Experimental observation on anomalous emission in Mg vapor

When the 3s3p ¹P level of an Mg atom is resonantly excited by a laser, an anomalous emission with a wavelength of 5184 Å can be observed, which corresponds to the transition for 3s4s ³S to 3s3p ³P₂. According to the temporal behavior of this emission and its intensity dependence on atom density, it is believed that the experiment seems to show the transition from a spontaneous process to a cooperative process. The population inversion between 3s4s ³S and 3s3p ³P₂ is created by inelastic collisions of the lower excited 3s3p ¹P atoms.     

The violet emissions produced by laser excitation of Na vapor in the 570–595 nm region

We have observed atomic Na and molecular Na₂ emissions in the violet region when Na vapor in a heatpipe (～10³—10¹⁶ atoms/cm³) is irradiated with a pulsed dye laser with output wavelength in the 570–597 nm region. The Na atomic emissions probably result from recombination of Na⁺ + e^- and energy-pooling involving highly excited atoms and molecules, while the diffuse violet emission bands are probably produced through collisions among excited Na atoms and Na₂ molecules.     

Polarization effects in theP 3/2→P 1/2 fine structure transition cross section forK(4P)-He collisions

Taking the energy dependence of theP _3/2→P _1/2 fine structure transition cross section ofK(4P) colliding with He as an example, theoretical and experimental studies have been made to illustrate the large possibilities opened by the combination of beam experiments with laser excitation in the investigation of the atomic collisional processes. Explicit calculations, experimentally confirmed, show a strong dependence of the above process on the laser excitation schema for producing the excited stateK(4² P _3/2).     

Optical losses in YVO4: RE (RE = Nd3+, Er3+, Tm3+) laser crystals

The relevance of processes contributing to depletion of pump and upper laser levels has been assessed based on experimental data obtained during measurement of excited state absorption, steady state emission and dynamics of excited states as a function of excitation power and activator concentration. It has been concluded that the excited state absorption in YVO₄: Nd and YVO₄: Er is not significant except for that from the ⁴ I _11/2 level of Er³⁺. In these systems, the interionic processes are dominant. In particular, the reported decrease of the YVO₄: Er laser slope efficiency when the Er³⁺ concentration increased from 0.5 to 1 at % is due mainly to the up-conversion by energy transfer from the pump level and upper laser level. Excited state absorption cannot contribute to depletion of excited states involved in the ³ F ₄-³ H ₆ laser operation near 1800 nm in the YVO₄: Tm crystal. However, the heavy doping required to enhance the cross-relaxation process which feeds the upper laser level brings about the migration-accelerated energy transfer to energy sinks.     

Optical resolution beyond the natural linewidth: A level-crossing experiment on the 32 P 3/2 level of sodium using a tunable dye laser

A level crossing experiment on the hyperfine structure of the 3² P _3/2 level of Na²³ was performed using a nitrogen laser pumped dye laser for the excitation of the Na atoms. The fluorescent light was observed in time intervals which were initiated up to seven lifetimes after excitation. Therefore the signal was only determined by atoms having survived in the excited state up to the initiating time. The minimum linewidth observed was 6 times smaller than the natural width. Neighbouring crossing signals, which overlap in a level crossing experiment using time integral observation of the fluorescent light, could be resolved. The accuracy of the hyperfine constants of the 3² P _3/2 level could be improved.     

Influence of collisions and pulse intensity on multiple photon absorption in SF6

Using a pyroelectric detector, the multiple photon absorption (MPA) of the SF₆ molecule in a wide range of pressures (10^-3 -1 torr) has been studied. The significant role of collisions in MPA has been shown. The fraction of molecules excited under essentially collisionless conditions has been defined. It is shown that under collisionless excitation of SF₆ (p < 10^-2 torr) at energy fluences E < 10^-1 J/cm² the intensity of the laser pulse plays the essential role, while in presence of collisions MPA is determined mainly by the energy fluence in the pulse.     

Polarization effects in ionizing thermal energy collisions of laser-excited Ne(3p 3 D 3) atoms with Ar atoms

Using transverse and longitudinal excitation of a collimated metastable Ne(3s ³ P _2.0) beam with average velocities of 500, 800, and 1,200 m/s by means of a single mode dye laser on the²⁰Ne(3s ³ P ₂→3p ³ D ₃) transition, we have investigated ionizing collisions of polarized Ne(3s ³ P ₂) and Ne(3p ³ D ₃) atoms with Ar atoms. The product electrons were energy analyzed with high resolution (9–25 meV). The resulting Ne(3p ³ D ₃) electron spectra exhibit a strong dependence on the three types of laser polarization (π _∥,π_⊥, σ_?), chosen to prepare the excited atoms. In contrast, the Ne(3s ³ P ₂) spectra are only weakly dependent on polarization. Detailed model calculations have been carried out for the Ne(3p)+Ar cross sections, using computed excited-state potential curves, semi-empirical ionic potentials, and local autoionization width functions. A semiclassical closecoupling method is applied to describe the evolution of the polarized collision system in the coupled entrance channels. It is found that a single autoionization widthΓ(R) is not sufficient to describe the measured polarization effects properly. The dependence ofΓ on the initial and final state is expressed in terms of few reduced electronic transition matrix elements, which are determined by comparison of measured and calculated total cross sections and Ar⁺(² P _3/2)/Ar⁺(² P _1/2) branching ratios for ionizing collisions of the various Ne(3pJ=1,2,3) multiplet states with Ar. The matrix elements corresponding to Ar(3pσ)→Ne(2pσ) electron transfer during autoionization are found to dominate, but Ar(3pπ)→Ne(2pπ) transfer has also to be included. The resulting calculated electron spectra reproduce the measured polarization effects in a semi-quantitative way.     

Er3+离子掺杂钡镓锗玻璃上转换发光机理研究

研究了Er³⁺离子掺杂钡镓锗玻璃的吸收光谱、拉曼光谱和上转换光谱.分析了Er³⁺离子在钡镓锗玻璃中的上转换发光机理.结果表明：玻璃的最大声子能量为828cm^-1，紫外截止波长为275nm.采用800nm和980nmLD激发玻璃样品，在室温下观察到强烈的上转换绿光和红光发射.随着Er³⁺离子浓度的增加，绿光发光强度先增加后减小，而红光发光强度呈单调递增趋势.能量分析表明：800nmLD激发产生的绿光主要源于Er³⁺离子4I_13/2能级的激发态吸收过程；红光发射主要源于Er³⁺离子4I_13/2能级与4I_11/2能级之间的能量转移过程.980nmLD激发产生的绿光主要源于Er³⁺离子4I_11/2能级之间的能量转移过程；而红光发射主要源于Er³⁺离子4I_13/2能级与4I_11/2能级之间的能量转移过程和4I_13/2能级的激发态吸收过程.通过量子效率分析，发现采用800nmLD激发Er³⁺离子掺杂浓度为1mol% 的样品时，上转换绿光发光效率最高. 关键词： 上转换发光机理 3+离子掺杂')" href="#">Er³⁺离子掺杂 钡镓锗玻璃     

Orientation of Cs 6p 2P3/2 atomic photofragments in a magnetic field: interference in the photodissociation of diatomic molecules

In a magnetic field, Cs₂ molecules were excited from the ground X¹Σ⁺_g(v_X=0,J_X=55) level to the D ¹Σ⁺_u(v=46,J=54) level by dissociation laser light linearly polarized parallel to the field, for which the magnetic sublevels were degenerated and thus all the transitions between them were simultaneously stimulated. Probe laser light excited the dissociated Cs 6p²P_3/2 atomic fragments to 6p²D_3/2 level and the resultant 6p²P_1/2 - 6d²D_3/2 emission was detected as the function of the wavelength of the probe light. The populations of the 6p²P_3/2,mj magnetic sublevels were determined from the relative strengths of the 6p²P_3/2,mj - 6d²D_3/2,m'j transitions induced by the probe light. Non-zero orientation O₀ was found in the ensemble of dissociated Cs 6p²P_3/2 atomic fragments. The orientation O₀ increased as the magnetic field strength increased. It was demonstrated both experimentally and theoretically that the orientation O₀ was induced through the interference in the excitation and dissociation paths in the presence of an external magnetic field, even when all degenerated transitions between the magnetic sublevels of the molecules are simultaneously excited by the light linearly polarized parallel to the field.     

Molecule formation and energy transfer processes in a vapor with high density of 3P-excited sodium atoms

A rich fluorescence spectrum extending between 4000 and 8200 Å has been observed whenever sodium vapor is excited by dye laser light tuned to the 3²S → 3²P transition. Molecule formation due to collisions between excited and unexcited atoms is manifested by the presence of an emission band of sodium in the spectral range 4160–4570 Å.     

Study of emission from discharge in a Ne-InI mixture, aiming to create a laser operating by a self-terminating transition at 451.1 nm in In

With the aim of creating a laser operating by a self-terminating transition in the blue spectral region, it is suggested to use the 6s ² S _1/2→5p ² P _3/2 transition at 451.1 nm in In atoms. Indium iodide was used as a donor of In atoms for an active medium in a discharge. Emission and absorption spectra of the active medium, as well as the time characteristics of pumping pulses and emission due to transitions from the resonance level of In, were measured.     

Übertragung von Polarisation bei sensibilisierenden Stößen angeregter Natriumatome

The transfer of magnetic polarization between the levels² P _1/2 and² P _3/2 in sensitizing collisions of excited sodium atoms and noble-gas atoms has been studied. Deviating from a previous study on this topic the nuclear spin was now decoupled by means of a strong magnetic field. As a result moreD ₂σ^?-quanta could be detected in the sensitized fluorescence following an excitation withD ₁σ⁺-light. From the measurement of the fluorescence intensitiesI _D1σ± andI _D2σ±, cross-sections peculiar to polarization transfer could be derived. In the case of He and Ne these cross-sections together with the cross-sections of normal sensitizing collisions could be traced back to Grawert's parametera ₁ anda ₂ hence confirming the assumption of the spin being “at rest” during the collision.     

Evolution of molecular states studied in collisions of ions with laser excited atoms by a crossed beam experiment

Differential scattering cross sections in the energy rangeE _CM=25–50 eV have been measured in a crossed beam machine for the scattering of Na⁺ by laser excited Na(3² P _3/2). The superelastically scattered ions resulting from the collisional deexcitation process 3² P _3/2-² S _1/2 are sharply peaked at a constant reduced scattering angle of 180eV degrees. Through the choice of either linearly or circularly polarized light, one can selectively excite the magnetic sublevels of the Na atoms. This ability to align or orient the Na^* allows us to discuss in considerable detail both the transition from the space-fixed (atomic) to the body-fixed (molecular) system and the dynamics in the merging region of the two frames. We find that the symmetry axis of the excited electron charge cloud is locked to the internuclear axis and hence to the body-fixed reference frame at an internuclear separation of about 35 a.u. A pronounced asymmetry of the scattering from atoms excited with LHC or RHC polarized light is discussed in terms of simple models.     

Fourier Transform and Intracavity Laser Spectroscopy of NiCl System H: Identification of a [12.3] Σ State

The (0,0) vibronic band of NiCl system H near 12 259 cm⁻¹ was recorded at high resolution in absorption using intracavity laser spectroscopy (ILS) and in emission by Fourier transform (FT) spectroscopy. Though it was originally assigned in 1962 as the (1,1) vibronic band of ²Π_3/2-X²Δ_5/2, we have shown that this transition is the (0,0) vibronic band associated with a newly identified ²Σ⁺ excited state and the X²Π_3/2 ground state. The molecular constants for the new ²Σ⁺ electronic state were derived from the rotational analysis. For the ILS absorption spectra, the NiCl molecules were produced in a nickel hollow cathode, operated with a small amount of CCl₄. Line positions were referenced to iodine spectra observed from a heated extracavity cell using the intracavity laser as the light source. For the FT spectra, excited NiCl molecules were produced in a King-type carbon tube furnace.     

Two-step excitation of Rb atoms on He nanodroplets

We present the first sequential laser excitation of atom-doped helium nanodroplets. Rubidium atoms on the surface of helium nanodroplets are selectively excited with a continuous wave laser to the 5²P_1/2 state so as not to desorb from the nanodroplets. From there they are excited by a laser pulse to the 5²D state; a laser-induced fluorescence (LIF) spectrum is recorded by monitoring the 6²P ?\rightarrow 5²S_1/2 emission. The LIF spectrum differs from that of the two-photon one-color direct excitation spectrum 5²D ?\leftarrow 5²S_1/2, indicating that the system does relax vibrationally during the lifetime of the 5²P_1/2 state. To model the LIF spectra we use calculated energy levels of the Rb atom as a function of its distance R from the center of the helium nanodroplet. The Franck-Condon factors of the resulting potential energy curves agree with the experimental spectra. In the future the 5²P_1/2 state can be used as a springboard to reach high-lying ²S and ²D states, and possibly create an artificial super-atom.     

Population inversion in thallium by flashlamp-photodissociation of TII

A population inversion between the 6² P _3/2 and 6² P _1/2 state of thallium has been achieved for the first time by incoherent photodissociation of TII. This is accomplished by using wall-ablating flashlamps of short risetime and appropriate light filtering. The inversion lasts about 4 μs and is terminated by quenching collisions.     

Observations of four-wave mixing processes in barium vapour

Emission at fifty discrete wavelengths is observed when Ba I is excited by two laser beams, a dye laser tuned to the λ 7911 Å intercombination line, 6s²¹S₀-6s6p ³P₁ and a ruby laser. The wavelengths range from 2312 Å to 8027 Å. Most of the emission lines can be attributed to four-wave mixing processes in barium.     

Spectroscopic diagnostics of a laser erosion plasma formed from CuSbS<Subscript>2</Subscript> polycrystals

The spectra and dynamics of emission from regions of a laser plasma torch located at different distances from a polycrystalline CuSbS₂ target irradiated by a neodymium laser (W=(3–5)×10⁸ W/cm², ?=20 ns, f=12 Hz, 73x03BB;=1.06μm) were investigated. The emission data were used to estimate the average temperature (≤0.82 eV) and the electron density ((1.82?1.92)×10¹⁶ cm^?3) in the laser torch and the recombination times of ions (t _r(S²⁺)=15 ns, t _r(Cu⁺)=65?85 ns), as well as to analyze the efficiency of filling of excited atomic levels. A model describing the target destruction and the evolution of the processes accompanying spread of the laser plasma is proposed.     

On the gamma decay of analogue resonances in the58Fe(p, γ)59Co reaction

The spectrum of the delayed light radiation from a pulsed corona discharge in pure argon was investigated in cylindrical geometry. The band-like structure near 309 nm can be attributed to molecular transitions in the OH-radical of the typeA ² Σ ⁺ ?X ² Π(0?0). The weak bands at 337 nm and 357 nm originate from transitions in the N₂ molecule. The molecular states of OH and N₂ are excited by collisions of³P₂-metastable argon atoms (formed in the gas discharge) with H₂O and N₂ molecules present as small impurities. The pressure dependence of the time constant (some 100 μs) of the afterglow is discussed.     

Penning ionization of NO and O2(1Δg) by argon in the 3P1 state

Electronically excited argon in the ³ P ₁ state was generated in a flow system by resonance absorption of the λ=106·7 nm emission line. This photochemical source is particularly convenient for kinetic studies since Ar(³ P ₁) alone is produced in the primary exciting step. Energy transfer from excited argon may lead to Penning ionization:

This process has been studied for M=NO and M=O₂(¹Δ _g ). Relative concentrations of Ar* were estimated from the Penning ion current, and it is shown that Ar* is probably in the initially excited ³ P ₁ state and not in the metastable ³ P ₂ state. Kinetic studies showed that Penning ionization of NO occurs for about one in every five gas kinetic collisions with Ar(³ P ₁). The Penning process can only compete effectively with radiative loss of Ar(³ P ₁) as a result of extensive imprisonment of resonance fluorescence. Penning ionization of O₂(¹Δ _g ) is shown to proceed at nearly the same rate as ionization of NO. The decrease in Penning ion current on addition of a quenching gas, such as N₂ or O₂, is used to derive rate constants for the quenching process relative to the rate of quenching by NO. Estimated absolute rate constants are presented in a table.