Energy Pooling Collisions Research Articles

Energy-transfer processes of Xe (6p[1/2]0, 6p[3/2]2, and 6p[5/2]2) atoms under the condition of ultrahigh pumped power

The kinetic processes of Xe (6p[1/2] $_0$ , 6p[3/2] $_2$ , and 6p[5/2] $_2$ ) atoms under the focused condition were investigated. The atomic density of the laser prepared state significantly increases. Therefore, the probability of the energy-pooling between two high-lying atoms increases. There are three major types of the energy-pooling collisions. The first type is the energy-pooling ionization. Once the excitation laser is focused, the obvious ionization can be observed from the side window whenever the laser prepared state is 6p[1/2] $_0$ , 6p[3/2] $_2$ , or 6p[5/2] $_2$ state. Ionization of Xe is attributed to the energy-pooling ionization or a Xe $^*$ atom reabsorbing another excitation photon. The second type is energy-pooling with big energy difference. When the 6p[1/2] $_0$ state is the laser prepared state, the energy-pooling collision between two 6p[1/2] $_0$ atoms can produce one 5d[3/2] $_1$ atom and one 6s $'$ [1/2] $_0$ atom. The third type is energy-pooling with small energy difference. The intensities of fluorescence lines are much stronger that five secondary 6p states act as the upper states, and the rising edges of these fluorescence lines are much steeper. The primary mechanism of generating the secondary 6p atoms is energy-pooling collision instead of collision relaxation. Based on the collision probability, the rate of energy-pooling between two 6p[1/2] $_0$ atoms is deduced (6.39 $\times$ 10 $^8$ s $^{-1}$ ). In addition, the 6s atoms also increase under the focused condition. Therefore, all the fluorescence lines are serious trailing by radiation trapping.

Power degradation due to thermal effects in Potassium Diode Pumped Alkali Laser

Abstract This paper presents results of our study of the performance of a Potassium DPAL operating in pulsed mode with pump pulses from 0.05 to 5 ms long at different pump powers and alkali cell temperatures. The experiments showed the DPAL output power degradation in time with a characteristic time in the range from 0.5 ms to 4.5 ms. We attribute the power degradation to heating of the vapor. The recorded spectrum of the side fluorescence indicates that multi-photon excitation, energy pooling collisions and ionization are also present.

Ionization of lithium vapor by nanosecond resonant laser pulses tuned to 2S → 2P transition

A theoretical study is reported for the resonant excitation and ionization of dense lithium vapor induced by nanosecond laser pulses, tuned to the resonance transition 2S–2P. The lithium vapor with density (1014–1016 cm−3) is assumed to be excited and ionized by a laser beam with laser power of (105–106 W cm−2) according to the experimental conditions of Skenderovic et al. (Phys Rev A 62:052707, 2000). The time evolution of electron energy distribution function and the electron density, the population density of the excited states as well as the atomic ion, are solved numerically. The numerical calculations of the electron energy distribution function show that nonequilibrium plasmas are produced in lithium vapor by laser irradiation of the nS–nP resonance line. The electrons in these plasmas are heated by superelastic collisions with atoms in the nP state giving a distribution of electrons in energy that is characterized by a series of spikes at energy separated by the nS–nP transition energy. In addition, the competition between photoionization processes and collisional ionization processes for producing the Li+ as well as energy pooling collisions process of the excited lithium atoms plays essential roles in populating the highly excited states. Moreover, the results are found to be consistent with the experimental observations.

Rate coefficients measurement for the energy-pooling collisions Cs(5D) + Cs(5D) → Cs(6S) + Cs(nl = 9D, 11S, 7F)

We report experimental rate coefficients for the energy-pooling collisions Cs(5D)+Cs(5D)→Cs(6S)+Cs(nl=9D,11S,7F). In the experiment the Cs(5D) state was populated via photodissociation of Cs2 molecules using an argon-ion laser at wavelength 488.0nm. We also consider the competing process 6P1/2+7S→6S+(nl=9D,11S,7F) that might also populate 9D, 11S and 7F. An intermodulation technique was used to select the fluorescence contributions due only to the process 6P1/2+7S→6S+(nl=9D,11S,7F). The excited atom (nlJ) density and spatial distribution were mapped by monitoring the absorption of a counterpropagating probe laser beam tuned to various nlJ→n′lJ′′ transitions. The measured excited atom densities are combined with measured fluorescence ratios to yield rate coefficients for the energy-pooling collisions Cs(5D)+Cs(5D)→Cs(6S)+Cs(nl=9D,11S,7F). The rate coefficients for nl=9D, 11S, 7F are (4.1±2.0)×10−10cm3s−1, (1.6±0.8)×10−10cm3s−1 and (3.6±1.8)×10−10cm3s−1, respectively. The contributions to the rate coefficients from other energy transfer processes are also discussed.

Dominant wing spectroscopy of energy pooling collisions near the boundary layer involving thermal caesium vapour

We have observed the dominant wing spectroscopy of energy pooling collision near the boundary layer involving Cs atoms under the condition of moderate-to-high optical depths at line-centre. It appears from our experimental investigations that the energy-pooling fluorescence presents about 16 spectral lines, and all the lines can be assigned to the Cs atomic transitions. We find that all lines of the energy-pooling retrofluorescence from the heated Cs atomic vapour cell show two-peak profiles. In addition, its pumping power linear dependence in the energy pooling process has been measured and analysed.

Tunable and frequency-stabilized diode laser using temperature-dependent energy pooling fluorescence

We have demonstrated a robust method of tuning and stabilizing a diode laser frequency to the fluorescence peaks of the energy pooling occurred at thermal cesium vapor-glass interface. This technique is based on temperature-dependent shift of the two off-core fluorescence peaks caused by 6P3∕2+6P3∕2→7P(3∕2,1∕2)∕8S1∕2+6S1∕2 energy pooling collisions. We achieved laser linewidth of 1.1MHz and continuous tunability over ±200–600MHz within a temperature range of 360–420K by applying the wavelength modulation technology. Tunable frequency locking in such a wide range was constructed inexpensively with low laser power. It can also be extended to other wavelengths by using different atomic species.

Rydberg levels population via energy pooling collisions in resonantly laser excited dense In vapour

The production of Rydberg atoms via collisions in a resonantly laser excited dense In vapour is reported. When a dense In vapour confined in a quartz cell, whose temperature is raised above 820 °C, is excited by 100 kW cm−2 laser pulses at 410.3 nm, resonant with the fundamental transition 5 2P1/2 → 6 2S1/2, the fluorescence spectrum shows radiative emissions from Rydberg states, namely those corresponding to the n 2P → 6 2S1/2 series with 9 ⩽ n ⩽ 23. Fluorescences corresponding to the 5 2D → 5 2P1/2,3/2 transitions are also observed. Analysis of these signals' intensity as a function of several different experimental parameters, such as the atomic density and the laser power density, indicates that the population in the Rydberg levels is produced mainly by energy pooling collisions (EPC). The EPC cross section for the population of the Rydberg levels is also given. The influence on these effects of the presence of a fine structure in the In ground state (5 2P1/2,3/2) is also discussed, as well as the presence of a buffer gas inside the quartz cell.

Spectroscopic investigation of sensitized-Cs (62 P3/2–62P1/2) laser retrofluorescence in a pure optically thick vapour near a dissipative surface

A low-power, monochromatic, tunable diode laser is used to selectively populate the cesium 62P3/2 (Fe = 2, 3, 4, 5) hyperfine-structure levels in a pure optically thick vapour in the presence of a dissipative surface. The integrated retrofluorescence intensities for the 852 nm (62P3/2 → 62S1/2), 894 nm (62P1/2 → 62S1/2)> and 455 nm (72P3/2 → 62S1/2) lines have been measured and analyzed. When the laser frequency is scanned through the [62S1/2(Fg) → 62P3/2(Fe)] hyperfine resonance line, the sensitized retrofluorescence spectral signal corresponding to the 894 nm line has a profile significantly different from the retrofluorescence signal at the 852 nm line, but rather similar to the profiles of the lines associated with the energy-pooling collisions. The population of the 62P1/2 atomic level in an optically thick vapour cannot be explained only by the fine-structure excitation transfer process [Cs (62P3/2) + Cs (62S1/2) ↔ Cs (62P1/2) + Cs (62S1/2)] usually accepted in an optically thin vapour. We have investigated inelastic collisions in the populating mechanisms of 62P1/2 level starting from the 62P3/2 level exited by the monochromatic laser taking into account the presence of an electrically conductive surface. It appears from our experimental and theoretical investigations that, the spectral properties of the laser-induced Cs 894 nm sensitized retrofluorescence in a pure optically thick vapour near a dissipative surface cannot be explained by both the conventional mechanism and cascade collisions. The satisfactory interpretation of the experimental results is an open problem of atomic spectroscopy.PACS Nos.: 32.30, 32.50, 32.70, 32.80, 34.10, 34.50, 42.62

Laser energy-pooling processes in an optically thick Cs vapor near a dissipative surface

We characterize, for the first time to our knowledge, the laser-induced backward fluorescence (retrofluorescence) spectra that result from energy-pooling collisions between Cs atoms near a dissipative thin Cs layer on a glass substrate. We resolve, experimentally and theoretically, the laser spectroscopic problem of energy-pooling processes related to the nature of the glass–metallic vapor interface. Our study focused on the integrated laser-induced retrofluorescence spectra for the 455.5-nm (72P3/2–62S1/2) and 852.2-nm (62P3/2–62S1/2) lines as a function of laser scanning through pumping resonance at the 852.2-nm line. We experimentally investigate the retrofluorescence from 420 to 930 nm, induced by a diode laser tuned either in the wings or in the center of the pumping resonance line. We present a detailed theoretical model of the retrofluorescence signal based on the radiative transfer equation, taking into account the evanescent wave of the excited atomic dipole strongly coupled with a dissipative surface. Based on theoretical and experimental results, we evaluate the effective nonradiative transfer rate A¯62P3/2→62S1/2sf for atoms in the excited 62P3/2 level located in the near-field region of the surface of the cell. Values extracted from the energy-pooling process analysis are equivalent to those found directly from the 852.2-nm resonance retrofluorescence line. We show that the effective energy-pooling coefficients k˜72P3/2 and k˜72P1/2 are approximately equal. The agreement between theory and experiment is remarkably good, considering the simplicity of the model.

Characterization of the retrofluorescence inhibition at the interface between glass and optically thick Cs vapor

New experimental results and new phenomena related to the study of the retrofluorescence spectrum induced by a diode laser at the interface between glass and cesium vapor are presented. The Cs 62P3/2(Fe) hyperfine states are populated with a low-intensity tunable diode laser with a 10-MHz spectral bandwidth. We report an integrated atomic retrofluorescence spectrum in the 852.2-nm (62P3/2–62S1/2) resonance line and 917.2-nm (62D5/2–62P3/2) line generated by energy-pooling collisions. Emission spectra of the molecular fluorescence signal have been observed. At the resonance line a large proportion of the atoms excited by the laser are located in the vicinity of the surface. The interactions between the excited atomic 62P3/2 state and the surface appear as a spectral inhibition of the integrated retrofluorescence spectrum for both the atomic line and the molecular band. This spectral inhibition indicates that the nonradiative transformation process of changing atomically excited energy into thermal energy is preferred. We report the analysis of the dominant processes in the vicinity of the 852.2-nm resonance line, which can influence the retrofluorescence hyperfine spectrum at the boundary between the glass window and the saturated cesium vapor. Only the nonradiative transfer by evanescent waves toward the dissipative surface is retained. Using this mechanism, we formulate, for the first time to our knowledge, a simple model of a backscattered hyperfine fluorescence signal. The glass–vapor interface is considered as two distinct regions: a wavelength-thickness vapor layer joined to the surface and a more remote vapor region. The first region is analyzed as a spectral filter that annihilates the absorbed photons and the second one as a rich spectral light source. The experimental setup is described, and measured integrated retrofluorescence spectra are compared with predictions made by the model. The consistency between theory and experiment is remarkably good considering that the model depends only on two unknown parameters: the nonradiative transfer rate and the absorption shape line of the filtering region.

The influence of radiation trapping on the measurements of cross sections for excited-atom–excited-atom collisions

Radiation trapping has an important influence on the measurement of the cross sections of collisions between excited atoms, like energy-pooling collisions, Penning ionization, and associative ionization. In this paper, we first set up the exact relations for computing the cross sections from measurements influenced by trapping and discuss their practical applicability. Since the observation geometry is usually not known exactly, we discuss ways to calibrate it out. In contrast to the untrapped case, no complete elimination of geometry effects is possible. The sensitivity of various experimental geometries to modelling errors is discussed.

Coherent population trapping studied through energy transfer and energy-pooling collisions

The coherent population trapping phenomenon in sodium is probed through energy transfer and energy pooling collisions. Quenching of the excited state population (dark resonance) is measured through the detection of the collisional induced fluorescence up to sodium densities as large as 10 15 cm −3. Two dark resonances have been studied and a different dependence on the sodium vapor density has been observed. For the first time an enhancement of the upper level population and, hence, of the collisional energy transfer processes has been measured correlated to the double coherent excitation.

Role of spontaneous emission in ultracold two-color optical collisions

We have observed violet photon emission resulting from energy-pooling collisions between ultracold Rb atoms illuminated by two colors of near-resonant infrared laser light. We have used this emission as a probe of doubly excited state ultracold collision dynamics. By varying the detuning of the lasers, we have clearly identified the effect of spontaneous emission on the collision process.

Effects of alignment on strontium energy pooling collisions

Effects of alignment on strontium energy pooling collisions

Reverse energy pooling in a K-Na mixture

We report experimental rate coefficients for the reverse heteronuclear energy-pooling collisions $\mathrm{K}(5D)+\mathrm{Na}(3S)\ensuremath{\rightarrow}\mathrm{K}(4P)+\mathrm{Na}(3P)$ and $\mathrm{K}(7S)+\mathrm{Na}(3S)\ensuremath{\rightarrow}\mathrm{K}(4P)+\mathrm{Na}(3P)$ at thermal energies. Both reactions are exothermic and very high rates were observed showing that reverse exothermic energy-pooling is an order of magnitude more efficient than the corresponding forward endothermic energy-pooling reactions. This is in accordance with the general behavior of the exothermic and endothermic energy-pooling rate coefficients in alkali-metal atoms. In the experiment the potassium atoms were excited in two steps to either the $5D$ or $7S$ state via the $4P$ level using two broadband cw dye lasers. A double-modulation technique has been used to select the fluorescence contributions at the $\mathrm{Na}{(3P}_{J})$ exit channels due only to the above reactions. The ground-state sodium and potassium atom densities were measured by the absorption of lines from a K-Na hollow-cathode lamp. The measured densities and fluorescence intensities have been used to obtain absolute reverse energy-pooling rate coefficients. The contribution to the rate coefficients from other processes are discussed.

Experimental study of caesium energy pooling collisions and modelling of the excited atom density in the presence of optical pumping and radiation trapping

An experimental study of caesium energy pooling collisions, , at thermal energies, has been carried out in a capillary cell using diode laser excitation. Use of the capillary cell minimizes the effects of radiation trapping, but nonetheless, such effects still play a significant role in the analysis. Consequently, a rate equation model, which treats simultaneous effects of saturation, optical pumping, and radiation trapping, has been developed and is used to determine the atom density under these experimental conditions. The excited atom densities are combined with measured fluorescence ratios to determine rate coefficients for the caesium energy pooling process. Our values for these rate coefficients are in agreement, within combined error bars, with values we have recently obtained under very different experimental conditions.

Energy-pooling collisions in potassium: 4PJ+4PJ→4S+(nl=5P,6S,4D)

We report experimental rate coefficients for the energy-pooling collisions $\mathrm{K}{(4P}_{J})+\mathrm{K}{(4P}_{J})\ensuremath{\rightarrow}\mathrm{K}(4S)+\mathrm{K}(\mathrm{nl})$ with product states $nl=5P,$ $6S,$ and $4D.$ The experimental procedure and analysis are similar to those used in a recent study of energy-pooling collisions in cesium. In potassium, it was found that ${4P}_{1/2}{+4P}_{1/2}$ collisions are more efficient than ${4P}_{3/2}{+4P}_{3/2}$ collisions for populating $5P,$ while the opposite is true for populating $6S.$ Since fluorescence from $4D$ was not seen, we can only report an upper limit for that rate coefficient.

Velocity dependence of energy pooling collisions in strontium

Velocity dependence of energy pooling collisions in strontium

Energy-pooling collisions in cesium: 6PJ+6PJ-->6S+(nl=7P,6D,8S,4F).

We report experimental rate coefficients for the energy-pooling collisions Cs(6${\mathit{P}}_{1/2}$)+Cs(6${\mathit{P}}_{1/2}$)\ensuremath{\rightarrow}Cs(6${\mathit{S}}_{1/2}$)+Cs(${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$) and Cs(6${\mathit{P}}_{3/2}$)+Cs(6${\mathit{P}}_{3/2}$)\ensuremath{\rightarrow}Cs(6${\mathit{S}}_{1/2}$)+Cs(${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$) where ${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$=7${\mathit{P}}_{1/2}$, 7${\mathit{P}}_{3/2}$, 6${\mathit{D}}_{3/2}$, 6${\mathit{D}}_{5/2}$, 8${\mathit{S}}_{1/2}$, 4${\mathit{F}}_{5/2}$, or 4${\mathit{F}}_{7/2}$. Atoms were excited to either the 6${\mathit{P}}_{1/2}$ or 6${\mathit{P}}_{3/2}$ state using a single-mode Ti:sapphire laser. The excited-atom density and spatial distribution were mapped by monitoring the absorption of a counterpropagating single-mode ring dye laser beam, tuned to either the 6${\mathit{P}}_{1/2}$\ensuremath{\rightarrow}8${\mathit{S}}_{1/2}$ or 6${\mathit{P}}_{3/2}$\ensuremath{\rightarrow}7${\mathit{D}}_{3/2,5/2}$ transitions, which could be translated parallel to the pump beam. Transmission factors, which describe the average probability that photons emitted within the fluorescence detection region can pass through the optically thick vapor without being absorbed, were calculated for all relevant transitions. Effective lifetimes of levels populated by energy-pooling collisions are modified by radiation trapping, and these factors were calculated using the Molisch theory. These calculated quantities have been combined with the measured excited-atom densities and fluorescence ratios to yield absolute energy-pooling rate coefficients. It was found that the rate for production, in all cases, is greatest for 6D, but that 1/2-1/2 collisions are significantly more efficient than 3/2-3/2 collisions for populating 7P. It was also found that 7${\mathit{P}}_{1/2}$ is populated two to three times more efficiently than 7${\mathit{P}}_{3/2}$ in 1/2-1/2 collisions, but that the 7P fine-structure levels are approximately equally populated in 3/2-3/2 collisions. \textcopyright{} 1996 The American Physical Society.

Energy pooling in barium with state excitation

Energy-pooling collisions between low-lying excited states of Ba have been studied. We have used a CW dye laser to excite the level in Ba. Radiative decay and collisions with Ba or buffer-gas atoms (Ar, He) populate also the , and metastable levels. The spatial density distributions of these excited levels were measured by the absorption of lines from a Ba hollow-cathode lamp as a function of laser frequency. When the laser was on the exact atomic resonance we observed fluorescence from the , , , , , , and states populated by energy-pooling collisions of Ba(, ). By changing the buffer gas pressure the fluorescence intensity ratio between - and - transitions changes dramatically. This is found to be due to redistribution of population among metastable levels, both in magnitude and space. In addition, we have found that the and metastable levels are also populated when the laser is tuned to the blue from the 553.5 nm line under which conditions a pronounced red-shifted light cone (cone emission) is observed.