多脉冲激光增强太赫兹辐射的PIC模拟

 模拟了强激光和稀薄非均匀等离子体相互作用在界面辐射超强太赫兹波的物理过程,提出了利用多脉冲激光增强太赫兹辐射的方案,详细研究了多脉冲激光的脉冲个数（取１～４个）、脉冲间距等因素对太赫兹辐射功率和频率的影响。当入射激光包含4个脉冲时,辐射最强,此时的辐射功率是相同条件下单脉冲的6倍,可达到7.16 MW,辐射的太赫兹波的脉宽约为330 fs,总能量约为1 μJ。研究结果表明:多脉冲激光可以显著增强太赫兹辐射,且随着脉冲个数的增加,激起的电子静电波振幅变大,辐射功率也随之变大,直到尾流场饱和;当脉冲间距等于入射激光脉宽时辐射最强。     

激光同步辐射作为阿秒X射线辐射源的特性研究

 研究了逆流相对论电子与激光脉冲相互作用获得激光同步辐射的频率上移、微分散射截面等特性。发现逆流相对论电子与短脉冲激光相互作用，可以获得阿秒X射线辐射脉冲。短脉冲激光条件下得到的后向散射光的频率上移与长脉冲激光条件下得到的后向散射光的频率上移是完全一致的，同时发现随着入射电子初始能量的增加，散射光的准直性越来越好，后向散射光脉冲的脉宽越来越短。     

Radiation damping effects on the interaction of ultraintense laser pulses with an overdense plasma

A strong effect of radiation damping on the interaction of an ultraintense laser pulse with an overdense plasma slab is found and studied via a relativistic particle-in-cell simulation including ionization. Hot electrons generated by the irradiation of a laser pulse with a radiance of I lambda(2)>10(22) W microm(2)/cm(2) and duration of 20 fs can convert more than 35% of the laser energy to radiation. This incoherent x-ray emission lasts for only the pulse duration and can be intense. The radiation efficiency is shown to increase nonlinearly with laser intensity. Similar to cyclotron radiation, the radiation damping may restrain the maximal energy of relativistic electrons in ultraintense-laser-produced plasmas.     

高能电子在强激光场中的同步辐射获得超短X射线脉冲

 研究了逆流相对论高能电子与强激光脉冲相互作用的同步辐射过程,当电子具有合适的初速度且传播方向与激光的传播方向相反时,电子在激光脉冲中心作圆周运动。由于电子的运动半径比传统同步辐射环中电子的运动半径小几个数量级,因此电子的辐射能量大大增加。研究发现此过程可以获得阿秒和泽秒X射线脉冲;同时发现随着入射电子初能量的增加和激光能量的增强,获得X射线脉冲脉宽越来越短,强度越来越大。这使得激光同步辐射可以成为一种强大的短波长短脉宽的辐射光源。     

电子在激光驻波场中运动产生的太赫兹及X射线辐射研究

采用单电子模型和经典辐射理论分别对低能和高能电子在线偏振激光驻波场中的运动和辐射过程进行了研究. 结果表明: 垂直于激光电场方向入射的低速电子在激光驻波场中随着光强的增大, 逐渐从一维近周期运动演变为二维折叠运动, 并产生强的微米量级波长的太赫兹辐射; 高能电子垂直或者平行于激光电场方向入射到激光驻波场中, 都会产生波长在几个纳米的高频辐射; 低能电子与激光驻波场作用中, 激光强度影响着电子的运动形式、辐射频率以及辐射强度; 高能电子入射时, 激光强度影响了电子高频辐射的强度, 电子初始能量影响着辐射的频率; 电子能量越高, 产生的辐射频率越大. 研究表明可以由激光加速电子的方式得到不同能量的电子束, 并利用电子束在激光驻波场的辐射使之成为太赫兹和X射线波段的小型辐射源. 研究结果可以为实验研究和利用激光驻波场中的电子辐射提供依据.     

Generation of continuous-wave 243-nm radiation by sum-frequency mixing

We have generated tunable cw radiation near 243 nm with a linewidth of less than 4 MHz by sum-frequency mixing the 351 nm radiation from an argon-ion laser with the 789 nm radiation from a ring dye laser in a crystal of ammonium dihydrogen phosphate held at moderate temperature. An external ring cavity, resonant with the dye laser, gives a power enhancement of about 12 in the sum-frequency generated radiation. Thermal lensing due to laser heating of the nonlinear crystal, distorded the 351 nm mode structure. This effect could limit the efficiency of the sum frequency mixing process.     

Plasma mechanisms of pulsed terahertz radiation generation

We present the results on generating terahertz radiation in the plasma of an optical discharge arising in the atmosphere during the focusing of femtosecond laser radiation. Different generation schemes related to focusing of the optical radiation by spherical and axicon lenses, with a constant electric field imposed on the laser spark region, as well as with the use of bichromatic laser radiation, are studied. Directivity patterns and polarization distributions of the terahertz radiation are analyzed in detail for different generation techniques. Comparison with the experimental results obtained by other research groups is given. Possible nonlinear mechanisms of the terahertz radiation generation are discussed.     

The influence of resonance IR laser radiation on magnetoabsorption in quantum wires

The coefficient of interband absorption of a weak electromagnetic wave by quantum wires in a transverse magnetic field and an intense laser radiation field is calculated. It is shown that, if the laser radiation frequency is equal either to the size quantization frequency (dimensional infrared resonance) or to a hybrid frequency (magnetoinfrared resonance), laser illumination can determine the shape of absorption oscillations. In particular, it is shown that the second magnetoabsorption peak is split into two peaks, the half-widths of which and the distance between which depend on the intensity of resonance laser radiation. The influence of the polarization of IR radiation on the interband absorption in quantum wires is discussed. The dynamics of the frequency dependence of the optical absorption coefficient with increasing intensity of resonance laser radiation is studied.     

Resonant interaction of femtosecond radiation with a cloud of cold <Superscript>87</Superscript>Rb atoms

The resonant interaction of ⁸⁷Rb atoms in a magneto-optical trap with femtosecond laser radiation in the spectral range 760–820 nm has been investigated experimentally. It has been demonstrated that femtosecond laser radiation with a spectral width of 10 nm interacts with an atomic ensemble as a set of spectrally narrow modes and as an ionizing laser field simultaneously. The dynamics of trap loading in the presence of ionization by femtosecond radiation has been studied, and the 5D _5/2 level population produced by an additional weak laser field has been measured.     

Highly efficient difference-frequency generation in KTP

A conversion efficiency as high as 22%from dye-laser radiation to the near infrared with difference-frequency mixing of Nd:YAG laser radiation and its second-harmonic-pumped dye laser in an only 5 mm long KTP crystal is reported for the generation of tunable near infrared radiation.     

腔靶产生的平面辐射场特性的数值模拟

 计算了不同腔靶构型参数对靶板能量效率和辐照均匀度的影响, 由此给出有较大能量效率和辐照均匀度的腔靶构型。合适的平面靶与腔壁的面积比既使平面靶的能量利用效率趋近理想又使得平面靶不太大以满足均匀度要求。     

He-Ne激光器放电点火电压的实验研究

寻找能降低He—Ne激光器点火电压的外加催离剂．实验对He—Ne激光器的点火电压在阴、阳极被可见光照射、低放射源作用于放电管和阴极附近加强电场的条件下进行了测量．对不同外加条件作用下He—Ne激光器点火电压实验数据的误差进行了分析．实验结果指出，用可见光照射阴极或阳极不能降低He—Ne激光器的点火电压；能明显降低点火电压的因素可以是低放射源或外加强电场．     

Modeling of blood vessel heating by laser radiation

A model for the calculation of heating of a blood vessel, which is modeled by an infinite circular cylinder and located in the hypodermic layer, under the action of laser radiation is proposed. Heating of such a vessel under the action of radiation with wavelengths most often used for laser therapy is calculated within the framework of the model proposed. The heating process is compared with the case of skin heating by laser radiation in the multilayer model of the skin.     

Mid-IR Dual-Wavelength Difference Frequency Generation Using Fiber Lasers as Pump and Signal Light Sources

A continuous-wave mid-IR difference frequency laser source, which respectively uses an ytterbium-doped fiber laser as the pump source and a multiwavelength erbium-doped fiber laser cascaded with an erbium-doped fiber amplifier as the signal source, is demonstrated. Our experimental results show that two stable mid-IR radiation lines with a spacing of about 5.4nm may be simultaneously emitted by a suitable setting the pump and signal polarization orientations. The number of the mid-IR radiation lines is limited by the quasi-phase-matching acceptance bandwidth. By changing the PPMgLN temperature the two mid-IR radiation lines may be synchronously tuned in the mid-IR range between 3295 and 3356.3nm.     

Acoustic Diagnostics of Laser Sparks in the Atmosphere

The results of an experimental study of the parameters of acoustic radiation generated by a laser spark made by focusing of a CO₂ high-power pulsed laser radiation outdoors in a slightly dusty atmosphere are presented. An analysis of the acoustic pulse spectrum shows that the position of its maximum is determined by the local plasma-formation radius, and the position of its low-frequency minimum is determined by the laser spark length. A new method of laser spark diagnostics in real time is suggested that enables one to estimate the plasma-formation size distribution function and the transmission factor for laser radiation propagated in the atmosphere under conditions of laser breakdown. The results obtained are in agreement with the available experimental data.     

对史密斯-帕塞尔自由电子激光光栅的研究

为了研究史密斯-帕塞尔自由电子激光的输出频率和光栅槽深、光栅槽长、光栅槽宽的关系,对于基于矩形光栅的史密斯-帕塞尔自由电子激光利用粒子模拟软件进行模拟和理论分析。首先,利用粒子模拟软件模拟对于基于矩形光栅的史密斯-帕塞尔自由电子激光进行了研究,发现史密斯-帕塞尔自由电子激光的输出频率随光栅槽深、光栅槽长、光栅槽宽的增大而减少。接着,对史密斯-帕塞尔自由电子激光的光栅槽进行了理论分析,发现每个光栅槽都可以等效为一个LC谐振电路,并发现在史密斯-帕塞尔自由电子激光中存在两种辐射,一种是史密斯-帕塞尔辐射,另一种是LC振荡辐射。最后,对光栅槽的LC振荡辐射进行了估算,发现史密斯-帕塞尔自由电子激光输出频率的模拟值与光栅槽的LC振荡辐射估算值的数量级均为102 GHz,且变化规律上一致。据此推测决定史密斯-帕塞尔自由电子激光输出频率的应该是光栅槽,而不是谐振腔。     

Nonlinear Thomson scattering from relativistic laser plasma interaction

As an electron oscillates in an intense laser field, it acquires a highly nonlinear motion and emits X-ray radiation by nonlinear Thomson scattering. In this paper we present a numerical and experimental analysis of this radiation. We show that this radiative process becomes dominant at relativistic laser intensities (a0>1), for which the laser light scatters off MeV electrons accelerated in the plasma.     

Simultaneous effects of pressure and temperature on the binding energy and diamagnetic susceptibility of a laser dressed donor in a spherical quantum dot

Binding energies and diamagnetic susceptibility of an impurity in a spherical GaAs quantum dot under the simultaneous influence of static pressure, temperature and laser radiation are investigated. Pressure- and temperature-dependent dressed potential which is produced by the combined effects of laser radiation and impurity considerably change the energy spectrum and diamagnetic susceptibility of the system. It is shown that binding energies and diamagnetic susceptibility increase with increasing pressure. Moreover, laser radiation effects on the diamagnetic susceptibility are not significant in comparison with its effects on the binding energy.     

Calculation of the fluorescence spectrum of two interacting atoms in external field

The radiation line profile for two identical dipole-dipole interacting two-level atoms in an external laser field is calculated. The stochastic component of the laser radiation is explicitly taken into account simulating it by the optical white noise. An explicit analytical expression for the radiation line profile is found for the case where the regular field component can be neglected.