Elena P. Vidolova-Angelova

Investigation of lutetium rydberg states by laser multistep resonance ionization spectroscopy

Laser multistep excitation and electric-field ionization spectroscopy have been used to investigate experimentally highly excited states (HES) of lutetium in the vicinity of the first ionization limit. The investigation includes the measurement of energy levels (ionic signal vs last transition frequency) and radiation lifetime (ionic signal vs ionizing electric-field pulse delay) of the states investigated. Even Rydberg states of 4f14 6s2nd have been observed with two-step laser excitation. The maximum experimental error is 0.3 cm−1 for the energy and 20% for the radiation lifetime measurements. This is the very first time that results for the lifetimes as well as for a large part of the energy values have been obtained. Our present experimental results compare well with previously calculated values obtained by relativistic perturbation theory using the zero-order model approximation, and with the available experimental values.

Observations and theoretical analysis of highly excited singlet and triplet states of cadmium

We have recorded the - 50) bound Rydberg spectrum of cadmium. We have fully resolved the multiplet up to n = 19 and partially up to n = 24. Furthermore, we have observed the odd singlet and triplet 5sn f Rydberg series for n = 10 - 22 and n = 4 - 21, respectively. We have applied two- and three-step laser schemes to excite Cd vapour in a heat pipe-like oven which was operated as a thermionic diode for detection. Theoretical calculations were performed for the energies of the 5sn p and 5sn f series using perturbation theory with a zero-order model approximation. There is a good agreement between theoretical and experimental results for the 5sn p series, the deviation decreasing with n and being 1 - 2 for n = 50. The agreement for the 5sn f is satisfactory. From the quantum defect of the 5sn f series we approximate a value of the effective dipole polarizability of the ion of in units of the Bohr radius.

Rydberg and Autoionization Tm States Investigation by the Three-Step Laser Excitation and Electric Field Ionization Method

The energies of 190 Rydberg and autoionization 4f13 6snp-states of the Tm atom (ground electron configuration 4f13 6s2, nuclear chargeZ=69) have been measured by the laser multistep excitation with subsequent electric field ionization method. The investigation range of these states has been extended towards states with higher and lower values of the principal quantum number. As a result the energies of 160 states have been obtained for the first time. The experiment has been carried out on an automated laser photoionization spectrometer. The measurement accuracy has been ±0.5 cm−1.

Laser resonance ionization spectroscopy of the cerium atom

About 70 odd-parity high-lying levels have been observed as a result of two-step laser excitation and electric field ionization. The energies are determined from the registered dependence of the observed ion signal on the wavelength of the exciting laser radiation by adding the known first step frequency. The maximum experimental error is . The investigation also includes the estimation of the radiative lifetime of some Rydberg states. The ion signal as a function of the ionizing electric field delay is considered to represent the radiative decay curve and is used for estimating the radiative lifetime. New results on the highly excited levels have been obtained. About 40 single laser-induced transitions to Ce intermediate even-parity states by one-step laser excitation and photoionization have also been observed, some of which have not been seen previously.

Determination of traces of lutetium in geological samples by resonance ionization spectroscopy

Trace amounts of Lu in geological samples have been measured at the 10–5% level by use of atomization in vacuum. Atoms of Lu are selectively excited by a two-step laser excitation scheme to an auto-ionizing level. This level represents a permanent channel of decay enabling the excited Lu atoms to be ionized effectively. The ions are registered via a time-of-flight mass separator by a secondary electron multiplier. The integral ionic signal recorded is proportional to the amount of Lu in the samples. The calibration is characterized with very good linearity (3% average and 8% maximum deviation from linearity). The results obtained are compared with the concentration of Lu in samples previously measured by neutron activation analysis. For three of the samples a slight deviation (<20%) from the control data is observed. For the fourth sample the deviation is 70%. The possible reasons for this are analysed. If it is assumed that the measurement error originates from the experimental conditions, it might be due to some type of matrix effect (to avoid it, a special procedure of matrix exchange is required). Taking into account the linearity of the calibration and the ionic signal intensity registered, amounts of Lu at least one order of magnitude less than those of the lowest calibration point (1.432 ng of Lu) could be measured.

Injection seeding in a dual-cavity gain-switched Ti:Sapphire laser

Abstract An experimental investigation of a pulsed tunable injection-seeding system pumped by a Nd:YAG laser is presented. The slave laser (SL) of the system is a gain-switched Ti:Sapphire laser with a dual-channel competitive cavity which consists of a main ring channel and an auxiliary linear one with different lengths. The use of this configuration results in full and reliable suppression of both the perturbing reverse radiation from the SL to the master laser (ML) and the broadband spectral background of the SLs ring channel. This is achieved irrespective of the ratio between the energies of the SL and ML, fluctuations of laser parameters, and spectral detuning. We take advantage of the gain-switched regime of the Ti:Sapphire laser to avoid simultaneous competition between the SLs channels; this allows us to obtain spectrally pure, unidirectional output radiation with high seeding and overall efficiency. The principle of operation of the ring-linear-cavity Ti:Sapphire slave laser provides a natural optical isolation between the SL and ML; this makes such lasers suitable for use as regenerative amplifiers when seeded by single-frequency diode lasers as well as in chirped-pulse-amplification systems to amplify ultrashort laser pulses without the necessity of optical isolators.

Multiply-self-seeded pulsed Ti:Sapphire laser

Multiply-self-seeded single-longitudinal-mode (SLM) pulsed Ti:Sapphire (Ti:S) laser is reported. The compact laser cavity contains a novel multipass selective reflector (MPSR) based on a grazing-incidence diffraction grating. It operates equivalently to a succession of coupled SLM Littman-type cavities. The multiple self-seeding, provided by the MPSR, results in a considerable decrease of both the laser threshold energy and the pulse build-up time as well as an increase of the tuning range, as compared to those of the conventional Littman-configuration Ti:S lasers. Results of the experimental and theoretical investigation of the laser are presented and discussed. Output energy of about 8 mJ at a slope efficiency of 33% and overall efficiency of about 14%, in combination with a high spectral purity of the output radiation, are achieved. Experimental comparison of the MPSR laser with Littman-type SLM configurations with and without nonselective retroreflector is also done.

Dynamic Methods for Investigating the Conformational Changes of Biological Macromolecules

Fast conformational changes of biological macromolecules such as RNA folding and DNA—protein interactions play a crucial role in their biological functions. Conformational changes are supposed to take place in the sub milliseconds to few seconds time range. The development of appropriate dynamic methods possessing both high space (one nucleotide) and time resolution is of important interest. Here, we present two different approaches we developed for studying nucleic acid conformational changes such as salt‐induced tRNA folding and interaction of the transcription factor NF‐κB with its recognition DNA sequence. Importantly, only a single laser pulse is sufficient for the accurate measuring the whole decay curve. This peculiarity can be used in dynamical experiments.

Enhanced operation of tunable dye and Ti:sapphire lasers using a multipass selective reflector

A laser cavity containing highly selective reflector based on a multipass grazing-incidence diffraction grating is described. The operation of the multipass selective reflector (MPSR) is demonstrated and studied experimentally in the case of pulsed dye laser pumped by frequency-doubled Nd:YAG laser. Numerical calculations concerning gain- switched Ti:Sapphire laser with MPSR are also done. An increasing of the spectrally pure output energy more than 5 times is achieved. Decrease of the threshold energy and broadening of the tuning range of several times are also observed depending on the pumping conditions. The calculations show that, in the case of gain-switched Ti:Sapphire laser pumped by Nd:YAG laser, the temporal characteristics of the radiation, the build-up time and the pulse duration are considerably shortened by using MPSR. The improved energy, spectral, and temporal parameters of tunable lasers with MPSR make them suitable for different applications (spectroscopy, biology, DIAL, etc.) as a separate sources or as a part of injection-seeding tunable laser systems.

Injection seeding in a ring-linear dual-cavity tunable laser

A comparative experimental study of two versions of an injection-seeding laser system containing a slave laser (SL) with a ring-linear dual-channel competitive cavity and with a simple ring one is presented. The spectral purity of the SL output radiation and efficiency of the SL reverse wave suppression in dependence on the seeding conditions are investigated. It is shown that in the case of a dual-cavity competitive SL with a ring main channel both the spectral background and reverse radiation are fully suppressed. This is realized in a compact scheme without optical isolators and at any ratios between the SL energy and the seeding source one.