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Schematic diagram of the experimental set-up: TOF— time-of-flight mass spectrometer; MCP—microchannel plate detector; L—lens; P—polarizer.
Source publication
Single-colour resonance three-photon ionization of Sm atoms is studied
within the 542.4–581.6 nm spectral range. Wavenumber dependence of the
Sm+
ion yield shows more than 600 maxima of different amplitudes and shapes. Most of the resonance
structure observed is due to two-photon excitation of even-parity bound states lying in the
34 713.1–40 526....
Citations
... Such process, including non-resonant population of the excited level with subsequent one-photon resonantly enhanced two-photon ionization, should also be taken into account when interpreting the resonance structure of three-photon ionization spectra. In particular, a number of unidentified maxima observed at three-photon ionization of the Sm atom [24] are, in our opinion, related to exactly such resonant transitions. Funding: This research received no external funding. ...
Within the framework of a three-level model, the process of three-photon ionization with one-photon resonance between two excited levels (with the lower one being initially unpopulated) is considered using the density matrix method. It is shown that such resonance can result in the appearance of a maximum in the three-photon ionization spectrum when detuning between the resonance wavenumber and the wavenumber of the transition responsible for the lower excited level being populated exceeds the laser radiation linewidth by more than three orders of magnitude.
... Since the invention of strong pulsed lasers the multiphoton ionization processes of atoms have been well studied and understood [1][2][3][4][5][6]. Although the study on the multiphoton processes started by investigating nonresonant multiphoton ionization, the progress in laser technology offered the tunability for the laser wavelength so that the resonant excitation between the bound states takes place, which significantly enhances the ionization yield [7,8]. Thus, resonance ionization spectroscopy (RIS) or resonance-enhanced multiphoton ionization (REMPI) spectroscopy has become an effective technique for the various kinds of analysis [9][10][11][12][13][14]. ...
We theoretically study the ionization efficiency of Doppler-broadened atoms through a one-photon resonant two-photon ionization process using nanosecond pump and ionizing laser pulses. Under the presence of significant ( > tens of GHz) Doppler broadening, the bandwidth of the transform-limited nanosecond pump pulse is far smaller than the Doppler width, and the use of the broadband nanosecond pulse rather than the transform-limited nanosecond pulse seems to be much more efficient to pump and eventually ionize atoms. It turns out, however, that the transform-limited nanosecond pump pulse with sufficient high intensity can outperform the broadband nanosecond pump pulse in the high intensity regime for the ionizing pulse, at which the other broadening mechanisms because of the strong pump and fast ionization play more important roles than the bandwidth of the pump pulse. Using a set of density matrix equations, we present specific numerical results for muoniums ( μ + e − ) with enormous Doppler widths (80 and 230 GHz), which support the above argument.
... Одним з факторів, який обмежує ефективне використання методу одноколірної трифотонної резонансно-іонізаційної спектроскопії високозбуджених парних станів атома самарію, є те, що не всі можливі двофотонні переходи, що дозволені правилами відбору, чітко проявляються у вигляді резонансних максимумів у спектрах трифотонної іонізації, виміряних при певному значенні інтенсивності лазерного випромінювання [11]. Йдеться про двофотонні переходи, яким відповідають максимуми малої амплітуди. ...
... Вимірювання проводилися на установці, детально описаній в [11]. Випромінювання імпульсного лазера FL 2001 (Lambda Physik) з накачкою другою гармонікою Nd: YAG-лазера фокусувалося у вакуумну камеру, де перетиналося під прямим кутом з пучком атомів самарію. ...
... На рис. 1 приведено залежність N + (ω), виміряну в околі двофотонних пере- [9,11]) при різних значеннях інтенсивності лазерного випромінювання в області взаємодії. Добре видно, що при малій інтенсивності амплітуда максимуму, зумовленого двофотонним переходом з рівня 7 F 4 , є значно більшою за амплітуду максимуму, що відповідає двофотонному переходу з рівня 7 F 2 (рис. 1, крива 1). ...
... In particular, at an atomic source operating temperature of ~930 K, the relative popula tion of levels is 0.18 ( 7 F 0 ), 0.35 ( 7 F 1 ), 0.26 ( 7 F 2 ), 0.13 ( 7 F 3 ), 0.05 ( 7 F 4 ), 0.02 ( 7 F 5 ), and 0.005 ( 7 F 6 ). For this reason, the resonance structure of the three photon ionization spectra of the samarium atom includes maxima caused by transitions (mostly, two photon ones) from all seven levels of the ground term [2]. The main method of treating such spectra is combining the observed maxima into groups related to excitation of the same upper states from different initial levels of the ground term 7 F [3]. ...
... EXPERIMENT Studies were performed using the experimental setup described in detail in [2]. The linearly polarized radiation of an FL 2001 pulsed dye laser (Lambda Physik) with a linewidth of ≈0.2 cm -1 and pulse dura tion of ≈12 ns was focused by a lens with a focal length of 22 cm into a vacuum chamber where it crossed a beam of samarium atoms. ...
... Its correlation function of the first order has the form where e(t) is the stochastically fluctuating complex amplitude of the electric field. System of equations (2) corresponds to the case of zero detuning of the two photon resonance: ...
Amplitude ratios of resonance maxima caused by two-photon transitions from different levels of the ground term of the samarium atom are studied experimentally and theoretically as functions of the laser-radiation field strength. The results of these studies are shown to be promising for identifying the resonance structure of three-photon ionization spectra of the samarium atom. A not yet observed excited even-parity state with energy E ≈ 36789.1 cm−1 and hypothetical values of total angular momentum J = 5, 6 has been discovered.
... The development of lasers enabled application of methods of multistep laser spectroscopy to studying higher lying states [4], which allowed obtaining exten sive data on highly excited even parity states of samar ium [5][6][7][8][9][10][11][12][13][14][15][16]. However, despite the large number of experimental studies carried out thus far, these data are still far from being complete. ...
... The studies were conducted using the experimental arrangement described in detail in [7]. The output of an FL 2001 pulsed tunable dye laser (Lambda Physik) with a linewidth of ~0.2 cm -1 was focused into a vac uum chamber where it crossed an atomic beam of samarium at the right angle. ...
... The superscripts ("a-i") in the table denote levels that were previously observed in [6][7][8][9][10][11][12][13][14][15][16]. Comparison of the energy values measured in this work with the data of other authors shows that they are in good agreement with each other. ...
Highly excited even-parity states of the samarium atom in the range between 34104 and 39155 cm−1 have been studied by the method of one-color three-photon resonance ionization spectroscopy. The energies and total angular momenta of 342 states have been determined. Seven new even-parity states of samarium have been discovered.
... the ground state [12,13]. The studies on even-parity highly excited states of the Sm atom are mainly in the region above 36 000 cm −1 [14][15][16][17][18] and below which only a few works have been carried out [19][20][21]. With all of the facts in mind, this work systematically studies the spectra of even-parity highly excited states of the Sm atom in the 30 040-38 065 cm −1 range with the RIS method in order to obtain their energy levels, the relative line intensities of the related transitions and their unique J-assignment. ...
... On the other hand, since different excitation paths from [16][17][18][19][20] are employed, the J = 0 states are detected for the first time. As their line intensities are weak in most cases, it may be the possible reason that the J = 0 states are unavailable in those references. ...
... As shown in table 2, 19 states, marked with the symbol '#', are reported for the first time in this work, while the rest of the 31 states can be found previously without the information on the relative intensities of the spectra [16][17][18][19][20]. Therefore, this work not only observes new states and confirms the previous states, but also adds the extra information on relative line intensities to all of the states observed, which plays an important role in analysing the spectral features. ...
Spectra of even-parity highly excited states of the Sm atom have been systematically studied using the two-color three-step excitation and photoionization detection method. With three different excitation paths distinguished by three different intermediate states with the 4f66s6p configuration, the atom is resonantly excited to given highly excited states in the energy region between 30 040 and 38 065 cm−1, where it is detected by photoionization. The wavelength of the second laser is scanned from 440 to 700 nm, while that of the first laser is fixed at 638.96, 636.92 or 627.50 nm. Based on precise calibration of the wavelength, the energy levels of 198 even-parity states are determined with the relative line intensities of the related transitions. A unique value of J, the total angular momentum, is assigned to all detected states by comparing the three spectra obtained with the different excitation paths. Except that the energy levels of 113 states are confirmed in this work, the rest of the information mentioned above has not been previously reported.
... Figure 2shows the level scheme for the photo-ion generation. [5].The one starting from 7 F 2 is a two photon resonant excitation with near resonant in first step while the other one starting from 7 F 4 is resonant in both first and second excitation steps. The third photon ionizes in non-resonant process in both cases. ...
The performance of Time-of-Flight Mass Spectrometer (TOF-MS) has been studied with laser produced photoions of various densities using a reflectron TOF-MS built in our laboratory. In this, the source of atoms is a resistively heated atomic beam source. As the atomic species reach the interaction region, the interaction with pulsed laser results in ions. Samarium was used as the source element to observe all its isotopes by resonant non selective excitation of one of the ground state transitions. However, as the temperature of the source is increased, the collective plasma effect of ions and electrons becomes important. As a result of this the Time-of-Flight signal (in linear mode) of Sm isotopes became poorly resolved from a well resolved condition. The number density of the ions produced in these conditions and hence the plasma parameters were calculated. The plasma parameters like Debye length (λD), the number density (ND), and frequency (fpi) confirms the collective effect. In order to avoid this undesired effect, the optimum operating condition with respect to oven temperature and laser intensity was estimated.
... The investigations were performed on a setup described in detail in [2]. Focused radiation of a tun able pulsed FL-2001 dye laser (Lambda Physik) intersected a beam of samarium atoms. ...
... Second, not all peaks are pure, i.e., they do not correspond to the excitation of only one state. A large number of peaks observed in the dependence N + (ω) is related to the simultaneous excitation of two or even more states, which cannot be separated because the frequencies of the transitions are very close [2]. This does not allow us to unambiguously separate the contribution of a par ticular transition to the amplitude of such peaks. ...
The manifestation of double resonances upon the three-photon ionization of the samarium atom has been studied in a frequency range of 17200–18400 cm−1. Thirty peaks caused by double resonances have been found in the dependence of the yield of Sm+ ions on the laser radiation frequency. The majority of these peaks greatly exceed in amplitude the peaks associated with ordinary two-photon resonances. The influence of double resonances on the three-photon ionization has been theoretically analyzed using the density matrix approximation. The calculations show that the probability of the three-photon resonance ionization can increase by more than two orders of magnitude due to the additional one-photon population of an intermediate level. The double resonance slows down the rate of increase in the probability of ionization with an increase in the laser radiation intensity compared to ordinary two-photon resonance.
... The level energies, relative intensities and possible J values of even-parity Rydberg states obtained in this experiment. The level energies and the possible J values reported in Refs.[16] and [18] are also listed for comparison. The typical experimental uncertainties are estimated to be less than ±0.1 cm −1 , and the relative intensities are normalized and classified into three ranges:0–0.3, ...
... The typical experimental uncertainties are estimated to be less than ±0.1 cm −1 , and the relative intensities are normalized and classified into three ranges:0–0.3, 0.3–0.6 and 0.6–1[18]; the remainder are taken from Ref.[16]. It is necessary to point out that although the Rydberg states shown inTable 1 were obtained previously, [16,18] they could not be identified from the valence states in the same energy region. ...
... 0.3–0.6 and 0.6–1[18]; the remainder are taken from Ref.[16]. It is necessary to point out that although the Rydberg states shown inTable 1 were obtained previously, [16,18] they could not be identified from the valence states in the same energy region. In this work, however, the advantage of autoionization detection enables us to discriminate them successfully from the valence states. ...
In this work, a three-step autoionization detection method and direct photoionization detection method are employed to measure the highly excited even-parity states of the Sm atom in the energy region between 36360 cm−1 and 40800 cm−1. Comparisons between the results from the two detection techniques enable us to discriminate the Rydberg states from the valence states in the same energy region with the information of level energies, possible J values and their relative intensities. Furthermore, in the experiment two different excitation schemes are designed to obtain the spectra of highly excited even-parity states of the Sm atom. With a detailed analysis of the experimental data, this work not only confirms the results about many spectral data from the literature with different excitation schemes, but also reports new spectral data on 29 Rydberg states and 23 valence states.
... This study, which continues the investigations performed in [7], is devoted to the analysis of the SRS manifestation during three-photon ionization of a samarium atom and determination of the conditions affecting its efficiency. STATEMENT OF THE EXPERIMENT Investigations were performed on the experimental setup described in detail in [8]. The radiation of an FL-2001 pulsed tunable dye laser (Lambda Physik) was focused on an Sm atomic beam. ...
... At this value of ε , the dependence N + ( ω ) exhibits a maximum number of resonant peaks [10].Figure 1 shows the dependence N + ( ω ) measured in the vicinity of the single-photon 4 f 6 6 s 2 7 F 3 4 f 5 5 d 6 s 2 transition (whose position is indicated by an arrow), which has a pronounced resonant character, as is evidenced by the presence of 20 peaks of different amplitude and shape. Identification of the resonant peaks according to the data of [8, 9,11121314 is given inTable 1. Note that only energies and total angular momenta are generally known for higher states of the Sm atom, whereas there are no data on the electronic configurations and terms. ...
The manifestation of spontaneous Raman scattering upon the three-photon ionization of a samarium atom has been investigated. The dependence of the Sm+ yield on the laser frequency, along with the peaks due to the two-photon excitation of bound states from different levels of the 4f
66s
27F ground term, exhibits a strong peak due to single-photon excitation of the 4f
55d6s
27D°3 state from the 4f
65d6s
9H
2 excited state. The 4f
65d6s
9H
2 state was populated as a result of spontaneous Raman scattering. The large amplitude of the observed peak indicates a high efficiency of this process. The estimations performed indicate that the probability of resonant ionization through an excited state populated due to spontaneous Raman scattering can be comparable with the probability of three-photon ionization through the two-photon intermediate resonance. The necessary conditions for implementing this channel of resonant three-photon ionization are formulated.
