首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
The microchip lasers based on the neodymium or the ytterbium doped yttrium-aluminium garnet crystal and Q-sw itched by the Cr4+:YAG film are considered. The optimal (maximizing of energy) values of the pumping beam radius, the absorber parameters (the thickness and tetravalent chromium ion concentration), and the output mirror reflectivity are determined. The possibility of higher values of energy in the Yb:YAG laser pulse, in comparison with a more traditional Nd:YAG laser, is also substantiated. PACS 42.60.Gd  相似文献   

2.
This paper reports on an experimental method for measuring in Nd:YAG the Nd doping concentration (C) with high sensitivity (0.01 at.%Nd) and high spatial resolution (50 m). The method is based on the measurement of the fluorescence lifetime f of the upper Nd laser level. Additional parameters required to determine C are the intrinsic fluorescence lifetime 0 and the quenching parameter Q. The measured values of f, 0 (256.47±0.14 s) and Q (4.45±0.40×1020 cm-3) allow us to calculate the Nd concentration C with an absolute accuracy of 0.1 at.%Nd. By using this method C is measured at the outer surfaces of standard laser rods and at the faces of boule slices (with diameters of up to 50 mm). The obtained results demonstrate a detection sensitivity of 0.01 at.%Nd. PACS 42.70.Hj; 81.70.Fy  相似文献   

3.
A compact eye-safe optical parametric oscillator (OPO) using a noncritically phase-matched KTP crystal intracavity pumped by a passively Q-switched Nd:YVO4 laser is experimentally demonstrated. To enhance the performance of passive Q-switching, a Cr4+:YAG saturable absorber crystal is coated as an OPO output coupler in a nearly hemispherical cavity. With an incident pump power of 2.5 W, the compact intracavity OPO cavity, operating at 62.5 kHz, produces average powers at 1573 nm up to 255 mW and peak powers higher than 1 kW. PACS 42.60.Gd; 42.65.Yj; 42.55.Xi  相似文献   

4.
Optimizing non-resonant frequency conversion in periodically poled media   总被引:1,自引:0,他引:1  
Non-resonant frequency conversion into the blue, green, orange, and red spectral regions is reported. Fundamental light sources were continuous-wave non-planar monolithic single-mode ring Nd:YAG lasers as well as a standing-wave multi-mode Nd:YAG laser. Periodically poled KTiOPO4 was employed as the nonlinear medium, but the considerations could also be applied to other periodically poled materials. A multi-pass scheme resulted in a normalized conversion efficiency as high as 27.2 %W-1 for frequency doubling in the small-signal regime at 1064 nm. PACS 42.65.Ky; 42.79.Nv; 42.70.Mp  相似文献   

5.
The generation of [Fe]K line radiation has been studied on a compact, ultrashort, laser based hard X-ray source, particularly suited for high-repetition-rate laser systems (1 to >10 kHz). Sub-millijoule, 25 fs Ti:sapphire laser pulses are applied to generate hard X-ray radiation on a commercially available ferric audio cassette tape target. Spectroscopic investigations reveal strong iron K emission in addition to a weak bremsstrahlung continuum. Under single exposure and single pulse conditions the X-ray yield is low. Energy conversion efficiencies of about K=2×10-7 are observed. Prepulse and multiple shot exposure techniques, both successfully used with high energy/low repetition rate systems, are investigated for these low energy/high repetition rate conditions. Depending on the applied pulse energy and intensity, the X-ray yield can be enhanced by more than three orders of magnitude. Photon fluxes exceeding 2×109Kphotons/s are generated with the presented tape target yielding conversion efficiencies of nearly K=10-5. PACS 42.65.-k; 52.38.Ph; 52.50.Jm  相似文献   

6.
We introduce o(p+1q+1)-invariant bilinear differential operators on the space of tensor densities on Rn generalizing the well-known bilinear sl2-invariant differential operators in the one-dimensional case, called Transvectants or Rankin–Cohen brackets. We also consider already known linear o(p+1q+1)-invariant differential operators given by powers of the Laplacian.  相似文献   

7.
We find a unique torsion free Riemannian spin connection for the natural Killing metric on the quantum group C q [ SL2], using a recent frame bundle formulation. We find that its covariant Ricci curvature is essentially proportional to the metric (i.e. an Einstein space). We compute the Dirac operator and find for q an odd rth root of unity that its eigenvalues are given by q-integers [m] q for m=0,1...,r–1 offset by the constant background curvature. We fully solve the Dirac equation for r=3.  相似文献   

8.
The simultaneous excitation and nonlinear interaction of the space-charge and photoconductivity gratings are studied experimentally in photorefractive Bi12SiO20 and Bi12TiO20. The measurements are performed using the diffraction technique, which implies the illumination of the crystal by an oscillating interference pattern (r=532 nm) along with the application of dc and ac electric fields and detection of the diffracted probe beam (p=650 nm). Such illumination excites the running photoconductivity grating, which interacts with the ac component of the applied field giving rise to the space-charge wave. Being the eigenmode of the space-charge oscillations, this wave reveals itself as a low-frequency resonant maximum at the frequency-transfer function of the detected signal. The drift mobilities of electrons are estimated using the developed technique: =(1.1–1.4)×10-2 cm2/Vs (Bi12SiO20, T=296–298 K) and =2.8×10-3 cm2/Vs (Bi12TiO20, T=293 K). PACS 42.65.Sf; 42.70.Nq  相似文献   

9.
Liu  Yang  Yang  Jihua  Yang  Wensheng  Xie  Tengfeng  Bai  Yubai  Li  Tiejin 《Journal of nanoparticle research》2000,2(3):309-313
Two SnO2 nanoparticles were synthesized by hydrothermal method at 170°C and 180°C, respectively. Transmission electron microscope observations reveal that the diameters of both the nanoparticles are around 6nm. At the same time, surface photovoltage spectroscopy measurements show that the nanoparticle synthesized at 180°C has more surface electronic states at 0.3eV below the conduction band than the one synthesized at 170°C. This means that the temperatures chosen in hydrothermal synthesis have significant influence on the surface electronic characteristics of resultant SnO2 nanoparticles but the effect on their sizes is not obvious. However, after being calcined at 500°C for 2h, the diameter of the nanoparticle synthesized at 180°C increased to 23nm and that of the nanoparticle synthesized at 170°C increased to 32nm as calculated from X-ray diffraction pattern.  相似文献   

10.
We report on the evaluation of a microstructured optical fiber (MOF) designed for non-linear signal processing applications, i.e., with a very small guided mode (waist 1 m). Calculations predict an intrinsic (assuming propagation in the fundamental mode and zero-loss coupling) non-linear coefficient of 40 W-1km-1 at =1.55 m, but they also predict a basic multimode character. NSOM measurements validate directly the high intrinsic value (32±10 W-1km-1) and also show that with an optimized coupling, the overall losses in efficiency taking into account coupling losses and weak excitation of higher-order modes and leaky modes are only 2.5 dB. This performance is adequate for use in all-optical data processing lines, all the more since it is maintained for relevant propagation lengths and peak power densities. PACS 42.65.Wi; 42.81.Wg  相似文献   

11.
Diode-pumped passively Q-switched Nd : YAG laser at 1123 nm   总被引:1,自引:0,他引:1  
A diode-pumped Nd:YAG laser at 1123 nm is passively Q-switched by using a low doping concentration Cr4+:YAG crystal as a saturable absorber. When pumped by a 1.5-W laser diode, the laser produces pulses of 50-ns duration with a pulse energy of as much as 15 J and a peak power of 300 W at a pulse-repetition rate of 10 kHz. PACS 42.60.Gd; 42.55.Rz; 42.55.Xi  相似文献   

12.
Preferentially oriented sol–gel (Pb,Ca)TiO3/(Pb,La)TiO3/(Pb,Ca)TiO3 and (Pb,La)TiO3/(Pb,Ca)TiO3/(Pb,La)TiO3 multilayer heterostructure thin films deposited on silicon-based substrates have been studied and compared with identically prepared (Pb,La)TiO3 (PTL) and (Pb,Ca)TiO3 (PTC) films. The existence in their texture of two components that contribute to the net polarization in the direction normal to the plane of the film, 001 and 111, results in significant ferroelectric and pyroelectric properties. Pr=26 Ccm-2 and =28.5×10-9 Ccm-2K-1, and Pr=17 Ccm-2 and =22.8×10-9 Ccm-2K-1, have been achieved, respectively, in the PTL/PTC/PTL and PTC/PTL/PTC heterostructures. The surface roughness of these films provides a high specific surface that can be interesting for infrared detectivity. An increase of the dielectric permittivity in the whole temperature interval up to the transition temperature has been observed for both heterostructures with respect to the PTL and PTC films. This effect is due to a release of stress in the heterostructures that is revealed by the increase of the tetragonal distortion, c/a, of these films. PACS 68.55.Jk; 77.80.-e; 77.84.Dy  相似文献   

13.
The applicability of (K ,) - and (K , N)-reactions on13,14C and14,15N nuclei to the study of -transitions in primary and daughter -hypernuclei is discussed. The intensity of -deexcitation of 13C state |S 12C(15·11 MeV; 1+1): 1/2+ has been shown to be comparable with the intensity of baryon decay. Isospin selection rules are used to distinguish excitation energy ranges of primary hypernuclei, where the identification of the secondary -lines is probable.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.  相似文献   

14.
The breakup of 12C states into three -particles is discussed in the context of the continuum three-body problem. New information from the -decay of 12N populating 0+, 1+, and 2+ states in 12C is presented. The breakup mechanism of the 1+ state at 12.71MeV is clarified, the spin of the 10.3MeV state is determined as 0+, and evidence for a previously unknown 2+ state at 14.1(2)MeV is given.  相似文献   

15.
An analytic gravitational fieldZ (Z y ) is shown to include electromagnetic phenomena. In an almost flat and almost static complex geometryds 2 =zdzdz of four complex variables z=t, x, y, x the field equationsR Rz = –(U U Z ) imply the conventional equations of motion and the conventional electromagnetic field equations to first order if =(Z v) and =(z ) are expressed in terms of the conventional mass density function , the conventional charge density function , and a pressurep as follows: v=const=p/c 2–10–29 gm/cm3.  相似文献   

16.
A cluster of two atoms described by thes-f model with Coulomb repulsion has been considered. The interaction between localized 4f electrons (S=1/2) is taken in the molecular field approximation. The thermodynamic quantities like magnetization, specific heat and correlation functions n , n , S z n , S z n , S z (n n ), n n and S + a + a as functions of temperature are presented for different band fillingN=0, 0.5, 1, 1.5, 2. The dependence of Curie temperature onN is calculated. The phase diagram forN=1 (T=0K) shows the possibility of existence of two phases: paramagnetic and ferromagnetic.The Curie temperature and the specific heat as functions ofN exhibit similar trends as found in experiments on doped magnetic semiconductors.  相似文献   

17.
We investigate the stochastic counterpart of the Smoluchowski coagulation equation, namely the Marcus–Lushnikov coagulation model. It is believed that for a broad class of kernels, all particles are swept into one huge cluster in an arbitrarily small time, which is known as a complete and instantaneous gelation phenomenon. Indeed, Spouge (also Domilovskii et al. for a special case) conjectured that K(i, j)=(ij) , >1, are such kernels. In this paper, we extend the above conjecture and prove rigorously that if there is a function (i, j), increasing in both i and j such that j=1 1/(j(i, j))< for all i, and K(i, j)ij(i, j) for all i, j, then complete and instantaneous gelation occurs. Evidently, this implies that any kernels K(i, j)ij(log(i+1)log(j+1)) , >1, exhibit complete instantaneous gelation. Also, we conjuncture the existence of a critical (or metastable) sol state: if lim i+j ij/K(i, j)=0 and i, j=1 1/K(i, j)=, then gelation time T g satisfies 0<T g<. Moreover, the gelation is complete after T g.  相似文献   

18.
Nano-thick Ag films were electrolessly deposited on TiN/p-Si(100) substrates. The substrates were prepared by sputtering TiN on p-Si(100) wafers. An activation process of the substrates was performed by immersing the substrates in a solution of 0.0019 moLL-1PdCl2+0.45 moLL-1HF+8.7 moLL-1aceticacid+0.036 moLL-1 HCl so as to obtain the Pd seed layer. The general composition of the electroless Ag bath was 0.0032 moLL-1AgNO3+2.24 moLL-1NH3+0.56 moLL-1aceticacid+0.1 moLL-1 NH2NH2 at pH 10.2. The morphologies of the Pd seed layer and the Ag films were characterized by atomic force microscopy (AFM). The effect of the Pd activation on electroless Ag deposition was tested by open circuit potential with time technology (OCP-t). For comparison, the morphology of the films deposited by electrochemical deposition on the substrates was also studied by AFM. PACS 82.45.Mp; 81.15.Pq; 81.10.Dn  相似文献   

19.
Let U(a, ) be a representation of the Poincaré group with mass and helicity zero, realized in the space of C -functions with compact support on 3, without the origin. Let U (2)(a, ) denote the tensorial product of U(a, ) by itself. We explicitly determine the cocycles of extension of U(a, ) by U (2)(a, ) and we prove that the nontrivial cohomology is indexed by (u(),),u()D 1 ]0,3\,.  相似文献   

20.
Information on available polystyrene calibration spheres is presented regarding the particle diameter, uncertainty in the size, and the width of the size distribution for particles in a size range between 20 and 100nm. The use of differential mobility analysis for measuring the single primary calibration standard in this size range, 100nm NIST Standard Reference Material®1963, is described along with the key factors in the uncertainty assessment. The issues of differences between international standards and traceability to the NIST Standard are presented. The lack of suitable polystyrene spheres in the 20–40nm size range will be discussed in terms of measurement uncertainty and width of the size distributions. Results on characterizing a new class of molecular particles known as dendrimers will be described and the possibilities of using these as size calibration standards for the size range from 3 to 15nm will be discussed.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号