Enhanced stimulated Raman scattering in H<Subscript>2</Subscript> by seeding an SRS line into an H-ɛ Balmer line: Amplification-coupled laser wavelength shifter

The stimulated Raman scattering (SRS) in H₂ gas above the dissociation energy limit was recorded using a 266-nm UV laser. All of the observed Stokes and anti-Stokes SRS lines showed a normal behavior except the third Stokes SRS lines at 397.8 nm, which showed a substantial intensity enhancement of about a 36%-conversion efficiency of the pump energy. This enhancement in the SRS line is attributed to the seeding of the SRS line into the Balmer H-? line at 397 nm in molecular hydrogen. To the best of our knowledge, there is no report of any work on enhanced stimulated Raman scattering in H₂ by the seeding of the H-? Balmer line into the SRS line and attaining a very high intensity at the third Stokes SRS lines at 397.8 nm. The cell pressure and the laser pulse energy dependence of these SRS lines substantiate our explanation.     

Mo:Y multilayer mirror technology utilized to image the near-field output of a Ni-like Sn laser at 11.9 nm

Although bright x-ray sources exist at shorter wavelengths, the development of sophisticated diagnostics with x-ray laser sources has been restricted to wavelengths longer than 12.5 nm because of the limitations of the widely used Mo:Si multilayer mirrors. With the novel Mo:Y multilayer mirrors that we present, many x-ray laser applications can be extended to the 7-12-nm range. We demonstrate this new capability by imaging the near-field output of the Ni-like Sn laser at 11.9 nm.     

Stimulated Raman scattering of picosecond pulses in a YVO<Subscript>4</Subscript> crystal

Stimulated Raman scattering (SRS) with a picosecond pulse in YVO₄ crystals in a transient state was investigated. The picosecond gain of YVO₄ crystals pumped by a 532-nm laser evaluated by means of the threshold was 16.13 cm/GW.     

A method for reducing the stimulated Raman scattering threshold in liquids embedded into photonic crystals

We study stimulated Raman scattering (SRS) in liquids (water and ethanol) embedded into photonic crystals (artificial opals) under excitation with 60 ps laser pulses at 532 nm. We observe a substantial decrease of the SRS threshold when the focused laser beam excites the crystals near their surface. The spatial distance between the beam center and the surface of the crystals is close to their nanoscale structure. The decrease in the SRS threshold is due to a substantial increase in the photonic-state density near the edges of the photonic crystal stop zones and the so-called Mie resonances in active media near the nanosized globules. This leads to a considerable increase in the local-electric-field intensity, causing the SRS threshold reduction. Such a method of reducing the SRS threshold opens up a way of creating new efficient laser sources based on photonic crystals and their use for different applications in nanotechnologies.     

Stimulated Raman hyperspectral imaging based on spectral filtering of broadband fiber laser pulses

We demonstrate a technique of hyperspectral imaging in stimulated Raman scattering (SRS) microscopy using a tunable optical filter, whose transmission wavelength can be varied quickly by a galvanometer mirror. Experimentally, broadband Yb fiber laser pulses are synchronized with picosecond Ti:sapphire pulses, and then spectrally filtered out by the filter. After amplification by fiber amplifiers, we obtain narrowband pulses with a spectral width of <3.3 cm(-1) and a wavelength tunability of >225 cm(-1). By using these pulses, we accomplish SRS imaging of polymer beads with spectral information.     

Measurement of spatial gain distribution for a neonlike germanium 19.6-nm laser

We measure the transverse spatial distribution of the gain region for the 19.6-nm neonlike germanium laser line by use of a short amplifier, which is backlit by a longer laser, both of which are created by illumination of a germanium slab target with a series of short 100-ps pulses from the Nova laser. The backlighting technique enables us to reduce greatly the refraction effects that dominated previous imaging experiments and made direct gain measurements impossible. Measurements are made with a two-dimensional high-resolution spatial-imaging diagnostic, and simulations of the gain are compared with experiments.     

Comparative study of pulsed laser diode end-pumped thulium-doped 2-µm Q-switched lasers

We report pulsed laser diode(LD)end-pumped acoustic Q-switched Tm:YAG laser,Tm:LuAG laser,and Tm:LuYAG laser and the physical properties and spectra of Tm:YAG,Tm:LuAG,and Tm:LuYAG are analyzed.The Tm:LuYAG laser is pumped by 785-nm and 788-nm pulses separately,and is compared with Tm:YAG laser.Different output energy values and output wavelengths of Tm:LuAYG lasers pumped by LDs with different wavelengths are obtained and compared with each other.When the repetition frequency is 100 Hz,the pulsed Tm:YAG laser has single pulse energy of 15.9 mJ,pulse width of 126.7 ns,and the center wavelength of 2013.36 nm,and the pulsed Tm:LuAG laser possesses single pulse energy of 11.8 mJ,pulse width of 252.4 ns,and the center wavelength of 2023.65 nm,and the pulsed Tm:LuYAG laser output energy values are 12.32 mJ and 12.25 mJ with the slope efficiencies of 12.5%and 11.85%,the center wavelengths of 2017.89 nm and 2027.11 nm,respectively,while the pump sources are 785-nm and 788-nm pulsed LDs,respectively.     

Two-color laser PEEM imaging of horizontal and vertical components of femtosecond surface plasmon polaritons

Explicit visualization of different components of surface plasmon polaritons (SPPs) propagating at dielectric/metal interfaces is crucial in offering chances for the detailed design and control of the functionalities of plasmonic nanodevices in the future. Here, we reported independent imaging of the vertical and horizontal components of SPPs launched from a rectangular trench in the gold film by a 400-nm laser-assisted near-infrared (NIR) femtosecond laser time-resolved photoemission electron microscopy (TR-PEEM). The experiments demonstrate that distinct imaging of different components of SPPs field can be easily achieved by introducing the 400-nm laser. It can circumvent the risk of sample damage and information loss of excited SPPs field that is generally confronted in the usual NIR laser TR-PEEM scheme. The underlying mechanism for realizing distinct imaging of different components of the SPPs field with two-color PEEM is revealed via measuring the double logarithmic dependence of photoemission yield with the 800-nm and 400-nm pulse powers of different polarizations. Moreover, it is found that the PEEM image quality of the vertical and horizontal components of the SPPs field is nearly independent of the 400-nm pulse polarization. These results pave a way for SPPs-based applications and offer a possible solution for drawing a space—time field of SPPs in three dimensions.     

水中受激拉曼散射的能量增强及受激布里渊散射的光学抑制

为提高液体介质中受激拉曼散射的输出能量,提出了通过温度调控来抑制受激布里渊散射的方法,设计了532 nm多纵模宽带脉冲激光泵浦的受激拉曼散射发生系统,测量了不同温度下水中前向受激拉曼散射及后向受激布里渊散射的输出能量,分析了水温、泵浦激光线宽及热散焦效应对受激拉曼散射输出能量影响的物理机制.实验结果表明:通过降低水温可实现对受激布里渊散射过程的有效抑制,同时减小热散焦效应带来的光束畸变,从而有效提高受激拉曼散射的输出能量.研究结果对液体介质中的受激拉曼散射多波长转换具有重要意义.     

Ultrafast Raman loss spectroscopy (URLS): instrumentation and principle

In this paper, we report on the concept and the design principle of ultrafast Raman loss spectroscopy (URLS) as a structure‐elucidating tool. URLS is an analogue of stimulated Raman scattering (SRS) but more sensitive than SRS with better signal‐to‐noise ratio. It involves the interaction of two laser sources, namely, a picosecond (ps) Raman pump pulse and a white‐light (WL) continuum, with a sample, leading to the generation of loss signals on the higher energy (blue) side with respect to the wavelength of the Raman pump unlike the gain signal observed on the lower energy (red) side in SRS. These loss signals are at least 1.5 times more intense than the SRS signals. An experimental study providing an insight into the origin of this extra intensity in URLS as compared to SRS is reported. Furthermore, the very requirement of the experimental protocol for the signal detection to be on the higher energy side by design eliminates the interference from fluorescence, which appears on the red side. Unlike CARS, URLS signals are not precluded by the non‐resonant background and, being a self‐phase‐matched process, URLS is experimentally easier. Copyright © 2011 John Wiley & Sons, Ltd.     

Low‐noise,vibrational phase‐sensitive chemical imaging by balanced detection RIKE

We perform a back‐to‐back comparison between two nonlinear vibrational imaging techniques: stimulated Raman scattering (SRS) and balanced detection Raman‐induced Kerr effect (BD‐RIKE). Using a compact fiber‐based laser system for generation of pump and Stokes signals, we image polymer beads as well as human hepatocytes under the same experimental conditions. We show that BD‐RIKE, despite the slightly lower signal levels, consistently offers an improved signal‐to‐noise ratio with respect to SRS, resulting in significantly higher image quality. Importantly, we observe that such quality is not affected by the static birefringence of the sample, which makes BD‐RIKE a robust and attractive alternative to SRS. We also highlight a unique advantage of the technique, which is its capability to easily access both the real and imaginary parts of the nonlinear susceptibility, thus allowing for vibrational phase imaging. The phase information can be readily obtained from BD‐RIKE with minimal experimental effort and provides an additional chemical selectivity channel for coherent Raman microscopy. Copyright © 2014 John Wiley & Sons, Ltd.     

New aspects of micromachining and microlithography using 157-nm excimer laser radiation

The use of F₂ excimer laser sources, emitting at 157 nm, constitutes a new promising tool for scientific, industrial and lithography applications. The 157-nm laser emission enables high-resolution processes and the high photon energy offers the unique possiblity of photoionizing molecules in a single step. Therefore a lower fragmentation or thermal loading takes place. The 157-nm radiation will enable fundamental research and development for deep UV (DUV) high-resolution optical microlithography in the manufacturing of integrated circuits. This is the next step from the technology of ArF lasers at 193 nm. Furthermore, benefits are expected for key technologies requiring high-resolution processing and the micromachining of tough materials like Teflon or fused silica for micro-optics fabrication. Such applications require F₂ excimer laser sources with high performance, reliability and efficiency. The world of nanotechnology is just beginning to reveal its potential.     

Four-wave parametric processes in multicascade SRS conversion of neodymium laser radiation into an eye-safe region

Four-wave parametric processes in multicascade SRS conversion of neodymium laser radiation into an eye-safe region are studied in relation to the phase mismatch of parametric coupling, which is determined by the refractive index dispersion of the SRS medium. The numerical simulation showed that the generation of multicascade SRS at a particular wavelength in the IR region can be even more efficient than the single-cascade conversion if the parametric coupling between the first Stokes and anti-Stokes components is weak and higher Stokes components are strongly parametrically coupled with each other. This situation is observed in the eye-safe IR region, where the refractive index dispersion of solid-state SRS media is minimal, which allows one to optimize the SRS conversion by choosing an SRS medium and its length.     

Spectral filtering of dual lasers with a high-finesse length-tunable cavity for rubidium atom Rydberg excitation

We propose and demonstrate an alternative method for spectral filtering and frequency stabilization of both 780-nm and 960-nm lasers using a high-finesse length-tunable cavity(HFLTC). Firstly, the length of HFLTC is stabilized to a commercial frequency reference. Then, the two lasers are locked to this HFLTC using the Pound–Drever–Hall(PDH) method which can narrow the linewidths and stabilize the frequencies of both lasers simultaneously. Finally, the transmitted lasers of HFLTC with each power up to about 100 μW, which act as seed lasers, are amplified using the injection locking method for single-atom Rydberg excitation. The linewidths of obtained lasers are narrowed to be less than 1 k Hz, meanwhile the obtained lasers' phase noise around 750 k Hz are suppressed about 30 d B. With the spectrally filtered lasers, we demonstrate a Rabi oscillation between the ground state and Rydberg state of single-atoms in an optical trap tweezer with a decay time of(67 ± 37) μs, which is almost not affected by laser phase noise. We found that the maximum short-term laser frequency fluctuation of a single excitation lasers is at ～ 3.3 k Hz and the maximum long-term laser frequency drift of a single laser is ～ 46 k Hz during one month. Our work develops a stable and repeatable method to provide multiple laser sources of ultra-low phase noise, narrow linewidth, and excellent frequency stability, which is essential for high precision atomic experiments, such as neutral atom quantum computing, quantum simulation, quantum metrology, and so on.     

New crystals for Raman lasers

Steady-state and transient stimulated Raman scattering (SRS) in crystals is analyzed. The basic laws of an increase in the SRS gain in crystals are revealed, and methods for searching and creating new SRS laser materials are developed. New crystals for picosecond and nanosecond SRS lasers are proposed, fabricated, and characterized. These materials have the highest SRS cross section, a low SRS threshold, and a wide spectral range of operation.     

Optical parametric oscillation in periodically poled lithium niobate driven by a diode-pumped Q-switched erbium fiber laser

We describe what is to our knowledge the first nanosecond periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO) driven by a fiber laser. The source was frequency doubled by a PPLN sample before pumping a second, 20-mm-long, PPLN crystal. The OPO threshold was <10muJ, with pump depletions of as much as 45% and a tunable signal range of 945-1450 nm (1690-4450-nm idler range). We demonstrated 130-nm signal tuning by varying the pump wavelength and doubling crystal's temperature. Also, we achieved 15-nm tuning with all crystals at a constant temperature. The results demonstrate the potential of the fiber laser:PPLN combination for practical, versatile, and tunable sources.     

351nm激光入射大腔靶的受激Raman散射光谱

 报道了“神光 Ⅱ”装置上Au大柱腔靶产生的受激Raman散射光谱。通过分析实验条件和测量结果，排除了散射光谱来自增强非相干Thomson散射的可能性，发现用丝化不稳定性与受激Raman散射的耦合能合理解释观测到的Raman光谱。考虑到丝化不稳定性与SRS的耦合，测量到的散射光谱依然能用于密度诊断，其结果与对流SRS理论的计算值相差不到10%。     

1．053μm激光在腔靶中反常吸收和超热电子的研究

从１９９０年到１９９３年，在神光Ⅰ上我们利用多种能量卡计和谱仪，全面系统地研究了基频光在腔靶中产生的反常吸收和超热电子。实验获得了腔靶反常吸收光谱、能量和硬Ｘ光谱，给出了ＳＲＳ能谱和能量、超热电子能量和温度与激光参数和靶型的关系，证明了采用短波长激光。     

Two-photon optical-beam-induced current solid-immersion imaging of a silicon flip chip with a resolution of 325 nm

We report high-resolution subsurface imaging of a silicon flip chip by detection of the photocurrent generated by the two-photon absorption of 1530-nm light from a femtosecond Er:fiber laser. The technique combines the focal sensitivity of two-photon excitation with the enhanced optical resolution of high-numerical-aperture solid-immersion imaging. Features on a sub-1-microm scale are clearly resolvable with high contrast, showing a resolution of 325 nm.     

ICF点火靶内环激光SRS抑制方法理论研究

激光等离子体相互作用(LPI)是制约在美国国家点火装置(NIF)上实现间接驱动惯性约束聚变的关键问题之一。LPI的激发不仅依赖于激光束功率密度与光束品质,还强烈依赖于光束所经过的等离子体状态。模拟显示,内环激光通道上靠近腔壁的He等离子体是受激拉曼散射(SRS)产生的主要区域。通过改变黑腔设计参数(包括构型、尺寸和填充物材料等)可以一定程度优化特定区域的等离子体状态,进而抑制LPI的产生。据此,提出了使用大黑腔高激光能量和改变填充气体组分两条控制SRS增长的技术路线。线性分析表明,两条技术路线效果明显,可分别将SRS峰值增益降低70%与63%。