2D materials may pave a new avenue to overcome numerous challenges in modern technologies, such as room temperature (RT) photodetection of light with photon energy below their band gaps. Here, we reported the pioneering RT MoS-based photodetection in the terahertz (THz) region via introducing Mo and S vacancies for rational band gap engineering. Both the generation and transport of extra carriers, driven by THz electromagnetic radiations, were regulated by the vacancy concentration as well as the resistivity of MoS samples. Utilizing the balance between the carrier concentration fluctuation and carrier-scattering probability, a high RT photoresponsivity of 10 mA/W at 2.52 THz was realized in an Mo-vacancy-rich MoS sample. This work overcomes the challenge in the excessive dark current of RT THz detection and offers a convenient way for further optoelectronic and photonic devices based on band gap-engineered 2D materials.
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http://dx.doi.org/10.1021/acsami.9b21671DOI Listing
February 2020

Surface Nonlinear Optics on Centrosymmetric Dirac Nodal-Line Semimetal ZrSiS.

Adv Mater 2020 Jan 21;32(2):e1904498. Epub 2019 Nov 21.

State Key Laboratory of Crystal Materials and Institute of Crystal Materials, Shandong University, Jinan, 250100, China.

Gapless surface states (SSs) are features of topological semimetals and are extensively observed. Nowadays, the emerging question is whether the SSs possess exotic and applicable properties. Here, associated with the symmetrical selection rule for nonlinear optical materials, the surface nonlinear optics on a centrosymmetric Dirac nodal-line semimetal ZrSiS crystal is studied and it is found that the SSs bring record nonlinear susceptibilities. The unprecedented conversion efficiencies for second and third harmonic generations are 0.11‰ and 0.43‰, respectively, more than ten orders of magnitude larger than the typical surface second harmonic generation. This work discovers a new route toward studying the SSs for applications in nonlinear photonics.
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http://dx.doi.org/10.1002/adma.201904498DOI Listing
January 2020

Power scaling of the self-frequency-doubled quasi-two-level Yb:YCOB laser with a 30% slope efficiency.

Opt Lett 2019 Nov;44(21):5157-5160

The lab-on-chip integration of photonic devices has been attracting increasing attention recently. Multifunctional materials provide natural platforms for the desirable performance by the coupling of different functionalities. The insufficient coupling efficiency of the laser and nonlinear processes in self-frequency-doubled (SFD) lasers is the limiting factor for the output power and further practical applications. Here we demonstrate a SFD Yb-doped calcium yttrium oxoborate (Yb:YCOB) crystal laser with an unprecedented slope efficiency of 30% and output power of 6.2 W at 513 nm. The successful realization of this laser operating in a quasi-two-level configuration is based on enhanced coupling of the laser and frequency-doubling processes using a monolithic configuration, benefiting from an ultimately small laser quantum defect, the anisotropic gain cross sections, and the high effective nonlinearity of the monoclinic YCOB outside the principal planes. Solid-state lasers in the spectral range around 510 nm are scarce, and the results not only present a significant advancement in the field of SFD lasers, but also pave the way for future applications of such green lasers, especially in areas such as medical treatment, daily life, and scientific investigations.
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http://dx.doi.org/10.1364/OL.44.005157DOI Listing
November 2019

Artificial Second-Order Nonlinear Optics in a Centrosymmetric Optical Material BiVO: Breaking the Prerequisite for Nonlinear Optical Materials.

ACS Omega 2019 Jan 14;4(1):1045-1052. Epub 2019 Jan 14.

State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, PR China.

Second-order nonlinear optics (NLO) is the foundation of frequency conversion for the generation of coherent light at frequencies where lasers have no emissions or operate poorly. The prerequisite for NLO materials is noncentrosymmetric symmetry that can generate an effectively non-counterbalanced spontaneous electronic polarization. Here, we propose that this material restriction can be broadened by controlling the electron distribution with a local internal electrostatic field (IEF), and we demonstrate artificially created and manipulated second harmonic generation (SHG) in a centrosymmetric optical material, a superimposed Co- and Mo-doped BiVO thin film with 2/ point group symmetry, where a homojunction producing tunable effective polarization is formed. The SHG was characterized and tuned by IEF. This work breaks the structural symmetry constraint on NLO materials. Besides, the phase-matching-like condition was realized for the further improvement of the efficient frequency conversion. Because polarization is also a prerequisite for many other functions besides SHG, we believe that this work should provide some inspiration for the further development of optoelectronic, photonic, and electronic materials.
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http://dx.doi.org/10.1021/acsomega.8b02453DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6648906PMC
January 2019

Kerr-lens mode-locked Pr:LuLiF laser.

Opt Lett 2019 Aug;44(15):3665-3668

We demonstrate the Kerr-lens mode-locked Pr:LuLiF (Pr:LLF) laser pumped by a blue laser diode (LD). By theoretical calculation of the group velocity dispersion in the laser gain, the compensation was employed for the realization of the continuous-wave mode-locked laser at the wavelength of 604 nm with the pulse width of 1.1 ps which, to the best of our knowledge, is the shortest pulse width in the Pr ion doped crystal lasers pumped with LDs. It can be believed that the present Pr:LLF laser should provide some inspiration for the development of the blue LD pumped visible lasers, especially in the mode-locking laser operation.
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http://dx.doi.org/10.1364/OL.44.003665DOI Listing
August 2019

Fs-laser-written thulium waveguide lasers Q-switched by graphene and MoS.

Opt Express 2019 Mar;27(6):8745-8755

We report the generation of mid-infrared (~2 µm) high repetition rate (MHz) sub-100 ns pulses in buried thulium-doped monoclinic double tungstate crystalline waveguide lasers using two-dimensional saturable absorber materials, graphene and MoS. The waveguide (propagation losses of ~1 dB/cm) was micro-fabricated by means of ultrafast femtosecond laser writing. In the continuous-wave regime, the waveguide laser generated 247 mW at 1849.6 nm with a slope efficiency of 48.7%. The laser operated at the fundamental transverse mode with a linearly polarized output. With graphene as a saturable absorber, the pulse characteristics were 88 ns / 18 nJ (duration / energy) at a repetition rate of 1.39 MHz. Even shorter pulses of 66 ns were achieved with MoS. Graphene and MoS are therefore promising for high repetition rate nanosecond Q-switched infrared waveguide lasers.
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http://dx.doi.org/10.1364/OE.27.008745DOI Listing
March 2019

Demonstration of a White Laser with V C MXene-Based Quantum Dots.

Adv Mater 2019 Jun 29;31(24):e1901117. Epub 2019 Apr 29.

State Key Laboratory of Crystal Materials and Institute of Crystal Materials, Shandong University, Jinan, 250100, China.

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 traditional 2D materials. Here, a white laser with V C MXene quantum dots (MQDs) is originally demonstrated by constructing a broadband nonlinear random scattering system with enhanced gain. The excitation-dependent photoluminescence of V C MQDs is enhanced by passivation and characterized, and their localized nonlinear random scattering is realized by the generation of excitation-power-dependent solvent bubbles. With the optimized excitation, the blue, green, yellow, and red light is amplified and simultaneously lased. This work not only provides a kind of promising material for white lasers, but also a design strategy of novel photonics for further applications.
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http://dx.doi.org/10.1002/adma.201901117DOI Listing
June 2019

High-efficiency 3  μm Er:YGG crystal lasers.

Opt Lett 2018 Dec;43(23):5873-5876

By balancing energy transfer and thermal effects, we demonstrate efficient erbium-doped yttrium gallium garnet (Er:YGG) crystal lasers at a wavelength of 2.82-2.92 μm for the first time, to the best of our knowledge. Associated with the influence of doping concentration on energy transfer and thermal effects, the Er doping concentration was optimized to be 10 at.%, and with the optimized crystal, the maximum continuous-wave output power was 1.38 W, corresponding to the slope efficiency of 35.4% approaching the theoretical quantum limits. The thermal effects during the laser process were discussed. We believe that this work should be helpful for optimizing the erbium-doped gain for the 3 μm laser and the development of 3 μm lasers.
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http://dx.doi.org/10.1364/OL.43.005873DOI Listing
December 2018

Room-Temperature Ultrabroadband Photodetection with MoS by Electronic-Structure Engineering Strategy.

Adv Mater 2018 Dec 11;30(50):e1804858. Epub 2018 Oct 11.

Institute of Functional Crystal Materials, Tianjin University of Technology, Tianjin, 300384, China.

Photodetection using semiconductors is critical for capture, identification, and processing of optical information. Nowadays, broadband photodetection is limited by the underdeveloped mid-IR photodetection at room temperature (RT), primarily as a result of the large dark currents unavoidably generated by the Fermi-Dirac distribution in narrow-bandgap semiconductors, which constrains the development of some modern technologies and systems. Here, an electronic-structure strategy is proposed for designing ultrabroadband covering mid- and even far-IR photodetection materials operating at RT and a layered MoS is manifested with an engineered bandgap of 0.13 eV and modulated electronic state density. The sample is designed by introducing defect energy levels into layered MoS and its RT photodetection is demonstrated for wavelengths from 445 nm to 9.5 µm with an electronic state density-dependent peak photoresponsivity of 21.8 mA W in the mid-IR region, the highest value among all known photodetectors. This material should be a promising candidate for modern optoelectronic devices and offers inspiration for the design of other optoelectronic materials.
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http://dx.doi.org/10.1002/adma.201804858DOI Listing
December 2018

A Wide-Range Photosensitive Weyl Semimetal Single Crystal-TaAs.

Adv Mater 2018 Oct 10;30(43):e1801372. Epub 2018 Sep 10.

State Key Laboratory of Crystal Materials and Institute of Crystal Materials, Shandong University, Jinan, 250100, China.

Mid- and even long-infrared photodetection is highly desired for various modern optoelectronic devices, and photodetectors that operate at room temperature (RT) remain challenging and are being extensively sought. Recently, the Weyl semimetal has attracted much interest, and its Lorentz invariance can be broken to have tilted chiral Weyl cones around the Fermi level, which indicates that the photocurrent can be generated by the incident photons at arbitrarily long wavelengths. Furthermore, the atypical linear dispersion bands in Weyl cones result in high carrier mobility and quadratic energy dependence of the density of states, which can enhance the efficiency of the photocurrent and suppress thermal carriers, in addition to its favorable large absorption coefficient. In this study, a Weyl semimetal TaAs photodetecting prototype is reported, which operates at RT with an outstanding response that ranges from the visible to the long-infrared range. This study indicates that the Weyl semimetal TaAs should boost the development of modern optoelectronics and photonics.
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http://dx.doi.org/10.1002/adma.201801372DOI Listing
October 2018

78  fs SWCNT-SA mode-locked Tm:CLNGG disordered garnet crystal laser at 2017  nm.

Opt Lett 2018 Sep;43(17):4268-4271

A passively mode-locked Tm:CLNGG laser using single-walled carbon nanotubes (SWCNT) as a saturable absorber (SA) is demonstrated at 2017 nm. Pulses as short as 78 fs are generated at an 86 MHz repetition rate with an average output power of 54 mW. By increasing the output coupling from 0.5% to 1.5%, a higher power of 100 mW is achieved for slightly longer pulses with a duration of 105 fs at 1996 nm.
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http://dx.doi.org/10.1364/OL.43.004268DOI Listing
September 2018

Validation of the angular quasi-phase-matching theory for the biaxial optical class using PPRKTP.

Opt Lett 2018 Sep;43(17):4276-4279

We report the first experimental validation of angular quasi-phase-matching (AQPM) theory in a biaxial crystal by performing second-harmonic generation (SHG) in the periodically-poled Rb-doped KTiOPO (PPRKTP) crystal cut as a sphere. Both AQPM and birefringence phase-matching (BPM) angles were measured thanks to a Kappa circle.
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http://dx.doi.org/10.1364/OL.43.004276DOI Listing
September 2018

Pushing Nonlinear Optical Oxides into the Mid-Infrared Spectral Region Beyond 10 μm: Design, Synthesis, and Characterization of LaSnGaO.

J Am Chem Soc 2018 04 23;140(13):4684-4690. Epub 2018 Feb 23.

Key Lab of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry , Chinese Academy of Sciences , Beijing 100190 , China.

Mid-infrared (mid-IR) coherent light is crucial for several applications in science as well as daily life, and its development especially in powerful augmentation is constrained by the availability of nonlinear optical (NLO) materials. The development of useful mid-IR NLO materials is limited by the requirements of a wide mid-IR transparent window, high laser damaged threshold (LDT), and strong NLO effect. It is common knowledge that oxides are not suitable mid-IR NLO materials, as their IR absorption cutoff wavelengths are usually <6 μm; however, their LDTs and NLO effects can be large. Herein, we focused on langasite oxides and built structure-composition-property maps that describe the NLO properties in these materials by combining computational property prediction and experimental characterization. Accordingly, rational molecular design was performed, a new member of the langasite family, LaSnGaO (LGSn), was synthesized, and single crystals were grown. The produced material exhibits the widest transparent region (0.27-11.0 μm) among available oxides, the largest LDT (846 MW/cm) among materials that are transparent to 10 μm, and the strongest SHG effect among langasites. The discovery of LGSn facilitates the application of oxides as NLO crystals in the mid-IR spectral region beyond 10 μm. More generally, the developed strategy could be used to guide and accelerate the systematic discovery of functional materials through understanding the key structure-composition-property relationships using the predictive power of computational tools.
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http://dx.doi.org/10.1021/jacs.8b01009DOI Listing
April 2018

Nonlinear optical response during the electron transition process originated from 3D spin-orbit splitting in NiO nanosheets.

Opt Express 2018 Jan;26(2):1230-1236

NiO, a 3d transition-metal oxide with the strong electron correlation, has attracted great physical attention due to the spin-orbit splitting of 3d electrons. By taking advantage of electron transition process originated from 3d spin-orbit splitting, it may be applied to many photonics areas by linear or nonlinear optical response. To further broaden the photonics applications of NiO, we originally explore the nonlinear optical response, saturable absorption, during the electronic transition due to 3d spin-orbit splitting under a strong optical field and successfully applied in the ultrafast photonics as a mode-locker for the generation of visible laser pulses, which is the result of dynamic balancing process by the electron transition arising from ground state (A) to excited state (E) of spin-orbit splitting in the Ni 3d configurations. With the NiO nanosheet film for saturable absorption, we experimentally realize a pulsed visible laser at a wavelength of 640.3 nm for the first time to our knowledge. These results indicate that the study of electron transition process generated by 3d spin-orbit splitting in 3d transition-metal oxides should be helpful for the development of ultrafast photonics and related devices design.
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http://dx.doi.org/10.1364/OE.26.001230DOI Listing
January 2018

Output power enhancement of a self-frequency-doubled laser by selective excitation of inequivalent active centers in LaCaBO (Nd:LCB) crystal.

Opt Lett 2017 Dec;42(23):4861-4864

We demonstrated the output power enhancement of a self-frequency-doubled laser with Nd-doped lanthanum calcium borate LaCaBO (Nd:LCB) crystals by selective excitation of its inequivalent active centers. When the Nd ions located in the Ca sites were excited in the Nd:LCB crystal, the fundamental laser at the wavelength of 1066 nm was successfully realized, which can keep the self-frequency-doubled wavelength away from the self-absorption peak of Nd ions at about 523 nm. By optimizing the key parameters, the maximum output power of 801 mW was achieved with the frequency-doubling at the wavelength of 533 nm, and the enhancement of output power was about 7.8 times compared with the results by excitation of Nd ions in the La sites. Up to now, this output power of the self-frequency-doubled laser represents the highest one in the Nd:LCB crystal, and the efficient emission at 533 nm should have promising applications in the visible range, such as laser displays, optical data storage, laser printing, etc. Meanwhile, the selective excitation of inequivalent active ions and the enhancement of the self-frequency-doubled laser may provide some inspiration for the investigation of multi-functional materials.
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http://dx.doi.org/10.1364/OL.42.004861DOI Listing
December 2017

High repetition rates optically active langasite electro-optically Q-switched laser at 1.34 μm.

Opt Express 2017 Oct;25(20):24007-24014

An electro-optically Q-switched pulsed laser at 1.34 μm with a repetition rate of 100 kHz applying optically active langasite (LaGaSiO) crystal has been reported. With Nd:YVO as laser crystal, the electro-optically Q-switched pulsed lasers were obtained with the maximum repetition rate of 100 kHz, maximum average output power of 2.42 W, and a minimum pulse width of 2.4 ns. Based on the theory of rate equations, the optimal pulse energy of the electro-optical Q-switching could be calculated. The experimental results have been found to be matched well with the theoretical calculations. To the best of our knowledge, this work presents the highest repetition rate and shortest pulse width which are achieved by an electric-optic LGS Q-switching at the wavelength of 1.34 μm, and it enriches the material categories for generating the high repetition rate pulsed laser.
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http://dx.doi.org/10.1364/OE.25.024007DOI Listing
October 2017

Ultrabroadband MoS Photodetector with Spectral Response from 445 to 2717 nm.

Adv Mater 2017 May 23;29(17). Epub 2017 Feb 23.

State Key Laboratory of Crystal Materials and Institute of Crystal Materials, Shandong University, Jinan, 250100, China.

Photodetectors with excellent detecting properties over a broad spectral range have advantages for the application in many optoelectronic devices. Introducing imperfections to the atomic lattices in semiconductors is a significant way for tuning the bandgap and achieving broadband response, but the imperfection may renovate their intrinsic properties far from the desire. Here, by controlling the deviation from the perfection of the atomic lattice, ultrabroadband multilayer MoS photodetectors are originally designed and realized with the detection range over 2000 nm from 445 nm (blue) to 2717 nm (mid-infrared). Associated with the narrow but nonzero bandgap and large photoresponsivity, the optimized deviation from the perfection of MoS samples is theoretically found and experimentally achieved aiming at the ultrabroadband photoresponse. By the photodetection characterization, the responsivity and detectivity of the present photodetectors are investigated in the wavelength range from 445 to 2717 nm with the maximum values of 50.7 mA W and 1.55 × 10 Jones, respectively, which represent the most broadband MoS photodetectors. Based on the easy manipulation, low cost, large scale, and broadband photoresponse, this present detector has significant potential for the applications in optoelectronics and electronics in the future.
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http://dx.doi.org/10.1002/adma.201605972DOI Listing
May 2017

Broadband atomic-layer MoS2 optical modulators for ultrafast pulse generations in the visible range.

Opt Lett 2017 Feb;42(3):547-550

Visible lasers are a fascinating regime, and their significance is illustrated by the 2014 Noble prizes in physics and chemistry. With the development of blue laser diodes (LDs), the LD-pumped solid-state visible lasers become a burgeoning direction today. Constrained by the scarce visible optical modulators, the solid-state ultrafast visible lasers are rarely realized. Based on the bandgap structure and optoelectronic properties of atomic-layer MoS2, it can be proposed that MoS2 has the potential as a visible optical modulator. Here, by originally revealing layer-dependent nonlinear absorption of the atomic-layer MoS2 in the visible range, broadband atomic-layer MoS2 optical modulators for the visible ultrafast pulse generation are developed and selected based on the proposed design criteria for novel two-dimensional (2D) optical modulators. By applying the selected MoS2 optical modulators in the solid-state praseodymium lasers, broadband mode-locked ultrafast lasers from 522 to 639 nm are originally realized. We believe that this Letter should promote the development of visible ultrafast photonics and further applications of 2D optoelectronic materials.
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http://dx.doi.org/10.1364/OL.42.000547DOI Listing
February 2017

Theoretical investigations of broadband mid-infrared optical parametric amplification based on a La3Ga5.5Nb0.5O14 crystal.

Opt Express 2016 Oct;24(21):23957-23968

Recent progress in strong-field physics has stimulated the quest for intense mid-infrared ultrashort light sources. Optical parametric amplification (OPA) is one promising method to build up such sources, however, its development significantly relies on the availability of suitable nonlinear crystals. Here, we introduce a positive uniaxial crystal La3Ga5.5Nb0.5O14 (LGN), which exhibits a favorable set of optical properties for the application in a mid-IR OPA. We theoretically evaluate the performance of LGN as the nonlinear crystal of a mid-infrared OPA, with an emphasis on the bandwidth characteristic. We find that this crystal can support broadband amplifications across its entire mid-infrared transparent region up to 6 μm, outperforming other commonly-used mid-infrared crystals in terms of gain bandwidth. Few-cycle mid-infrared pulses at various wavelengths can be generated from the LGN-based optical parametric chirped-pulse amplifiers.
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http://dx.doi.org/10.1364/OE.24.023957DOI Listing
October 2016

Acentric langanite La3Ga5.5Nb0.5O14 crystal: a new nonlinear crystal for the generation of mid-infrared parametric light.

Opt Express 2016 Aug;24(16):17603-15

The mid-infrared spectral range extending from 2 to 6 μm is significant for scientific and technological applications. A promising nonlinear oxide crystal La3Ga5.5Nb0.5O14 (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.
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http://dx.doi.org/10.1364/OE.24.017603DOI Listing
August 2016

Efficient high repetition rate electro-optic Q-switched laser with an optically active langasite crystal.

Sci Rep 2016 07 27;6:30517. Epub 2016 Jul 27.

State Key Laboratory of Crystal Materials and Institute of Crystal Materials, Shandong University, Jinan 250100, China.

With an optically active langasite (LGS) crystal as the electro-optic Q-switch, we demonstrate an efficient Q-switched laser with a repetition rate of 200 kHz. Based on the theoretical analysis of the interaction between optical activity and electro-optic property, the optical activity of the crystal has no influence on the birefringence during Q-switching if the quarter wave plate used was rotated to align with the polarization direction. With a Nd:LuVO4 crystal possessing a large emission cross-section and a short fluorescence lifetime as the gain medium, a stable LGS Q-switched laser was designed with average output power of 4.39 W, corresponding to a slope efficiency of 29.4% and with a minimum pulse width of 5.1 ns. This work represents the highest repetition rate achieved so far in a LGS Q-switched laser and it can provide a practical Q-switched laser with a tunable high repetition rates for many applications, such as materials processing, laser ranging, medicine, military applications, biomacromolecule materials, remote sensing, etc.
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http://dx.doi.org/10.1038/srep30517DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4962309PMC
July 2016

Megahertz-level, high-power picosecond Nd:LuVO4 regenerative amplifier free of period doubling.

Opt Express 2016 Jun;24(13):13963-70

We report on a high repetition rate, high-power picosecond Nd:LuVO4 regenerative amplifier. Period doubling caused energy instability was eliminated at megahertz-level repetition rate with the modified seeding source. A multi-pass cell was used to improve the seed pulse energy to achieve complete suppression of the onset of bifurcation. At a maximum repetition rate of 1.43 MHz, the system produced 7.0-ps-long pulses with an average output power of 25.1 W, corresponding to a pulse energy of 17.6 μJ. At 100 kHz, the pulse energy increased to 205 μJ with an average power of 20.5 W. Moreover, the injected pulses with pulse duration of 5.1 ps broadened to 8.9 ps because of gain narrowing in the amplifier.
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June 2016
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