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.     

c向切割掺杂LiNbO3晶体中的光耦合

实验研究了三种c向切割的不同掺杂的LiNbO3：Fe晶体中入射光与反射光的耦合情况.发现沿-c轴方向入射时透射光与反射光强的准周期振荡行为是光生伏打机制占优势的瞬态能量转移和扩散机制引起的相反方向的能量转移所致，不是光生伏打场的表面击穿引起的.当入射光沿+c方向入射时，由于两种机制引起的能量转移方向相同，因而不会产生这种振荡. 关键词： 准周期振荡 反射光栅 瞬态能量转移 扩散机制     

Generation of acoustically distributed feedback lasers based on gyrotropic crystals

Oscillation conditions were determined for acoustically distributed feedback (ADFB) lasers based on gyrotropic uniaxial and cubic crystals. The lasing threshold was shown to be higher for the modes with clockwise polarization than for those with counterclockwise polarization. It is established that the regions of maximal amplification for clockwise (counterwise) waves of the gyrotropic crystal are displaced in the direction of decreased (increased) phase detuning, respectively, relative to amplification regions that correspond to the absence of crystal gyrotropy. The ADFB laser was shown to be capable of generating at the Bragg frequency. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 331–335, May–June, 2008.     

High-power laser performance of a-cut and c-cut Yb:LuVO4 crystals

We report high-power laser operation that was achieved with a-cut and c-cut Yb:LuVO(4) crystals. Up to 8.3 W of pi-polarized output power was generated from an a-cut, 2 mm uncoated crystal with an optical conversion efficiency of 59%. The highest slope efficiency was 80%. Laser oscillation obtained with c-cut crystal was also linearly polarized, with two orthogonal polarization components along [110] and [(-)110] directions. The highest output power achieved was 4.5 W, with an optical conversion efficiency of 33% and a slope efficiency of 40%.     

High efficiency UV solid state lasers based on Ce:LiCaAlF6 crystals

We report the spectroscopy and laser results of cerium-doped colquiriite LiCaAlF₆ (LiCAF) single crystals. High quality samples have been grown using the Czochralski technique and characterized by means of X-ray Laue diffractometry, absorption and emission spectra. Moreover, we measured the lifetime and deduced the emission cross-sections of the laser transition. Using this crystal we realized two lasers devices: a high-efficiency laser emitting at 289 nm with a repetition rate (RR) of up to 2 kHz and a widely tunable laser (from 280 nm to 317 nm) with an RR of up to 4.3 kHz. The high quality of the crystal made it possible to obtain the highest slope efficiency (49%) ever reported to our knowledge for a Ce:LiCAF laser. PACS 42.55.Rz; 78.55.Hx; 81.10.Fq     

Kilohertz raman lasers based on bno and kgw crystals for a wide spectral range

Efficient Raman lasers based on Ba(NO₃)₂ and KGd(WO₄)₂ crystals which produce nanosecond pulses with repetition rates of 1 and 4 kHz at 26 wavelengths between 280 and 1600 nm are developed and studied. A maximum SRS conversion efficiency of 25% is obtained. It is found that the divergence of the beams generated by the Raman laser can be significantly reduced by using quasi-Bessel pump beams and an unstable telescope cavity.     

New scintillators based on barium fluoride crystals and ceramics

Experimental studies on the optical properties of new crystals and ceramics based on CeF₃- and CdF₂-doped barium fluoride were aimed at producing scintillators with a higher light yield level (particularly in the ultra-short wavelength range with a luminescence time of 0.6–0.8 ns) that could be used in the development of fast and low-cost optical sensors for positron emission tomography (PET). Ceramics manufactured on the basis of BaF₂ single crystals with various concentrations of Ce and Cd are transparent in the 300–600 nm wavelength range; this is comparable to BaF₂ single crystals.     

光子晶体在半导体激光器中的应用

激光的发明，将人类带入光通信、光存储、光显示的高科技文明中，随着高科技的不断发展、进步和应用范围的不断扩大，对激光的要求更高，例如低阈值、高效率、高亮度、高速、小体积、好的模式特性等，这些要求在现有的传统激光器理论及技术中是难以达到的。但是当人们将光子晶体的理论与现有激光物理和技术相结合时，则有望突破传统激光器的性能瓶颈。例如，提高自发辐射速率，同时获得更高的自发辐射向受激辐射的耦合效率，实现激光器的无阈值工作；利用光子晶体对光子态的调制作用，可以获得比传统激光器大几个数量级的光学腔品质因子，大幅度提高激光的亮度、单色性；结合光子晶体微腔及其显著增加的光学腔品质因子，可以提高激光器的调制速率等，因此，人们预期光子晶体科学与技术将成为未来光电子领域发展的核心之一。文章介绍了光子晶体在半导体激光器中的应用，指出光子晶体科学技术引入发展了几十年的半导体激光器中，使半导体激光器展现出更加优异的性能。最后文章作者展望了光子晶体激光器的未来发展和应用的方向。     

光子晶体在半导体激光器中的应用

激光的发明,将人类带入光通信、光存储、光显示的高科技文明中,随着高科技的不断发展、进步和应用范围的不断扩大,对激光的要求更高,例如低阈值、高效率、高亮度、高速、小体积、好的模式特性等,这些要求在现有的传统激光器理论及技术中是难以达到的。但是当人们将光子晶体的理论与现有激光物理和技术相结合时,则有望突破传统激光器的性能瓶颈。例如,提高自发辐射速率,同时获得更高的自发辐射向受激辐射的耦合效率,实现激光器的无阈值工作;利用光子晶体对光子态的调制作用,可以获得比传统激光器大几个数量级的光学腔品质因子,大幅度提高激     

New possibilities of X-ray nanocrystallography of biological macromolecules based on X-ray free-electron lasers

X-ray serial nanocrystallography is a new technique for determining the three-dimensional structure of biological macromolecules from data on the diffraction of ultrashort pulses generated by X-ray free-electron lasers. The maximum achievable resolution for a set of experimental data as a function of the sample sizes and parameters of the equipment is estimated based on simulations of the diffraction process with allowance for changes in the electronic structure of the atoms of the sample under the influence of X-rays. Estimates show that nanocrystallography greatly enhances the possibilities of X-ray analysis, reducing the requirements for the minimum permitted size of the crystals and enabling to explore poorly crystallizable molecular objects, such as many membrane proteins and complexes of macromolecules.     

Laser-related spectroscopy of ion-doped crystals for tunable solid-state lasers

In this work an overview of transition metal (TM) ion- and rare earth (RE) ion-doped crystals for application as tunable solid-state lasers will be given. Spectroscopic and laser results will be presented including recent research and advances in this field. Within this work tunability is defined as the possibility to achieve laser oscillation in the vibronic sideband of a transition. Tunable solid-state lasers are of interest for a wide field of applications, e.g. in scientific research, in medicine, for measurement and testing techniques, ultra short pulse generation, and communication. They can also be used as coherent light sources for second-harmonic generation, for optical parametric oscillators, and for sum- and difference-frequency generation. Tunable laser media based on 3d?3d transitions of transition-metal ions and 4f?5d transitions of rare-earth ions cover nowadays almost the whole spectral range between 270 nm and 4500 nm, see Fig. 1 [1-15]. In comparison to laser systems based on the 4f?4f transitions of trivalent rare-earth ions, tunable lasers based on 3d?3d and 4f?5d transitions are in general affected by a higher probability of excited-state absorption (ESA), a higher probability of non-radiative decay, and a higher saturation intensity leading to higher laser thresholds. Often laser oscillation cannot be obtained at all. These general topics will be considered in Sect. 1, where the basic aspects of tunable solid-state lasers are discussed: these are the preparational, the spectroscopic, and the laser aspect. In Sect. 2, the investigation of transition metal ion-doped crystals with respect to the realization of tunable laser oscillation is presented. The work is focused on transition-metal ions of the 3d row (Fe row) and divided into two subsections according to the octahedral and tetrahedral coordinations of the ion investigated. Each subsection is structured according to the electron configurations: 3d¹, 3d³, 3d⁴, and 3d⁸ for the octahedrally coordinated ions and 3d¹, 3d², and 3d⁴ for the tetrahedrally coordinated ions. Section 3 deals with interconfigurational transitions of divalent and trivalent rare-earth ions. Finally, in Sect. 4 the work is summarized. Received: 22 December 2000 / Published online: 30 March 2001     

Comparison between c-cut and a-cut Nd:YVO4 lasers passively Q-switched with a Cr4+:YAG saturable absorber

Comparison between c-cut and a-cut Nd:YVO₄ microchip lasers passively Q-switched with a Cr⁴⁺:YAG saturable absorber is experimentally made. The lower emission cross section of the c-cut Nd:YVO₄ crystal can enhance the passive Q-switching effect to produce a peak power 10 times higher than that obtained with the a-cut crystal. The experimental result further reveals that a c-cut Nd:YVO₄ crystal is a very convenient material for short-pulse (sub-nanosecond) and high-peak-power (>10 kW) lasers. Received:10December2001/Revisedversion:22January2002 / Published online: 14 March 2002     

GaAs/AlGaAs photonic crystals for VCSEL-type semiconductor lasers

The results of modelling of the influence of photonic crystal on the performance of VCSEL-type semiconductor laser structure are shown and indicate that the use of those structures would significantly improve the working parameters of the devices. The method of fabrication of photonic crystals in the Bragg mirrors of GaAs/AlGaAs-based VCSELs is presented.     

Novel photonuclear techniques based on femtosecond lasers

The results of X-ray diagnostics of plasma created at a material surface by a laser pulse with an intensity of up to 2.5 × 10¹⁸ W/cm² are presented. The experimental data are compared with the results of numerical modeling of the laser-plasma interaction while accounting for the detector-response function. Examples of possible nuclear problems that can be solved with the use of laser plasma as a source of charged particles and X-ray quanta are given.     

正交偏振激光角度测量技术综述

机械导轨运动副滚转角的高精度测量一直是一个难题。研究了很多光学方法,但由于其角位移方向正好垂直于探测光束,所以仍没有得到很好的解决。利用激光偏振面对旋转的敏感性,通过测量由此引起的正交偏振激光光强、相位或频差的变化,可有效地解决滚转角的测量问题。介绍了目前国内外基于正交偏振激光的滚转角测量技术,根据其测量原理分为光强差测量、相位差测量和频率差测量三类。对每种测量方法的原理和发展现状进行了评述,比较了各种方法的优缺点,讨论了其发展趋势。     

基于DFB激光器的光学微波信号的产生

采用量子阱混杂的材料集成技术制备并联分布反馈激光器和Y形波导耦合器集成的新型光电器件.两个并联分布反馈激光器的激射模式在频率上稍有差别,这两束不同频率的激光在Y形波导耦合器拍频产生光学微波信号.分别独立调节注入到两个激光器的电流大小,可以得到从13 GHz到42 GHz连续可调的光学微波信号. 关键词： 光学微波信号生成 分布反馈激光器 Y形波导 拍频