Spontaneous amplified emission of a Na2 diffuse violet band produced through two-photon excitation of sodium vapor

We report observation of enhanced emission of the diffuse violet band at 436.0 nm when sodium vapor is optically pumped with a pulsed dye laser with output wavelength in the 570–595 nm region. A significant enhanced emission is observed in the forward direction along the propagating laser beam when the laser wavelength is tuned to near the two-photon excited 4d state of the Na atom. At a vapor density higher than 10¹⁵ cm^-3 the diffuse violet emission is predominantly produced through processes associated with the excitation of Na₂. The dependence of the enhanced emission on vapor density and laser power density is presented.     

The process of energy transfer between excited sodium atoms

Two experiments were carried out to test a process proposed by Allegrini et al. as a viable explanation of the fluorescence from high lying levels which is observed when sodium vapor is illuminated by resonance radiation. In the first experiment a cell with sodium vapor was illuminated by a cw dye laser tuned to the 3S → 3P transition, and the linewidth and lineshape of the fluorescence from the 3D → 3P transition were measured. In the second experiment the cell was illuminated by two pulsed lasers, one tuned to the 3S → 3P resonance and the second well off resonance with this transition. The photoionization current was measured, as was the fluorescence intensity from the 6S → 3P and 5D → 3P transitions. We conclude that the Allegrini process does not significantly contribute to the populations in the 5D, 6S and 3D states.     

Flow imaging by use of femtosecond-laser-induced two-photon fluorescence

A novel technique is demonstrated for the imaging of turbulent flows in which a single window to the flow is the only optical access required. A femtosecond laser is used to excite two-photon fluorescence in a disodium-fluorescein-seeded water jet. The fluorescence signal is generated at only the focal point of the laser because of the highly nonlinear nature of the two-photon absorption, and it is collected in a direction counterpropagating to the excitation beam. Tight focusing of the laser is used to limit the probe volume, and the two-dimensional mean and rms concentration images are collected by raster scanning the laser.     

Light-induced ejection of alkali atoms in polysiloxane coated cells

Summary An intense laser-induced fluorescence of sodium and of other alkali atoms (K, Rb) at room and lower temperatures has been observed in polysiloxanecoated cells, producing a vapor density of the metal which is much higher than that corresponding to the thermal equilibrium between the vapor and the condensed phase. This enhancement is attributed to the light-induced ejection of atoms absorbed by the polysiloxane coating. The atomic density of the vapor can be manipulated by changing either the laser power or frequency. The dependence of the atomic density on these and other parameters as well as its time-dependent behavior are studied experimentally. A tentative interpretation of the phenomenon is discussed in terms of the properties of solutions of the alkali metals in several solvents.     

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.     

Spectral narrowing of a dye laser oscillation using an intracavity vapor prism

A new method for narrowing the oscillation spectrum of a broad-band dye laser is reported in this paper. The narrowing is achieved by a vapor prism placed inside the laser cavity, which is based on an anomalous dispersion of the atomic vapor so that the narrowing effect occurs only in the vicinity of the absorption line. Using a sodium vapor prism inside a Rhodamine 6G dye laser cavity, an oscillation linewidth less than 0.01 nm was attained at a sodium temperature of 320°C.     

Water vapor concentration measurement in air using filament-induced fluorescence spectroscopy

Water vapor fluorescence in air induced by femtosecond laser filaments was systematically investigated. The fluorescence signal intensity was found to be linearly proportional to the water vapor concentration, which opens up the possibility of absolute humidity measurements, even remotely.     

Two-photon conical emission

A two-photon resonantly enhanced four-wave mixing (FWM) process leading to the conical emission of two new frequency components has been observed in atomic sodium vapor. A dye laser tuned close to the 3s → 3d two-photon allowed transition produces broad-band emission near the frequencies of the 3d → 3p and 3p → 3s transitions. This radiation is emitted in the forward direction in the form of cones surrounding the transmitted laser beam. The dependence of the cone angle on the emission wavelength and atomic number density is in excellent agreement with the predictions of a model that ascribes the origin of the conical emission to a phase-matched four-wave mixing process.     

Frequency locking of dye lasers by selective reflection on a glass/sodium vapor interface

The use of a pyrex/sodium vapor interface as a selective dye laser mirror is shown to produce frequency locking of the laser emission near the sodium D lines. The spectral shift of a few GHz from the line center and the magnitude of the energy spectral condensation measured are accounted for the calculations.     

Population inversion in sodium D_2 transition based on sodium-ethane excimer pairs

Sodium-ethane excimer pairs are studied and proved to be a great choice of excimer pumped sodium laser(XPNa L)gain media.The lifetime of the sodium D_2 line is studied in a sodium-ethane excimer system excited by a 553 nm laser,and the observed phenomenon of lifetime lengthening is discussed.Amplified spontaneous emission(ASE) of the sodium D_2 line is successfully obtained,and its time-resolved and spectroscopic characteristics are studied experimentally.According to the intensity of the ASE signal under different sodium vapor atom densities,the sodium D_2 line gain feature of sodium-ethane excimer pairs excited by the 553 nm laser is concluded.     

Laser sounding of molecular iodine in the atmosphere

The lidar equation for the fluorescence of ¹²⁷I₂ molecules is numerically solved. All the radiation wavelengths of a copper vapor laser are considered with the aim of choosing the one that is the most appropriate for detection of the minimum possible concentration of iodine molecules when this laser is used as a radiation source of a fluorescence lidar.     

Investigation of collisionally induced stimulated scattering in sodium vapor with temporal and spectral resolution

In this work we present fully time-resolved spectra of Amplified Spontaneous Emission (ASE) and Stimulated Raman Scattering (SRS) in sodium vapor. We observe that the ASE signal precedes the SRS emission, and the peak of the amplified Stokes pulse is delayed with respect to the peak of the laser pulse. The time evolution of the line widths of the ASE and Raman signals is also shown. We find that the line widths of the stimulated fluorescence component (ASE) and the stimulated Raman radiation change with time. Both spectra start as small narrow fluctuating lines, then the line widths reach maximum values and thereafter decrease with time.     

Honeycomb pattern formation by laser-beam filamentation in atomic sodium vapor

We have observed transverse pattern formation leading to highly regular structures in both the near and far fields when a near-resonant laser beam propagates without feedback through an atomic sodium vapor. One example is a regular far-field honeycomb pattern, which results from the transformation of the laser beam within the vapor into a stable three-lobed structure with a uniform phase distribution and highly correlated power fluctuations. The predictions of a theoretical model of the filamentation process are in good agreement with these observations.     

Optical Relaxation Phenomena in a Rubidium Vapor Cell with an Antirelaxation Coating under Bichromatic Laser Irradiation

Journal of Experimental and Theoretical Physics - The excitation of long-term fluorescence by variously configured beams of bichromatic laser radiation in a rubidium vapor cell has been studied....     

Formation of the contour of a spectral line upon partial frequency redistribution

The problem of the radiation transfer in an atomic gas in a laser radiation field is numerically solved under the conditions of partial frequency redistribution and cylindrical geometry of the medium. The light scattering by atoms is modeled by the angle-averaged distribution function R _III. The influence of the partial frequency redistribution on the formation of the sodium emission line λ = 589.6 nm and on the characteristic deexcitation time of the sodium vapor is studied in relation to the vapor optical thickness.     

Evaluation of a Continuous Flow Furnance Atomizer for Laser Excited Atomic Fluorescence Spectrometry

A system for continuous sample introduction into a ceramic atomization furnace for laser excited atomic fluorescence spectrometry (LEAFS) was developed. The system was evaluated using two different excitation sources, a nitrogen laser-pumped dye laser and a copper vapor laser-pumped dye laser. Pure aqueous Pb solutions were used for system optimization and analytical calibration curves. These curves were linear over at least three     

Direct simulation monte carlo of pulsed laser ablation of metals with clusterization processes in vapor

A mathematical model is proposed to describe laser ablation of metals in vacuum under the action of nanosecond laser pulses of moderate intensity taking into account the processes of cluster formation and decay in the vapor cloud. To describe the laser radiation absorption and metal heating, the thermal model based on the unsteady one-dimensional heat equation with a volume heat source is used, and the method of statistical modelling is employed for modelling vapor expansion and the processes of cluster formation. The efficiency of the proposed complex model is considered by the example of pulsed laser ablation of a niobium target. The work was supported financially by INTAS (grant No. 03-51-5208).     

用于二聚物三能级蒸气激光系统的环形谐振腔设计

针对二聚物三能级蒸气激光系统增益相对于泵浦光方向显著的不对称特性,本文设计了一种稳定的能够充分利用介质增益特性的环形谐振腔,给出了象散和慧差补偿及泵浦激光与谐振腔匹配的条件。文中还给出了Na_2B~1Ⅱ_u-X~1∑_g~+跃迁激光谐振腔设计数据。     

水杨酸钠在极性溶剂中的荧光和激光特性的研究

采用XeCl激光作为泵浦源,首次系统研究了水杨酸钠在水、甲醇、乙醇以及水醇混合物等极性溶剂中的荧光和激光特性.探明它有很强的激发态自吸收作用.从分子结构的角度分析了水杨酸钠荧光积分强度的温度特性.