are connected with the studies of structure and dynamics of diatomic molecules and atoms by laser spectroscopy in external fields.

The diatomic molecules remain a challenging object for high resolution laser spectroscopy studies. The related information on molecular structure is in the focus of the most recent frontier studies of cold and ultra-cold processes and Bose-Einstein condensation, molecular lasers, astrophysical studies, etc. Recent achievements in the long-range photoassociation spectroscopy requires knowledge on the large distance properties and scattering potentials, which makes it necessary to combine the studies of diatomic molecules and the consequent atomic parts. It has been proved that ab initio structure calculations still lack for the accuracy to simulate molecular spectra, thus, experimental studies remain of basic importance. From the point of application, the data on diatomic molecules are of basic importance in environmental control, atmospheric optics, gas dynamics, flame processes, external field distribution control. As far as industrial applications are concerned, the heteronuclear alkali diatomics are convenient test molecules to develop non-contact "optical tester" for fast, non-destructive electric field distribution control on micro-scale open surfaces. The non-contact "optical tester" is based on a laser light spot, which irradiates a gas of polar molecules or atoms surrounding the surface and produces a snapshot photograph (map) of the electric field distribution.

High resolution laser induced fluorescence spectroscopy of diatomic molecules in the ground and excited electronic states had been or are applied to the mixed alkali dimers (NaK, NaRb, NaCs, and RbCs). Special attention is put to:

1. the ground state studies up to high vibrational level close to the dissociation limit;
2. restoring unknown excited state potentials using excitation with a scanned diode laser, dye laser and standard (fixed) laser lines;
3. studies of the perturbed excited states, including singlet-triplet complexes that are strongly mixed by spin-orbit interaction.

Kinetic studies. Recording LIF kinetics after pulsed excitation in order to determine relaxation rates, spontaneous lifetimes, transition electric dipole moments, collision processes cross sections for NaK, NaRb, Te₂.
Stark and Zeeman effects in molecules and atoms. Recent research activities are connected with laser spectroscopy studies of electric field induced parity mixing in diatomic molecules and atoms. In particular:

1. quasi-linear Stark effect has been studied in the ¹Π states of diatomic molecules (NaK, NaRb, RbCs), by LIF intensity and polarization changes under polarized optical excitation, in order to determine permanent electric dipole moments and Lambda-doubling constants;
2. Stark effect in the excited states of atoms (such as Cs) is studied using two-step laser excitation and observing changes in spectra and polarization of LIF.

Electric radiofrequency – optical double resonance method has been used to measure directly e/f splitting in a particular rotational state J of the short living electronically excited ¹Π states. RFODR signals are observed in laser induced fluorescence at optical frequency when 10⁷ - 10⁹ Hz external electric radio frequency field is applied.
Direct measurements of e/f splitting in a particular rotational state J is achieved by applying a electric field and monitoring the resonance signal at optical frequency. As a result, ultra-high resolution and high accuracy Λ - splitting values have been measured for NaK and NaRb ¹Π states low rotational levels non-accessible by ordinary high resolution spectroscopy techniques.
Optical electric field imaging. The aim is to develop the methodology of optical mapping (imaging) of the electric field potential distribution on the open surface of semiconductor devices. As distinct from conventional contact-based testing techniques, the optical testing method will allow simultaneous in situ testing of the large number of contact points and mapping of the electric potential with the high spatial resolution typical for an optical microscope.
Optical electric field imaging based on electric field induced changes in Rydberg atoms and diatomic molecules. The polarization changes due to e/f mixing in the excited states of heteronuclear alkali diatomics (NaK, NaRb, NaCs) are used for electric field mapping. Another tracer gas media is achieved at two-step excitation of alkali atoms (such as Cs, or others) where electric field induced destruction of coherence between magnetic sublevels offers high electric field sensitivity.