Influence of laser linewidth on external-cavity frequency doubling efficiency of a 1.56μm master oscillator fiber power amplifier

By using an external-cavity frequency-doubling master oscillator fiber power amplifier (MOPA), a 700~mW continuous-wave single-frequency laser source at 780~nm is produced. It is shown that the frequency doubling efficiency is improved when the seed diode laser is optically locked to a resonant frequency of a confocal Fabry--Perot (F-P) cavity. This phenomenon can be attributed to the narrowing of the 1.56~μ m laser linewidth and explained by our presented theoretical model. The experimental results are found to be in good agreement with the theoretical predictions.     

A 515-nm laser-pumped idler-resonant femtosecond BiB3O6 optical parametric oscillator

We report on an idler-resonant femtosecond optical parametrical oscillator(OPO)based on BiB₃O₆(BiBO)crystal,synchronously pumped by a frequency-doubled,mode-locked Yb:KGW laser at 515 nm.The idler wavelengths of OPO can be tuned from 1100 nm to 1540 nm.At a repetition rate of 75.5 MHz,the OPO generates as much as 400 mW of idler power with 3.1 W of pump power,the corresponding pulse duration is 80 fs,which is 1.04 times of Fourier transform-limited(FTL)pulse duration at 1305 nm.In addition,the OPO exhibits excellent beam quality with M²<1.8 at 1150 nm.To the best of our knowledge,this is the first idler-resonant femtosecond OPO pumped by 515 nm.     

Upconversion in Highly Doped Er~(3 )-Yb~( 3 ) Fiber Pumped by Ti∶Sapphire Laser at 800 nm

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｔｈｅｉｎｆｒａｒｅｄｔｏｖｉｓｉｂｌｅｕｐｃｏｎｖｅｒｓｉｏｎｐｒｏｃｅｓｓｅｓｉｎｒａｒｅｅａｒｔｈｄｏｐｅｄｆｉｂｅｒｈａｖｅｂｅｅｎａｔｔｒａｃｔｉｎｇｇｒｅａｔｉｎｔｅｒｅｓｔｂｅｃａｕｓｅｏｆｉｔｓａｐｐｌ?..     

Low temperature enhancement of alignment-induced spectral broadening of femtosecond laser pulses

The propagation of femtosecond laser pulses in N2-filled hollow fibers is studied both theoretically and experimentally. The laser pulse aligns the N2 molecules and changes the refractive index, which meanwhile modulates the spectrum of the pulse in turn. The dependence of the spectral modulation on the gas temperature is investigated. We find that both spectral broadening and frequency red-shift are enhanced at low temperature. The degree of enhancement is found to be dependent on the pulse duration. Based on our findings, we propose a method for femtosecond pulse spectral broadening and few-cycle pulse generation via the molecular alignment.     

The geometric phase in nonlinear frequency conversion

The geometric phase of light has been demonstrated in various platforms of the linear optical regime, raising interest both for fundamental science as well as applications, such as flat optical elements. Recently, the concept of geometric phases has been extended to nonlinear optics, following advances in engineering both bulk nonlinear photonic crystals and nonlinear metasurfaces. These new technologies offer a great promise of applications for nonlinear manipulation of light. In this review, we cover the recent theoretical and experimental advances in the field of geometric phases accompanying nonlinear frequency conversion. We first consider the case of bulk nonlinear photonic crystals, in which the interaction between propagating waves is quasi-phase-matched, with an engineerable geometric phase accumulated by the light. Nonlinear photonic crystals can offer efficient and robust frequency conversion in both the linearized and fully-nonlinear regimes of interaction, and allow for several applications including adiabatic mode conversion, electromagnetic nonreciprocity and novel topological effects for light. We then cover the rapidly-growing field of nonlinear Pancharatnam-Berry metasurfaces, which allow the simultaneous nonlinear generation and shaping of light by using ultrathin optical elements with subwavelength phase and amplitude resolution. We discuss the macroscopic selection rules that depend on the rotational symmetry of the constituent meta-atoms, the order of the harmonic generations, and the change in circular polarization. Continuous geometric phase gradients allow the steering of light beams and shaping of their spatial modes. More complex designs perform nonlinear imaging and multiplex nonlinear holograms, where the functionality is varied according to the generated harmonic order and polarization. Recent advancements in the fabrication of three dimensional nonlinear photonic crystals, as well as the pursuit of quantum light sources based on nonlinear metasurfaces, offer exciting new possibilities for novel nonlinear optical applications based on geometric phases.     

Noise-free frequency conversion of quantum states

In this paper,the frequency conversion of quantum states based on the intracavity nonlinear interaction is proposed.The fidelity of an input state after frequency conversion is calculated,and it is shown the noise-free frequency conversion of a quantum state can be achieved by injecting a strong signal field.The dependences of conversion efficiency on the pump parameter,extra losses and input state amplitude are also analysed.     

A mechanically tuned Kerr comb in a dispersion-engineered silica microbubble resonator

This paper discusses the developement and investigation of a silica microbubble resonator(MBR) that is optimized to cancel mode dispersion with material dispersion, at a wavelength of approximately 1550 nm and maintain a quality factor of an optical mode as large as 5.4 × 10~7. Benefitting from the near-zero dispersion and high quality factor, a primary optical comb is generated in the MBR using cascaded four-wave mixing processes, which span over 300 nm with several tens of teeth. Furthermore, the frequency comb could be gradually tuned by mechanically stretching the MBR. This tunable Kerr comb has multiple potential applications in precision measurements and sensing applications, such as molecular spectroscopy and ranging.     

Nonlinear images of scatterers in chirped pulsed laser beams

The bandwidth and the duration of incident pulsed beam are proved to play important roles in modifying the nonlinear image of amplitude-type scatterer.It is found that the initially positive chirp-type bandwidth can suppress the nonlinear image,while the negative one can enhance it,and that both effects are inversely proportional to the incident pulse duration.Numerical simulations further demonstrate that the location of nonlinear image is at the conjugate plane of the scatterer and that,for negatively pre-chirped pulsed beam,the nonlinear image peak intensity can be higher than that in the corresponding monochromatic case under certain conditions.Moreover the effect of group velocity dispersion on nonlinear image is found to be similar to that of chirp-type bandwidth.     

A Novel Tunable Dual-frequency Laser with Large Frequency Difference

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High-energy picosecond single-pass multi-stage optical parametric generator and amplifier

We demonstrate a new management of multi-stage optical parametric generator(OPG)and amplifier(OPA)to obtain high-energy picosecond sources with high beam quality.The setup of multi-stage OPG-OPA requires mode-matching between the pump beam and the stable mode of the OPG-OPA.In a proof-of-principle experiment,the single-pass multi-stage OPG-OPA consists of three walk-off compensated KTP crystal pairs and two lenses,pumped by an 86 ps,1064 nm 10 kHz picosecond laser.The signal light at~1.77μm has an average output power of 502 mW with record energy up to 50.2μJ.The beam quality factor of the signal light can be improved toM²_x ×M²_yafter filtering out about 40%signal power.To the best of our knowledge,it is the first picosecond single-pass multi-stage OPG-OPA pumped at kHz regime.     

飞秒激光中脉冲内差频技术进展

中红外激光具有多种优势,可以广泛地用到生物、化学、物理等科学研究领域。通常采用直接激射和非线性频率转换这两种方式产生中红外激光,然而,为了实现中红外宽带超短脉冲的发射,非线性频率下转换是现今的唯一方法。脉冲内差频（IP-DFG）是一种简单的非线性频率转换方法,文中对红外IP-DFG的工作做了详细的回顾,从中红外激光晶体和基于IP-DFG产生具有超宽带的中红外超短脉冲的先进工作两个方面做了综述和评论,分别比较了非线性晶体类型、驱动脉冲源、产生超宽带中红外脉冲的光谱范围、转化效率等,并在最后讨论和阐明了IP-DFG领域面临的机遇和挑战。

     

飞秒激光非线性频率转换的自适应优化过程

使用闭环控制的自适应控制光学系统对飞秒激光的波前进行调控,可以有效改善激光与物质相互作用中由于相位畸变或光路偏差导致的效率下降。利用可编程纯相位的液晶空间光调制器结合模拟退火算法设计的自适应优化系统,在BBO晶体的飞秒倍频过程中实现了对相位畸变和光路偏差导致倍频效率下降的自动补偿,从而实现飞秒倍频效率的最优化。     

激光大气成丝中的非线性光频转换

超快强激光在光学介质（如空气）中传播时由于克尔自聚焦效应和等离体散焦效应动态平 衡会发生一种独特的非线性激光成丝现象。激光成丝过程会诱导一些独特的物理现象,如非线性 光频转换产生超连续光谱、等离子体诱导高压放电、锥形辐射等,在大气传感、天气控制等研究 领域具有重要的应用前景。本文针对飞秒激光大气成丝过程中与传输介质相互作用所诱导的非线 性发光过程,介绍了激光大气成丝所产生的超连续光谱（白光）激光、谐波产生和太赫兹波辐射 三种非线性光频转换现象,并着重探讨了太赫兹波辐射的物理机理、研究现状和应用前景。     

基于飞秒光频梳的双频He-Ne激光器频率测量

利用光纤飞秒光频梳和外腔可调谐半导体激光器, 建立了一套双频He-Ne激光器频率测量系统. 选用铷钟作为系统的频率基准, 通过将外腔半导体激光锁定至光频梳使得其频率溯源至铷钟, 再利用外腔可调谐半导体激光与双频He-Ne激光器输出的正交偏振激光拍频, 同时测量两路正交偏振激光频率. 将可调谐半导体激光器锁定至光频梳第1894449个梳齿, 其绝对频率为473612190000.0±2.7 kHz, 相对不确定度为5.7×10^-12. 对商品双频He-Ne激光器进行频率测量实验, 双频He-Ne激光器水平方向偏振激光频率均值为473612229934 kHz, 竖直方向偏振激光频率均值为473612232111 kHz, 平均时间为1024 s的相对Allan标准差为5.2×10^-11, 频差均值为2.177 MHz, 标准偏差为2 kHz.     

Optimization of type-II frequency doubling of spatial and temporal limited laser light in nonlinear crystals

Type-II frequency doubling of short Gaussian laser pulses is studied theoretically. The situation is analysed when the group velocity mismatch and the walk-off angle of the interacting waves limit the frequency conversion efficiency. It is shown that with collinear ‘o’ and ‘e’ polarized fundamental waves a temporal and spatial separation of the fundamental beams is necessary to compensate for both effects. Results of the presented model are discussed for KDP crystals.     

Ba1-xB2-y-zO4SixAlyGaz晶体和频可调谐深紫外飞秒激光器

介绍了一种基于新型非线性晶体Ba_1-xB_2-y-zO₄Si_xAl_yGa_z 的可调谐深紫外飞秒激光光源. 从理论上分析了基频光和倍频光在通过非线性晶体时所造成的空间走离和群速度失配, 为了补偿空间走离以及波长调谐过程中晶体折射造成的光束偏离现象, 将两块相同的倍频晶体成镜像放置来产生二次谐波. 并调节延迟线的长度来补偿基频光和倍频光之间的群速度失配, 从而提高和频转换效率. 然后通过和频方式进行三倍频和四倍频来突破晶体相位匹配条件的限制, 产生了波长低于200 nm的深紫外飞秒激光. 利用钛宝石激光器提供基频光光源, 最终在250–300 nm, 192.5–210 nm 范围内获得了高重频、可调谐超短脉冲紫外和深紫外激光. 并在基频光波长为800 nm时, 得到的二倍频、三倍频和四倍频的功率分别为1.28 W, 194 mW和5.8 mW, 相对于前一级的转换效率依次为46.14%, 15.16%和3%. 采用互相关法测量得到266.7 nm紫外激光的脉冲宽度约为640.4 fs.     

Micromachining soda-lime glass by femtosecond laser pulses

The physical process of forming a modified region in soda-lime glass was investigated using 1 kHz intense femtosecond laser pulses from a Ti: sapphire laser at 775 nm. Through the modifications induced by the femtosecond laser radiation using selective chemical etching techniques, we fabricated reproducible and defined microstructures and further studied their morphologies and etching properties. Moreover, a possible physical mechanism for the femtosecond laser modification in soda-lime glass was proposed.     

BBO晶体中级联非线性效应的实验研究

采用800 nm和400 nm两束飞秒激光脉冲在BBO晶体中同时满足相位匹配条件,产生差频、和频及其级联效应.实验运用了中心波长800 nm、重复频率10 Hz、脉宽60 fs及光斑直径7 mm的钛蓝宝石再生放大飞秒激光,输出约为10 mJ的能量以7:3分束.其中7 mJ光脉冲用一块非线性晶体BBO倍频至400 nm获得1.45 mJ能量,然后与另一束800 nm的3 mJ基频激光以非共线方式注入到另一块BBO中,在兼顾和频与差频的相位匹配条件下,即晶体对于和频与差频相位匹配状态同时存在少量失谐时,会同时产生267 nm与800 nm的和频与差频效应,新产生光波与原入射激光脉冲又经过进一步非线性混频作用,最终得到多达10余束可见、紫外的一维列阵.分析了此级联非线性效应的产生机理并讨论了入射光强度,啁啾,延迟等因素对级联效果的影响.     

高功率全正色散锁模掺Yb3+双包层光纤飞秒激光器

以芯径为30 μm的掺Yb³⁺双包层光纤为增益介质, 利用非线性偏振旋转技术以及光栅-小孔结构组成的光谱滤波器提供有效的振幅调制, 实现了稳定的全正色散耗散孤子锁模运转. 激光器直接输出重复频率为76.6 MHz、平均功率达6.3 W的超短脉冲, 单脉冲能量可达82 nJ. 直接输出脉冲宽度为1.33 ps, 经腔外压缩后的宽度为377 fs. 通过调节光栅角度还实现了输出脉冲中心波长在1025—1078 nm范围内的调谐.     

飞秒钛宝石光学频率梳的精密锁定

经相位锁定后的飞秒钛宝石光学频率梳已经广泛用于绝对光频的测量，这是光频标领域一个革命性的突破.在自建的90MHz飞秒钛宝石激光器的基础上首先采用光子晶体光纤将其光谱展宽到一个光倍频程，接着利用锁相环技术分别将重复频率和载波包络频移同时高精度地锁定到一台稳定度为6×10^－14的Cs钟上，进而得到了稳定度相同的飞秒光学频率梳.