基于两步混合激发Na_2-Na系统的可调谐红外受激辐射

本文报道了与两步混合激发Na_2-Na系统相联系的受激电子喇曼散射过程产生了在3.38—3.46μm范围内连续可调谐的红外受激辐射的研究结果。对这种可调谐红外受激辐射的产生机制和实验结果作了仔细的分析和讨论。 同时,还计算了该红外受激辐射的相对强度并与实验结果进行了比较。最后指出这一工作与前人所做工作的不同之处及所具有的显著特点。     

锂蒸气中双光子泵浦的六波、四波混频和受激辐射

本文报道锂蒸气中由双光子泵浦所产生的位于紫外、可见和红外区的相干和受激辐射。包括:由一特殊六波混频过程产生的在1.03μm附近的可调谐相干辐射,由锂分子双光子离解或原子串级跃迁产生的波长为812.6nm的受激辐射,以及由四波混频产生的位于323.3nm和670.8nm的相干辐射。 关键词：     

由混合激发钠分子—原子系统产生的强度振荡变化的红外受激喇曼散射

本文报道以等频二步激发钠分子-原子系统,观测到强度随泵浦光的调谐而呈振荡变化的3P—4P受激喇曼散射,以及对应4D—4P和4F—3D跃迁的红外受激辐射和由四波混频产生的816.8～822.1nm区内可调谐相干辐射。文中对这些过程进行了分析讨论。     

原子—分子混合激发及所产生的受激和相干辐射

用适当波长的激光混合激发原子－分子样品，和通过原子－分子碰撞能量转移，可产生从紫外到红外宽波段范围内的受激和相干辐射，其中包括固定波长辐射，可调谐辐射以及宽带辐射以及宽辐射。这是一个物理涵义极为丰富并具有应用前景的研究领域。     

原子－分子混合激发及所产生的受激和相干辐射

用适当波长的激光混合激发原子－分子样品，和通过原子－分子碰撞能量转移，可产生从紫外到红外宽波段范围内的受激和相干辐射，其中包括固定波长辐射、可调谐辐射以及宽带辐射。这是一个物理涵义极为丰富并具有应用前景的研究领域。     

光纤维中的喇曼混频

我们在656厘米^-1到1343厘米^-1的频率范围研究了光纤维的调谐喇曼混频(RM)效应。在实验中观察到下列现象:相干反斯托克斯喇曼散射(CARS)的大小与逆喇曼吸收(VRA)的大小成反比;RM对受激喇曼散射(SRS)的强度分布有强烈影响。除了观测到相干斯托克斯(CSRS)和CARS辐射,还观测到二级相干斯托克斯(SOCSRS)和相干反斯托克斯(SOCARS)辐射。对实验结果进行了讨论。 关键词：     

由双光子共振激发钾蒸气产生红外受激辐射以及紫外和可见相干辐射

当双光子共振激发钾原子到7S能级时,测得了一系列位于红外区的光泵受激辐射和串级受激辐射.由光泵受激辐射与泵浦光的双光子共振四波混频过程,产生了对应于6P-4S和5P-4S的强相干辐射.而这两个相干辐射又具有泵浦光的作用,通过接联的四波混频过程产生位于紫外和可见区的许多相干辐射.文中对测到的红外受激辐射以及紫外和可见相干辐射的产生过程进行了讨论.     

电子-光子符合散射实验中受激原子态电荷云分布的研究

根据电子原子碰撞受激态退激偶极辐射的电子-光子符合实验的一般性理论，采用扭曲波近似方法，计算了电子与碱金属钠原子碰撞退激辐射光子的Stokes参数.引入取向和排列参数，用以描述受激态电荷云的分布，得到了与已有实验数据一致的结果. 关键词： 取向 排列 Stokes参数 电子-光子符合测量     

钠蒸气中受激电子喇曼散射

本文报道了钠原子3S-4S跃迁的受激电子喇曼散射的首次观测。获得了2.38μm～2.65μm的可调谐红外输出;计算了受激电子喇曼散射的功率增益系数并测量了红外输出随染料激光频率调谐的变化,其结果符合较好;给出了泵浦功率阈值随钠蒸气压变化的实验曲线;测得光子转换效率约为30％。在此同时,观测到了钠原子4S-3P跃迁的放大自发辐射。     

基于VO2和石墨烯实现hBN声子极化激元和自发发射率的主动调谐

鉴于极化激元对介电环境异常敏感的特性,本文中提出了双曲材料六方氮化硼(hBN)和石墨烯与相变材料二氧化钒(VO₂)组成的异质结构,用来研究hBN声子极化激元(PhPs)的主动可调谐性.研究结果表明,通过控制hBN/VO₂异质结构中VO₂相变可实现对hBN PhPs的主动调谐,获得主动可调谐的自发发射(SE)率.当在hBN/VO₂异质结构中添加石墨烯时,会在hBN双曲线带内耦合产生双曲等离子体-声子极化激元(HPPPs),而在双曲线带外产生表面等离子体-声子极化激元(SPPPs),通过控制VO₂相态和调节石墨烯化学势亦可实现石墨烯/hBN/VO₂异质结构的耦合色散及SE率的主动调谐.该研究为使用诸如相变材料和石墨烯等功能材料调谐各向异性光学材料与光的相互作用机制提供了理论指导.     

Emission of Concentrated Solutions of Organic Compounds Excited with High-Power Laser Radiation

Specific features of emission of concentrated (C 1.2·10¹⁹ cm^–3) solutions of organic molecules (rhodamine 6G, rhodamine C, phenalemine 512, and substituted paraterphenyl (LOC-1)) are investigated as functions of the exciting photon energy (at _exc = 308 and 532 nm) and power density of exciting radiation (up to 1 GW/cm²). One of the observed emission types – band emission – is studied. The intensity of band emission (its short- and long-wavelength maxima) is investigated versus the exciting radiation power density, and its time and polarization characteristics are also analyzed. The results obtained together with the specific features of the emission spectrum of concentrated rhodamine-C solution, measured after passage of sounding radiation with maximum at the wavelength equal to that of the short-wavelength maximum of band emission, demonstrate that the band emission is simply superfluorescence.     

The effect of mid-infrared and far-infrared emission,generated at NH3 excitation by intense radiation of a TEA CO2 laser,on ammonia absorption

The effect of Mid-InfraRed (MIR) ( 12 m) and Far-InfraRed (FIR) ( 100 m) emission from excited ammonia on the absorption of intense radiation of a TEA CO₂ laser has been studied experimentally under collisional and collisionless excitation conditions with ammonia pressures from 0.5 to 0.03 Torr. The energy of MIR and FIR emission was studied as a function of NH₃ pressure and laser energy fluence. Particular emphasis was given to the kinetics of MIR and FIR emission generation at different NH₃ pressures and to the measurement of the time delay of re-emitted pulses relative to the exciting CO₂ laser pulse. It has been found that the re-emission in the MIR range is highly collisional in nature. The intensity of MIR emission drops sharply (asp ³) with decreasing NH₃ pressure and its delay time relative to the exciting laser pulse increases. At the same time, re-emission in the FIR range (in the case of resonant excitation of NH3 at the 9R (30) line of CO₂ laser) is observed during an exciting pulse up top < 0.03 Torr. When binding the rotational sub-levels of a molecule with transitions, FIR emission acts as rotational relaxation and thus leads to an increase in NH₃ IR absorption even at collisionless excitation.     

Investigation of sensitized anti-stokes phosphors using sinusoidal modulation of the pump intensity

We describe a simple and relatively inexpensive method of investigating the processes by which incident IR radiation is converted to visible emission in anti-Stokes phosphors by multiphoton excitation. The procedure involves sinusoidal modulation of the intensity of the IR exciting radiation and analysis of the harmonic content of the visible output from the phosphor. A two-photon process, for example, results in some second harmonic modulation of the visible emission. The harmonic content depends on the relaxation times involved and on the nature of the conversion process. The experiments thus enable one to establish the order of the conversion process, to distinguish between possible mechanisms and to determine certain relaxation times. Representative results for the ytterbium-sensitized anti-Stokes phosphors Y₂O₂S-Ho-Yb and Y₂O₂S-Er-Yb are described.     

两个级联型三能级原子受激辐射的非线性性质

本文研究了两个级联型三能级原子同单模腔场的非线性相互作用,研究表明:在激发场场强达到一定阈值以后,两个原子的合作辐射效应变成同步辐射,即多原子系统在一定阈值条件下可以有组织成相当于一个大原子的系统,而产生同步有序辐射。同时,由于这种同步辐射效应,两原子系统的受激辐射的二阶相干度相对于单原子系统的要大,即聚束效应强而反聚束效应弱。另外,两原子系统由于多光子过程的加强而有更深的压缩效应,此时要求的激发场场强也比单原子系统的要强。     

Stimulated infrared emission under excitation of condensed molecular dielectrics with giant pulses of a ruby laser

Stimulated infrared (IR) emission from a condensed dielectric medium under exposure to a giant pulse of a ruby laser is reported. This effect was predicted in the theoretical paper [1]. Experimental studies were carried out for a number of molecular liquids in two experimental geometries. In the first case (“in transmission” geometry) the propagation direction of the detected IR radiation coincided with that of the exciting radiation. In the second case IR radiation generated was detected in the opposite direction. The angle of divergence of IR radiation was found to be of 10⁻² rad, while the conversion efficiency with respect to the pumping intensity depended on the type of molecular liquid and varied in the range of 0.05–0.6%. Possible microscopic mechanisms of generation of IR radiation under pumping of the dielectric medium with visible or ultraviolet (UV) radiation are analyzed.     

Polarization characteristics of stimulated emission of organic molecules when excited by intense XeCl laser radiation

We study the influence of the molecular structure, medium, and exciting-radiation parameters on the polarization, energy, and spectral characteristics of the emission of laser-active media based on the dicarboxylic derivative of p-terphenyl, rhodamine 101, and phenalemine 512. We found that the polarization of the stimulated emission of molecules when strongly excited under the conditions studied significantly depends on their structure, the pumping mode, the intensity and polarization of the exciting radiation, the shape and dimensions of the excited volume, and the phase state of the medium.     

Third harmonic enhancement due to Fano interference in semiconductor quantum well

We investigate the emission spectra of the semiconductor quantum well for few-cycle and sub-cycle pulse exciting. We find that Fano interference may induce third harmonic enhancement. Third harmonic enhancement varies with the magnitude and duration of the incident pulse, and may be enhanced by approximately one order of magnitude for the low intensity region of the sub-cycle incident pulse exciting.     

FIR Stark spectroscopy on optically pumped CH3OH laser

An extensive theoretical and experimental analysis of the absorption and emission spectrum of a CH₃OH FIR-laser excited by a conventional CO₂ laser is presented. Particular interest is devoted to the Stark shifts of the pump and lasing lines and to the electric field dependence of the Fir-laser output of the various lines. The offsets with respect to the exciting radiation and the Stark shifts of the IR absorption (pump) lines are measured by means of the transferred Lamb dip technique. The theoretical behaviours of the Stark patterns are calculated for several choices of the quantum numbers and selection rules involved in the transitions. A large variety of experimental results are reported and compared to theory. Non-linear Stark shifts have been observed for the 37.5m FIR laser line and for the IR-pump transitions excited by the 9-P(38) and 10-R(38) CO₂ laser Lines. Line assignments are proposed and new FIR laser lines are reported.     

Broadband enhancement of spontaneous emission in a photonic-plasmonic structure

We demonstrate that a broadband enhancement of spontaneous emission can be achieved within a photonic-plasmonic structure. The structure can strongly modify the spontaneous emission by exciting plasmonic modes. Because of the excited plasmonic modes, an enhancement up to 30 times is observed, leading to a 4 times broader emission spectrum. The reflectance measurement and the finite-difference time-domain simulation are carried out to support these results.     

Spectra of secondary emission during generation of optical harmonics in globular photonic crystals

Secondary emission spectra of globular silica photonic crystals when their surfaces were exposed to laser pulses 250 fs long at a power density to 1 TW/cm² have been studied. Optical harmonics and plasma emission were detected in this case. For the opal matrix containing pores filled with air, in the reflection mode, the third optical harmonic with a conversion efficiency of ～10% arises. The highest conversion efficiency for exciting radiation with wavelengths of 1026 or 513 nm is implemented when the frequencies of the exciting radiation or the second harmonic are near the stop band edge. In globular photonic crystals filled with sodium nitrite or barium titanate ferroelectrics, the second optical harmonic is observed. The exciting radiation conversion efficiency to the second optical harmonic was a few percent and depended on the frequency of exciting radiation and photonic crystal globule diameters. It is found that the plasma emission intensity increases with the exciting radiation power density. The dependences of the intensity of the second and third optical harmonics on the pump intensity are constructed for various photonic crystal globule diameters.