重复频率锁定的783 nm飞秒光纤激光器研制

设计并搭建了重复频率长时精确锁定的783 nm飞秒光纤激光器。该激光器基于全保偏非线性干涉环镜(NALM),实现掺铒光纤振荡器锁模脉冲输出,由与脉冲分离器级联的环境稳定掺铒光纤双级放大器进行功率放大,实现了平均功率1.30 W、脉冲宽度130 fs、重复频率77.1 MHz、1560 nm脉冲输出;通过周期极化铌酸锂(PPLN)光学晶体倍频,获得了平均功率为0.52 W、脉冲宽度为140 fs、783 nm脉冲输出。通过重复频率监测及锁相环技术,进一步将掺铒光纤振荡器的重复频率溯源至参考铷原子钟,12 h内频率抖动峰-峰值为5 mHz、标准偏差为1.2 mHz。该激光器系统具有稳定性高、集成度高、体积小的特点。     

基于非线性偏振旋转锁模技术的光纤飞秒激光振荡器

基于非线性偏振旋转（nonlinear polarization rotation, NPR）锁模机制的光纤激光器因其结构紧凑、可靠性高而备受关注。基于这一锁模原理设计并搭建了掺镱光纤飞秒激光器。当双向泵浦功率为380 mW,在1 030 nm波段获得了基频重复率为22.8 MHz的锁模脉冲。脉冲宽度为224 fs,平均功率180 mW,单脉冲能量8 nJ,10 dB带宽约为40 nm,信噪比大于50 dB。该激光器采用环形腔结构产生稳定的锁模飞秒脉冲输出,可实现自启动锁模。泵浦功率增加到1.6 W可观察到最高三阶被动谐波锁模,三次谐波对应68.5 MHz重复频率。该激光器由于在线宽、脉宽、脉冲能量上的优势,在光谱测量、拉曼成像等领域具有应用意义。     

基于石墨烯可饱和吸收体的掺铒光纤环形腔脉冲激光器

利用新型材料石墨烯作为可饱和吸收体,设计了用于光纤通信和材料加工的环形腔结构脉冲光纤激光器,实验研究了石墨烯可饱和吸收产生脉冲输出的原理以及输出脉冲激光的特性.通过激光诱导沉积法将石墨烯材料转移到光纤端面并将其置于环形激光腔结构中;采用974 nm半导体激光器作为抽运源,掺铒光纤作为增益介质,调节偏振控制器的角度得到了稳定的锁模输出脉冲.获得的锁模脉冲中心波长为1 560.1 nm,重复频率为7.89 MHz,脉冲光谱3 dB带宽为0.27 nm,脉冲宽度为14.7 ps.实验显示,由于石墨烯具有良好的可饱和吸收性能,损伤阈值比较高,有望取代单壁碳纳米管成为一种新型的激光锁模材料.     

可调谐锁模光纤激光器泵浦的超连续谱光源

为了实现平坦度更好、光谱覆盖可见光波段的超连续谱激光输出,研究了泵浦波长可调谐的全光纤结构超连续谱光纤激光器。设计搭建了一台非线性偏振旋转锁模脉冲光纤激光器,实现了9种中心波长的耗散孤子皮秒脉冲输出,波长调谐范围为1 041~1 076nm;以它作为种子源进行了两级功率放大,并泵浦10m长的光子晶体光纤,在泵浦激光功率为500mW时,得到9种输出光谱特性不同的超连续谱激光,得到当泵浦激光中心波长为1 050nm时,更利于实现光谱范围更宽、平坦度更好、可见光分量更多的超连续谱激光输出。为进一步拓宽超连续谱激光的光谱范围、提升光谱平坦度,将泵浦激光功率提升至1.45 W,最终实现了输出功率为600mW、短波边界为470nm、600~1 700nm内10dB光谱宽度为1 053nm的超连续谱激光输出。     

NALM锁模全保偏光纤掺铒光学频率梳

飞秒光学频率梳是当今激光技术领域的重要研究方向。实验基于非线性放大环形镜(NALM)锁模激光器实现了全保偏光纤结构的掺铒光学频率梳。在基于NALM锁模的光纤激光器内部加入非互惠相移器,降低了锁模阈值,实现了超短脉冲激光器的自启动。经过脉冲放大和压缩,脉冲的峰值功率可达61.3 kW。将此高功率超短脉冲注入55 cm的保偏高非线性光纤(PM-HNLF)中,激光器的输出光谱被拓展至一个倍频层(1 030～2 200 nm)。辅以f-2f自参考探测技术,成功探测到了信噪比高达40 dB、线宽为40 kHz的载波包络偏频信号(f_0)。此外,通过使用两套电路反馈系统,将f_0信号与激光器重复频率信号(f_r)的频率抖动量分别降低至521.71 mHz和240μHz,实现了相位稳定的掺铒光学频率梳。     

被动锁模掺铒光纤激光器中的有理数谐波锁模现象的研究

在分析有理数谐波锁模的理论和非线性放大环镜（NALM）传输特性的基础上,对被动锁模掺铒光纤激光器进行了相关的研究。实验中除了观测到了稳定的谐波锁模脉冲外,还观察到了的有理数谐波锁模脉冲的产生现象,分析其脉冲重复频率也证实此类脉冲序列具有属于3阶、5阶和6阶有理数谐波锁模脉冲序列重复频率的一样的规律。     

用于高精度光纤陀螺的掺铒光纤宽带光源的优化

为优化双程后向结构的掺铒光源,分析了光纤长度、泵浦功率和温度的变化对光源平均中心波长的影响,初步确定了掺铒光纤长度的优化范围,并在全温度范围内进行实验验证。实验选用的980nm泵浦源电流为110mA,掺铒光纤的长度为12.5m,该装置的输出功率为13.26mW,光源的平均波长稳定性为0.6℃-1。通过建立光谱分布优化仿真模型,实现输出光谱的近高斯分布,3dB带宽达到32nm。经过优化后得到的掺铒光纤光源具有输出功率高、平均波长稳定性好、输出光谱呈高斯分布等优势,是高精度光纤陀螺的理想光源。     

163 MHz/786 fs高基础重复频率掺镱飞秒光纤激光振荡器

高重复频率光纤激光器因其光斑质量好、集成化程度高、光光转化率高等优势在光学频率梳、工业加工、超高速光学采样等领域有着举足轻重的作用。利用非线性偏振旋转（NPR）的锁模机理,设计并搭建了一款基础重复频率为163 MHz的“十字腔”型孤子锁模光纤飞秒激光器。该激光器锁模后在450 mW的泵浦功率下可以输出200 mW的最大功率,光谱半高宽为30 nm,输出脉宽为786 fs。通过进一步分析激光器泵浦功率与输出功率之间的关系,得到泵浦功率处于400～500 mW时,激光器处于最佳锁模状态,并且可以实现自启动锁模。所设计的激光器由于其更加紧密的光学频率梳齿、更好的成像质量和更快的成像速度,在精密光谱、天文探测等领域具有应用意义。     

基于FBG的波长可调谐环形掺铒光纤激光器

在介绍光纤光栅波长调谐原理的基础上,设计了一种环形腔掺铒光纤激光器。利用光纤光栅(FBG)作为波长调谐元件,在20~170 ℃的温度范围内,实现了输出激光波长在1 547.7~1 556.5 nm内的连续可调,调谐线性度达99.96%,激光光谱的3 dB带宽均小于0.05 nm,20 dB带宽均小于0.08 nm,边模抑制比大于52 dB,输出功率可达21.2 mW。结果表明:可调谐掺铒光纤激光器具有可用带宽较宽、功率高、线宽窄、与光纤元件天然兼容等优点。     

基于光子晶体光纤参量振荡器的CARS成像光源研究

研究了一种基于光子晶体光纤参量振荡器的相干反斯托克斯拉曼散射(CARS)成像光源。该光源采用中心波长为1 030nm的皮秒光纤激光器作为泵浦源,以无截止单模光子晶体光纤作为参量增益,通过搭建光参量振荡器,实现平均功率为10mW的参量激光输出。在色散滤波效应的作用下,该光源输出波长可实现连续可调,调谐范围为782～793nm,对应的波数覆盖范围为2 901～3 078cm-1。该光源产生的两束激光脉冲可实现空间自同步、时间自重合,用于CARS成像测量时,无需空间、时间对准,有望推动CARS成像光源向全光纤化、小型化的方向发展。     

Ultrastructure and reproduction behaviour of single CHO-K1 cells exposed to near infrared femtosecond laser pulses

In the present work, the authors investigated ultrastructural changes as well as the reproduction behaviour of preselected single CHO-K1 cells exposed to 170 femtosecond laser pulses at different power output levels in comparison with cells outside the illumination volume. The ultrashort laser pulses were provided by an 80 MHz Ti:sapphire laser at 780 nm. The cells were scanned ten times with a scan rate of 1/16 s(-1). Single CHO-K1 cells exposed to low mean power of 2 mW revealed no significant changes in ultrastructure after laser exposure. In some cases, changes of mitochondria with slight disordering of cristae were found. Cytoplasm was filled with vesicles that seemed to be released from Golgi stacks. Cells irradiated with higher powers demonstrated more dramatic changes in ultrastructure. A considerable number of swollen mitochondria in conjunction with loss of cristae was observed. The main event of mitochondrial changes was the formation of electron dense bodies in the mitochondrial matrix. In addition, lumen of endoplasmatic reticulum was enlarged. Highest applied mean laser power of 12.5 mW lead to complete destruction of mitochondria and their transformation to electron dense structures containing membrane material. Compared with cell targets irradiated with 2 mW mean power, the release of vesicles from Golgi stacks seemed to be rather moderate. Cells localised outside the laser beam revealed no ultrastructural changes. Low mean laser power at 2 mW was unable to impair the reproduction behaviour of CHO-K1 cells. At higher laser power output levels, CHO-K1 cells started to delay cell division. At 12.5 mW, no cell division occurred. The obtained results may be helpful in recommending parameters for safe femtosecond laser microscopy of living specimens.     

应用800nm飞秒激光制备长周期光纤光栅

利用800 nm钛蓝宝石飞秒激光器制备了长周期光纤光栅,并实验验证了长周期光纤光栅的高温特性.基于摄像头和电动位移平台设计了激光精确对准光纤纤芯的方案;以计算机控制1.3 mW飞秒激光,使用逐点曝光法在未经载氢处理的光纤上刻写了长周期光纤光栅,实验显示该光栅在1 200～1 700 nm波段的主谐振峰值可达-17 dB.利用高温箱对长周期光纤光栅进行高温传感特性实验,在300～800℃得到的主谐振峰温度响应灵敏度为0.056 nm/℃,线性度为0.992.实验结果表明,提出的以800 nm钛蓝宝石飞秒激光器制备长周期光纤光栅的方法稳定可靠,写制的光栅在高温环境下变化均匀,不易退化,响应特性良好,适用于高温检测.     

Multiphoton confocal microscopy using a femtosecond Cr:forsterite laser

With its output wavelength covering the infrared penetrating window of most biological tissues at 1,200-1,250 nm, the femtosecond Cr:forsterite laser shows high potential to serve as an excellent excitation source for the multiphoton fluorescence microscope. Its high output power, short optical pulse width, high stability, and low dispersion in fibers make it a perfect replacement for the currently widely used Ti:sapphire laser. In this paper, we study the capability of using a femtosecond Cr:forsterite laser in multiphoton scanning microscopy. We have performed the multiphoton excited photoluminescence spectrum measurement on several commonly used bioprobes using the 1,230 nm femtosecond pulses from a Cr:forsterite laser. Efficient fluorescence can be easily observed in these bioprobes through two-photon or three-photon excitation processes. These results will assist in the selection of dichroic beam splitter and band pass filters in a multiphoton microscopic system. We have also performed the autofluorescence spectrum measurement from chlorophylls in live leaves of the plant Arabidopsis thaliana excited by 1,230 nm femtosecond pulses from the Cr:forsterite laser. Bright luminescence from chlorophyll, centered at 673 and 728 nm, respectively, can be easily observed. Taking advantage of the bright two-photon photoluminescence from chlorophyll, we demonstrated the two-photon scanning paradermal and cross-sectional images of palisade mesophyll cells in live leaves of Arabidopsis thaliana.     

Acousto-optic modulator system for femtosecond laser pulses

Femtosecond laser pulses have made a revolution in multiphoton excitation microscopy, micromachining, and optical storage for their unprecedented high peak power. However, modulation of their intensity with acousto-optic modulator (AOM) is frustrated by dispersion which results in a significant stretch in pulse width. Here we report a scheme composed of two acousto-optic deflectors (AODs) to modulate the intensity of the femtosecond laser pulses with simultaneous compensation for the temporal dispersion. With commercial AODs, we demonstrated such an AOM system for the femtosecond laser pulses with overall transmission efficiency of around 80%. The pulse width of the exit beam is 115-177 fs for an input pulse of 110 fs, across the wavelength range of 720-920 nm when the temporal dispersion compensation is optimally tuned at 800 nm. The fluorescence intensity in a two-photon microscopy experiment performed using this system increased 5.5-fold over that of the uncompensated AOM.     

Picosecond pulsed two-photon imaging with repetition rates of 200 and 400 MHz

We show the viability of high-resolution two-photon fluorescence imaging of fixed and live cells by exciting the fluorophores with a train of near-infrared pulses with duration in the picosecond range. This is exemplified with a compact, diode-pumped Nd:YVO₄ laser, emitting trains of 7-ps pulses at a wavelength of 1064 nm, with a repetition rate of 200 MHz at two separate outputs. Incoherent combination of the outputs enabled two-photon excitation with a repetition rate of 400 MHz. For a numerical aperture of 1.4 (oil), we used an average illumination power of up to 20–40 mW at the sample. The pulses were coupled into a beam scanning microscope, either directly or through a single mode glass fibre. Compared with standard femtosecond titanium–sapphire excitation conditions, our experiments were performed with a 2.5 or 5 times higher repetition rate, 30–70 times longer pulses and 10–35 times lower pulse peak intensity. The experiments indicate the possibility of significantly relaxing the temporal pulse width constraints for a series of applications.     

基于XeF(C-A)放大器的混合(固态/气态)超高功率飞秒激光系统

提出了基于前端发生器和终端放大器,使用光泵浦XeF(C-A)激活介质的太瓦级混合激光器(THIA00)系统.前端发生器由长532 nm的连续激光泵浦的钛宝石飞秒脉冲振荡器,脉冲展宽机构,532 nm的脉冲激光泵浦的再生多通道放大器,衍射光栅压缩器和二次谐波发生器(KDP)组成.其光束输出参数为:脉冲持续时间50 fs,...     

FGZ-8半导体激光治疗机设计与研制

采用二合一光纤系统、高效率光纤耦合装置、Al Ga In P半导体激光器、方便适用的光纤定位装置以及稳定可靠的电源控制系统 ,研制了一种新型 6 5 0 nm半导体激光治疗仪 ,其光纤端输出达 10 9m W。该仪器已在生物医学领域成功应用。