Ytterbium-sensitized thulium-doped fiber laser with a single-mode output operating at 1900-nm region

A single-mode laser is demonstrated using a newly developed double-clad thulium-ytterbium-doped fiber (TYDF) in a linear cavity formed by two fiber Bragg gratings (FBGs). The YTF used is drawn from a D-shape preform fabricated using the modified chemical vapor deposition and solution doping technique. The laser is operated at 1 901.6 nm via the transition of thulium ions from 3F4 to 3H6 with the assistance of ytterbium to thulium ion energy transfer. The efficiencies of the laser are 0.71% and 0.75% at 927- and 905-nm multimode pumping, respectively. The thresholds of the launched pump power for 927- and 905-nm pumping are 1 314 and 1 458 mW, respectively. A 7-mW output is obtained at a 905-nm pump power of 2 400 mW.     

Mechanism of refrigeration cycle on laser cooling of solids

A simple model is developed to study the laser cooling of solids.The condition of laser cooling of a solid is developed.By using some parameters of the Yb 3＋ ion,which is most widely used in laser cooling,we then calculate the cooling power and the cooling efficiency.In order to make a more precise analysis, the effect of fluorescent reabsorption,which is unavoidable in the cooling process,is discussed using the random walk model.Taking Tm 3＋ ion as an example,we derive the average number of absorption events and determine the change in quantum efficiency due to reabsorption.Finally,we obtain the red-shift of the fluorescent wavelength and the requirement of sample dimension.     

Small signal gain and loss measurement of a CW Nd:YAG laser using an antiresonant ring interferometer

An antiresonant ring (ARR) interferometer configuration is introduced for the characterization of a continuous wave (CW) Nd:YAG laser output. The output of the ARR device is precisely characterized todetermine the gain and loss of a laboratory CW Nd:YAG laser by using the Findlay-Clay approach. TheARR arm is then experimentally arranged inside the cavity of an arranged high power side-pumped CWNd:YAG laser. A coated beam splitter with 50–50% reflectivity at normal incidence is placed inside thecavity to provide a wide range of reflectivity from 0 to 100%. This is performed by a rotatable stage and tilting the beam splitter by 10°with the steps of 0.05. By changing the input electrical power of the laser pump the variation of the output laser power is monitored for 20 individual reflectivity of ARR arm.Average pump threshold power of about 180 W is obtained. With the help of the derived equations and obtained threshold power, small signal gain and loss associated with the emerging beam is estimated. It is verified that the former is very dependent to the input parameters. Laser efficiency is also measures 5.6% which is quite comparable with the reported values.     

Quantum limit in low-loss ring laser gyros

Contrary to expectations, a measurement of the random walk in the ring laser gyro (RLG) as a functionof laser power P shows that it is not consistent with the P~-1/2 rule. In the experiment, the random walkand laser power are tested and recorded at different discharge currents. The random walk decreases withincreasing power, but with a rate much less than the theoretical value according to current literature. Inorder to solve the inconsistency above, we derive the expression for the random walk in RLGs based onlaser theory. Theoretical analysis shows that, accumulating effects of lower energy level due to its limitedlifetime lead to additional quantum noise from spontaneous emission. Results show that the random walkin the RLGs consists of two components. The former decreases with increasing power according to theP~-1/2 rule, whereas the other is power-independent. Thus far, the power-independent quantum limit hasnot appeared in the literature; therefore, the expressions for RLGs should be modified to describe the low-loss RLGs exactly, where the power-independent term takes a relatively larger proportion. The findingsare significant to the further reduction of quantum limit in low-loss RLGs.     

Forward and backward intensity noises induced by stimulated Brillouin scattering in optical fiber

The characteristic of intensity noise is degraded when stimulated Brillouin scattering (SBS) occurs in the fiber transmission systems. We use the localized fluctuating model to study SBS and obtain the curves of intensity fluctuations versus the single-pass gain. Corresponding experiments are also conducted. For the forward light, the relative intensity noise (RIN) dramatically increases at first and gradually stabilizes when the input power is above the SBS threshold. For the backward light, the RIN increases dramatically with the input power near the threshold. As the input power continues to increase, the RIN decreases quickly at first and subsequently decreases slowly. This observation is attributed to the lower frequencies.     

Nonsingular terminal sliding mode approach applied to synchronize chaotic parameters and systems with unknown nonlinear inputs

This paper deals with the design of a novel nonsingular terminal sliding mode controller for finite-time synchro-nization of two different chaotic systems with fully unknown parameters and nonlinear inputs. We propose a novel nonsingular terminal sliding surface and prove its finite-time convergence to zero. We assume that both the master＇s and the slave＇s system parameters are unknown in advance. Proper adaptation laws are derived to tackle the unknown parameters. An adaptive sliding mode control law is designed to ensure the existence of the sliding mode in finite time. We prove that both reaching and sliding mode phases are stable in finite time. An estimation of convergence time is given. Two illustrative examples show the effectiveness and usefulness of the proposed technique. It is worthwhile noticing that the introduced nonsingular terminal sliding mode can be applied to a wide variety of nonlinear control problems.     

Efficient Tm：YAG Ceramic Laser at 2 μm

We demonstrate a high-efficiency continuous-wave Tm： YAG ceramic laser pumped with a Ti：sapphire laser. An output power up to 860mW is obtained under an absorbed pump power of 2.21 W at 785nm, corresponding to a slope efficiency of 42.1% and optical to optical efficiency of 22%. The measured central wavelength is 2012nm.     

Proton Inelastic Mean Free Path in a Group of Organic Materials in 0.05-10MeV Range

Inelastic mean free paths （MFPs） of 0.05-10 MeV protons in a group of 10 organic compounds are systematically calculated. The calculations are based on the method newly derived from the Ashley optical-data model and from the higher-order correction terms in stopping power calculations. Especially, in this method the new and empirical Bloch correction for the inelastic MFP is given. An evaluation for the optical energy loss function is incorporated into the present calculations because of the lack of available experimental optical data for the considered organic compounds expect for kapton. The proton inelastic MFPs for these 10 organic compounds in the energy range from 0.05 to 10 MeV are presented here for the first time, and the combination of these inelastic MFP data and our previous data of stopping power calculation for these bioorganic compounds may form a useful database for Monte Carlo track-structure studies of various radiation effects on these materials.     

Laser-Diode End-Pumped Nd:YVO4 Slab Laser under Direct Pumping into the Emitting Level

We present an 880-nm laser-diode partially end-pumped Nd：YVO4 slab cw laser with output 126.7 W by using a hybrid resonator. The slop efficiency and optical-to-optical efficiency with respect to absorbed pumping power are 73.2% and 58.7%, respectively. At the output power of 100 W, the beam propagation M2 factors are 1.1 in the unstable direction and 1.15 in the stable direction.     

一种新的分段非线性混沌映射及其性能分析

研究了logistic混沌映射的相关性质,指出当系统参数取值改变时,产生的混沌序列在相空间不具有遍历性.基于以上分析,构造了一种分段logistic混沌映射,对logistic映射和定义的分段logistic映射的分岔图和Lyapunov指数进行了研究,同时通过实验对这二种映射生成序列的随机性、相关系数、功率谱等性能进行了比较分析.在此基础上,定义了一种新的混沌系统性能评价指标——分岔迭代次数.结果表明,定义的分段logistic映射不仅具有良好的遍历性,而且对应的混沌系统相关评价指标的性能良好. 关键词： 混沌系统 相关系数 Lyapunov指数 功率谱