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We have investigated the dependence of lasing modes of dye-doped microdroplets on dye concentrations. Single droplets were confined in an ion trap and irradiated by a pulsed green laser. Polarization characteristics of both emission spectra and microscopic images were obtained for various dye concentrations. As the concentration decreases, the laser lines shift toward shorter wavelength and the structures of the spectra become more complicated while microscopic spatial images changed drastically. Polarization analyses have revealed that, at the most dilute concentration, only lasing with polarization perpendicular to the radial direction occurs in a droplet.

Polarization properties of single lasing microdroplets levitated in an ion trap have been investigated in both emission spectra and microscopic images. The polarization phenomena strongly depend on the observation direction and the orientation of a transparent axis of the polarization analyzer. We suggest such effects originate because excited molecular dipoles preserve the memory of the polarization of the pump field well.

Novel modes of laser emission from levitated microdroplets have been observed. A single dye-doped glycerol droplet of micrometer size was confined in an ion trap and irradiated by a pulsed or a cw green laser. Photographic images of the emitting droplet and emission spectra were simultaneously recorded and compared each other for various intensities of the exciting laser. Both the images and the spectra obtained from the strongly excited droplet have no resemblance to those from the weakly excited one. With stronger excitation, lasing action was found to occur in the droplet in specific surface azimuthal modes. Relations between lasing modes and spectra are discussed.

Collective motions and anharmonic oscillations induced by a mixture of two ion species with different masses in a rf ion trap are reported. The absorption spectra of the probing rf power by the resonant oscillations of ion clouds have been observed for several ion species with various mixing ratios. It is shown that significant nonlinear effects manifest themselves strongly when the mass difference is in a certain range. One of such nonlinear effects, the first observation of significant hysteresis in the absorption spectrum of the probing rf field, is understood to be due to the anharmonic force term of the third order induced by the interactions of two ion clouds. The term has been estimated by fitting the observed absorption profile to the approximate solution of Duffing's equation.

A strong anharmonicity has been observed in the oscillation of ion clouds in an rf ion trap when two species of ions are stored simultaneously. This anharmonic term in the trapping potential is shown to be induced by the presence of two different species of ions.

We have demonstrated the existence of metastable excited rhodamine molecular ions when created in laser desorption ionization. Rhodamine ions were stored in a rf ion trap, and photodissociation was used to probe the metastable population as a function of trapping time. From the dependence of the population decay on buffer gas pressure and by extrapolating it to zero pressure we have obtained the lifetime of the metastable state of the ions in isolated condition.

Optogalvanic spectroscopy (OGS) is a method for efficiently detecting atomic and molecular spectra. This technique has been used in frequency locking and stabilization of lasers. So far, various state-selective spectroscopies have been reported. In this note, we suggest that the isotope shifts observed in two-step OGS are affected by the incident direction of exciting lasers, and we estimate the isotope shift of the 1s2–2p4 transition of neon. The schematic energy diagram of a neon atom is shown in Fig. 1. We used a tunable single mode laser diode (LD; Newport, 2010M) with a spectral width of 4MHz, resonant with 1s2–2p4 transition, and a multimode (consisting of 3 to 5 lines) He–Ne laser (Melles Griot, LHP925) with a longitudinal mode spacing of 257MHz, resonant with 2p4–3s2 transition. As shown in Fig. 2, the two laser beams were crossed at an angle of less than 10 and were counterpropagated (case A) and copropagated (case B). A commercial hollow cathode lamp (Hamamatsu Photonics, L2783-3NE-LI) with a Ne pressure of 800 Pa was dc discharged. The discharge voltage and laser power were set to values that prevented self-absorption and self-reversal. The He–Ne laser was chopped at a frequency of f (typically 330Hz), and the two-step excitation signal was detected by a lock-in amplifier. Figure 3 shows the OGS signals obtained without a He–Ne laser (we call it conventional OGS in this note) and detected by scanning the LD frequency through the 1s2–2p4 transition of Ne, along with two-step OGS signals in cases A and B. The conventional OGS signal (1s2–2p4) is relevant to the stationary state of Ne, and the line is Doppler broadened. The isotopic component of Ne appears at the right foot of that of Ne. The resolution in two-step OGS is higher than that in conventional OGS. The central frequency of the 633 nm line (2p4–3s2 transition) of Ne is higher than that of Ne, and this shift is denoted by II. This value is reported to be 0.9GHz by Stahlberg et al. by considering that the He–Ne laser line consists of the lines only from the isotope Ne. In both cases A and B in Fig. 2, the velocity components of Ne atoms are toward the He–Ne laser in order to be Doppler shifted by II and resonant with the 2p4–3s2 transition of Ne atoms. In case A, such Ne atoms are away from the LD and the frequency of the LD should be higher (blue shifted) than the central frequency of the 1s2– 2p4 transition by II. On the other hand, in case B, the two laser beams are in the same direction and the frequency of the LD should be red shifted by II. The higher resolution seen in the two-step excitation is explained by such velocity selection. The apparent isotope shift is determined by deconvoluting the observed curve with two Gaussian peaks, as shown for case B in Fig. 3. The isotope shift for the 1s2–2p4 transition should be the mean value of the two apparent shifts obtained by the two schemes of two-step OGS. The isotope shift thus obtained is estimated at 1:8 0:1GHz. If a He–Ne laser with a single mode is used, the peaks of two-step OGS will become much sharper and a more accurate value of the isotope shift will be obtained.

Cross sections for single electron capture from He atom by highly stripped, C q + , N q + , O q + , F q + , Ne q + ( q =4–9) and Kr q + ( q =10–25) ions have been calculated using the multichannel Landau-Zener model. The collision energy is 600 eV/amu except for Kr q + , whose energy is q ×1 keV. The selective electron capture into a single or at most two n -shells is predicted for the cases of q ≤9. The n -distributions obtained by the present calculation are quite consistent with our earlier observation and the total cross sections agree reasonably well with the measured data in spite of the simple model. In the case of Kr q + , where q is larger than 10, more and more shells can be populated and the total cross sections increase monotonically with the increase of q .

Translational energy spectra of He + ions produced by one-electron capture processes in collisions of 0.8 and 2 keV He 2+ with H 2 and 0.8 keV He 2+ with N 2 have been measured with an electrostatic energy analyzer. The spectra show only a single broad peak with the energy gain of about 11 eV for all the cases. The peak in each spectrum becomes broader with the increase of the collision energy. It is found that the product He + is in the ground state and the capture process is associated with the dissociation and/or ionization of the product molecular ion.

The vibrational and rotational population distributions expected of the diatomic species AB just after splitting from the tri-atomic complex [ABC] have been calculated on the basis of the statistical model including the law of angular momentum conservation. It has been shown that the angular momentum possessed by the complex [ABC] exerts considerable influence upon the initial and non-thermal distribution of populations in the vibrational and rotational levels of AB.

Time characteristics of the secondary emission from iodine molecules excited with light pulses from a cavity-dumped, single-frequency Ar + ion laser at 514.5 nm have been compared with existing theories. It has been found that the experimental data are well explained quantitatively by the theories, provided the 21 hyperfine lines as well as collisional effects and Doppler broadening are taken into account. The cross sections for the phase-changing and population-changing collisions have also been determined. The contributions of coherent and incoherent secondary emission processes are discussed.

The spectrum of secondarily emitted light from iodine vapor excited by a single-mode Ar + ion laser has been measured in the forward scattering geometry with a resolution of 80 MHz. The observed spectrum has been found to consist of sharp and broad components. This result is shown to be reproduced fairly well by a Monte Carlo simulation of the molecular collision. The cross sections for the soft and hard velocity-changing collisions of an I 2 molecule in the excited state have been obtained as 230 A 2 and 80 A 2 , respectively.

A micro-channel plate dynode type image intensifier whose output window is a fibre face plate coated with phosphor on its inner surface has been applied to a low f -number spectroscopic detector for studies of very weak light signals sent from the crossing between an electronic or ionic beam and an atomic or molecular beam. It can reduce long exposures extending over nights for optimum density spectrograms to be obtained in the conventional way, down to scores of minutes and to several seconds. The resolution and sensitivity are both nearly satisfactory, as far as atomic lines, continua, and diatomic band-heads are concerned.

Initial and nonthermal population distributions among the rotational and vibrational levels of the two diatomic species split from a four-atomic collision intermediate have been studied on the basis of the statistical model which ensures that the angular momentum of the whole system is conserved throughout the course of the splitting. A number of curves have been calculated with the aid of an electronic computer, for the initial rotational population distribution (i. r. p. d.) and the initial vibrational population distribution (i. v. p. d.). The i. r. p. d. computed varies considerably, according as the moments of inertia of the diatomic fragments are equal to or different from each other, and the excess energy E possessed by the intermediate is large or small compared with the vibrational quanta of the fragments. On the contrary, the i. v. p. d. computed remains unchanged in most cases, when the vibrational energy is expressed in the unit of E . Some of the population distributions predicted by the stat...

Energy gain spectra of charge-changing projectile ions arc measured for electron capture by fully stripped carbon, nitrogen, and oxygen ions from atomic hydrogen at the collision energy of 1.5× q keV. The electron is confirmed to be selectively captured into a particular single level of the hydrogen-like product ion; n =4 of C 5+ and n =5 of N 6+ and O 7+ , respectively, which are in agreement with the theoretical predictions.

One-electron capture processes into B 2+ (2s) and B 2+ (2p) have been investigated in B 3+ –He collision at low velocities (1.3-2.3×10 7 cm/sec) using a translation energy spectroscopy. Energy dependence of the relative population between B 2+ (2s) and B 2+ (2p) is obtained and compared with the theoretical result of Shipsey et al.

Helium ion impact on H 2 O exhibits quite a different spectrum from that electron-impact on H 2 O gives. In the former, the OH + A , 3 Π→ X , 3 Σ - band-system can be observed in addition to the OH A , 2 Σ + → X , 2 Π. On the contrary, there is no trace of the OH + bands in the latter. These experimental evidences have been obtained by the crossed-beam technique.