Acousto-Optic Power Summation for Mutually Noncoherent Pulsed Lasers

A method of the power summation for mutually noncoherent pulsed lasers of the same type using time interleaving is proposed and validated experimentally. The method uses an acoustic-optic deflector, which commutates radiation of different sources into one output channel simultaneously with radiation presenting in this channel. It is crucially important that the power of the final output radiation is equal to the power sum of the input sources, and the angular and coordinate parameters of an output beam are the same as that for the input sources. The experiments were carried out with single-mode diode lasers on a wavelength of 1.3 μm using a ТеО₂-crystal-based deflector. The method is appropriate for the power summation for fiber-optic, diode, and solid-state lasers. We have estimated the main interrelated parameters.     

Application of mid-infrared laser radiation for lithotripsy

The perforation effects of Er:YAG (2940 nm) and Ho:YAG (2100 nm) lasers radiation on human urinary stones model made from compressed plaster and real human samples were compared in vitro. For mid-infrared laser radiation delivery the special COP/Ag hollow glass waveguides were used. From the interaction experiments the perforation rates were derived and compared for both lasers. From the results it can be evaluated that Er:YAG laser radiation is favourable in comparison with Ho:YAG laser in case of artificial samples perforation efficiency.     

Organic Materials for Optical Technologies

Photophysical processes in pyrane substitutes excited by high-power laser radiation are investigated. It is demonstrated that the examined molecules offer promise as active media of tunable lasers (including solid-state lasers), optical radiation limiters with = 532 nm, and emitting layers of organic light diodes.     

States that give the maximum signal-to-quantum noise ratio for a fixed energy

Under a radiation power constraint, the maximum signal-to-quantum noise ratio obtainable for any state of a radiation field is found. This maximum value is achieved by the two-photon coherent states introduced previously to describe two-photon lasers.     

Antenna model for wire lasers

An antenna model is proposed for long (L > A) lasers with subwavelength cross sections (wire lasers). It is shown that the far-field pattern of the wire lasers is determined by the ratio of the wavelength to the length. The radiation of the wire laser is predicted to be concentrated in a narrow beam theta approximately radical(2lambda/L) for laser modes where the longitudinal phase velocity is in synchronism with the velocity of light in air. Experimental results obtained using a terahertz quantum cascade wire laser are in agreement with the model.     

高功率掺镱光纤激光器的辐照影响分析及研究进展

高功率掺镱光纤激光器在空间环境中的应用日益增多,但掺镱光纤材料在空间辐照条件下会产生色心效应,导致损耗增加,影响光纤器件以及激光器整机的性能,从而给高功率光纤激光器在空间环境的长期稳定工作带来隐患。从空间辐照对高功率光纤激光器性能的影响机理、抑制方法和研究进展等3个方面进行介绍。首先介绍了空间辐照对高功率掺镱光纤激光器中关键光学器件、放大级热负载、非线性效应等方面的影响分析,其次介绍了抑制辐照效应的典型方法及其在高功率掺镱光纤激光器中的可行性分析,最后介绍了国内外典型的高功率掺镱光纤激光器的辐照影响及抑制的研究成果,并展望了未来发展趋势。     

4H‐SiC: a new nonlinear material for midinfrared lasers

Nonlinear optical (NLO) frequency conversion is commonly used for generating midinfrared (MIR) lasers that offer light sources for a variety of applications. However, the low laser damage thresholds of NLO crystals used so far seriously limit the output power of MIR lasers. Here, a new nonlinear material 4H‐SiC is demonstrated for producing MIR laser. Broadband MIR radiation ranging from 3.90 to 5.60 μm is generated in 4H‐SiC by phase‐matched difference‐frequency generation for the first time. The results may open a door to practically utilize wide‐bandgap semiconductors with high laser damage thresholds as NLO materials for high power output of MIR lasers.     

Autoinjection of Single-Pulse Priming Radiation in a Laser with a Bifurcated Anisotropic Resonator

The optical schemes of lasers with autoinjection of priming radiation in a bifurcated anisotropic resonator are described that make it possible to increase the efficiency of the formation of highly coherent giant pulses by raising the priming radiation intensity level. The parameters of radiation of that kind of ruby lasers have been experimentally studied with Q-switching of a low Q resonator by a bleaching filter and electrooptical switching of the generation channel into the resonator with a higher Q and/or the gain coefficient of an active element, and/or the active material space factor of the resonator.     

Key methods for intensifying soft X-ray emission from a laser plasma for lithography

A two-pulse two-wave (Nd and CO₂ lasers) scheme is proposed for irradiating a laser target, which ensures the highest factor of laser radiation conversion to the X-ray range (13.5 nm ± 1%). Analytic estimates are obtained for parameters of pulses and of the target made of Xe or Li. Numerical optimization is performed for X-ray emission from a spherical Xe target exposed to a CO₂ laser pulse. The maximal factor of conversion of laser radiation to X rays is ～1%. Angular and spectral characteristics of X-ray radiation are obtained. The flux of fast Xe ions ejected from the target and damaging the Mo/Si coating of X-ray mirrors is estimated.     

Role of pulse shaping in control of focus and intensity of terahertz radiation

In this work, we uncover the role of lasers pulse shaping for controlling the terahertz peaks with their separation in addition to their intensities. We have developed a mathematical model for obtaining the amplitude, frequency, and power of the emitted Terahertz radiation for the lasers whose shape is tailored based on the index and skew parameter. Then the results are compared with the case of Gaussian laser pulse in collisional plasma. We optimize the process by applying magnetic field and by varying the index of the lasers for compensating the negative influence of collisions on the THz emission. Specifically the effect of laser beam width, magnetic field and collision frequency is investigated on the electric field of the terahertz radiation and the efficiency of the mechanism.     

The effect of selective chemical etching on the directivity pattern for radiation of a semiconductor laser

The effect of the selective wet chemical etching of the emitting surface on the directivity pattern of radiation in the plane normal to the p-n junction is studied for InGaP/GaAs lasers with InGaAs quantum wells. It is found by atomic-force microscopy that the cylindrical lens (converging or diverging, depending on the type of etchant) is self-formed on the emitting surface due to the different etching rate of wide-gap layers (InGaP) and active layers (GaAs, InGaAs) of the lasers. By adjusting the corresponding etching time, the aperture angle of the laser radiation pattern in the plane normal to the p-n junction can be changed in the range of 57°–82° at the initial aperture angle at the half maximum level of 6°.     

位移效应对量子点激光器的性能影响

从理论上分析了位移效应对量子点激光器的影响, 并推导了量子点激光器阈值电流相对变化、输出功率相对变化的位移损伤公式. 对量子点激光器进行了中子辐照实验, 观察到了阈值电流的增加. 结合实验结果确定了量子点载流子非辐射复合速率的损伤因子的表达式, 公式计算结果与实验结果符合较好, 证明了模型的正确性. 得到的公式可用于预测量子点激光器在辐射环境下的性能变化, 有着较大实际应用价值. 关键词： 量子点激光器 位移损伤 缺陷     

Evidence of high harmonics from echo-enabled harmonic generation for seeding x-ray free electron lasers

Echo-enabled harmonic generation free electron lasers hold great promise for the generation of fully coherent radiation in x-ray wavelengths. Here we report the first evidence of high harmonics from the echo-enabled harmonic generation technique in the realistic scenario where the laser energy modulation is comparable to the beam slice energy spread. In this experiment, coherent radiation at the seventh harmonic of the second seed laser is generated when the energy modulation amplitude is about 2-3 times the slice energy spread. The experiment confirms the underlying physics of echo-enabled harmonic generation and may have a strong impact on emerging seeded x-ray free electron lasers that are capable of generating laserlike x rays which will advance many areas of science.     

Generation of Terahertz radiation with two color semiconductor lasers

We discuss and analyze concepts for the generation of tuneable continuous wave terahertz (THz) radiation with two color diode lasers. First, different geometries of two color lasers are reviewed. We show that the THz power of two color lasers in combination with external photomixers becomes sufficient for scanning THz imaging applications when optical amplification with a tapered amplifier is implemented. Then, the concept of direct emission of THz radiation out of a two‐color semiconductor laser is reviewed and the potential of this concept with respect to THz bandwidth and achievable THz power is critically analyzed.     

Many-particle quantum theory for a class of free-electron devices

The small signal, cold beam regime of a wide class of free-electron lasers including magnetic and optical helical wigglers and stimulated Cerenkov radiation is discussed based on the many-particle fully quantized Bambini-Renieri Hamiltonian. The central topic is the photon statistics under various conditions and the significance of cooperative effects.     

A model for analytical description of magnetic field effects and losses in a planar undulator radiation

We analyze the influence of constant magnetic constituents on the radiation of high energy electrons in a planar undulator. Broadening and spectrum shift effect of the constant field is compared with other common spectrum distortions in UR sources. Analytical formulation of the effect of the constant magnetic field enables us to obtain and study exact expressions for the UR intensity. They reveal the possibilities to influence off-axis effects and give practical recommendations for the undulators with radiation properties, best profitable for free electron lasers. Several examples of undulators are considered, recommendations specific for each case are given.     

Blue‐green light generation using high brilliance edge emitting diode lasers

A review about second harmonic generation using edge emitting diode lasers and nonlinear crystals to obtain laser radiation in the blue‐green spectral range is presented. Therefore, pump laser radiation with high brightness and narrow bandwidth is necessary. Thus, this review gives an overview of the advances made with distributed feedback and Bragg reflector lasers, tapered lasers and amplifiers as well as external cavity diode lasers and master oscillator power amplifier schemes to achieve high brilliance emission. Since periodically poled materials have enabled high second harmonic conversion efficiencies with low and moderate pump powers, the review is focused on frequency doubling using those materials. The most commonly used materials, their properties and limitations are discussed briefly. Single pass and resonant SHG setups with waveguide and bulk nonlinear crystals are discussed and an emphasis on building compact and integrated devices is made.     

碱土金属原子激光的共振辐射俘获效应

根据Holstein理论研究了碱土金属原子激光中的共振辐射俘获效应，分别计算了Ca，Sr和Ba蒸气激光在不同半径时产生共振辐射俘获效应的阈值温度、基态粒子数密度和共振能级的有效寿命.发现计算得到的阈值温度与实验报道的开始产生激光的工作温度一致，表明共振辐射俘获效应是这类激光形成粒子数反转的一个重要机制. 关键词： 共振辐射俘获 碱土金属原子激光 阈值温度     

切伦科夫自由电子激光中自发辐射与受激辐射的关系

本文从单粒子理论出发,导出了切化科夫自由电子激光中自发辐射与受激辐射的关系。结果表明:在切化科夫自由电子激光中也存在着类似于wiggler自由电子激光中的Madey公式的关系。文中还利用得出的结果对倾斜角度受激切伦科夫辐射的增益进行了计算。 关键词：