超短光脉冲宽度已被压缩到8fs

超短光脉冲技术除了在物质的超快过程的测量中有重要意义外,其本身的理论和技术也有重大科学和实际意义.自进入八十年代以来,超短光脉冲技术已从微微秒范畴深入到毫微微秒范畴.世界各国的科学家们为获得更短的光脉冲做了大量研究工作.1982年Shank等人[1]获得了30fs的光脉冲,1984年Fuji-moto等人[2]把光脉冲压缩到16fs.不久前有人报道已把光脉冲压缩到12fs.最近Bell实验室的Knox等人[3]又把光脉冲压缩到10fs以内,达到8fs(在半高全宽度内,光脉冲持续的时间不到四个光振动周期),向获得真正的1fs光脉冲的方向前进了一大步. Knox等人还是用光的…     

超短光脉冲

超短光脉冲通常是指脉冲宽度处于亚毫微秒和微微秒范围的光脉冲.目前超短光脉冲的获得主要采用锁模技术.自从1964年Hargro-ve等人首先利用声波损耗调制对氦氖激光器实现主动锁模之后,1965年Mocker等人又利用饱和吸收体对固体激光器实现了被动锁模,从而开始了对超短光脉冲的大量     

最短的光脉冲

激光器出现五年之后,人们就获得了微微秒光脉冲,微汲秒光脉冲的出现,开拓了微微秒激光光谱学这一正在迅速发展中的领域.目前这项技术已成功地扩展至亚微微秒范围(10-13秒).这就为更精确地研究物理、化学、生物学中的快速过程提供了前所未有的工具. 据美国罗彻斯特大学的Mourou 和Sizer报道,现已产生了目前最短的激光脉冲,此光脉冲的持续时间不大于 70fs(7 ×10-13秒)[1].尽誉还没有准确测量这样短光脉冲脉宽的设备,但他们确信,实际上光脉冲宽度可能更短些. 贝尔实验室曾报道产生了脉宽为90fs的光脉冲,并经过压缩手段脉宽达到了50fs.Mourou…     

亚微微秒光谱学

近十年来,超短激光脉冲及其在微微秒现象研究中的应用取得了惊人的进展.现在这种技术巳扩展到亚微微秒(10-13s)领域,为精密地研究物理学、化学和生物学中以前无法分辨的超快速光过程提供了激动人心的可能性. 在激光器发明以后大约五年,微微秒光脉冲就出现了.1966年,A.德马里(Demaria)、D.A.斯切特(Stetster)和H.海纳(Heynan)[1]在闪光灯泵浦钕玻璃激光器中用非线性吸收物质,首次产生脉宽小于10ps的脉冲.至今钕玻璃激光器产生脉冲的宽度还停留在微微秒区,它能产生很高的峰功率,这对于许多应用是很需要的,但是它本质上是一个低重复率系统,…     

光化学和光生物学中的微微秒闪光光解和光谱

我们研制了一种微微秒闪光光解的装置,能用照相记录探索性研究中瞬变的中间物的光谱,可以和用光导摄像管、光多道分析器对400～950nm范围内任何一个波长进行详细动力学研究的装置联用。样品被波长为530,694或1060nm,5～8ps(微微秒)间隔的单个光脉冲激发,并用也是微微秒间隔的时期—延迟连续脉冲控制。在几个微微秒到几个毫微秒的范围内,时间分辨力可以达到±4微微秒。     

1064nm纳秒激光脉冲激发的外腔式PbWO4拉曼激光器

研究了外腔式PbWO4拉曼激光器在纳秒脉冲抽运下的输出特性。利用主动调Q的Nd:YAG激光器产生的脉冲宽度为31.4ns,最大输出能量为200mJ的1064nm激光作为抽运源。拉曼激光谐振腔采用的是平凹腔设计。测量了输出的拉曼光脉宽与抽运能量的关系,分析了输出的拉曼光脉冲波形图和光谱图,测量了输出的拉曼光脉冲能量与抽运能量的关系,计算了转换效率与抽运能量的关系。当注入抽运光能量达到42mJ时,得到了一阶斯托克斯光脉冲的最大能量和转换效率分别为10mJ和24%,获得外腔式PbWO4拉曼激光器的一阶斯托克斯光脉冲波长为1177.6nm,典型的一阶斯托克斯光脉冲脉宽为20ns。     

亚微微秒脉冲

自从第一代微微秒范围的光脉冲问世以来这十年间脉冲发生技术不断改进,现在足以能通过连续波染料激光锁模产生0.3微微秒的短脉冲。这类脉冲为研究物质的光学性质提供了迄今所达到的最高分辨率。 关于连续波染料激光器被动锁膜的第一个报告是在1972年国际量子电子学会议上发表的。其后,F.O,Nei等取得了类的似结果。在早期研究工作中,短脉冲曾达到1.5P.S(微微秒)到1974年,人们用连续工作的罗丹明6G激光和以倾腔结构工作的DODC1激光获得了微微秒脉冲。贝尔实验室     

《超短光脉冲》

本书是由美国、英国和西德一些从事微微秒激光物理和技术研究中的主要科学家撰写的。主要反映了1977年以前微微秒激光物理和技术的成就。现已译成俄文,莫斯科大学的C.A.Aхманов为俄文版写了绪言,在绪言中介绍了1977年到1980年超短光脉冲的成就。并补充了1977年以来的文献。“超短光脉冲”一书中,大多数作者都是超短光脉冲研究中的先驱者。因而,可以从这本书得到第一手材料,不仅可以了解这个领域的现状,对于了解微微秒激光发展史和远景也是有所裨益的。全书除第一章绪言外,主要内客分六章。绪言是由本书的主编、洛斯·阿拉莫斯实验室的S.L.Shapiro撰写的。他从事超短脉冲测量和微微秒非线性光学的研究。现正根据美国能源计划对光合作用的原初过     

基于超连续谱的可调谐同步脉冲产生及噪声分析

实验研究了基于超连续谱滤波的可调谐双色同步皮秒脉冲产生技术,将全保偏掺铒锁模光纤激光器输出的脉冲分为两路,其中一路耦合到高非线性光纤,获得了覆盖掺镱光纤发射谱带的超连续谱,通过结合窄带可调谐滤波器和全保偏掺镱放大器,实现了平均功率为70 mW,脉冲宽度为4.0 ps,中心波长为1025～1055 nm的可调谐脉冲。掺铒光纤激光器的另一路输出光经过窄带滤波器和掺铒光纤放大器,实现了中心波长为1580 nm,平均功率为200 mW,脉冲宽度为4.2 ps的激光输出。上述基于超连续谱滤波的可调谐双色皮秒脉冲具有良好的同步特性,可以作为相干反斯托克斯拉曼散射的泵浦光和斯托克斯光。研究发现,选取超连续谱平坦位置的光谱成分作为掺镱放大器的种子光时,脉冲幅值及平均功率抖动更小,相对强度噪声更低。     

外腔式SrWO4拉曼激光器的输出特性研究

研究了外腔式SrWO4拉曼激光器在ns脉冲抽运下的输出特性。利用主动调Q的Nd∶YAG激光器产生的脉冲宽度为11.7 ns,输出能量为80 mJ的激光作为抽运源,拉曼激光谐振腔采用平平腔,实验采用4片对一阶斯托克斯脉冲和二阶斯托克斯脉冲不同反射率的输出耦合镜,测量了输出能量与抽运能量的关系,计算了转换效率与抽运能量的关系。当输出耦合镜对一阶斯托克斯脉冲的反射率为39.9%时,实验得到一阶斯托克斯脉冲的最大能量和转换效率分别为23.9 mJ和36.2%,当输出耦合镜对一阶斯托克斯脉冲和二阶斯托克斯脉冲的反射率分别为80.5%和12.4%时,得到二阶斯托克斯脉冲的最大输出能量和转换效率分别为16.4 mJ和25.4%,典型的一阶斯托克斯脉冲和二阶斯托克斯脉冲的脉冲宽度分别为6.1 ns和5.8 ns。     

Cascaded compression of the first and second Stokes pulses during forward transient stimulated Raman amplification

The results of numerical modelling of cascaded compression of the first and second Stokes pulses during regenerative regime of the forward transient stimulated Raman amplification are presented for the case when the walk-off length of the first Stokes pulse due to group velocity mismatch is shorter than the length of the nonlinear medium. The influence of the initial amplitudes of the seed first Stokes pulses, its durations and its time delay with respect to the pump pulse, the Kerr nonlinearity of the medium on the conversion efficiency, duration and propagation factor M² of the first and second Stokes pulse are studied. It is demonstrated that for the pump pulse duration of 1 ps the duration of the compressed second Stokes pulses in a KGW crystal near the beam axis may be approximately 14 times shorter than the pump pulse duration. It is shown that the propagation factor of the compressed pulses increases significantly because of complex spatial-temporal dynamics of compression and the influence of Kerr nonlinearity of Raman medium.     

Coupled-cavity passively Q-switched two-Stokes microchip laser

Experimental and theoretical studies of the coupled-cavity diode-pumped Nd:YAG/Cr:YAG microchip lasers with intracavity Raman conversion of laser pulses in a Ba(NO₃)₂ crystal into two Stokes pulses have been made. Two lasers with a different cavity length have been investigated. The minimal pulse durations at the 2nd Stokes wavelength were ??100 ps in the short-cavity laser at pulse energy of 5???J, and the pulse repetition rate reached 20?C24?kHz. The laser and Stokes pulse dynamics, as well as the spatial intensity distribution of the laser and the 1st Stokes beams at the output mirror have been recorded. A model describing such coupled-cavity microchip Raman lasers has been developed. The numerically simulated laser and Stokes pulse dynamics, and the calculated pulse energy, duration, and repetition rate are in good agreement with the experimental data.     

Sub-nanosecond microchip laser with intracavity Raman conversion

Efficient sub-nanosecond pulse operation of microchip lasers with intracavity Raman conversion and pulse compression is presented for the first time. The microchip lasers were composed of Nd:LSB or Nd:YAG laser crystals, Cr⁴⁺:YAG saturable absorber, and Ba(NO₃)₂ Raman medium. The pulse duration obtained at the Stokes wavelength (1196 nm) was as short as 118 ps. Optical conversion efficiency of laser-diode pump power to the Stokes power of 8% was reached. Pulse energy and peak power of Stokes emission were 1.2 μJ and 5.4 kW, correspondingly. Numerical calculations are in good agreement with obtained experimental results. Received: 20 December 2002 / Revised version: 6 March 2003 / Published online: 5 May 2003 RID="*" ID="*"Corresponding author. Fax: +1-716/645-6945, E-mail: ankuzmin@acsu.buffalo.edu RID="**" ID="**"Present address: University at Buffalo, SUNY, The Institute for Lasers, Photonics, and Biophotonics, 458 NSC, Buffalo, NY 14 260-3000, USA     

短脉冲激光刻蚀加工铜材料的机制

 利用数值模拟方法，研究波长1 064 nm、脉冲宽度介于1~20 ps的激光在刻蚀铜靶时，单次脉冲作用下非平衡场刻蚀和热平衡刻蚀两种机制的竞争过程。结果表明：随着脉冲宽度的增加，刻蚀过程由非平衡电荷分离场刻蚀占主导地位转变为热平衡刻蚀起主要作用，且脉冲宽度和激光峰值功率密度增大到一定程度后，各种电子加速机制在不同时刻开始突显，电子能量分布出现多峰结构。在能量密度为15 J/cm2的激光作用下，1和5 ps脉宽对应的非平衡场刻蚀深度分别为110和101 nm，10和20 ps脉宽分别为25和18 nm。     

对受激布里渊散射激光进行组束的数值模拟及方案设计

 提出了时间上串行的多路激光脉冲通过受激布里渊散射(SBS)池进行组束的方法,并对其进行了数值模拟研究。利用6束每束能量为45J的KrF激光进行组束, 可获得能量为141.89J,脉宽为670ps的Stokes输出光。根据模拟结果设计出了时间上串行的SBS激光组束的两个方案, 对其进行了讨论。数值模拟还发现在介质的增益系数更大、声子寿命更短的情况下,输出激光脉冲的脉宽可以压缩得更窄。     

Chirped-pulse stimulated Raman scattering in barium nitrate with subsequent recompression

We report a 30% internal conversion efficiency for the first Stokes pulse in stimulated Raman scattering of femtosecond pulses that are dispersively stretched to 250 ps, obtained by use of an all-solid-state laser system. A transfer of the linear chirp is observed, leading to a Raman pulse duration of 190 fs after recompression. Compressed pulse energies of 80 muJ at a repetition rate of 1 kHz are obtained, with a potential for an easy increase to more than 150 muJ. The temporal and spectral characteristics of the Raman and pump pulses are calculated, and the results explain the observed transient features in the presence of chirp.     

Tunable,sub-nanosecond KrF-Raman laser in the ultraviolet

A 0.5 cm^–1 bandwidth injection-locked KrF laser pumps a rare-gas Brillouin cell to produce a reflected pulse with a leading edge risetime of 1 ns, tunable from 248.1 to 248.7 nm. Consistent with Lamb theory of laser amplifiers, subsequent excimer amplification of this pulse produces an intense 500 ps spike on the pulse leading edge. Stimulated Raman scattering then separates the spike from the parent pulse, yielding a tunable short pulse at the first Stokes (S ₁) wavelength. Varying the Raman cell length results in a variable Raman threshold and an adjustable short pulse duration: 250 ps pulses at energies of 3–4 mJ at 268 nm with a 50 cm methane cell and 350 ps, 5 mJ pulses from a 100 cm cell are measured with a streak camera. First pass Raman conversion of the spike toS ₁ followed by second pass backward Raman amplification, where the parent 248 nm pulse serves as the pump beam for the reflectedS ₁ pulse, yields simultaneousS ₁ pulses of 20–25 mJ in the 800 ps range andS ₂ pulses of 550 ps at 5–6 mJ near 290 nm. This laser will avoid collision effects during laser excitation and enable quantitative, single pulse imaging of OH radicals in turbulent combustion because of its high pulse energy.     

Simultaneous intracavity optical parametric oscillation and stimulated Raman scattering pumped by a doubly passively Q-switched Nd:GGG laser

By using a doubly passively Q-switched Nd:Gd₃Ga₅O₁₂(Nd:GGG) laser with Cr⁴⁺:YAG and GaAs as saturable absorbers as pump laser, simultaneous intracavity optical parametric oscillation and stimulated Raman scattering based on a single X-cut KTiOPO₄ (KTP) crystal have been realized. Under an incident diode pump power of 10.5 W, the output powers at the signal wave near 1,569 nm and the first Stokes emission near 1,094 nm were 218 and 72 mW, corresponding to the optical-to-optical conversion efficiencies of 2.08 and 0.69 %, respectively. The measured shortest pulse duration at the signal wave near 1,569 nm was 580 ps, generating a pulse peak power of 43.7 kW, while the minimum pulse duration at the first Stokes emission near 1,094 nm was 1.61 ns. By adjusting the tilt angle of the KTP crystal, up to the third Stokes scattering was also obtained.     

Measurement of the shape of picosecond light pulses using stimulated Raman scattering

The vibrational amplitude and the intensity of the Stokes light generated by transient stimulated Raman scattering rise and decay very rapidly. The time duration of the Stokes pulse and of the phonon pulse is much shorter than the pump pulse duration. It is shown that both phonon and Stokes pulses can be used to probe the shape of ultrashort light pulses.     

Laser and self-Raman-laser oscillations of PBMoO4:Nd3+ crystal under laser diode pumping

Different regimes of laser operation and stimulated Raman scattering (SRS) for a laser diode (LD)-pumped PbMoO4:Nd3+ crystal have been investigated. Under 1.5 W LD pumping, the output power of the PbMoO4:Nd3+ laser in the free-running mode at 1056 nm reached 0.65 W with a slope efficiency of up to 53%. Using different LiF: F-2 saturable absorbers, we achieved a maximum pulse energy of 11 microJ at a 1.4 ns pulse duration and a maximum output power of 0.35 W (10 microJ) at a 7 ns pulse width in the passively Q-switched mode. PbMoO4:Nd3+ self-Raman-laser operation at 1163 nm (first Stokes) was obtained for the first time, to our knowledge. The self-Raman-laser output pulse energy was measured to be as high as 6 microJ and the pulse duration was estimated to be shorter than 500 ps.