On-line ion cooling and bunching for collinear laser spectroscopy

A new method has been developed for increasing the sensitivity of collinear laser spectroscopy. The method utilizes an ion-trapping technique in which a continuous low-energy ion beam is cooled and accumulated in a linear Paul trap and subsequently released as a short (10-20 micros) bunch. In collinear laser measurements the signal-to-noise ratio has been improved by a factor of 2 x 10(4), allowing spectroscopic measurements to be made with ion-beam fluxes of approximately 50 ions s(-1). The bunching method has been demonstrated in an on-line isotope shift and hyperfine structure measurement on radioactive (175)Hf.     

双纵模稳频氦氖激光器的光谱与频率复现性分析

对双纵模稳频氦氖激光器的光谱及其频率复现性进行了理论估计,进行了633 nm碘稳定氦氖激光器的拍频实验,实验采用内腔激光器,并采用双纵模稳频的方法,通过观测激光器的两个偏振态互相垂直的相邻纵模的输出,并使二者稳定到功率相等的参考点处,获得激光稳定输出。实验通过观察双纵模稳定激光的模式输出,分析了影响激光频率复现性与频率稳定度的因素,测量了稳定激光的功率和频率稳定度。通过拍频测量,对激光器的频率复现性进行了分析,复现性用频差可以达到(1～2)×10-8量级。通过实验表明,双纵模稳频氦氖激光器的频率复现性完全符合用于长度精密测量的稳频激光器的要求,激光器可以很稳定地工作,稳定度用阿伦偏差表示可以达到10-10量级,可以作为实用的稳频激光标准。     

Iodine stabilised 640 nm helium-neon laser

The wavelength of a helium-neon laser operating at 640 nm coincides with two strong absorption lines in the spectrum of iodine-127 when the gain tube is filled with neon-22. The absorption lines have been identified by measuring their hyperfine structure and the performance of the laser has been investigated. The beat frequency pair variance between two similar lasers was 7.6 kHz for a 10-second averaging time and the wavelength of component g of the 8-5 P(10) line was measured as 640.2834686 nm.     

Measurement of the 1s-2s energy interval in muonium

The 1s-2s interval has been measured in the muonium (&mgr;(+)e(-)) atom by Doppler-free two-photon pulsed laser spectroscopy. The frequency separation of the states was determined to be 2 455 528 941.0(9.8) MHz, in good agreement with quantum electrodynamics. The result may be interpreted as a measurement of the muon-electron charge ratio as -1-1.1(2.1)x10(-9). We expect significantly higher accuracy at future high flux muon sources and from cw laser technology.     

同时辐射六种可见波长的CW-氦氖激光器的稳频及其输出的650nmCW氦氖受激Raman辐射

在中国计量科学研究院研制的612激光管上,利用反射率为99.95%宽带激光反射镜,得到同时辐射六种波长的连续振荡,其波长为:611.8,629.8,632.8,635.1,640.1和650um,测量了它们的物理参数,验证了650nm为氦氖Raman激光.对六种波长在简易装置上进行了稳频,各条激光谱线的频率稳定性优于10~(-10),利用锁模技术,各条激光谱线的频率稳定性可达10~(-12).     

Uniform molecular analysis using femtosecond laser mass spectrometry

The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd.     

Refractive-index gratings written by near-ultraviolet radiation

This is the first report, to our knowledge, of refractive-index grating side writing in 10 mol.% GeO(2)-doped fiber by the near-UV light of a cw Ar(+) laser (333-364 nm). An induced-index magnitude as large as 1.9 x 10(-4) at 1.7x10(5) W/cm(2) UV power density has been achieved. The observed gratings have exhibited the same temperature stability as gratings written by a KrF excimer laser (248 nm).     

Swift heavy-ion irradiated active waveguides in Nd:YAG crystals: fabrication and laser generation

An Nd:YAG planar waveguide laser has been fabricated by ultra-low-fluence (2×10(12) cm(-2)) swift heavy-ion irradiation (60 MeV Ar(4+) ions). The appearance of the buried waveguiding has been associated with an increased refractive index layer as a consequence of the ion-induced electronic damage. Continuous-wave laser oscillations at 1064.2 nm have been observed from the waveguide under 808 nm optical excitation, with the absorbed pump power at threshold and laser slope efficiency close to 26 mW and 5.9%, respectively.     

Extending plasma accelerators: guiding with capillary tubes

In order to extend plasma accelerators, the laser beam has to be guided inside gas or plasma over a distance of the order of the dephasing length, which is typically much larger than the diffraction length z_R of the laser. A capillary tube can be used as a waveguide for high-intensity laser pulses over distances well in excess of z_R. Experimental demonstration of monomode guiding over 100 z_R of 10¹⁶ W/cm² pulses has been obtained in evacuated capillary tubes (45-70-μm inner diameter). A drop of transmission has been observed when the intensity of the amplified spontaneous emission (ASE) is high enough to ionize the capillary tube entrance. Propagation in helium gas-filled (10-40 mbar) capillary tubes has been studied at intensities up to 10¹⁶ W/cm²; a plasma column with on-axis density of the order of 10¹⁷ cm^-3 has been created on a length of the order of 4 cm. The use of a capillary tube for an extended accelerator is discussed for the ease of linear, resonant excitation of plasma waves by laser wakefield     

CO2的腔增强吸收与高灵敏吸收光谱研究

腔增强吸收光谱(CEAS)是在衰荡吸收光谱的基础上发展起来的一种新型的直接吸收光谱技术.文章报道了用中心输出波长为1.573μm的窄线宽连续可调谐半导体激光器(DFB封装)作光源,用两块高反射率平凹透镜(在1.573μm附近,凹面反射率R～99.4%,曲率半径r～1 m)组成对称共焦腔作吸收池的腔增强吸收光谱系统.采用扫描腔长的方法改变谐振腔的模式,当激光器的输出频率与谐振腔的某一腔模之间满足共振匹配关系时,激光被耦合到谐振腔内,用探测器接收透过谐振腔的光信号,同时用波长计精确测量激光器的输出波长.在33.5 cm长的吸收池内测量了吸收强度为1.816×10-23cm-1·(molecule·cm-2)-1的二氧化碳分子的弱吸收谱线,探测灵敏度达到了6.78×10-7 cm-1.实验结果表明,腔增强吸收光谱具有灵敏度高,装置简单,易于操作等优点.     

Measurements of electron transport in foils irradiated with a picosecond time scale laser pulse

The heating of solid foils by a picosecond time scale laser pulse has been studied by using x-ray emission spectroscopy. The target material was plastic foil with a buried layer of a spectroscopic tracer material. The laser pulse length was either 0.5 or 2 ps, which resulted in a laser irradiance that varied over the range 10(16)-10(19) W/cm(2). Time-resolved measurements of the buried layer emission spectra using an ultrafast x-ray streak camera were used to infer the density and temperature conditions as a function of laser parameters and depth of the buried layer. Comparison of the data to different models of electron transport showed that they are consistent with a model of electron transport that predicts the bulk of the target heating is due to return currents.     

Photonuclear physics when a multiterawatt laser pulse interacts with solid targets

When a laser pulse of intensity 10(19) W cm(-2) interacts with solid targets, electrons of energies of some tens of MeV are produced. In a tantalum target, the electrons generate an intense highly directional gamma-ray beam that can be used to carry out photonuclear reactions. The isotopes 11C, 38K, (62,64)Cu, 63Zn, 106Ag, 140Pr, and 180Ta have been produced by (gamma,n) reactions using the VULCAN laser beam. In addition, laser-induced nuclear fission in 238U has been demonstrated, a process which was theoretically predicted at such laser intensities more than ten years ago. The ratio of the 11C and the 62Cu beta(+) activities yields shot-by-shot temperatures of the suprathermal electrons at laser intensities of approximately 10(19) W cm(-2).     

Optical guidance of terrawatt laser pulses by the implosion phase of a fast Z-pinch discharge in a gas-filled capillary

A new method of optical guidance by the implosion phase of a fast Z-pinch discharge in a gas-filled capillary is proposed. An imploding plasma column has a concave electron-density profile in the radial direction, just before a stagnation phase driven by a converging current sheet and a shock wave. The feasibility of optical guidance of a high-intensity (>1 x 10(17) W/cm(2)) Ti:sapphire laser pulse by use of this method over a distance of 2 cm, corresponding to 12.5 times the Rayleigh length, has been experimentally demonstrated. The guiding-channel formation process was directly probed with a He-Ne laser beam. The electron density in the fully ionized channel was estimated to be 2.0 x 10(17) cm(-3) on the axis and 7.0 x 10(17) cm(-3) on the peaks of the channel edge, with a diameter of 70 mum, as indicated by the experimental results, which were corroborated by a magnetohydrodynamics simulation.     

High-Resolution Laser Photoacoustic Spectroscopy of HSiF(3): The 5nu(1) and 6nu(1) Overtone Bands

A spectrum of HSiF(3) has been recorded at room temperature with a gas pressure of 20-50 Torr in the near-infrared region. A laser photoacoustic spectrometer consisting of a longitudinal resonant cell coupled to a titanium:sapphire ring laser was employed. The 5nu(1) and 6nu(1) overtone bands of H(28)SiF(3) associated with the Si-H stretching have been observed at high resolution (3 x 10(-2) cm(-1)) in the regions 10 900-10 960 and 12 875-12 925 cm(-1), respectively. About 450 lines of the 5nu(1)-0 band have been assigned (J 相似文献   

Laser ablation of carbon at the threshold of plasma formation

The ionization of laser-ablated vapours with lasers producing ns duration pulses at various wavelengths has been studied in order to understand the mechanisms of the vapour-plasma transition. It has been established that there are several regimes characterizing the laser-target interaction which depend on laser intensity, wavelength, and pulse duration. The range of laser intensities for optimal laser evaporation is determined by the condition of transparent vapours. The intensity range is upper-limited by the opaque plasma formation due to vapour optical breakdown. Results are given for laser evaporation of graphite with Nd:YAG laser (1.064 7m), KrF laser (248 nm) and ArF laser (193 nm). For the UV laser wavelength the regime of skin-effect interaction was proposed as the mechanism of ion acceleration, and the range of validity of the skin-effect mode was established. With UV lasers the interaction has a bimodal nature: the interaction may proceed initially in the skin effect regime, resulting in a few high-energy ions, until hydrodynamic expansion begins at a later stage. The skin-effect interaction at the initial stage of the UV laser pulse gives the first, to our knowledge, explanation for the acceleration of ions up to ~100 eV at low laser intensities of 10⁸-10⁹ W/cm² and ns-range pulse duration.     

Experimental determination of the nu5 cis-bending vibrational frequency and Renner-Teller structure in ground state (X2Piu) C2H2+ using laser induced reactions

The spectrum of the nu(5) cis-bending vibration of ground state (X(2)Pi(u)) C(2)H(2)(+) has been recorded applying the method of laser induced reactions in a low-temperature 22-pole ion trap. It is obtained by counting the number of products of the reaction C(2)H(2)(+) (v(5) = 1) + H(2)--> C(2)H(3)(+) + H as a function of the laser wavelength. The vibronic transitions Delta-Pi and Sigma-Pi with their corresponding spin-orbit and Renner-Teller substructure have been observed. Using a perturbative analysis, the vibrational frequency has been determined to omega(5) = (710 +/- 4) cm(-1) and the Renner-Teller parameter epsilon(5) is on the order of 3 x 10(-2).     

Electron-yield enhancement in a laser-wakefield accelerator driven by asymmetric laser pulses

The effect of asymmetric laser pulses on electron yield from a laser wakefield accelerator has been experimentally studied using >10(19) cm(-3) plasmas and a 10 TW, >45 fs, Ti:Al2O3 laser. The laser pulse shape was controlled through nonlinear chirp with a grating pair compressor. Pulses (76 fs FWHM) with a steep rise and positive chirp were found to significantly enhance the electron yield compared to pulses with a gentle rise and negative chirp. Theory and simulation show that fast rising pulses can generate larger amplitude wakes that seed the growth of the self-modulation instability, and that frequency chirp is of minimal importance for the experimental parameters.     

High-power and high-contrast optical parametric chirped pulse amplification in beta-BaB2O4 crystal

We have developed a high-power laser system based on optical parametric chirped-pulse amplification in a beta-BaB2O4 crystal. The system provides gain of 10(8), a conversion efficiency of approximately 23%, an output energy of -65 mJ, and good amplified beam quality. The prepulse ratio has been measured to be 1.5 x 10(-8) or less. The spectral width was as broad as 16.5 nm centered at 1053 nm.     

Simple and highly accurate technique for time delay measurement in optical fibers by free-running laser configuration

A novel and simple technique for the measurement of time delay in the optical fiber by a free-running laser is proposed and demonstrated. The fiber to be measured was spliced to an erbium-doped fiber so as to form a ring-cavity laser. The mode beating frequency of the laser was measured to determine the round-trip time delay. This precise and efficient technique has an accuracy of 10(-8) for a fiber length of 100 km and of 10(-6) for a several-meters-long one.     

Study on the Spectrum of Miniature Optically Pumped NH3 Submillimeter-Wave Laser

By means of an iteration method and taking into account the broadening of the infrared pumping laser, the spectrum of a miniature, optically pumped, superradiant NH₃ submillimeter-wave(SMMW) gas laser pumped by CO₂-10R(8) has been calculated and studied by solving density matrix equations. Experimentally, the interferogram of miniature SMMW laser pumped by a TEA-CO₂ laser with 10R(8) line is measured. This is the first time that the theoretical spectrum has been in good agreement with experimental results.