Infrared spectroscopy of a dense potassium vapor jet

In this paper we report the development of new apparatus for the containment and study of dense alkali metal vapors, and the use of the apparatus to study the infrared spectra of potassium vapor. The apparatus is the first to employ aerodynamic confinement of a dense alkali vapor. We have recorded absorption spectra, thermal emission spectra, and laser-induced emission spectra of dense potassium vapor. These techniques all reveal a spectral feature near 1.1 μm which we believe originates in ³Σ⁺_g→³Σ⁺_u transitions of the K₂ molecule.     

Infrared laser-emission study in a resonantly excited sodium vapor

We report on a study of time dependence of ir laser emission at 3.41 μm in a dense Na vapor that is resonantly excited to the 3² P levels by a flashlamp, pumped dye laser. Energy-pooling collisions (excitation transfer) between excited atoms create a large population inversion among the 5² S _1/2 and 4² P _3/2 states which is destroyed by electron collisions as a result of subsequent plasma formation. The ir laser emission may serve as a new diagnostic tool to follow the time evolution of such media.     

Multiple conical emission from near resonant laser propagation in dense sodium vapor

Propagation of a near-resonant laser beam in sodium vapor with concentration of ～10¹⁵ at/cm³ is found to generate several distinct non-linear, near-resonant, near-axis emissions. Spectral, angular and polarization characteristics of the many emission features obtained with a tunable pulsed dye laser are given.     

Infrared absorption spectrum of the sodium uranyl acetate single crystal

The infrared absorption spectrum of the sodium uranyl acetate single crystal was studied experimentally at room temperature. The group-theoretical method is used to interpret the splitting of several bands in the spectrum into three components. The vibrations noted in the infrared spectrum are associated with types of symmetry.In conclusion, the authors thank Academician AS BSSR A. N. Sevchenko for his unflagging interest in the present investigation.     

透明致密单质钠

传统高压理论认为,高压可以有效地缩短金属内部的原子间距,导致价带和导带展宽,进而使其金属性增强.然而,目前实验可达到的压力条件已能够将物质压缩到原子的芯电子发生重叠的状态.这一高压效应会使金属发生复杂的结构相变,使之具有独特的晶体结构和无法用传统理论来描述的电子性质.传统理论曾预言,简单金属锂和钠在高压下会出现原子配对而导致的非金属相,但这一预言没有得到后续理论和实验的支持.本研究将理论模拟和高压实验相结合,发现金属钠在200万大气压下转变为一种新型物质状态——光学透明的宽带隙绝缘态.绝缘态钠具有简单而独特的晶体结构——c轴高度压缩的双六角密堆结构.高压钠的绝缘态不是早期理论预言的原子配对的结果,而是p和d轨道电子杂化,以及芯电子云之间高度交叠的结果.钠原子的价电子受芯电子排斥而高度局域在晶格间隙中,这些在间隙中被＂冻结＂的价电子完全失去了自由电子的特性,表现出绝缘特性.当压力促使原子的芯电子发生强烈重叠时,这种新型绝缘状态可以在其他元素和化合物中存在.     

透明致密单质钠

传统高压理论认为,高压可以有效地缩短金属内部的原子间距,导致价带和导带展宽,进而使其金属性增强.然而,目前实验可达到的压力条件已能够将物质压缩到原子的芯电子发生重叠的状态.这一高压效应会使金属发生复杂的结构相变,使之具有独特的晶体结构和无法用传统理论来描述的电子性质.传统理论曾预言,简单金属锂和钠在高压下会出现原子配对而导致的非金属相,但这一预言没有得到后续理论和实验的支持.本研究将理论模拟和高压实验相结合,发现金属钠在200万大气压下转变为一种新型物质状态——光学透明的宽带隙绝缘态.绝缘态钠具有简单而独特的晶体结构——c轴高度压缩的双六角密堆结构.高压钠的绝缘态不是早期理论预言的原子配对的结果,而是p和d轨道电子杂化,以及芯电子云之间高度交叠的结果.钠原子的价电子受芯电子排斥而高度局域在晶格间隙中,这些在间隙中被“冻结”的价电子完全失去了自由电子的特性,表现出绝缘特性.当压力促使原子的芯电子发生强烈重叠时,这种新型绝缘状态可以在其他元素和化合物中存在.     

Non-Markovian dynamics in a dense atomic vapor

Two- and three-pulse photon echo spectroscopy in a dense potassium vapor reveals a non-Markovian correlation function of frequency fluctuations. Through comparison with calculations using an exciton picture a slowly-decaying component of the correlation function is attributed to long-range resonant interactions. A time-resolved photon echo experiment shows the photon-echo-like behavior at short timescales.     

Non-Markovian dynamics in a dense potassium vapor

Transient four-wave mixing experiments on a dense potassium vapor, which has a dephasing time long compared to the collision duration, reveal distinct signatures of non-Markovian dynamics. Theoretical fits assuming stochastic fluctuation of the excited-state frequencies confirm that the two-time correlation function has a finite temporal width.     

Melting of dense sodium

High-pressure high-temperature synchrotron diffraction measurements reveal a maximum on the melting curve of Na in the bcc phase at approximately 31 GPa and 1000 K and a steep decrease in melting temperature in its fcc phase. The results extend the melting curve by an order of magnitude up to 130 GPa. Above 103 GPa, Na crystallizes in a sequence of phases with complex structures with unusually low melting temperatures, reaching 300 K at 118 GPa, and an increased melting temperature is observed with further increases in pressure.     

Stroboscopic backaction evasion in a dense alkali-metal vapor

We explore experimentally quantum nondemolition measurements of atomic spin in a hot potassium vapor in the presence of spin-exchange relaxation. We demonstrate a new technique for backaction evasion by stroboscopic modulation of the probe light. With this technique we study spin noise as a function of polarization for atoms with spin greater than 1/2 and obtain good agreement with a simple theoretical model. We point that, in a system with fast spin exchange, where the spin-relaxation rate is changing with time, it is possible to improve the long-term sensitivity of atomic magnetometry by using quantum nondemolition measurements.     

Cluster model of aluminum dense vapor plasma

The chemical model of aluminum vapor plasma, that take into account the formation of neutral and charged clusters, is suggested. Caloric and thermal equations of state and composition of plasma were received using the available information about properties of metal clusters. It is shown, that aluminum vapors are clusterized with decrease of temperature and with increase of density. Pressure dependence on internal energy is calculated and comparison with experimental data is made. The important role of aluminum clusters, especially in an initial phase of the metals vapor heating, is demonstrated. It is shown, that the region of plasma clusterization in gaseous phase agree with known literature data for binodal of vapor-liquid transition from gaseous region. Suggested cluster model may be used to forecast the location of metal vapors binodal. The conductivity of aluminum vapor plasma was calculated. The satisfactory agreement with available experimental data is received.     

Infrared absorption in spheroidal crystallites

Infrared absorption spectra of spheroidal particles of polar crystals are calculated by using the point matching method. Retardation effects are taken into account, so that the dependnece of the spectrum on the size of the particle can be investigated. It is found that the surface mode absorption peaks broaden and shift to lower frequencies with increasing particle size. Comparison with the absorption spectra of equivolumic spheres is performed and some consequences regarding the interpretation of experimental spectra are discussed.     

Electromagnetically induced diffraction in sodium vapor

By using a sodium atomic vapor we have observed a honeycomb-type multiple-diffraction pattern that was due to a grating induced optically by three noncollinear bichromatic excitation beams. In particular, when the two incident frequencies satisfy the two-photon resonance condition and the atomic density is high, the diffraction is enhanced by electromagnetically induced transparency, and strong Stokes and anti-Stokes components are generated in well-defined directions.     

Infrared absorption in rectangular crystallites

The calculation of the infrared absorption properties of rectangular ionic crystallites using an integral equation approach, in which retardation effects are taken into account, is discussed. A numerical solution of the integral equation is carried out for KCl samples, and the calculated spectrum is found to yield the main features of a previously recorded experimental spectrum.     

Seventh harmonic generation in sodium vapor

We present experimental evidence of both direct and cascade seventh harmonic generation by collimated laser beam in atomic systems. The phase-matching condition is fulfilled. The variation of seventh harmonic signals with sodium vapor pressure is described.     

Fifth harmonic generation in sodium vapor

We report experimental investigation of direct fifth harmonic of Nd³⁺: glass laser radiation (1060 nm) in metal vapor. Using various mixtures of sodium vapor and xenon in order to achieve a phase-matching, we observed direct as well as cascade nonlinear processes. The first measurement of effective fifth-order nonlinear susceptibility χ⁽⁵⁾_eff in atoms, is performed.