Photoinduced Second Harmonic Generation of Bi_2S_3 Microcrystallite Doped Silica Glass

Silica glasses doped with Bi2S3 microcystallite was prepared by the sol-gel process. Photoinduced second harmonic generation (SHG) was observed in the glass when it was irradiated with intense 1.06 mum and frequency doubled laser beams from a mode-locked Nd: YAG laser. It was found that the signal intensity increased with the irradiating time and approached a saturation gradually. The effect may be explained reasonably by the DC field model.

开放型TDLAS-WMS技术CO_(2)痕量气体检测

采用窄线宽、边模抑制高的DFB激光器研制一套开放型TDLAS波长调制技术气体检测装置。选取2004 nm处CO_(2)分子吸收峰作为吸收谱线,采用锁相放大器进行调制、解调后的二次谐波信号幅值检测气体浓度大小。设计基于开放环境中的Herriott型气体吸收池,使用ZEMAX非序列模式进行吸收池仿真,光线追迹后理论光程可达到1350 mm,实际光程由50 mm增加到300 mm,检测浓度下限数值由原先的1300 ppmv降低到214.28 ppmv,有效提高了系统的检测下限能力。配置不同浓度的CO_(2)气体检测,得到二次谐波信号幅值与浓度之间呈现很好的线性关系,其拟合系数为0.99839,可通过拟合直线方程计算得出待测气体的浓度。配置300 ppmv的CO_(2)进行Allan方差分析,积分时间到101.6 s时,Allan方差处于平稳状态,检测系统的灵敏度为1.512×10^(-5)。检测结果表明检测装置实现了对CO_(2)气体浓度准确测量。该装置可进行结核分枝杆菌呼吸产生的CO_(2)气体浓度进行检测,为肺结核病诊断提供依据。

HL-2M装置CO_(2)色散干涉仪研制

研制了一套新型CO_(2)激光色散干涉仪用于HL-2M装置初始放电期间的电子密度测量。该系统采用基于激光倍频的色散测量原理,能够消除机械振动产生的相位误差。该系统使用全新的调相式信号调制,研发了相应的数据采集/处理/上传系统。根据实验测量结果表明,CO_(2)激光色散干涉仪和微波干涉仪测量曲线基本一致,色散干涉仪系统的测量精度约为2×10^(17)m^(-3),密度测量上限能达到1010^(21)m^(-3)。

基于近红外吸收光谱技术的高精度CO_(2)检测系统的研制

为了准确测量地震断裂带溢出的痕量CO_(2)气体浓度,文中采用可调谐半导体激光吸收光谱(TDLAS)技术,选取波数4978.202 cm^(-1)作为CO_(2)检测系统的吸收谱线,采用有效光程为40 m的多通池,以STM32作为主控和数据处理核心器件,研制了高精度CO_(2)检测系统。针对系统中的探测器噪声与光学干涉条纹噪声,利用卡尔曼-小波分析算法滤波提升系统性能。实验表明,与滤波前相比,系统在50 ppmv CO_(2)浓度下的二次谐波信噪比提升了2.06倍。在不同CO_(2)浓度下(50、300、1000、4000、8000 ppmv),系统误差为2.57%~2.66%。系统测量4000 ppmv浓度下的CO_(2)时检测精密度达到20.9 ppmv。利用Allan方差分析得出,积分时间在约61 s时对应的最低探测下限(MDL)为5.2 ppmv,实现了对CO_(2)气体的高精度测量。结果表明,所设计的高精度CO_(2)系统可以在气体检测领域为预测地震前兆提供良好前景。

Tunable femtosecond near-infrared source based on a Yb:LYSO-laser-pumped optical parametric oscillator

We demonstrate a widely tunable near-infrared source from 767 nm to 874 nm generated by the intracavity second harmonic generation （SHG） in an optical parametric oscillator pumped by a Yb：LYSO solid-state laser. The home-made Yb：LYSO oscillator centered at 1035 nm delivers an average power of 2 W and a pulse duration as short as 351 fs. TWo MgO doped periodically poled lithium niobates （MgO：PPLN） with grating periods of 28.5-31.5 μm in steps of 0.5 μm and 19.5-21.3μm in steps of 0.2 μm are used for the OPO and intracavity SHG, respectively. The maximum average output power of 180 mW at 798 nm was obtained and the output pulses have pulse duration of 313 fs at 792 nm if a sech2-pulse shape was assumed. In addition, tunable signal femtosecond pulses from 1428 nm to 1763 nm are also realized with the maximum average power of 355 mW at 1628 nm.

超脉冲CO_(2)点阵激光联合强脉冲光治疗深Ⅱ度烧伤后瘢痕的效果分析

目的深Ⅱ度烧伤患者经治疗后均遗留不同程度的瘢痕,探讨早期采用超脉冲二氧化碳(CO_(2))点阵激光联合强脉冲光治疗对瘢痕色泽、颜色、厚度、柔软度、粗糙度、血管分布等临床影响。方法选取佛山市高明区人民医院烧伤整形科室收治的自2018年1月-2019年6月的50例深Ⅱ度烧伤患者做为研究对象,随机数字表法分为对照组(烧伤创面愈合2周后开始强脉冲光治疗,每4周1次,连续治疗3次,n=25)、研究组(在对照组患者基础上,待强脉冲光治疗结束1个月后,开始行超脉冲CO_(2)点阵激光治疗,每3个月1次,连续治疗3次,n=25),治疗后随访3个月。分别采用患者评估量表(PSAS),观察者评估量表(OSAS)、温哥华瘢痕评估量表(VSS)评价患者瘢痕恢复情况;比较临床治疗有效率。结果治疗前,两组间PSAS、OSAS、VSS评分比较无统计学差异(P>0.05);治疗结束随访3个月后,两组患者PSAS、OSAS、VSS评分均低于治疗前(P<0.05),且研究组患者上述评分较对照组降低更显著(P<0.05)。研究组患者临床治疗总有效率高于对照组(P<0.05)。结论针对深Ⅱ度烧伤患者愈合2周后遗留的瘢痕,先进行3次强脉冲光治疗后,间隔1个月,再联合3次超脉冲CO_(2)点阵激光治疗,可更好地减轻瘢痕色素沉着、使瘢痕表面更柔软、降低瘢痕的厚度,从而有效提高疗效。

Second harmonic generation in a high-Q lithium niobate microresonator fabricated by femtosecond laser micromachining

We report on second harmonic generation(SHG) in on-chip high-Q(>105) lithium niobate(Li Nb O3, LN) microresonators fabricated by femtosecond laser micromachining. We examine the efficiency of SHG with either a continuous-wave(CW) or an ultrashort pulsed pump laser. The normalized conversion efficiencies of SHG obtained with the CW and pulsed pump lasers are measured to be 1.35×10?5 m W?1 and 2.30×10?6 m W?1, respectively.

An on-Si directional second harmonic generation amplifier for MoS2/WS2 heterostructure

Transition metal dichalcogenides(TMD)heterostructure is widely applied for second harmonic generation(SHG)and holds great promises for laser source,nonlinear switch,and optical logic gate.However,for atomically thin TMD heterostructures,low SHG conversion efficiency would occur due to reduction of light-matter interaction length and lack of phase matching.Herein,we demonstrated a facile directional SHG amplifier formed by MoS2/WS2 monolayer heterostructures suspended on a holey SiO_(2)/Si substrate.The SHG enhancement factor reaches more than two orders of magnitude in a wide spectral range from 355 to 470 nm,and the radiation angle is reduced from 38°to 19°indicating higher coherence and better emission directionality.The giant SHG enhancement and directional emission are attributed to the great excitation and emission field concentration induced by a self-formed vertical Fabry-Pérot microcavity.Our discovery gives helpful insights for the development of two-dimensional(2D)nonlinear optical devices.

ReSe_(2)连续波锁模Nd:YVO_(4)腔内倍频绿光激光器

为了发展新型二维材料在倍频锁模激光器中的应用,本文采用ReSe_(2)二维材料作为可饱和吸收体锁模元件,研究二极管端面泵浦Nd:YVO_(4)腔内倍频绿光固体激光器,获得兆赫兹高重频、纳秒窄脉宽的绿光脉冲激光输出。采用紧凑V型腔设计和腔内倍频方案,实现1064 nm基频光的被动锁模振荡,结合非线性晶体LiB3O5和KTiOPO_(4)完成二次谐波频率变换,产生532 nm倍频激光脉冲。在LiB3O5晶体倍频作用下,连续波锁模脉冲绿光输出的重复频率为87.51 MHz,脉冲宽度为3.5 ns,平均功率可达到240 mW。在相同条件下,利用KTiOPO_(4)晶体倍频作用,最大输出功率可超过470 mW。研究结果为发展高采样率水下激光探测技术提供了可用的绿光脉冲源。

A pressure-calibration method of wavelength modulation spectroscopy in sealed microbial growth environment

A new pressure-calibration method for calibrating the reduction of second harmonic(2f)amplitude caused by pressure broadening effect in sealed microbial growth environment is present.The new method combines with linewidth compensation and modulation depth compensation and makes the 2f amplitude accurately retrieve metabolic CO_(2) in microbial growth.In order to verify the method,a simulation experiment is developed,in which the increasing CO_(2) concentration leads to the increasing pressure.Comparing with the relation between the traditional 2f amplitude and gas concentration,there is a monotonous relation between the calibrated 2f amplitude and CO_(2) concentration,particularly,a linear relation is present when the CO_(2) concentration is replaced with the CO_(2) particle number.In terms of microbial measurement,the growth of Escherichia coli is measured,and the culture bottle is sealed during the microbial growth process.The experimental results show that,comparing to the microbial growth retrieved by traditional 2f amplitude,the calibrated 2f amplitude can accurately retrieve microbial growth in sealed environment.

High efficiency second harmonic generation of nanojoule-level femtosecond pulses in the visible based on BiBO

We demonstrate high efficiency second harmonic generation(SHG) of near infrared femtosecond pulses using a BiB3 O6 crystal in a single-pass tight focusing geometry setup. A frequency doubling efficiency of 63% is achieved, which is,to the best of our knowledge, the highest value ever reported in the femtosecond regime for such low energy(nJ-level)pumping pulses. Theoretical analyses of the pumping scheme focusing waist and the SHG efficiency are performed, by numerically solving the three wave mixing coupled equations in the plane-wave scenario and by running simulations with a commercial full 3 D code. Simulations show a good agreement with the experimental data regarding both the efficiency and the pulse spectral profile. The simulated SHG pulse temporal profile presents the characteristic features of the group velocity mismatch broadening in a ‘thick' crystal.

Reversible phase transition for switchable second harmonic generation in 2D perovskite microwires

Highly efficient second-harmonic generation(SHG)has facilitated the development of nanophotonics and sustained promising applications,ranging from electro-optical modulation,frequency conversion,and optical frequency combs to pulse characterization.Although controllable SHG switching has been observed in nanophotonics structures and molecule systems,the relatively small SHG switching contrast impedes its application in switchable nonlinear optics.Herein,reversible phase transitions between glassy and crystalline states without material degradation are demonstrated based on solution-processed chiral perovskite microwire arrays.Breaking of lattice inversion symmetry and high crystallinity support efficient SHG in microwire arrays.By synergy of high-performance SHG and reversible phase transitions between glassy and crystalline states,reversible switching of SHG is demonstrated under facile conditions.The high SHG switching performances,together with a small footprint,pave the way toward the integration of switchable nonlinear devices based on microwire arrays.

Fabrication of amorphous nanoporous ZrO_(2)/SiO_(2) aerogel enabling nonlinear optical properties

Amorphous oxides have unique physicochemical properties with extensive opto-electronic applications such as the thin-film transistor,light-emitting diode backplanes,and supercontinuum generation.In this contribution,we synthesize the amorphous ZrO_(2)/SiO_(2) nanoporous aerogel with high structural integrity.With the femtosecond excitation laser at 800–1,064 nm,the broadband second harmonic generation is observed.The nonlinear optical properties of the as-prepared ZrO_(2)/SiO_(2) aerogel are investigated at 1.0μm and 1.5μm for the first time.Subsequently,the amorphous ZrO_(2)/SiO_(2) saturable absorber is originally applied in the Yb-doped and Er-doped fiber lasers to realize the mode-locking operations.In the Yb-doped fiber laser,the dissipative soliton resonance mode-locking operation is demonstrated with the largest pulse duration of 22 ns at a repetition rate of 7.8 MHz and a high signal-to-noise ratio of 64 dB.In the Er-doped fiber laser,a conventional soliton mod-locking regime is observed with an ultrashort pulse width of 960 fs,a repetition frequency of 6.55 MHz,and a time-bandwidth production of 0.347.Our work shows the good ability of the ZrO_(2)/SiO_(2) aerogel in generating ultrafast pulses and extends the saturable absorber into the amorphous material realm.

Angle Measurement Based on Second Harmonic Generation Using Artificial Neural Network

This article proposed an angle measurement method based on second harmonic generation(SHG)using an artifcial neural network(ANN).The method comprises three sequential parts:SHG spectrum collection,data preprocessing,and neural network training.First,the referenced angles and SHG spectrums are collected by the autocollimator and SHG-based angle sensor,respectively,for training.The mapping is learned by the trained ANN after completing the training process,which solves the inverse problem of obtaining the angle from the SHG spectrum.Then,the feasibility of the proposed method is verifed in multiple-peak Maker fringe and single-peak phase-matching areas,with an overall angle measurement range exceeding 20,000 arcseconds.The predicted angles by ANN are compared with the autocollimator to evaluate the measure-ment performance in all the angular ranges.Particularly,a sub-arcsecond level of accuracy and resolution is achieved in the phase-matching area.

中波红外激光技术最新进展

3～5μm中红外波段激光源是近年来备受国内外关注的研究热点,本文综合评述了产生中红外波段激光的5种主要方法(CO2激光倍频技术、泛频CO激光技术、光学参量振荡器、氟化氘激光器、Fe2+∶ZnSe固体激光技术)的国内外发展现状,总结分析了各种方法的关键技术和存在的问题,指出了该技术的未来发展趋势。

High-efficiency 50 W burst-mode hundred picosecond green laser

We report high-energy,high-efficiency second harmonic generation in a near-infrared all-solid-state burst-mode picosecond laser at a repetition rate of 1 kHz with four pulses per burst using a type-I noncritical phase-matching lithium triborate crystal.The pulses in each burst have the same time delay(~1 ns),the same pulse duration(~100 ps)and different relative amplitudes that can be adjusted separately.A mode-locked beam from a semiconductor saturable absorber mirror is pulse-stretched,split into seed pulses and injected into a Nd:YAG regenerative amplifier.After the beam is reshaped by aspheric lenses,a two-stage master oscillator power amplifier and 4f imaging systems are applied to obtain a high power of^100 W.The 532 nm green laser has a maximum conversion efficiency of 68%,an average power of up to 50 W and a beam quality factor M^2 of 3.5.

Wavelength and duration tunable soliton generation from a regeneratively mode-locked fiber laser

A 10-GHz soliton source with pulse duration between 4-8 ps and wavelength continuously tunable from 1530 nm to 1563 nm is presented. Using regeneratively mode-locking technology, the harmonically mode-locked fiber ring laser could work without pulse dropout at room temperature when no cavity length or polarization maintaining mechanism is available. Applying only one 980-nm laser diode pump, the average output power reaches more than 4 mW.

Laser at 532 nm by intracavity frequency-doubling in BBO

A simple and compact linear resonator green laser at 532 nm is generated by intracavity frequencydoubling of a diode-side-pumped acousto-optically（AO）Q-switched Nd：YAG laser at 1064 nm.Two acoustooptic Q-switches were placed orthogonally with each other to improve the hold-off capacity.As high as 214 W of continuous-wave（CW）and 154 W of quasi-continuous-wave（QCW）output power at 1064 nm were obtained when the pumping power was 1598 W.The type I phase-matched BBO crystal was used as the nonlinear medium in the second harmonic generation.A green laser with an average output power of 37 W was obtained at a repetition rate of 20 kHz and a pulse width of 54 ns,which corresponds to pulse energy of 1.85 mJ per pulse and a peak power34.26 kW,respectively.

Epitaxial growth of 2D gallium selenide flakes for strong nonlinear optical response and visible-light photodetection

As an emerging groupⅢ–Ⅵsemiconductor two-dimensional(2D)material,gallium selenide(GaSe)has attracted much attention due to its excellent optical and electrical properties.In this work,high-quality epitaxial growth of few-layer GaSe nanoflakes with different thickness is achieved via chemical vapor deposition(CVD)method.Due to the non-centrosymmetric structure,the grown GaSe nanoflakes exhibits excellent second harmonic generation(SHG).In addition,the constructed GaSe nanoflake-based photodetector exhibits stable and fast response under visible light excitation,with a rise time of 6 ms and decay time of 10 ms.These achievements clearly demonstrate the possibility of using GaSe nanoflake in the applications of nonlinear optics and(opto)-electronics.

Photon-interactions with perovskite oxides

Photons with variable energy, high coherency, and switchable polarization provide an ideal tool-kits for exploring the cutting-edge scientific questions in the condensed matter physics and material sciences. Over decades, extensive researches in the sample fabrication and excitation have employed the photon as one of the important means to synthesize and explore the low-dimensional quantum materials. In this review, we firstly summarize the recent progresses of the state-of-the-art thin-film deposition methods using excimer pulsed laser, by which syntactic oxides with atomic-unit-cell-thick layers and extremely high crystalline quality can be programmatically fabricated. We demonstrate that the artificially engineered oxide quantum heterostructures exhibit the unexpected physical properties which are absent in their parent forms. Secondly, we highlight the recent work on probing the symmetry breaking at the surface/interface/interior and weak couplings among nanoscale ferroelectric domains using optical second harmonic generation. We clarify the current challenges in the insitu characterizations under the external fields and large-scale imaging using optical second harmonic generation. The improvements in the sample quality and the non-contact detection technique further promote the understanding of the mechanism of the novel properties emerged at the interface and inspire the potential applications, such as the ferroelectric resistive memory and ultrahigh energy storage capacitors.