基于自相位调制光谱选择驱动的无标记自发荧光多倍频显微镜系统

由飞秒激光驱动的非线性光学显微镜技术在医学组织成像中具有很多独特的优势,包括多种成像模态、高对比度、高分辨率和无标记的深层光学切片能力等.由于缺乏波长可灵活调谐的飞秒激发光源,导致在多模态成像的同时难以兼顾每种模态的对比度,从而制约了非线性光学显微镜在医学诊断中的广泛应用.本文采用基于自相位调制光谱选择的光纤激光光源,获得了中心波长在990—1110 nm范围内可调谐的高能量飞秒脉冲,并用于驱动非线性光学显微镜.采用990 nm的飞秒脉冲,通过双光子激发荧光和二倍频对胃组织成像,进一步结合图像拼接技术成功获得了胃组织的双模态大视场图像;利用1110 nm的飞秒脉冲,实现了无标记自发荧光多倍频显微镜技术,同时高效激发了胃组织的双光子激发荧光、三光子激发荧光、二倍频和三倍频信号,获得了胃组织的多模态图像.     

中红外可调谐大能量飞秒脉冲激光产生

可调谐中红外飞秒光纤激光器具有非常普遍的应用,从而引起了人们的广泛关注。目前,非线性光纤中的拉曼孤子自频移效应是实现大范围可调谐飞秒脉冲激光的理想方法之一。然而,非线性光纤中其他高阶非线性效应的产生通常会限制拉曼孤子脉冲的能量提升。本文提出了利用有源掺杂光纤作为非线性介质和增益介质实现可调谐大能量中红外飞秒激光脉冲的方法。在理论上研究了有源掺杂非线性光纤中高阶孤子劈裂和孤子自频移效应的产生,以及线性增益对波长移动拉曼孤子能量、脉宽、光谱的影响。结果表明,通过为波长红移的低能量拉曼孤子提供线性增益,孤子脉冲的能量得到了显著提升且保持了其单脉冲特性,脉冲宽度为45 fs,且孤子脉冲的波长可通过所提供的增益进行大范围调谐。因此,利用有源掺杂光纤作为非线性介质是实现大能量可调谐中红外飞秒脉冲激光的一种有效方法。     

高非线性光子晶体光纤中飞秒脉冲的传输特性和超连续谱产生机制的实验研究及模拟分析

用实验和数值模拟两种方法研究了高非线性光子晶体光纤中飞秒激光脉冲的传输特性和超连续谱的产生机理，给出了抽运脉冲在三种不同中心波长情况下输出光谱展宽并形成超连续谱的实际测量及理论模拟结果.研究表明：在零色散波长抽运时，光谱展宽以自相位调制为主，同时三阶色散的影响明显，传输脉冲在时域内出现振荡次峰.而在反常色散区抽运时，光谱展宽的初期以自相位调制为主，随后根据抽运功率的不同孤子自频移、高阶光孤子的裂变和四波混频效应会逐渐增强，进而成为光谱展宽的主要原因.与此相应，在时域中能明显看到孤子的形成和红移，飞秒传输脉 关键词： 光子晶体光纤 高非线性光子晶体光纤 飞秒脉冲激光 超连续谱     

掺镱硼酸钙氧钇飞秒激光器及在拉锥光纤中产生跨倍频程超连续光

跨倍频程超连续光谱的产生是光学频率梳系统中测量载波包络相移频率的关键.本文采用拉锥单模光纤作为非线性光谱展宽介质, 将半导体激光(LD)抽运的掺镱硼酸钙氧钇(Yb:YCOB)振荡器输出的飞秒激光耦合到该拉锥光纤中, 通过飞秒激光在光纤中发生的相位调制、四波混频等非线性效应将光谱展宽至超过倍频程的范围.振荡器输出的飞秒激光脉冲宽度为130 fs, 中心波长为1052 nm, 重复频率为76.8 MHz, 平均功率为620 mW, 耦合进单模拉锥光纤后获得了光谱覆盖范围从550 nm至1350 nm的跨倍频程超连续光谱, 最大输出平均功率为323 mW, 耦合效率达到52%.为进一步实现全固态飞秒激光光学频率梳提供了重要基础.     

宽光谱全正色散锁模掺镱光纤激光器

介绍了一种全正色散宽光谱被动锁模掺镱光纤激光器,利用非线性偏振旋转技术实现全正色散掺镱光纤激光器的被动锁模.当泵浦功率输出为500mW时,激光脉冲输出功率大于139mW,重复频率约为28.1MHz,脉冲宽度为3.8ps.为了进一步研究全正色散光纤激光器的宽光谱输出特性,在腔内熔接50m单模光纤,同时去除双折射滤波片,在泵浦功率为500mW时,观察到稳定锁模单脉冲耗散孤子,光谱范围为1 005~1 140nm,输出激光脉冲最大平均功率为90mW,重复频率为3.58MHz,脉冲宽度为519ps.     

面向Li原子D1线频率测量应用的掺铒飞秒光纤光梳系统

报道了自主研制的面向Li原子D1线频率测量应用的掺铒飞秒光纤光学频率梳,包括飞秒激光源,频率探测及控制单元,光谱展宽及拍频单元.光纤光梳系统中飞秒激光光源是一套基于非线性偏振旋转锁模机制的掺铒飞秒光纤激光器,重复频率为196.5MHz,中心波长为1 572nm.利用f-2f法探测载波包络相移频率,获得信噪比约为40dB的信号(分辨率带宽300kHz).改变飞秒激光光源泵浦控制载波包络相移频率、频率稳定度是3.74×10-18/τ1/2;通过电光晶体和压电陶瓷改变飞秒激光光源腔长来控制重复频率frep、频率稳定度是1.75×10-13/τ1/2.利用高非线性光纤和倍频晶体将光纤光梳直接输出光谱由1 520～1 607nm扩展到671nm,获得了单模功率为208nW的光信号.与671nm单频激光拍频产生约为60dB(分辨率带宽1Hz)信号,满足Li原子D1线频率测量实验的需求.     

覆盖可见光波长的掺Er光纤飞秒光学频率梳

飞秒光学频率梳波长覆盖范围向可见光波长扩展对于碘稳频激光的绝对频率测量以及光钟研究中钟激光的绝对频率测量都具有十分重要的意义. 本文在自行研制掺Er光纤飞秒光学频率梳的基础上, 采用放大-倍频-扩谱的方案, 实现了激光输出波长向可见光波长的扩展. 掺Er光纤飞秒光学频率梳输出的一部分光激光脉冲, 功率约为8 mW, 首先经掺Er光纤放大器将功率提高到531 mW, 此后利用MgO: PPLN晶体倍频, 倍频后激光的功率为170 mW, 倍频效率为32%, 脉冲宽度为85 fs. 倍频后的激光通过光子晶体光纤进行光谱展宽. 通过优化入射光偏振状态可以实现波长覆盖500-1000 nm, 输出功率为85 mW, 耦合效率为50%. 采用小型化碘稳频532 nm Nd: YAG激光器输出激光与光学频率梳光谱展宽后的激光进行拍频可以获得30 dB的拍频信号. 覆盖可见光波长的掺Er光纤飞秒光学频率梳为可见光范围内激光的绝对频率测量提供了技术手段.     

全光纤高能量飞秒脉冲激光放大系统

研究了一种全光纤飞秒脉冲放大系统。其采用非线性放大环形镜结构的谐振腔输出宽光谱种子光,通过光纤啁啾脉冲放大技术抑制功率放大过程中的非线性累积;主放大部分结合双包层光纤与大模场光子晶体光纤熔接技术,输出中心波长1030nm,平均功率16.9W的高质量皮秒脉冲,经空间光栅对补偿色散后脉冲宽度324fs,单脉冲能量12.2μJ,峰值功率约26.4MW。该放大系统采用保偏光纤特种熔接技术实现全光纤化,相较于空间耦合放大具有光路结构简单,环境稳定性高等特点,有望推动高能量飞秒光纤激光工业化进程,提升其在复杂使用环境的适应性。     

光谱线宽与中心波长可同时调谐的高功率光纤激光实现3 kW输出

光谱灵活可调的高功率光纤激光在光谱合束、光声光谱检测和非线性频率变换等方面具有独特优势,近年来受到国内外研究人员的广泛关注。基于光谱灵活可调的超荧光光纤种子源,通过主振荡功率放大器结构实现了光谱中心波长1065～1085 nm可调谐、3 dB线宽2.4～13.8 nm可调谐的3 kW光纤激光输出。     

基于非线性放大环形镜的波长可调谐耗散孤子锁模光纤激光器

报道了一种基于非线性放大环形镜的"8"字形腔波长可调谐锁模掺镱光纤激光器。当泵浦功率为240 mW时,光纤激光器输出中心波长在1 064.1 nm处的耗散孤子,其光谱3 dB带宽为7.7 nm,重复频率为18.8 MHz,输出光信噪比高达71.2 dB,脉冲宽度为867 fs。分别通过调节偏振控制器和泵浦功率实现了锁模光纤激光器在1 032.8～1 065.1 nm以及1 037.4～1 041.9 nm内调谐输出。探究了不同锁模状态下的光谱与脉冲特性,获得了时间带宽积接近傅里叶变换极限的高斯型脉冲。该光纤激光器结构简单,易于调谐,稳定性好,可为实现波长调谐、耗散孤子锁模提供技术参考。     

Generation of wideband tunable femtosecond laser based on nonlinear propagation of power-scaled mode-locked femtosecond laser pulses in photonic crystal fiber

We implement an experimental study for the generation of wideband tunable femtosecond laser with a home-made power-scaled mode-locked fiber oscillator as the pump source.By coupling the sub-100 fs mode-locked pulses into a nonlinear photonic crystal fiber(NL-PCF),the exited spectra have significant nonlinear broadening and cover a spectra range of hundreds of nm.In experiment,by reasonably optimizing the structure parameters of NL-PCF and regulating the power of the incident pulses,femtosecond laser with tuning range of 900-1290 nm is realized.The research approach promotes the development of femtosecond lasers with center wavelengths out of the traditional laser gain media toward the direction of simplicity and ease of implementation.     

飞秒被动锁模环形腔掺Er3＋光纤激光器

在考虑增益、损耗、群速度色散、自相位调制、快速可饱和吸收体等各种参数同时作用情况下，分析了非线性偏振旋转效应自启动锁模机理，研究了腔体参数与锁模脉冲之间的关系，并给出飞秒被动锁模环形腔掺Er3＋光纤激光器实验原理。实验采用性能稳定的980nm半导体激光器作为抽运源，高掺杂短长度掺Er3＋光纤作为增益介质，利用非线性偏振旋转锁模技术，得到了稳定的飞秒自起振锁模光脉冲。抽运功率为23mW时，激光器输出锁模脉冲中心波长1552nm，3dB带宽为7.6nm，重复频率14.0MHz，平均输出功率0.43mW，自起振锁模泵浦阈值功率11.5mW,并观测到了稳定的高阶锁模脉冲输出。该激光器与报道过的相同结构光纤激光器相比,自起振泵浦阈值低、脉冲能量高、稳定性好，且频谱边带幅度小。     

Kilowatt-peak-power, single-frequency, pulsed fiber laser near 2 μm

We generated single-frequency pulses at kilowatt peak power from an all-fiber Tm-doped master oscillator power amplifier system, which is the first report of this kind (to the best of our knowledge) of a laser in the 2 μm region. Compared with the laser linewidth of seed pulses, spectral broadening by a factor of 3 was observed with the amplified pulses. This was attributed to self-phase modulation in passive pigtail fibers of the components (isolator and wavelength division multiplexing) that were placed after the fiber amplifier. The short pulse width (~7 ns) of the kilowatt-level pulses prevents an onset of stimulated Brillouin scattering in the long fiber. When launching the pulses into several-meter single-mode fiber, significant nonlinear spectral broadening occurs due to modulation instability in the fiber. This reaction is beneficial for generation of a mid- and long-wavelength IR supercontinuum in nonlinear IR fibers.     

高稳定性、高质量脉冲压缩飞秒光纤激光系统研究

报道了一款用于眼科手术的高稳定性、高质量脉冲压缩飞秒光纤主振荡功率放大系统. 振荡器采用混合腔方式增加了光纤双折射, 改善了非线性偏振旋转锁模在低重复频率下无法自启动的缺点, 提高了飞秒光纤激光器自启动锁模的稳定性. 研究了脉冲预啁啾与飞秒脉冲压缩质量的关系, 通过实验证明了光纤放大器的入射脉冲保持负的预啁啾状态可以得到最好的脉冲压缩结果. 实验最终实现了满足自启动锁模条件的重复频率19.4 MHz、平均功率1.2 W、脉冲宽度183 fs的激光脉冲, 目前这台激光器是国内首台具有自主知识产权并应用于动物角膜实验的飞秒光纤激光器.     

Chirped pulse amplification in single mode Tm:fiber using a chirped Bragg grating

We report femtosecond pulse generation and chirped pulse amplification in Tm:fiber. A mode-locked oscillator operating in the soliton regime produced 800 fs pulses with 5 nm spectral bandwidth, at 40 pJ pulse energy. This oscillator seeded a pre-amplifier that utilizes a Raman soliton self-frequency shift to produce wavelength tunable pulses with 3 nJ energy, reduced pulse duration of 150 fs, and increased bandwidth of 30 nm. For further amplification, the pulses were stretched up to 160 ps using a chirped Bragg grating (CBG). Stretched pulses were amplified to 85 nJ after compression in single-mode Tm:fiber and recompressed with the CBG as short as 400 fs. Compressed pulses were coupled into a highly nonlinear tellurite fiber to investigate the potential of this ultrashort pulse 2-μm fiber source as a pump for mid-IR supercontinuum generation.     

Passively mode-locked 10 GHz femtosecond Ti:sapphire laser

We report a mode-locked Ti:sapphire femtosecond laser emitting 42 fs pulses at a 10 GHz repetition rate. When operated with a spectrally integrated average power greater than 1 W, the associated femtosecond laser frequency comb contains approximately 500 modes, each with power exceeding 1 mW. Spectral broadening in nonlinear microstructured fiber yields comb elements with individual powers greater than 1 nW over approximately 250 nm of spectral bandwidth. The modes of the emitted comb are resolved and imaged with a simple grating spectrometer and digital camera. Combined with absorption spectroscopy of rubidium vapor, this approach permits identification of the mode index and measurement of the carrier envelope offset frequency of the comb.     

Low-repetition-rate,all-polarization-maintaining Yb-doped fiber laser mode-locked by a semiconductor saturable absorber

A low-repetition-rate, all-polarization-maintaining(PM)-fiber sub-nanosecond oscillator is presented, which is simple and low-cost, composed of standard components. The ring cavity is elongated by 114-m-long standard PM fiber, and passively mode-locked by a fiber pigtailed semiconductor saturable absorber. Linearly polarized pulses with 1.66 MHz repetition rate and 22 dB polarization extinction ratio are generated at a wavelength of 1030 nm, which is determined by an intracavity filter. In addition, to demonstrate that the oscillator is a good seed for high energy pulse generation, an all-fiber master oscillator power amplifier is built and amplified pulses with energy about 2 μJ are obtained.     

Diode-pumped Kerr-lens mode-locked femtosecond Yb:YAG ceramic laser

We experimentally demonstrated a diode-pumped Kerr-lens mode-locked femtosecond laser based on an Yb:YAG ceramic. Stable laser pulses with 97-fs duration, 2.8-nJ pulse energy, and 320-mW average power were obtained. The femtosecond oscillator operated at a central wavelength of 1049 nm and a repetition rate of 115 MHz. To the best of our knowledge, this is the first demonstration of a Kerr-lens mode-locked operation in a diode-pumped Yb:YAG ceramic laser with sub-100 fs pulse duration.     

Femtosecond mode-locked Yb fiber laser for single-mode fiber chirped pulse amplification system

High-peak-power laser systems are based on the chirped pulse amplification (CPA) technique. CPA laser system needs a mode-locked laser oscillator for stable ultrashort pulse laser generation. We report a single-mode fiber CPA system which consists of stable mode-locked Yb-doped fiber laser oscillator with a wide tuning range, chirped fiber Bragg grating stretcher, and two Yb-doped fiber amplifiers. The single-mode fibers can generate high-quality and single-mode beams which are stable for long time.     

基于石墨烯可饱和吸收体的纳秒锁模掺铥光纤激光器

报道了一种基于石墨烯可饱和吸收体的纳秒锁模掺铥光纤激光器.该激光器采用环形腔结构,利用自制的三层石墨烯薄膜作为可饱和吸收体实现锁模.同时在腔内插入一个窄带光纤光栅,约束腔内起振的纵模数,适当调节抽运功率和偏振控制器的角度,得到了重复频率为3.8 MHz、脉宽在3.8—94.3 ns之间灵活可调的2μm纳秒锁模脉冲输出,整个脉宽调节范围超过90 ns.此外,由于获得的兆赫兹纳秒锁模脉冲时间带宽积在49—1119范围内,即存在强烈的啁啾,因而可作为2μm波段啁啾脉冲放大系统中的种子源使用.